CHAPTER VIV WIRELESS TELEGRAPHY

CHAPTER VIV WIRELESS TELEGRAPHYProbably no branch of electrical science ever appealed more to the imagination of the experimenter than that coming under the heading of wireless telegraphy. Wherever you go, you are likely to see the ear-marks ofamateurwireless telegraph stations in the aerials and masts set up in trees and on house-tops. It is estimated that there are nearly a quarter of a million such stations in the United States.There is really no great mystery about this wonderful art which made possible the instantaneous transmission of messages over immense distances without any apparent physical connection save that of the earth, air, or water.Did you ever throw a stone in a pool of water? As soon as the stone struck, little waves spread out from the spot in gradually enlarging circles until they reached the shore or died away.By throwing several stones in succession, with varying intervals of time between them, it would be possible so to arrange a set of signals, that they would convey a meaning to a second person standing on the opposite shore of the pool.Wireless telegraphy is based upon the principle ofcreating and detectingwaves in a greatpoolof ether.Modern scientists suppose that all space is filled with an "imaginary" substance calledether. The ether is invisible, odorless, and practically weightless. This ether, however, bears no relation to the anaesthetic of that name which is used in surgical operations.It surrounds and penetrates all substances and all space.Fig. 193.—Little Waves spread out from the Spot.Fig. 193.—Little Waves spread out from the Spot.It exists in a vacuum and in solid rocks. Since the ether does not make itself apparent to any of our physical senses, some of these statements may seem contradictory. Its definite existence cannot be proved except by reasoning, but by accepting and imagining its reality, it is possible to understand and explain many scientific puzzles.A good instance is offered by the sun. Light and heat can be shown to consist of extremely rapid vibrations. That fact can be proved. The sun is over 90,000,000 miles away from our earth and yet light and heat come streaming down to us through a space that is devoid even of air. Something must exist as a medium to transmit these vibrations; it is the ether.Let us consider again the pool of water. The waves or ripples caused by throwing in the stone are vibrations of the water. The distance between two adjacent ripples is called thewave length.The distances between two vibrations of light can also bemeasured. They are so small, however, that they may be spoken of only inthousandthsof an inch. The waves created in the ether by wireless telegraph apparatus are the same as those of light except that their length usually varies from 75 to 9,000feetinstead of a fraction of a thousandth of an inch.Fig. 194.—A Simple Transmitter.Fig. 194.—A Simple Transmitter.A Simple Transmitteris illustrated in Figure 194. A telegraph key is connected in series with a set of cells and theprimaryof an induction coil, which, it will be remembered, is simply a coil consisting of a few turns of wire. This induces a high voltage in a second coil consisting of a larger number of turns and called thesecondary.The terminals of the secondary are led to a spark-gap—an arrangement composed of two polished brass balls, separated by a small air-gap. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.When the key at the transmitter is pressed, the battery current flows through the primary of the induction coil and generates in the secondary a current of very high voltage, 20,000 volts or more, which is able to jump an air-gap in the shape of a spark at the secondary terminals. The latter are connected to the earth and aerial, as explained above. The high potential currents are therefore enabled to charge the aerial. The charge in the aerial exerts a great tendency to pass into the ground, but is prevented from doing so by the small air-gap between the spark-balls until the charge becomes so great that the air-gap is punctured and the charge passes across and flows down into the ground. The passage of the charge is made evident by the spark between the two spark-balls.The electrical charges flowing up and down the aerial disturb the ether, strike it a blow, as it were. The effect of the blow is to cause the ether to vibrate and to send out waves in all directions. It may be likened to the pond of water which is suddenly struck a blow by throwing a stone into it, so that ripples are immediately sent out in widening circles.These Waves in the Etherare called electro-magnetic orHertzianwaves, after their discoverer, Hertz. The distance over which they pass is dependent upon the power of the transmitting station. The waves can be made to correspond to the dots and dashes of the telegraphic code by so pressing the key. If some means of detecting the waves is employed we may readily see how it is possible to send wireless messages.The Action of the Receiving Stationis just the opposite of that of the transmitter. When the waves pass out through the ether, some of them strike the aerial of the receiving station and generate a charge of electricity in it which tends to pass down into the earth. If the transmitting and receiving stations are very close together and the former is very powerful, it is possible to make a very small gap in the receiving aerial across which the charge will jump in the shape of sparks. Thus the action of the receptor simply takes place in a reversed order from that of the transmitter.If the stations are any considerable distance apart, it is impossible for the currents induced in the receiving aerial to produce sparks, and so some more sensitive means of detecting the waves from the transmitter is necessary, preferably one which makes itself evident to the sense of hearing.The telephone receiver is an extremely sensitive instrument, and it only requires a very weak current to operate it and produce a sound. The currents oroscillationsgenerated in the aerial, however, are alternating currents (see pages 97-99) ofhigh frequency, that is, they flow in one direction and then reverse and flow in the other several thousand times a second. Such a current cannot be made to pass through a telephone receiver, and in order to do so the nature of the current must be changed by converting it into direct current flowing in one direction only.Certain minerals and crystals possess the remarkable ability to do this,silicon, galena, and iron pyrites are among the best.Fig. 195.—A Simple Receptor.Fig. 195.—A Simple Receptor.The diagram in Figure 195 shows the arrangement of a simple receiving outfit. Thedetectorconsists of a sensitive mineral placed between two contacts and connected so that the aerial currents must pass through it on their way to the ground. A telephone receiver is connected to the detector so that therectified currents(currents which have been changed into direct current) pass into it and produce a sound. By varying the periods during which the key is pressed at the transmitting station, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.HOW TO BUILD WIRELESS INSTRUMENTSThe AerialEvery wireless station is provided with a system of wires elevated high in the air, above all surrounding objects, the purpose of which is to radiate or intercept the electromagnetic waves, accordingly as the station is transmitting or receiving. This system of wires is, as already has been stated, called theaerialorantenna.The arrangement of the aerial will greatly determine the efficiency and range of the apparatus.The aerial should be as long as it is reasonably possible to make it, that is from 50 to 150 feet.It will be necessary for most amateurs to put up their aerial in some one certain place, regardless of what else may be in the vicinity, but whenever possible the site selected should preferably be such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smoke-stacks, telephone wires, etc., because such objects will interfere with the aerial and noticeably decrease the range of the station, both when transmitting and receiving.Bare copper wire makes the best aerials. Aluminum wire is very often used and on account of its light weight causes very little strain on the poles or cross arms. Iron wire should never be used for an aerial, even if galvanized or tinned, because it tends to choke the currents which must flow up and down the aerial when the station is in operation.Fig. 196.—Molded Aerial InsulatorFig. 196.—Molded Aerial InsulatorThe aerial must be very carefully insulated from its supports and all surrounding objects. The insulation must be strong enough to hold the weight of the aerial and able to withstand any strain caused by storms.Special aerial insulators made of molded insulating material and having an iron ring imbedded in each end are the best.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Ordinary porcelain cleats may be used on small aerials where the strain is light.One insulator should be placed at each end of each wire close to the spreader or spar.Most aerials are made up of four wires. The wires should be placed as far apart as possible.There are several different forms of aerials, the principal ones of which are shown in Figure 199. They are known as the grid, “V," inverted “L,” and “T” types.Most amateurs support their aerials from a pole placed on the top of the house, in a tree, or erected in the yard. Many use two supports, since such an aerial has many advantages. The facilities to be had for supporting the aerial will largely determine which form to use.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.The grid aerial has no particular advantages or disadvantages.The “V” aerial receives waves much better when they come from a direction opposite to that in which the free end points. The "free" end of the aerial is the one not leading into the station.The inverted “L” aerial possesses the same characteristics as the “V” type.The “T” aerial is the best “all around" and is to be recommended whenever it is possible to put up an aerial of this sort.Much of the detail of actually putting up an aerial or antenna must be omitted, because each experimenter will usually meet different conditions.It should be remembered, however, that the success of the whole undertaking will rest largely upon the construction of a proper aerial. The most excellent instruments will not give very good results if connected to a poor aerial, while, on the other hand, inferior instruments will often give fair results when connected to a good aerial.Fig. 199.—Various Types of Aerials.Fig. 199.—Various Types of Aerials.The aerial should be at least thirty feet high.The wire should not be smaller than No. 14 B. & S.The masts which support the aerial should be of wood and provided with pulleys so that the wires may be lowered any time it may be necessary. The mast should be thoroughly braced with stays or guys so as to counteract the strain of the aerial.The aerial should not be hoisted up perfectly tight, but should be allowed to hang somewhat loose, as it will then put less strain on the ropes and poles that support it.When an aerial is to be fastened in a tree, it is best to attach it to a pole placed in the top of the tree, so that it will come well above any possible interference from the branches.The wires leading from the aerial to the instruments should be very carefully insulated throughout their length. This part of the aerial is called the "rat-tail" or lead-in.The illustrations in Figure 199 show the proper place to attach the “lead-in" form of aerial. The wires should gradually converge.Fig. 200.—A Ground Clamp for Pipes.Fig. 200.—A Ground Clamp for Pipes.It is very important that a good ground connection be secured for wireless instruments. A good ground is absolutely necessary for the proper working of the apparatus. Amateur experimenters usually use the water or gas-pipes for a ground, and fasten the wires by means of a ground clamp such as shown in Figure 200. In the country, where such pipes are not available, it is necessary to bury a sheet of copper, three or four feet square, in a moist spot in the earth and connect a wire to it.The Receiving ApparatusThe receiving instruments form the most interesting part of a wireless station and usually receive first attention from the amateurs. They are the ears of the wireless station and are wondrously sensitive, yet are very simple and easy of construction.The instruments necessary for receiving are:A Detector,A Tuning Coil or a Loose Coupler,A Fixed Condenser,A Telephone Receiver.Other devices, such as a test buzzer, variable condenser, etc., may be added and will improve the outfit.After the aerial has been properly erected, the first instrument necessary to construct will be either a tuning coil or a loose coupler. It is a good plan to make a tuning coil first, and a loose coupler after you have had a little experience with your apparatus.A Tuning Coilis a very simple arrangement making it possible to receive messages from greater distances, and also somewhat to eliminate any messages not desirable and to listen without confusion to the one wanted.A tuning coil consists of a single layer of wire wound upon a cylinder and arranged so that connection may be had with any part of it by means of sliding contacts.The cylinder upon which the wire is wound is a cardboard tube six and three-quarters inches long and two and seven-eighths inches in diameter outside. It should be given two or three coats of shellac both inside and out so that it is thoroughly impregnated, and then laid away until dry. This treatment will prevent the wire from becoming loose after the tube is wound, due to shrinkage of the cardboard.Fig. 201.—Details of the Tuning Coil.Fig. 201.—Details of the Tuning Coil.After having become dry, the tube is wound with a single layer of No. 25 B. & S. gauge green silk or cotton-covered magnet wire. The wire must be wound on very smoothly and tightly, stopping and starting one-quarter of an inch back from each end. The ends of the wire are fastened by weaving back and forth through two small holes punched in the cardboard tube with a pin.The winding should be given a single coat of clear varnish or white shellac and allowed to dry.The coil heads or end pieces are cut from one-half-inch wood according to the plan and dimensions shown in the accompanying illustration.The top corners are beveled and notched to receive the slider-rods. A circular piece of wood two and five-eighths inches in diameter and three-eighths of an inch thick is nailed to the inside of each of the coil heads to support the ends of the cylinder.The wooden parts should be stained mahogany or some other dark color and finished with a coat of shellac or varnish.The slider-rods are square brass 3-16 x 3-16 inches and seven and three-quarters inches long. A small hole is bored near the ends of each, one-quarter of an inch from the edge, to receive a round-headed brass wood screw which holds the rod to the tuner end.The sliders may be made according to the plan shown in Figure 201.The slider is made from a small piece of brass tubing, three-sixteenths of an inch square. An 8-32 flat-headed brass screw is soldered to one face, in the center. A small strip of phosphor bronze sheet or spring copper soldered to the bottom of the slider forms a contact for making connection to the wire on the cylinder. A small "electrose" knob screwed to the slider makes a neat and efficient handle.Two sliders are required, one for each rod.The tuning coil is assembled as shown in Figure 203. The cardboard tube is held in place by several small brass nails driven through it into the circular pieces on the coil heads.A slider is placed on each of the slider-rods and the rods fastened in the slots in the coil ends by a small round-headed brass screw, passing through the holes bored near the ends for that purpose.Fig. 202.—Side and End Views of the Tuning Coil.Fig. 202.—Side and End Views of the Tuning Coil.Two binding-posts are mounted on one of the coil ends. One should be connected to each of the slider-rods. A third binding-post is placed below in the center of the head and connected to one end of the wire wound around the cylinder.A small, narrow path along the coil, directly underneath each slider and to which the copper strip can make contact, must be formed by scraping the insulation off the wire with a sharp knife. The sliders should make contact with each one of the wires as they pass over, and should slide smoothly without damaging or disarranging any of the wires.Fig. 203.—Complete Double-Slider Tuning Coil.Fig. 203.—Complete Double-Slider Tuning Coil.When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.A Loose Coupleris a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.Fig. 204.—A Simple Loose Coupler.Fig. 204.—A Simple Loose Coupler.The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.The primary should be wound with a single layer of No. 22 single-silk-covered magnet wire. The secondary is wound with No. 29 single-silk.The head supporting the secondary is smaller than that used for the same purpose on the primary. The round boss to which the tube is fastened, however, is much thicker.The secondary slides on a "guide-rod" supported at one end by passing through the primary head and at the other by a brass upright. The upright may also be made of wood.If the secondary is "offset," that is, placed out of center slightly to one side, it will leave room so that the secondary slider will possibly pass inside of the primary without striking.Both the primary and the secondary must be fitted with "sliders" to make contact with the various turns of wire.The method of constructing a slider has already been described.The ends of the slider-rods are bent at right angles and fastened to the coil heads by two small screws passing through holes bored near the ends. A small narrow path must be scraped in the insulation under each so that the slider will make contact with each turn. The secondary head may be provided with a small electrose handle to facilitate sliding it back and forth.Two binding-posts are mounted on each of the coil heads.One post on each is connected to the end of the coil farthest from the head, and the other posts are each connected to the slider-rods.Figure 220 shows how to connect the loose coupler in the receiving set.In order to tune with a loose coupler, first adjust the slider on the primary until the signals are the clearest. Then set the secondary slider in the best place and move the secondary in and out of the primary until the signals are clearest.How to Build the Junior Loose CouplerA loose coupler of the sort just described is simple and quite easily constructed, but will not be found to work as well as one in which the secondary may be varied by means of a switch while it is inside of the primary.The base of the instrument measures twelve by three and five-eighths inches. The primary is composed of a single layer of No. 24 B. & S. gauge single-silk-covered wire wound on a cardboard tube two and three-quarter inches in diameter and three and three-quarter inches long. The winding is laid on in a single layer and should comprise about 150 turns. After winding on tightly, it should be given a coat of clean white shellac and allowed to dry. The shellac is for the purpose of fastening the wire down tightly to the tube so that it will not loosen when the slider is moved back and forth.The primary is mounted between two heads, the details of which are shown in Figure 205. One of the heads,B, has a flanged hole two and three-quarter inches in diameter cut through the center so as to receive the end of the tube and permit the secondary to pass inside.Fig. 205.—Details of the Wooden Parts.Fig. 205.—Details of the Wooden Parts.The secondary winding is composed of a single layer of No. 28 B. & S. gauge silk-covered wire and divided into six equal sections. The secondary is supported by two circular wooden pieces,CandF, and slides back and forth on two guide-rods. The guide-rods should be brass. Iron or steel rods running through the center of a loose coupler will seriously weaken the signals, and such practice must by all means be avoided.Fig. 206.—Side View of the Loose Coupler.Fig. 206.—Side View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.The secondary sections are connected to six contacts and a switch-arm mounted on the end of the secondary so that by turning the switch either one, two, three, four, five, or six sections of the winding may be connected.Fig. 208.—End Views of the Loose Coupler.Fig. 208.—End Views of the Loose Coupler.Fig. 209.—Complete Loose Coupler.Fig. 209.—Complete Loose Coupler.The two binding-posts near the secondary end of the coupler are connected to the terminals of the secondary winding by means of two flexible wires. They have not been shown in several of the illustrations because they would be liable to confuse the drawing.The primary is provided with a slider moving back and forth over a narrow path scraped through the insulation so that it may make contact with each wire independently.DetectorsDetectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.Fig. 210.—A Crystal Detector.Fig. 210.—A Crystal Detector.The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.The mineral is contained in a small brass cup mounted on the base below the end of the knob.Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.Fig. 211.—Details of the Crystal Detector.Fig. 211.—Details of the Crystal Detector.The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral.It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena.A Double Slider Tuning Coil.A Double Slider Tuning Coil.A Junior Loose Coupler.A Junior Loose Coupler.Crystal Detectors.Crystal Detectors.Crystal Detectors.Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler."Fig. 212 Details of the "Cat Whisker" Detector.Fig. 212 Details of the "Cat Whisker" Detector.The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth.A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip.The detector shown in Figure 214 is more elaborate than any of the others described so far.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.The base is a wooden block, three and one-half by one and three-quarters inches by one-half inch. The binding-posts are of the type commonly used on electrical instruments. One of the posts is pivoted so that it will swing from side to side. A short piece of brass rod fitted with a rubber or fiber knob passes through the wire hole in the post. A piece of No. 30 B. & S. gauge bronze wire is soldered to the end of the rod. A small brass cup contains the mineral, which may be eithergalena, orsilicon. By twisting the post and sliding the rod back and forth, any portions of the mineral surface may be selected.Fixed Condenser.The construction of the condenser is illustrated in Figure 205. Take twenty-four sheets of thin typewriter paper, three by four inches, and twenty-three sheets of tinfoil, two by four inches. Pile them up, using first a sheet of paper then a sheet of tinfoil, then paper, and so on, so that every two sheets of tinfoil are separated by a sheet of paper. Each sheet of tinfoil must, however, project out beyond the edge of the paper. Connect all the tinfoil projections on one end of the condenser together and and attach a small wire. Connect all those on the opposite side in a similar manner. Then fasten a couple of rubber bands around the condenser to hold it together.Fig. 215.—Building up a Fixed Condenser.Fig. 215.—Building up a Fixed Condenser.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.If it is desired to give the condenser a finished appearance, it may be placed in a brass tube fitted with two wooden or fiber ends. The ends are provided with binding-posts to which the terminals of the condenser are connected.Telephone Receiversfor use with wireless instruments must be purchased. Their construction is such that they cannot be made by the experimenter.Fig. 217.—A Telephone Head Set.Fig. 217.—A Telephone Head Set.A seventy-five ohm, double-pole telephone receiver will do for stations not wishing to receive farther than fifty miles.In order to secure the best results from wireless instruments, it is necessary to have receivers especially made for wireless. Each receiver should have 1000 ohms resistance. Some boys may find it necessary to purchase one receiver at a time. Two receivers, a double headband, and a double cord, forming a complete head set as shown in Figure 217, should be secured as soon as possible.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Connecting the Receiving ApparatusFigure 218 shows how to connect a double-slide tuner, a detector, a fixed condenser and a pair of telephones to the aerial and ground. The same instruments with a loose coupler in place of the double-slide tuner are shown in Figure 219.The diagrams in Figure 220 are the same circuits as those shown in Figures 218 and 219, but show different instruments.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.After the instruments are connected, place a piece of galena or silicon in the cup of the detector and bring the wire down on it. Then move the sliders on the tuning coil or loose coupler and adjust the detector until you can hear a message buzzing in the telephones. It may require a little patience and practice, but if you persist you will soon learn how to adjust the apparatus so as to receive the signals loudly and clearly with very little trouble.The Transmitting ApparatusSpark coils have already been described in Chapter XII. They may be used to transmit wireless messages simply by connecting to a spark-gap and a key.Spark coils which are especially made for wireless telegraphy will usually send farther than an ordinary spark coil used for experimental purposes.Fig. 221.—A Wireless Spark Coil.Fig. 221.—A Wireless Spark Coil.A good one-inch coil costs from $4.50 to $5.00 and will send from three to five miles if used with a fair aerial.A spark coil requires considerable current for its successful operation and will give the best results if operated on storage cells, dry cells, or bichromate cells. If dry cells are used, it is a good plan to connect them in series multiple as shown in Figure 69.Spark-gaps may be made by mounting two double binding-posts on a wooden base as shown in Figure 222.Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.Fig. 222.—Small Spark Gaps.Fig. 222.—Small Spark Gaps.The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.Fig. 223.—Diagram showing how to connect a Simple Transmitter.Fig. 223.—Diagram showing how to connect a Simple Transmitter.If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.Several tubes may be arranged in a rack as shown in Figure 225.A helix consists of a spiral of brass ribbon set in a wooden frame. The two strips composing the frame are each nine inches long. The spiral consists of eight turns of brass ribbon, three-eighths of an inch wide, set in saw-cuts made in the frame. A binding-post is connected to the outside end of the ribbon.Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap.The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end.Fig. 224.—A Test-Tube Leyden Jar.Fig. 224.—A Test-Tube Leyden Jar.In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading.The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest.Anoscillation transformeris sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time.Fig. 226.—A Helix and Clip.Fig. 226.—A Helix and Clip.An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226.Fig. 227.—An Oscillation Transformer.Fig. 227.—An Oscillation Transformer.The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put.AN OSCILLATION HELIX.AN OSCILLATION HELIX.AN OSCILLATION CONDENSER.AN OSCILLATION CONDENSER.An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230.Fig 228.—Circuit showing how to connect a Helix and a Condenser.Fig 228.—Circuit showing how to connect a Helix and a Condenser.The aerial should be connected to the postAand the ground toB. The postsEandFlead to the transmitter, andCandDto the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench.A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.Fig 230.—An Aerial Switch.Fig 230.—An Aerial Switch.Two or three months’ steady practice with a chum should enable the young experimenter to become a very fair wireless telegraph operator. Then by listening for some of the high power wireless stations which send out the press news to ships at sea during the evening it should be possible to become very proficient. The press news is sent more slowly than ordinary commercial wireless messages, and is therefore easy to read and a good starting point for the beginner learning to read.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig. 232.—The Continental Alphabet.Fig. 232.—The Continental Alphabet.A Coherer OutfitA Coherer Outfitis usually capable of only receiving messages coming from a distance of under one mile. In spite of this fact, however, it is an exceedingly interesting apparatus to construct and experiment with, and for this reason is found fully described below.A coherer set will ring a bell or work a sounder for short distances and therefore is the best sort of an arrangement for demonstrating the workings of your wireless apparatus to your friends.The first thing that you need for a coherer is a pair of double binding-posts. Mount these about an inch and three-quarters apart on a wooden base, six inches long and four inches wide as shown in Figure 233.Fig. 233.—A Coherer and a Decoherer.Fig. 233.—A Coherer and a Decoherer.Get a piece of glass tubing about an inch and one-half long and about one-eighth of an inch inside diameter. You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space.The filings must be very carefully prepared, and in order to make them, first use a coarse-grained file on the edge of a five-cent piece. Do not use the fine dust and powder, but only the fairly coarse filings. Mix a few silver filings from a ten-cent piece with the nickel in such proportion that the mixture is 90% nickel and 10% silver.Fig. 234.—Details of the Coherer.Fig. 234.—Details of the Coherer.You will have to experiment considerably to find out just the right amount of filings to place in the tube, and how far apart to place the brass rods or plugs.Remove the gong from an old electric bell and mount the bell on the base as shown in Figure 233. It should be in such a position that the bell hammer will touch the coherer very lightly when the bell is ringing.The two binding-posts, tube rods, and filings constitute thecoherer. The bell is thedecoherer.The next thing required in order to complete the apparatus is a relay. You may use the relay described in Chapter X or build one according to the plan shown in Figure 235. This relay consists of a single electro-magnet mounted on a wooden base, two inches wide and four inches long. The armature is a piece of soft iron rod one-quarter of an inch in diameter and one-eighth of an inch long, riveted to the end of a thin piece of spring brass, about No. 34 B. & S. gauge in thickness.Fig. 235.—The Relay.Fig. 235.—The Relay.The other end of the spring is fitted to a bracket and provided with a thumbscrew to adjust the tension of the spring.The under side of the armature and the upper side of the magnet core are each fitted with a small silver contact.The contacts should meet squarely when the armature is drawn down on to the core by a current of electricity passing through the electro-magnet.By turning the adjusting screw, the armature can be raised or lowered. It should be adjusted so that it almost touches the core and is only just far enough away to slip a piece of thick paper under.The terminals of the magnet are connected to the two binding-posts on the base markedSandS. One of the binding-posts,P, is connected to the brass upright, and the other is connected to the core of the magnet.Figure 236 shows how to connect up the outfit. It will require some very nice adjusting before you will be able to get it to working properly.Fig. 236.—The Complete Coherer Outfit.Fig. 236.—The Complete Coherer Outfit.If you wish to use the outfit for demonstration purposes or for sending messages for very short distances, as for instance across a room, you do not need an aerial but merely a pair of "catch-wires."The "catch-wires" are two pieces of stiff copper wire, about two feet long, placed in the lower holes in the double binding-posts forming part of the coherer.In order to set the apparatus for operation, raise the adjusting screw of the relay until the armature is quite far away from the core. Then push the armature down against the contact on the core. The decoherer should then immediately operate and begin to tap the coherer. Then turn the thumbscrew until the armature is brought down to the core in such a position that it is as close as it is possible to get it without ringing the bell.The transmitter should consist of a spark coil, battery, key, and a spark-gap. The gap should be connected to the secondary of the coil and adjusted so that the electrodes are only about one-eighth of an inch apart. The key is placed in series with the primary of the coil and the battery, so that pressing the key will send a stream of sparks across the gap. Fit the spark-gap with two catch-wires similar to those on the coherer and place the transmitter about four or five feet away from the coherer outfit.You are now likely to find that if you press the key of the transmitter, the decoherer will ring. It is possible that it will continue to ring after you have stopped pressing the key. If such is the case, it will be necessary to turn the adjusting screw on the relay so as to move the armature upward a short distance away from the core.If the decoherer will not operate each time when you press the key, the brass plugs in the coherer need adjusting. You must not be discouraged if you have some difficulty in making the apparatus work at first. After you learn how to adjust it properly, you will find that you can move the transmitter quite a distance away from the coherer and it will still operate very nicely.After you manage that, you can place the apparatus in separate rooms and find it possible to work it just the same, because ordinary walls will not make any difference to wireless waves.Bear in mind that the nearer the coherer plugs are to each other, the more sensitive the coherer will be, but that if too close, the decoherer will not be able to shake the filings properly and will not stop when you stop pressing the key.The operation of the apparatus depends upon the fact that when properly adjusted the resistance of the filings between the two brass plugs is too great to allow sufficient battery current to flow to attract the armature of the relay. As soon as any wireless waves from the transmitter strike the catch-wires of the coherer, they cause the filings to cling together or cohere. When in this state, they have a low resistance and permit the current to flow in the relay circuit and draw down the armature. The armature closes the second circuit and sets the decoherer into operation. The decoherer shakes the filings and causes them to decohere or fall apart and so makes them ready again for the next signal.A coherer set of this sort may be used on an aerial and ground by substituting the coherer for the detector, but otherwise following any of the receiving circuits which have already been shown.A WIRELESS TELEPHONE

CHAPTER VIV WIRELESS TELEGRAPHYProbably no branch of electrical science ever appealed more to the imagination of the experimenter than that coming under the heading of wireless telegraphy. Wherever you go, you are likely to see the ear-marks ofamateurwireless telegraph stations in the aerials and masts set up in trees and on house-tops. It is estimated that there are nearly a quarter of a million such stations in the United States.There is really no great mystery about this wonderful art which made possible the instantaneous transmission of messages over immense distances without any apparent physical connection save that of the earth, air, or water.Did you ever throw a stone in a pool of water? As soon as the stone struck, little waves spread out from the spot in gradually enlarging circles until they reached the shore or died away.By throwing several stones in succession, with varying intervals of time between them, it would be possible so to arrange a set of signals, that they would convey a meaning to a second person standing on the opposite shore of the pool.Wireless telegraphy is based upon the principle ofcreating and detectingwaves in a greatpoolof ether.Modern scientists suppose that all space is filled with an "imaginary" substance calledether. The ether is invisible, odorless, and practically weightless. This ether, however, bears no relation to the anaesthetic of that name which is used in surgical operations.It surrounds and penetrates all substances and all space.Fig. 193.—Little Waves spread out from the Spot.Fig. 193.—Little Waves spread out from the Spot.It exists in a vacuum and in solid rocks. Since the ether does not make itself apparent to any of our physical senses, some of these statements may seem contradictory. Its definite existence cannot be proved except by reasoning, but by accepting and imagining its reality, it is possible to understand and explain many scientific puzzles.A good instance is offered by the sun. Light and heat can be shown to consist of extremely rapid vibrations. That fact can be proved. The sun is over 90,000,000 miles away from our earth and yet light and heat come streaming down to us through a space that is devoid even of air. Something must exist as a medium to transmit these vibrations; it is the ether.Let us consider again the pool of water. The waves or ripples caused by throwing in the stone are vibrations of the water. The distance between two adjacent ripples is called thewave length.The distances between two vibrations of light can also bemeasured. They are so small, however, that they may be spoken of only inthousandthsof an inch. The waves created in the ether by wireless telegraph apparatus are the same as those of light except that their length usually varies from 75 to 9,000feetinstead of a fraction of a thousandth of an inch.Fig. 194.—A Simple Transmitter.Fig. 194.—A Simple Transmitter.A Simple Transmitteris illustrated in Figure 194. A telegraph key is connected in series with a set of cells and theprimaryof an induction coil, which, it will be remembered, is simply a coil consisting of a few turns of wire. This induces a high voltage in a second coil consisting of a larger number of turns and called thesecondary.The terminals of the secondary are led to a spark-gap—an arrangement composed of two polished brass balls, separated by a small air-gap. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.When the key at the transmitter is pressed, the battery current flows through the primary of the induction coil and generates in the secondary a current of very high voltage, 20,000 volts or more, which is able to jump an air-gap in the shape of a spark at the secondary terminals. The latter are connected to the earth and aerial, as explained above. The high potential currents are therefore enabled to charge the aerial. The charge in the aerial exerts a great tendency to pass into the ground, but is prevented from doing so by the small air-gap between the spark-balls until the charge becomes so great that the air-gap is punctured and the charge passes across and flows down into the ground. The passage of the charge is made evident by the spark between the two spark-balls.The electrical charges flowing up and down the aerial disturb the ether, strike it a blow, as it were. The effect of the blow is to cause the ether to vibrate and to send out waves in all directions. It may be likened to the pond of water which is suddenly struck a blow by throwing a stone into it, so that ripples are immediately sent out in widening circles.These Waves in the Etherare called electro-magnetic orHertzianwaves, after their discoverer, Hertz. The distance over which they pass is dependent upon the power of the transmitting station. The waves can be made to correspond to the dots and dashes of the telegraphic code by so pressing the key. If some means of detecting the waves is employed we may readily see how it is possible to send wireless messages.The Action of the Receiving Stationis just the opposite of that of the transmitter. When the waves pass out through the ether, some of them strike the aerial of the receiving station and generate a charge of electricity in it which tends to pass down into the earth. If the transmitting and receiving stations are very close together and the former is very powerful, it is possible to make a very small gap in the receiving aerial across which the charge will jump in the shape of sparks. Thus the action of the receptor simply takes place in a reversed order from that of the transmitter.If the stations are any considerable distance apart, it is impossible for the currents induced in the receiving aerial to produce sparks, and so some more sensitive means of detecting the waves from the transmitter is necessary, preferably one which makes itself evident to the sense of hearing.The telephone receiver is an extremely sensitive instrument, and it only requires a very weak current to operate it and produce a sound. The currents oroscillationsgenerated in the aerial, however, are alternating currents (see pages 97-99) ofhigh frequency, that is, they flow in one direction and then reverse and flow in the other several thousand times a second. Such a current cannot be made to pass through a telephone receiver, and in order to do so the nature of the current must be changed by converting it into direct current flowing in one direction only.Certain minerals and crystals possess the remarkable ability to do this,silicon, galena, and iron pyrites are among the best.Fig. 195.—A Simple Receptor.Fig. 195.—A Simple Receptor.The diagram in Figure 195 shows the arrangement of a simple receiving outfit. Thedetectorconsists of a sensitive mineral placed between two contacts and connected so that the aerial currents must pass through it on their way to the ground. A telephone receiver is connected to the detector so that therectified currents(currents which have been changed into direct current) pass into it and produce a sound. By varying the periods during which the key is pressed at the transmitting station, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.HOW TO BUILD WIRELESS INSTRUMENTSThe AerialEvery wireless station is provided with a system of wires elevated high in the air, above all surrounding objects, the purpose of which is to radiate or intercept the electromagnetic waves, accordingly as the station is transmitting or receiving. This system of wires is, as already has been stated, called theaerialorantenna.The arrangement of the aerial will greatly determine the efficiency and range of the apparatus.The aerial should be as long as it is reasonably possible to make it, that is from 50 to 150 feet.It will be necessary for most amateurs to put up their aerial in some one certain place, regardless of what else may be in the vicinity, but whenever possible the site selected should preferably be such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smoke-stacks, telephone wires, etc., because such objects will interfere with the aerial and noticeably decrease the range of the station, both when transmitting and receiving.Bare copper wire makes the best aerials. Aluminum wire is very often used and on account of its light weight causes very little strain on the poles or cross arms. Iron wire should never be used for an aerial, even if galvanized or tinned, because it tends to choke the currents which must flow up and down the aerial when the station is in operation.Fig. 196.—Molded Aerial InsulatorFig. 196.—Molded Aerial InsulatorThe aerial must be very carefully insulated from its supports and all surrounding objects. The insulation must be strong enough to hold the weight of the aerial and able to withstand any strain caused by storms.Special aerial insulators made of molded insulating material and having an iron ring imbedded in each end are the best.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Ordinary porcelain cleats may be used on small aerials where the strain is light.One insulator should be placed at each end of each wire close to the spreader or spar.Most aerials are made up of four wires. The wires should be placed as far apart as possible.There are several different forms of aerials, the principal ones of which are shown in Figure 199. They are known as the grid, “V," inverted “L,” and “T” types.Most amateurs support their aerials from a pole placed on the top of the house, in a tree, or erected in the yard. Many use two supports, since such an aerial has many advantages. The facilities to be had for supporting the aerial will largely determine which form to use.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.The grid aerial has no particular advantages or disadvantages.The “V” aerial receives waves much better when they come from a direction opposite to that in which the free end points. The "free" end of the aerial is the one not leading into the station.The inverted “L” aerial possesses the same characteristics as the “V” type.The “T” aerial is the best “all around" and is to be recommended whenever it is possible to put up an aerial of this sort.Much of the detail of actually putting up an aerial or antenna must be omitted, because each experimenter will usually meet different conditions.It should be remembered, however, that the success of the whole undertaking will rest largely upon the construction of a proper aerial. The most excellent instruments will not give very good results if connected to a poor aerial, while, on the other hand, inferior instruments will often give fair results when connected to a good aerial.Fig. 199.—Various Types of Aerials.Fig. 199.—Various Types of Aerials.The aerial should be at least thirty feet high.The wire should not be smaller than No. 14 B. & S.The masts which support the aerial should be of wood and provided with pulleys so that the wires may be lowered any time it may be necessary. The mast should be thoroughly braced with stays or guys so as to counteract the strain of the aerial.The aerial should not be hoisted up perfectly tight, but should be allowed to hang somewhat loose, as it will then put less strain on the ropes and poles that support it.When an aerial is to be fastened in a tree, it is best to attach it to a pole placed in the top of the tree, so that it will come well above any possible interference from the branches.The wires leading from the aerial to the instruments should be very carefully insulated throughout their length. This part of the aerial is called the "rat-tail" or lead-in.The illustrations in Figure 199 show the proper place to attach the “lead-in" form of aerial. The wires should gradually converge.Fig. 200.—A Ground Clamp for Pipes.Fig. 200.—A Ground Clamp for Pipes.It is very important that a good ground connection be secured for wireless instruments. A good ground is absolutely necessary for the proper working of the apparatus. Amateur experimenters usually use the water or gas-pipes for a ground, and fasten the wires by means of a ground clamp such as shown in Figure 200. In the country, where such pipes are not available, it is necessary to bury a sheet of copper, three or four feet square, in a moist spot in the earth and connect a wire to it.The Receiving ApparatusThe receiving instruments form the most interesting part of a wireless station and usually receive first attention from the amateurs. They are the ears of the wireless station and are wondrously sensitive, yet are very simple and easy of construction.The instruments necessary for receiving are:A Detector,A Tuning Coil or a Loose Coupler,A Fixed Condenser,A Telephone Receiver.Other devices, such as a test buzzer, variable condenser, etc., may be added and will improve the outfit.After the aerial has been properly erected, the first instrument necessary to construct will be either a tuning coil or a loose coupler. It is a good plan to make a tuning coil first, and a loose coupler after you have had a little experience with your apparatus.A Tuning Coilis a very simple arrangement making it possible to receive messages from greater distances, and also somewhat to eliminate any messages not desirable and to listen without confusion to the one wanted.A tuning coil consists of a single layer of wire wound upon a cylinder and arranged so that connection may be had with any part of it by means of sliding contacts.The cylinder upon which the wire is wound is a cardboard tube six and three-quarters inches long and two and seven-eighths inches in diameter outside. It should be given two or three coats of shellac both inside and out so that it is thoroughly impregnated, and then laid away until dry. This treatment will prevent the wire from becoming loose after the tube is wound, due to shrinkage of the cardboard.Fig. 201.—Details of the Tuning Coil.Fig. 201.—Details of the Tuning Coil.After having become dry, the tube is wound with a single layer of No. 25 B. & S. gauge green silk or cotton-covered magnet wire. The wire must be wound on very smoothly and tightly, stopping and starting one-quarter of an inch back from each end. The ends of the wire are fastened by weaving back and forth through two small holes punched in the cardboard tube with a pin.The winding should be given a single coat of clear varnish or white shellac and allowed to dry.The coil heads or end pieces are cut from one-half-inch wood according to the plan and dimensions shown in the accompanying illustration.The top corners are beveled and notched to receive the slider-rods. A circular piece of wood two and five-eighths inches in diameter and three-eighths of an inch thick is nailed to the inside of each of the coil heads to support the ends of the cylinder.The wooden parts should be stained mahogany or some other dark color and finished with a coat of shellac or varnish.The slider-rods are square brass 3-16 x 3-16 inches and seven and three-quarters inches long. A small hole is bored near the ends of each, one-quarter of an inch from the edge, to receive a round-headed brass wood screw which holds the rod to the tuner end.The sliders may be made according to the plan shown in Figure 201.The slider is made from a small piece of brass tubing, three-sixteenths of an inch square. An 8-32 flat-headed brass screw is soldered to one face, in the center. A small strip of phosphor bronze sheet or spring copper soldered to the bottom of the slider forms a contact for making connection to the wire on the cylinder. A small "electrose" knob screwed to the slider makes a neat and efficient handle.Two sliders are required, one for each rod.The tuning coil is assembled as shown in Figure 203. The cardboard tube is held in place by several small brass nails driven through it into the circular pieces on the coil heads.A slider is placed on each of the slider-rods and the rods fastened in the slots in the coil ends by a small round-headed brass screw, passing through the holes bored near the ends for that purpose.Fig. 202.—Side and End Views of the Tuning Coil.Fig. 202.—Side and End Views of the Tuning Coil.Two binding-posts are mounted on one of the coil ends. One should be connected to each of the slider-rods. A third binding-post is placed below in the center of the head and connected to one end of the wire wound around the cylinder.A small, narrow path along the coil, directly underneath each slider and to which the copper strip can make contact, must be formed by scraping the insulation off the wire with a sharp knife. The sliders should make contact with each one of the wires as they pass over, and should slide smoothly without damaging or disarranging any of the wires.Fig. 203.—Complete Double-Slider Tuning Coil.Fig. 203.—Complete Double-Slider Tuning Coil.When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.A Loose Coupleris a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.Fig. 204.—A Simple Loose Coupler.Fig. 204.—A Simple Loose Coupler.The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.The primary should be wound with a single layer of No. 22 single-silk-covered magnet wire. The secondary is wound with No. 29 single-silk.The head supporting the secondary is smaller than that used for the same purpose on the primary. The round boss to which the tube is fastened, however, is much thicker.The secondary slides on a "guide-rod" supported at one end by passing through the primary head and at the other by a brass upright. The upright may also be made of wood.If the secondary is "offset," that is, placed out of center slightly to one side, it will leave room so that the secondary slider will possibly pass inside of the primary without striking.Both the primary and the secondary must be fitted with "sliders" to make contact with the various turns of wire.The method of constructing a slider has already been described.The ends of the slider-rods are bent at right angles and fastened to the coil heads by two small screws passing through holes bored near the ends. A small narrow path must be scraped in the insulation under each so that the slider will make contact with each turn. The secondary head may be provided with a small electrose handle to facilitate sliding it back and forth.Two binding-posts are mounted on each of the coil heads.One post on each is connected to the end of the coil farthest from the head, and the other posts are each connected to the slider-rods.Figure 220 shows how to connect the loose coupler in the receiving set.In order to tune with a loose coupler, first adjust the slider on the primary until the signals are the clearest. Then set the secondary slider in the best place and move the secondary in and out of the primary until the signals are clearest.How to Build the Junior Loose CouplerA loose coupler of the sort just described is simple and quite easily constructed, but will not be found to work as well as one in which the secondary may be varied by means of a switch while it is inside of the primary.The base of the instrument measures twelve by three and five-eighths inches. The primary is composed of a single layer of No. 24 B. & S. gauge single-silk-covered wire wound on a cardboard tube two and three-quarter inches in diameter and three and three-quarter inches long. The winding is laid on in a single layer and should comprise about 150 turns. After winding on tightly, it should be given a coat of clean white shellac and allowed to dry. The shellac is for the purpose of fastening the wire down tightly to the tube so that it will not loosen when the slider is moved back and forth.The primary is mounted between two heads, the details of which are shown in Figure 205. One of the heads,B, has a flanged hole two and three-quarter inches in diameter cut through the center so as to receive the end of the tube and permit the secondary to pass inside.Fig. 205.—Details of the Wooden Parts.Fig. 205.—Details of the Wooden Parts.The secondary winding is composed of a single layer of No. 28 B. & S. gauge silk-covered wire and divided into six equal sections. The secondary is supported by two circular wooden pieces,CandF, and slides back and forth on two guide-rods. The guide-rods should be brass. Iron or steel rods running through the center of a loose coupler will seriously weaken the signals, and such practice must by all means be avoided.Fig. 206.—Side View of the Loose Coupler.Fig. 206.—Side View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.The secondary sections are connected to six contacts and a switch-arm mounted on the end of the secondary so that by turning the switch either one, two, three, four, five, or six sections of the winding may be connected.Fig. 208.—End Views of the Loose Coupler.Fig. 208.—End Views of the Loose Coupler.Fig. 209.—Complete Loose Coupler.Fig. 209.—Complete Loose Coupler.The two binding-posts near the secondary end of the coupler are connected to the terminals of the secondary winding by means of two flexible wires. They have not been shown in several of the illustrations because they would be liable to confuse the drawing.The primary is provided with a slider moving back and forth over a narrow path scraped through the insulation so that it may make contact with each wire independently.DetectorsDetectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.Fig. 210.—A Crystal Detector.Fig. 210.—A Crystal Detector.The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.The mineral is contained in a small brass cup mounted on the base below the end of the knob.Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.Fig. 211.—Details of the Crystal Detector.Fig. 211.—Details of the Crystal Detector.The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral.It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena.A Double Slider Tuning Coil.A Double Slider Tuning Coil.A Junior Loose Coupler.A Junior Loose Coupler.Crystal Detectors.Crystal Detectors.Crystal Detectors.Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler."Fig. 212 Details of the "Cat Whisker" Detector.Fig. 212 Details of the "Cat Whisker" Detector.The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth.A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip.The detector shown in Figure 214 is more elaborate than any of the others described so far.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.The base is a wooden block, three and one-half by one and three-quarters inches by one-half inch. The binding-posts are of the type commonly used on electrical instruments. One of the posts is pivoted so that it will swing from side to side. A short piece of brass rod fitted with a rubber or fiber knob passes through the wire hole in the post. A piece of No. 30 B. & S. gauge bronze wire is soldered to the end of the rod. A small brass cup contains the mineral, which may be eithergalena, orsilicon. By twisting the post and sliding the rod back and forth, any portions of the mineral surface may be selected.Fixed Condenser.The construction of the condenser is illustrated in Figure 205. Take twenty-four sheets of thin typewriter paper, three by four inches, and twenty-three sheets of tinfoil, two by four inches. Pile them up, using first a sheet of paper then a sheet of tinfoil, then paper, and so on, so that every two sheets of tinfoil are separated by a sheet of paper. Each sheet of tinfoil must, however, project out beyond the edge of the paper. Connect all the tinfoil projections on one end of the condenser together and and attach a small wire. Connect all those on the opposite side in a similar manner. Then fasten a couple of rubber bands around the condenser to hold it together.Fig. 215.—Building up a Fixed Condenser.Fig. 215.—Building up a Fixed Condenser.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.If it is desired to give the condenser a finished appearance, it may be placed in a brass tube fitted with two wooden or fiber ends. The ends are provided with binding-posts to which the terminals of the condenser are connected.Telephone Receiversfor use with wireless instruments must be purchased. Their construction is such that they cannot be made by the experimenter.Fig. 217.—A Telephone Head Set.Fig. 217.—A Telephone Head Set.A seventy-five ohm, double-pole telephone receiver will do for stations not wishing to receive farther than fifty miles.In order to secure the best results from wireless instruments, it is necessary to have receivers especially made for wireless. Each receiver should have 1000 ohms resistance. Some boys may find it necessary to purchase one receiver at a time. Two receivers, a double headband, and a double cord, forming a complete head set as shown in Figure 217, should be secured as soon as possible.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Connecting the Receiving ApparatusFigure 218 shows how to connect a double-slide tuner, a detector, a fixed condenser and a pair of telephones to the aerial and ground. The same instruments with a loose coupler in place of the double-slide tuner are shown in Figure 219.The diagrams in Figure 220 are the same circuits as those shown in Figures 218 and 219, but show different instruments.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.After the instruments are connected, place a piece of galena or silicon in the cup of the detector and bring the wire down on it. Then move the sliders on the tuning coil or loose coupler and adjust the detector until you can hear a message buzzing in the telephones. It may require a little patience and practice, but if you persist you will soon learn how to adjust the apparatus so as to receive the signals loudly and clearly with very little trouble.The Transmitting ApparatusSpark coils have already been described in Chapter XII. They may be used to transmit wireless messages simply by connecting to a spark-gap and a key.Spark coils which are especially made for wireless telegraphy will usually send farther than an ordinary spark coil used for experimental purposes.Fig. 221.—A Wireless Spark Coil.Fig. 221.—A Wireless Spark Coil.A good one-inch coil costs from $4.50 to $5.00 and will send from three to five miles if used with a fair aerial.A spark coil requires considerable current for its successful operation and will give the best results if operated on storage cells, dry cells, or bichromate cells. If dry cells are used, it is a good plan to connect them in series multiple as shown in Figure 69.Spark-gaps may be made by mounting two double binding-posts on a wooden base as shown in Figure 222.Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.Fig. 222.—Small Spark Gaps.Fig. 222.—Small Spark Gaps.The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.Fig. 223.—Diagram showing how to connect a Simple Transmitter.Fig. 223.—Diagram showing how to connect a Simple Transmitter.If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.Several tubes may be arranged in a rack as shown in Figure 225.A helix consists of a spiral of brass ribbon set in a wooden frame. The two strips composing the frame are each nine inches long. The spiral consists of eight turns of brass ribbon, three-eighths of an inch wide, set in saw-cuts made in the frame. A binding-post is connected to the outside end of the ribbon.Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap.The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end.Fig. 224.—A Test-Tube Leyden Jar.Fig. 224.—A Test-Tube Leyden Jar.In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading.The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest.Anoscillation transformeris sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time.Fig. 226.—A Helix and Clip.Fig. 226.—A Helix and Clip.An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226.Fig. 227.—An Oscillation Transformer.Fig. 227.—An Oscillation Transformer.The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put.AN OSCILLATION HELIX.AN OSCILLATION HELIX.AN OSCILLATION CONDENSER.AN OSCILLATION CONDENSER.An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230.Fig 228.—Circuit showing how to connect a Helix and a Condenser.Fig 228.—Circuit showing how to connect a Helix and a Condenser.The aerial should be connected to the postAand the ground toB. The postsEandFlead to the transmitter, andCandDto the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench.A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.Fig 230.—An Aerial Switch.Fig 230.—An Aerial Switch.Two or three months’ steady practice with a chum should enable the young experimenter to become a very fair wireless telegraph operator. Then by listening for some of the high power wireless stations which send out the press news to ships at sea during the evening it should be possible to become very proficient. The press news is sent more slowly than ordinary commercial wireless messages, and is therefore easy to read and a good starting point for the beginner learning to read.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig. 232.—The Continental Alphabet.Fig. 232.—The Continental Alphabet.A Coherer OutfitA Coherer Outfitis usually capable of only receiving messages coming from a distance of under one mile. In spite of this fact, however, it is an exceedingly interesting apparatus to construct and experiment with, and for this reason is found fully described below.A coherer set will ring a bell or work a sounder for short distances and therefore is the best sort of an arrangement for demonstrating the workings of your wireless apparatus to your friends.The first thing that you need for a coherer is a pair of double binding-posts. Mount these about an inch and three-quarters apart on a wooden base, six inches long and four inches wide as shown in Figure 233.Fig. 233.—A Coherer and a Decoherer.Fig. 233.—A Coherer and a Decoherer.Get a piece of glass tubing about an inch and one-half long and about one-eighth of an inch inside diameter. You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space.The filings must be very carefully prepared, and in order to make them, first use a coarse-grained file on the edge of a five-cent piece. Do not use the fine dust and powder, but only the fairly coarse filings. Mix a few silver filings from a ten-cent piece with the nickel in such proportion that the mixture is 90% nickel and 10% silver.Fig. 234.—Details of the Coherer.Fig. 234.—Details of the Coherer.You will have to experiment considerably to find out just the right amount of filings to place in the tube, and how far apart to place the brass rods or plugs.Remove the gong from an old electric bell and mount the bell on the base as shown in Figure 233. It should be in such a position that the bell hammer will touch the coherer very lightly when the bell is ringing.The two binding-posts, tube rods, and filings constitute thecoherer. The bell is thedecoherer.The next thing required in order to complete the apparatus is a relay. You may use the relay described in Chapter X or build one according to the plan shown in Figure 235. This relay consists of a single electro-magnet mounted on a wooden base, two inches wide and four inches long. The armature is a piece of soft iron rod one-quarter of an inch in diameter and one-eighth of an inch long, riveted to the end of a thin piece of spring brass, about No. 34 B. & S. gauge in thickness.Fig. 235.—The Relay.Fig. 235.—The Relay.The other end of the spring is fitted to a bracket and provided with a thumbscrew to adjust the tension of the spring.The under side of the armature and the upper side of the magnet core are each fitted with a small silver contact.The contacts should meet squarely when the armature is drawn down on to the core by a current of electricity passing through the electro-magnet.By turning the adjusting screw, the armature can be raised or lowered. It should be adjusted so that it almost touches the core and is only just far enough away to slip a piece of thick paper under.The terminals of the magnet are connected to the two binding-posts on the base markedSandS. One of the binding-posts,P, is connected to the brass upright, and the other is connected to the core of the magnet.Figure 236 shows how to connect up the outfit. It will require some very nice adjusting before you will be able to get it to working properly.Fig. 236.—The Complete Coherer Outfit.Fig. 236.—The Complete Coherer Outfit.If you wish to use the outfit for demonstration purposes or for sending messages for very short distances, as for instance across a room, you do not need an aerial but merely a pair of "catch-wires."The "catch-wires" are two pieces of stiff copper wire, about two feet long, placed in the lower holes in the double binding-posts forming part of the coherer.In order to set the apparatus for operation, raise the adjusting screw of the relay until the armature is quite far away from the core. Then push the armature down against the contact on the core. The decoherer should then immediately operate and begin to tap the coherer. Then turn the thumbscrew until the armature is brought down to the core in such a position that it is as close as it is possible to get it without ringing the bell.The transmitter should consist of a spark coil, battery, key, and a spark-gap. The gap should be connected to the secondary of the coil and adjusted so that the electrodes are only about one-eighth of an inch apart. The key is placed in series with the primary of the coil and the battery, so that pressing the key will send a stream of sparks across the gap. Fit the spark-gap with two catch-wires similar to those on the coherer and place the transmitter about four or five feet away from the coherer outfit.You are now likely to find that if you press the key of the transmitter, the decoherer will ring. It is possible that it will continue to ring after you have stopped pressing the key. If such is the case, it will be necessary to turn the adjusting screw on the relay so as to move the armature upward a short distance away from the core.If the decoherer will not operate each time when you press the key, the brass plugs in the coherer need adjusting. You must not be discouraged if you have some difficulty in making the apparatus work at first. After you learn how to adjust it properly, you will find that you can move the transmitter quite a distance away from the coherer and it will still operate very nicely.After you manage that, you can place the apparatus in separate rooms and find it possible to work it just the same, because ordinary walls will not make any difference to wireless waves.Bear in mind that the nearer the coherer plugs are to each other, the more sensitive the coherer will be, but that if too close, the decoherer will not be able to shake the filings properly and will not stop when you stop pressing the key.The operation of the apparatus depends upon the fact that when properly adjusted the resistance of the filings between the two brass plugs is too great to allow sufficient battery current to flow to attract the armature of the relay. As soon as any wireless waves from the transmitter strike the catch-wires of the coherer, they cause the filings to cling together or cohere. When in this state, they have a low resistance and permit the current to flow in the relay circuit and draw down the armature. The armature closes the second circuit and sets the decoherer into operation. The decoherer shakes the filings and causes them to decohere or fall apart and so makes them ready again for the next signal.A coherer set of this sort may be used on an aerial and ground by substituting the coherer for the detector, but otherwise following any of the receiving circuits which have already been shown.A WIRELESS TELEPHONE

CHAPTER VIV WIRELESS TELEGRAPHYProbably no branch of electrical science ever appealed more to the imagination of the experimenter than that coming under the heading of wireless telegraphy. Wherever you go, you are likely to see the ear-marks ofamateurwireless telegraph stations in the aerials and masts set up in trees and on house-tops. It is estimated that there are nearly a quarter of a million such stations in the United States.There is really no great mystery about this wonderful art which made possible the instantaneous transmission of messages over immense distances without any apparent physical connection save that of the earth, air, or water.Did you ever throw a stone in a pool of water? As soon as the stone struck, little waves spread out from the spot in gradually enlarging circles until they reached the shore or died away.By throwing several stones in succession, with varying intervals of time between them, it would be possible so to arrange a set of signals, that they would convey a meaning to a second person standing on the opposite shore of the pool.Wireless telegraphy is based upon the principle ofcreating and detectingwaves in a greatpoolof ether.Modern scientists suppose that all space is filled with an "imaginary" substance calledether. The ether is invisible, odorless, and practically weightless. This ether, however, bears no relation to the anaesthetic of that name which is used in surgical operations.It surrounds and penetrates all substances and all space.Fig. 193.—Little Waves spread out from the Spot.Fig. 193.—Little Waves spread out from the Spot.It exists in a vacuum and in solid rocks. Since the ether does not make itself apparent to any of our physical senses, some of these statements may seem contradictory. Its definite existence cannot be proved except by reasoning, but by accepting and imagining its reality, it is possible to understand and explain many scientific puzzles.A good instance is offered by the sun. Light and heat can be shown to consist of extremely rapid vibrations. That fact can be proved. The sun is over 90,000,000 miles away from our earth and yet light and heat come streaming down to us through a space that is devoid even of air. Something must exist as a medium to transmit these vibrations; it is the ether.Let us consider again the pool of water. The waves or ripples caused by throwing in the stone are vibrations of the water. The distance between two adjacent ripples is called thewave length.The distances between two vibrations of light can also bemeasured. They are so small, however, that they may be spoken of only inthousandthsof an inch. The waves created in the ether by wireless telegraph apparatus are the same as those of light except that their length usually varies from 75 to 9,000feetinstead of a fraction of a thousandth of an inch.Fig. 194.—A Simple Transmitter.Fig. 194.—A Simple Transmitter.A Simple Transmitteris illustrated in Figure 194. A telegraph key is connected in series with a set of cells and theprimaryof an induction coil, which, it will be remembered, is simply a coil consisting of a few turns of wire. This induces a high voltage in a second coil consisting of a larger number of turns and called thesecondary.The terminals of the secondary are led to a spark-gap—an arrangement composed of two polished brass balls, separated by a small air-gap. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.When the key at the transmitter is pressed, the battery current flows through the primary of the induction coil and generates in the secondary a current of very high voltage, 20,000 volts or more, which is able to jump an air-gap in the shape of a spark at the secondary terminals. The latter are connected to the earth and aerial, as explained above. The high potential currents are therefore enabled to charge the aerial. The charge in the aerial exerts a great tendency to pass into the ground, but is prevented from doing so by the small air-gap between the spark-balls until the charge becomes so great that the air-gap is punctured and the charge passes across and flows down into the ground. The passage of the charge is made evident by the spark between the two spark-balls.The electrical charges flowing up and down the aerial disturb the ether, strike it a blow, as it were. The effect of the blow is to cause the ether to vibrate and to send out waves in all directions. It may be likened to the pond of water which is suddenly struck a blow by throwing a stone into it, so that ripples are immediately sent out in widening circles.These Waves in the Etherare called electro-magnetic orHertzianwaves, after their discoverer, Hertz. The distance over which they pass is dependent upon the power of the transmitting station. The waves can be made to correspond to the dots and dashes of the telegraphic code by so pressing the key. If some means of detecting the waves is employed we may readily see how it is possible to send wireless messages.The Action of the Receiving Stationis just the opposite of that of the transmitter. When the waves pass out through the ether, some of them strike the aerial of the receiving station and generate a charge of electricity in it which tends to pass down into the earth. If the transmitting and receiving stations are very close together and the former is very powerful, it is possible to make a very small gap in the receiving aerial across which the charge will jump in the shape of sparks. Thus the action of the receptor simply takes place in a reversed order from that of the transmitter.If the stations are any considerable distance apart, it is impossible for the currents induced in the receiving aerial to produce sparks, and so some more sensitive means of detecting the waves from the transmitter is necessary, preferably one which makes itself evident to the sense of hearing.The telephone receiver is an extremely sensitive instrument, and it only requires a very weak current to operate it and produce a sound. The currents oroscillationsgenerated in the aerial, however, are alternating currents (see pages 97-99) ofhigh frequency, that is, they flow in one direction and then reverse and flow in the other several thousand times a second. Such a current cannot be made to pass through a telephone receiver, and in order to do so the nature of the current must be changed by converting it into direct current flowing in one direction only.Certain minerals and crystals possess the remarkable ability to do this,silicon, galena, and iron pyrites are among the best.Fig. 195.—A Simple Receptor.Fig. 195.—A Simple Receptor.The diagram in Figure 195 shows the arrangement of a simple receiving outfit. Thedetectorconsists of a sensitive mineral placed between two contacts and connected so that the aerial currents must pass through it on their way to the ground. A telephone receiver is connected to the detector so that therectified currents(currents which have been changed into direct current) pass into it and produce a sound. By varying the periods during which the key is pressed at the transmitting station, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.HOW TO BUILD WIRELESS INSTRUMENTSThe AerialEvery wireless station is provided with a system of wires elevated high in the air, above all surrounding objects, the purpose of which is to radiate or intercept the electromagnetic waves, accordingly as the station is transmitting or receiving. This system of wires is, as already has been stated, called theaerialorantenna.The arrangement of the aerial will greatly determine the efficiency and range of the apparatus.The aerial should be as long as it is reasonably possible to make it, that is from 50 to 150 feet.It will be necessary for most amateurs to put up their aerial in some one certain place, regardless of what else may be in the vicinity, but whenever possible the site selected should preferably be such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smoke-stacks, telephone wires, etc., because such objects will interfere with the aerial and noticeably decrease the range of the station, both when transmitting and receiving.Bare copper wire makes the best aerials. Aluminum wire is very often used and on account of its light weight causes very little strain on the poles or cross arms. Iron wire should never be used for an aerial, even if galvanized or tinned, because it tends to choke the currents which must flow up and down the aerial when the station is in operation.Fig. 196.—Molded Aerial InsulatorFig. 196.—Molded Aerial InsulatorThe aerial must be very carefully insulated from its supports and all surrounding objects. The insulation must be strong enough to hold the weight of the aerial and able to withstand any strain caused by storms.Special aerial insulators made of molded insulating material and having an iron ring imbedded in each end are the best.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Ordinary porcelain cleats may be used on small aerials where the strain is light.One insulator should be placed at each end of each wire close to the spreader or spar.Most aerials are made up of four wires. The wires should be placed as far apart as possible.There are several different forms of aerials, the principal ones of which are shown in Figure 199. They are known as the grid, “V," inverted “L,” and “T” types.Most amateurs support their aerials from a pole placed on the top of the house, in a tree, or erected in the yard. Many use two supports, since such an aerial has many advantages. The facilities to be had for supporting the aerial will largely determine which form to use.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.The grid aerial has no particular advantages or disadvantages.The “V” aerial receives waves much better when they come from a direction opposite to that in which the free end points. The "free" end of the aerial is the one not leading into the station.The inverted “L” aerial possesses the same characteristics as the “V” type.The “T” aerial is the best “all around" and is to be recommended whenever it is possible to put up an aerial of this sort.Much of the detail of actually putting up an aerial or antenna must be omitted, because each experimenter will usually meet different conditions.It should be remembered, however, that the success of the whole undertaking will rest largely upon the construction of a proper aerial. The most excellent instruments will not give very good results if connected to a poor aerial, while, on the other hand, inferior instruments will often give fair results when connected to a good aerial.Fig. 199.—Various Types of Aerials.Fig. 199.—Various Types of Aerials.The aerial should be at least thirty feet high.The wire should not be smaller than No. 14 B. & S.The masts which support the aerial should be of wood and provided with pulleys so that the wires may be lowered any time it may be necessary. The mast should be thoroughly braced with stays or guys so as to counteract the strain of the aerial.The aerial should not be hoisted up perfectly tight, but should be allowed to hang somewhat loose, as it will then put less strain on the ropes and poles that support it.When an aerial is to be fastened in a tree, it is best to attach it to a pole placed in the top of the tree, so that it will come well above any possible interference from the branches.The wires leading from the aerial to the instruments should be very carefully insulated throughout their length. This part of the aerial is called the "rat-tail" or lead-in.The illustrations in Figure 199 show the proper place to attach the “lead-in" form of aerial. The wires should gradually converge.Fig. 200.—A Ground Clamp for Pipes.Fig. 200.—A Ground Clamp for Pipes.It is very important that a good ground connection be secured for wireless instruments. A good ground is absolutely necessary for the proper working of the apparatus. Amateur experimenters usually use the water or gas-pipes for a ground, and fasten the wires by means of a ground clamp such as shown in Figure 200. In the country, where such pipes are not available, it is necessary to bury a sheet of copper, three or four feet square, in a moist spot in the earth and connect a wire to it.The Receiving ApparatusThe receiving instruments form the most interesting part of a wireless station and usually receive first attention from the amateurs. They are the ears of the wireless station and are wondrously sensitive, yet are very simple and easy of construction.The instruments necessary for receiving are:A Detector,A Tuning Coil or a Loose Coupler,A Fixed Condenser,A Telephone Receiver.Other devices, such as a test buzzer, variable condenser, etc., may be added and will improve the outfit.After the aerial has been properly erected, the first instrument necessary to construct will be either a tuning coil or a loose coupler. It is a good plan to make a tuning coil first, and a loose coupler after you have had a little experience with your apparatus.A Tuning Coilis a very simple arrangement making it possible to receive messages from greater distances, and also somewhat to eliminate any messages not desirable and to listen without confusion to the one wanted.A tuning coil consists of a single layer of wire wound upon a cylinder and arranged so that connection may be had with any part of it by means of sliding contacts.The cylinder upon which the wire is wound is a cardboard tube six and three-quarters inches long and two and seven-eighths inches in diameter outside. It should be given two or three coats of shellac both inside and out so that it is thoroughly impregnated, and then laid away until dry. This treatment will prevent the wire from becoming loose after the tube is wound, due to shrinkage of the cardboard.Fig. 201.—Details of the Tuning Coil.Fig. 201.—Details of the Tuning Coil.After having become dry, the tube is wound with a single layer of No. 25 B. & S. gauge green silk or cotton-covered magnet wire. The wire must be wound on very smoothly and tightly, stopping and starting one-quarter of an inch back from each end. The ends of the wire are fastened by weaving back and forth through two small holes punched in the cardboard tube with a pin.The winding should be given a single coat of clear varnish or white shellac and allowed to dry.The coil heads or end pieces are cut from one-half-inch wood according to the plan and dimensions shown in the accompanying illustration.The top corners are beveled and notched to receive the slider-rods. A circular piece of wood two and five-eighths inches in diameter and three-eighths of an inch thick is nailed to the inside of each of the coil heads to support the ends of the cylinder.The wooden parts should be stained mahogany or some other dark color and finished with a coat of shellac or varnish.The slider-rods are square brass 3-16 x 3-16 inches and seven and three-quarters inches long. A small hole is bored near the ends of each, one-quarter of an inch from the edge, to receive a round-headed brass wood screw which holds the rod to the tuner end.The sliders may be made according to the plan shown in Figure 201.The slider is made from a small piece of brass tubing, three-sixteenths of an inch square. An 8-32 flat-headed brass screw is soldered to one face, in the center. A small strip of phosphor bronze sheet or spring copper soldered to the bottom of the slider forms a contact for making connection to the wire on the cylinder. A small "electrose" knob screwed to the slider makes a neat and efficient handle.Two sliders are required, one for each rod.The tuning coil is assembled as shown in Figure 203. The cardboard tube is held in place by several small brass nails driven through it into the circular pieces on the coil heads.A slider is placed on each of the slider-rods and the rods fastened in the slots in the coil ends by a small round-headed brass screw, passing through the holes bored near the ends for that purpose.Fig. 202.—Side and End Views of the Tuning Coil.Fig. 202.—Side and End Views of the Tuning Coil.Two binding-posts are mounted on one of the coil ends. One should be connected to each of the slider-rods. A third binding-post is placed below in the center of the head and connected to one end of the wire wound around the cylinder.A small, narrow path along the coil, directly underneath each slider and to which the copper strip can make contact, must be formed by scraping the insulation off the wire with a sharp knife. The sliders should make contact with each one of the wires as they pass over, and should slide smoothly without damaging or disarranging any of the wires.Fig. 203.—Complete Double-Slider Tuning Coil.Fig. 203.—Complete Double-Slider Tuning Coil.When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.A Loose Coupleris a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.Fig. 204.—A Simple Loose Coupler.Fig. 204.—A Simple Loose Coupler.The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.The primary should be wound with a single layer of No. 22 single-silk-covered magnet wire. The secondary is wound with No. 29 single-silk.The head supporting the secondary is smaller than that used for the same purpose on the primary. The round boss to which the tube is fastened, however, is much thicker.The secondary slides on a "guide-rod" supported at one end by passing through the primary head and at the other by a brass upright. The upright may also be made of wood.If the secondary is "offset," that is, placed out of center slightly to one side, it will leave room so that the secondary slider will possibly pass inside of the primary without striking.Both the primary and the secondary must be fitted with "sliders" to make contact with the various turns of wire.The method of constructing a slider has already been described.The ends of the slider-rods are bent at right angles and fastened to the coil heads by two small screws passing through holes bored near the ends. A small narrow path must be scraped in the insulation under each so that the slider will make contact with each turn. The secondary head may be provided with a small electrose handle to facilitate sliding it back and forth.Two binding-posts are mounted on each of the coil heads.One post on each is connected to the end of the coil farthest from the head, and the other posts are each connected to the slider-rods.Figure 220 shows how to connect the loose coupler in the receiving set.In order to tune with a loose coupler, first adjust the slider on the primary until the signals are the clearest. Then set the secondary slider in the best place and move the secondary in and out of the primary until the signals are clearest.How to Build the Junior Loose CouplerA loose coupler of the sort just described is simple and quite easily constructed, but will not be found to work as well as one in which the secondary may be varied by means of a switch while it is inside of the primary.The base of the instrument measures twelve by three and five-eighths inches. The primary is composed of a single layer of No. 24 B. & S. gauge single-silk-covered wire wound on a cardboard tube two and three-quarter inches in diameter and three and three-quarter inches long. The winding is laid on in a single layer and should comprise about 150 turns. After winding on tightly, it should be given a coat of clean white shellac and allowed to dry. The shellac is for the purpose of fastening the wire down tightly to the tube so that it will not loosen when the slider is moved back and forth.The primary is mounted between two heads, the details of which are shown in Figure 205. One of the heads,B, has a flanged hole two and three-quarter inches in diameter cut through the center so as to receive the end of the tube and permit the secondary to pass inside.Fig. 205.—Details of the Wooden Parts.Fig. 205.—Details of the Wooden Parts.The secondary winding is composed of a single layer of No. 28 B. & S. gauge silk-covered wire and divided into six equal sections. The secondary is supported by two circular wooden pieces,CandF, and slides back and forth on two guide-rods. The guide-rods should be brass. Iron or steel rods running through the center of a loose coupler will seriously weaken the signals, and such practice must by all means be avoided.Fig. 206.—Side View of the Loose Coupler.Fig. 206.—Side View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.The secondary sections are connected to six contacts and a switch-arm mounted on the end of the secondary so that by turning the switch either one, two, three, four, five, or six sections of the winding may be connected.Fig. 208.—End Views of the Loose Coupler.Fig. 208.—End Views of the Loose Coupler.Fig. 209.—Complete Loose Coupler.Fig. 209.—Complete Loose Coupler.The two binding-posts near the secondary end of the coupler are connected to the terminals of the secondary winding by means of two flexible wires. They have not been shown in several of the illustrations because they would be liable to confuse the drawing.The primary is provided with a slider moving back and forth over a narrow path scraped through the insulation so that it may make contact with each wire independently.DetectorsDetectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.Fig. 210.—A Crystal Detector.Fig. 210.—A Crystal Detector.The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.The mineral is contained in a small brass cup mounted on the base below the end of the knob.Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.Fig. 211.—Details of the Crystal Detector.Fig. 211.—Details of the Crystal Detector.The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral.It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena.A Double Slider Tuning Coil.A Double Slider Tuning Coil.A Junior Loose Coupler.A Junior Loose Coupler.Crystal Detectors.Crystal Detectors.Crystal Detectors.Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler."Fig. 212 Details of the "Cat Whisker" Detector.Fig. 212 Details of the "Cat Whisker" Detector.The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth.A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip.The detector shown in Figure 214 is more elaborate than any of the others described so far.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.The base is a wooden block, three and one-half by one and three-quarters inches by one-half inch. The binding-posts are of the type commonly used on electrical instruments. One of the posts is pivoted so that it will swing from side to side. A short piece of brass rod fitted with a rubber or fiber knob passes through the wire hole in the post. A piece of No. 30 B. & S. gauge bronze wire is soldered to the end of the rod. A small brass cup contains the mineral, which may be eithergalena, orsilicon. By twisting the post and sliding the rod back and forth, any portions of the mineral surface may be selected.Fixed Condenser.The construction of the condenser is illustrated in Figure 205. Take twenty-four sheets of thin typewriter paper, three by four inches, and twenty-three sheets of tinfoil, two by four inches. Pile them up, using first a sheet of paper then a sheet of tinfoil, then paper, and so on, so that every two sheets of tinfoil are separated by a sheet of paper. Each sheet of tinfoil must, however, project out beyond the edge of the paper. Connect all the tinfoil projections on one end of the condenser together and and attach a small wire. Connect all those on the opposite side in a similar manner. Then fasten a couple of rubber bands around the condenser to hold it together.Fig. 215.—Building up a Fixed Condenser.Fig. 215.—Building up a Fixed Condenser.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.If it is desired to give the condenser a finished appearance, it may be placed in a brass tube fitted with two wooden or fiber ends. The ends are provided with binding-posts to which the terminals of the condenser are connected.Telephone Receiversfor use with wireless instruments must be purchased. Their construction is such that they cannot be made by the experimenter.Fig. 217.—A Telephone Head Set.Fig. 217.—A Telephone Head Set.A seventy-five ohm, double-pole telephone receiver will do for stations not wishing to receive farther than fifty miles.In order to secure the best results from wireless instruments, it is necessary to have receivers especially made for wireless. Each receiver should have 1000 ohms resistance. Some boys may find it necessary to purchase one receiver at a time. Two receivers, a double headband, and a double cord, forming a complete head set as shown in Figure 217, should be secured as soon as possible.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Connecting the Receiving ApparatusFigure 218 shows how to connect a double-slide tuner, a detector, a fixed condenser and a pair of telephones to the aerial and ground. The same instruments with a loose coupler in place of the double-slide tuner are shown in Figure 219.The diagrams in Figure 220 are the same circuits as those shown in Figures 218 and 219, but show different instruments.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.After the instruments are connected, place a piece of galena or silicon in the cup of the detector and bring the wire down on it. Then move the sliders on the tuning coil or loose coupler and adjust the detector until you can hear a message buzzing in the telephones. It may require a little patience and practice, but if you persist you will soon learn how to adjust the apparatus so as to receive the signals loudly and clearly with very little trouble.The Transmitting ApparatusSpark coils have already been described in Chapter XII. They may be used to transmit wireless messages simply by connecting to a spark-gap and a key.Spark coils which are especially made for wireless telegraphy will usually send farther than an ordinary spark coil used for experimental purposes.Fig. 221.—A Wireless Spark Coil.Fig. 221.—A Wireless Spark Coil.A good one-inch coil costs from $4.50 to $5.00 and will send from three to five miles if used with a fair aerial.A spark coil requires considerable current for its successful operation and will give the best results if operated on storage cells, dry cells, or bichromate cells. If dry cells are used, it is a good plan to connect them in series multiple as shown in Figure 69.Spark-gaps may be made by mounting two double binding-posts on a wooden base as shown in Figure 222.Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.Fig. 222.—Small Spark Gaps.Fig. 222.—Small Spark Gaps.The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.Fig. 223.—Diagram showing how to connect a Simple Transmitter.Fig. 223.—Diagram showing how to connect a Simple Transmitter.If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.Several tubes may be arranged in a rack as shown in Figure 225.A helix consists of a spiral of brass ribbon set in a wooden frame. The two strips composing the frame are each nine inches long. The spiral consists of eight turns of brass ribbon, three-eighths of an inch wide, set in saw-cuts made in the frame. A binding-post is connected to the outside end of the ribbon.Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap.The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end.Fig. 224.—A Test-Tube Leyden Jar.Fig. 224.—A Test-Tube Leyden Jar.In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading.The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest.Anoscillation transformeris sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time.Fig. 226.—A Helix and Clip.Fig. 226.—A Helix and Clip.An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226.Fig. 227.—An Oscillation Transformer.Fig. 227.—An Oscillation Transformer.The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put.AN OSCILLATION HELIX.AN OSCILLATION HELIX.AN OSCILLATION CONDENSER.AN OSCILLATION CONDENSER.An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230.Fig 228.—Circuit showing how to connect a Helix and a Condenser.Fig 228.—Circuit showing how to connect a Helix and a Condenser.The aerial should be connected to the postAand the ground toB. The postsEandFlead to the transmitter, andCandDto the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench.A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.Fig 230.—An Aerial Switch.Fig 230.—An Aerial Switch.Two or three months’ steady practice with a chum should enable the young experimenter to become a very fair wireless telegraph operator. Then by listening for some of the high power wireless stations which send out the press news to ships at sea during the evening it should be possible to become very proficient. The press news is sent more slowly than ordinary commercial wireless messages, and is therefore easy to read and a good starting point for the beginner learning to read.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig. 232.—The Continental Alphabet.Fig. 232.—The Continental Alphabet.A Coherer OutfitA Coherer Outfitis usually capable of only receiving messages coming from a distance of under one mile. In spite of this fact, however, it is an exceedingly interesting apparatus to construct and experiment with, and for this reason is found fully described below.A coherer set will ring a bell or work a sounder for short distances and therefore is the best sort of an arrangement for demonstrating the workings of your wireless apparatus to your friends.The first thing that you need for a coherer is a pair of double binding-posts. Mount these about an inch and three-quarters apart on a wooden base, six inches long and four inches wide as shown in Figure 233.Fig. 233.—A Coherer and a Decoherer.Fig. 233.—A Coherer and a Decoherer.Get a piece of glass tubing about an inch and one-half long and about one-eighth of an inch inside diameter. You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space.The filings must be very carefully prepared, and in order to make them, first use a coarse-grained file on the edge of a five-cent piece. Do not use the fine dust and powder, but only the fairly coarse filings. Mix a few silver filings from a ten-cent piece with the nickel in such proportion that the mixture is 90% nickel and 10% silver.Fig. 234.—Details of the Coherer.Fig. 234.—Details of the Coherer.You will have to experiment considerably to find out just the right amount of filings to place in the tube, and how far apart to place the brass rods or plugs.Remove the gong from an old electric bell and mount the bell on the base as shown in Figure 233. It should be in such a position that the bell hammer will touch the coherer very lightly when the bell is ringing.The two binding-posts, tube rods, and filings constitute thecoherer. The bell is thedecoherer.The next thing required in order to complete the apparatus is a relay. You may use the relay described in Chapter X or build one according to the plan shown in Figure 235. This relay consists of a single electro-magnet mounted on a wooden base, two inches wide and four inches long. The armature is a piece of soft iron rod one-quarter of an inch in diameter and one-eighth of an inch long, riveted to the end of a thin piece of spring brass, about No. 34 B. & S. gauge in thickness.Fig. 235.—The Relay.Fig. 235.—The Relay.The other end of the spring is fitted to a bracket and provided with a thumbscrew to adjust the tension of the spring.The under side of the armature and the upper side of the magnet core are each fitted with a small silver contact.The contacts should meet squarely when the armature is drawn down on to the core by a current of electricity passing through the electro-magnet.By turning the adjusting screw, the armature can be raised or lowered. It should be adjusted so that it almost touches the core and is only just far enough away to slip a piece of thick paper under.The terminals of the magnet are connected to the two binding-posts on the base markedSandS. One of the binding-posts,P, is connected to the brass upright, and the other is connected to the core of the magnet.Figure 236 shows how to connect up the outfit. It will require some very nice adjusting before you will be able to get it to working properly.Fig. 236.—The Complete Coherer Outfit.Fig. 236.—The Complete Coherer Outfit.If you wish to use the outfit for demonstration purposes or for sending messages for very short distances, as for instance across a room, you do not need an aerial but merely a pair of "catch-wires."The "catch-wires" are two pieces of stiff copper wire, about two feet long, placed in the lower holes in the double binding-posts forming part of the coherer.In order to set the apparatus for operation, raise the adjusting screw of the relay until the armature is quite far away from the core. Then push the armature down against the contact on the core. The decoherer should then immediately operate and begin to tap the coherer. Then turn the thumbscrew until the armature is brought down to the core in such a position that it is as close as it is possible to get it without ringing the bell.The transmitter should consist of a spark coil, battery, key, and a spark-gap. The gap should be connected to the secondary of the coil and adjusted so that the electrodes are only about one-eighth of an inch apart. The key is placed in series with the primary of the coil and the battery, so that pressing the key will send a stream of sparks across the gap. Fit the spark-gap with two catch-wires similar to those on the coherer and place the transmitter about four or five feet away from the coherer outfit.You are now likely to find that if you press the key of the transmitter, the decoherer will ring. It is possible that it will continue to ring after you have stopped pressing the key. If such is the case, it will be necessary to turn the adjusting screw on the relay so as to move the armature upward a short distance away from the core.If the decoherer will not operate each time when you press the key, the brass plugs in the coherer need adjusting. You must not be discouraged if you have some difficulty in making the apparatus work at first. After you learn how to adjust it properly, you will find that you can move the transmitter quite a distance away from the coherer and it will still operate very nicely.After you manage that, you can place the apparatus in separate rooms and find it possible to work it just the same, because ordinary walls will not make any difference to wireless waves.Bear in mind that the nearer the coherer plugs are to each other, the more sensitive the coherer will be, but that if too close, the decoherer will not be able to shake the filings properly and will not stop when you stop pressing the key.The operation of the apparatus depends upon the fact that when properly adjusted the resistance of the filings between the two brass plugs is too great to allow sufficient battery current to flow to attract the armature of the relay. As soon as any wireless waves from the transmitter strike the catch-wires of the coherer, they cause the filings to cling together or cohere. When in this state, they have a low resistance and permit the current to flow in the relay circuit and draw down the armature. The armature closes the second circuit and sets the decoherer into operation. The decoherer shakes the filings and causes them to decohere or fall apart and so makes them ready again for the next signal.A coherer set of this sort may be used on an aerial and ground by substituting the coherer for the detector, but otherwise following any of the receiving circuits which have already been shown.A WIRELESS TELEPHONE

Probably no branch of electrical science ever appealed more to the imagination of the experimenter than that coming under the heading of wireless telegraphy. Wherever you go, you are likely to see the ear-marks ofamateurwireless telegraph stations in the aerials and masts set up in trees and on house-tops. It is estimated that there are nearly a quarter of a million such stations in the United States.

There is really no great mystery about this wonderful art which made possible the instantaneous transmission of messages over immense distances without any apparent physical connection save that of the earth, air, or water.

Did you ever throw a stone in a pool of water? As soon as the stone struck, little waves spread out from the spot in gradually enlarging circles until they reached the shore or died away.

By throwing several stones in succession, with varying intervals of time between them, it would be possible so to arrange a set of signals, that they would convey a meaning to a second person standing on the opposite shore of the pool.

Wireless telegraphy is based upon the principle ofcreating and detectingwaves in a greatpoolof ether.

Modern scientists suppose that all space is filled with an "imaginary" substance calledether. The ether is invisible, odorless, and practically weightless. This ether, however, bears no relation to the anaesthetic of that name which is used in surgical operations.

It surrounds and penetrates all substances and all space.

Fig. 193.—Little Waves spread out from the Spot.Fig. 193.—Little Waves spread out from the Spot.

Fig. 193.—Little Waves spread out from the Spot.

It exists in a vacuum and in solid rocks. Since the ether does not make itself apparent to any of our physical senses, some of these statements may seem contradictory. Its definite existence cannot be proved except by reasoning, but by accepting and imagining its reality, it is possible to understand and explain many scientific puzzles.

A good instance is offered by the sun. Light and heat can be shown to consist of extremely rapid vibrations. That fact can be proved. The sun is over 90,000,000 miles away from our earth and yet light and heat come streaming down to us through a space that is devoid even of air. Something must exist as a medium to transmit these vibrations; it is the ether.

Let us consider again the pool of water. The waves or ripples caused by throwing in the stone are vibrations of the water. The distance between two adjacent ripples is called thewave length.

The distances between two vibrations of light can also bemeasured. They are so small, however, that they may be spoken of only inthousandthsof an inch. The waves created in the ether by wireless telegraph apparatus are the same as those of light except that their length usually varies from 75 to 9,000feetinstead of a fraction of a thousandth of an inch.

Fig. 194.—A Simple Transmitter.Fig. 194.—A Simple Transmitter.

Fig. 194.—A Simple Transmitter.

A Simple Transmitteris illustrated in Figure 194. A telegraph key is connected in series with a set of cells and theprimaryof an induction coil, which, it will be remembered, is simply a coil consisting of a few turns of wire. This induces a high voltage in a second coil consisting of a larger number of turns and called thesecondary.

The terminals of the secondary are led to a spark-gap—an arrangement composed of two polished brass balls, separated by a small air-gap. One of the balls, in turn, is connected to a metal plate buried in the earth, and the other to a network of wires suspended high in the air and insulated from all surrounding objects.

When the key at the transmitter is pressed, the battery current flows through the primary of the induction coil and generates in the secondary a current of very high voltage, 20,000 volts or more, which is able to jump an air-gap in the shape of a spark at the secondary terminals. The latter are connected to the earth and aerial, as explained above. The high potential currents are therefore enabled to charge the aerial. The charge in the aerial exerts a great tendency to pass into the ground, but is prevented from doing so by the small air-gap between the spark-balls until the charge becomes so great that the air-gap is punctured and the charge passes across and flows down into the ground. The passage of the charge is made evident by the spark between the two spark-balls.

The electrical charges flowing up and down the aerial disturb the ether, strike it a blow, as it were. The effect of the blow is to cause the ether to vibrate and to send out waves in all directions. It may be likened to the pond of water which is suddenly struck a blow by throwing a stone into it, so that ripples are immediately sent out in widening circles.

These Waves in the Etherare called electro-magnetic orHertzianwaves, after their discoverer, Hertz. The distance over which they pass is dependent upon the power of the transmitting station. The waves can be made to correspond to the dots and dashes of the telegraphic code by so pressing the key. If some means of detecting the waves is employed we may readily see how it is possible to send wireless messages.

The Action of the Receiving Stationis just the opposite of that of the transmitter. When the waves pass out through the ether, some of them strike the aerial of the receiving station and generate a charge of electricity in it which tends to pass down into the earth. If the transmitting and receiving stations are very close together and the former is very powerful, it is possible to make a very small gap in the receiving aerial across which the charge will jump in the shape of sparks. Thus the action of the receptor simply takes place in a reversed order from that of the transmitter.

If the stations are any considerable distance apart, it is impossible for the currents induced in the receiving aerial to produce sparks, and so some more sensitive means of detecting the waves from the transmitter is necessary, preferably one which makes itself evident to the sense of hearing.

The telephone receiver is an extremely sensitive instrument, and it only requires a very weak current to operate it and produce a sound. The currents oroscillationsgenerated in the aerial, however, are alternating currents (see pages 97-99) ofhigh frequency, that is, they flow in one direction and then reverse and flow in the other several thousand times a second. Such a current cannot be made to pass through a telephone receiver, and in order to do so the nature of the current must be changed by converting it into direct current flowing in one direction only.

Certain minerals and crystals possess the remarkable ability to do this,silicon, galena, and iron pyrites are among the best.

Fig. 195.—A Simple Receptor.Fig. 195.—A Simple Receptor.

Fig. 195.—A Simple Receptor.

The diagram in Figure 195 shows the arrangement of a simple receiving outfit. Thedetectorconsists of a sensitive mineral placed between two contacts and connected so that the aerial currents must pass through it on their way to the ground. A telephone receiver is connected to the detector so that therectified currents(currents which have been changed into direct current) pass into it and produce a sound. By varying the periods during which the key is pressed at the transmitting station, according to a prearranged code, the sounds in the receiver may be made to assume an intelligible meaning.

HOW TO BUILD WIRELESS INSTRUMENTSThe AerialEvery wireless station is provided with a system of wires elevated high in the air, above all surrounding objects, the purpose of which is to radiate or intercept the electromagnetic waves, accordingly as the station is transmitting or receiving. This system of wires is, as already has been stated, called theaerialorantenna.The arrangement of the aerial will greatly determine the efficiency and range of the apparatus.The aerial should be as long as it is reasonably possible to make it, that is from 50 to 150 feet.It will be necessary for most amateurs to put up their aerial in some one certain place, regardless of what else may be in the vicinity, but whenever possible the site selected should preferably be such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smoke-stacks, telephone wires, etc., because such objects will interfere with the aerial and noticeably decrease the range of the station, both when transmitting and receiving.Bare copper wire makes the best aerials. Aluminum wire is very often used and on account of its light weight causes very little strain on the poles or cross arms. Iron wire should never be used for an aerial, even if galvanized or tinned, because it tends to choke the currents which must flow up and down the aerial when the station is in operation.Fig. 196.—Molded Aerial InsulatorFig. 196.—Molded Aerial InsulatorThe aerial must be very carefully insulated from its supports and all surrounding objects. The insulation must be strong enough to hold the weight of the aerial and able to withstand any strain caused by storms.Special aerial insulators made of molded insulating material and having an iron ring imbedded in each end are the best.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Ordinary porcelain cleats may be used on small aerials where the strain is light.One insulator should be placed at each end of each wire close to the spreader or spar.Most aerials are made up of four wires. The wires should be placed as far apart as possible.There are several different forms of aerials, the principal ones of which are shown in Figure 199. They are known as the grid, “V," inverted “L,” and “T” types.Most amateurs support their aerials from a pole placed on the top of the house, in a tree, or erected in the yard. Many use two supports, since such an aerial has many advantages. The facilities to be had for supporting the aerial will largely determine which form to use.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.The grid aerial has no particular advantages or disadvantages.The “V” aerial receives waves much better when they come from a direction opposite to that in which the free end points. The "free" end of the aerial is the one not leading into the station.The inverted “L” aerial possesses the same characteristics as the “V” type.The “T” aerial is the best “all around" and is to be recommended whenever it is possible to put up an aerial of this sort.Much of the detail of actually putting up an aerial or antenna must be omitted, because each experimenter will usually meet different conditions.It should be remembered, however, that the success of the whole undertaking will rest largely upon the construction of a proper aerial. The most excellent instruments will not give very good results if connected to a poor aerial, while, on the other hand, inferior instruments will often give fair results when connected to a good aerial.Fig. 199.—Various Types of Aerials.Fig. 199.—Various Types of Aerials.The aerial should be at least thirty feet high.The wire should not be smaller than No. 14 B. & S.The masts which support the aerial should be of wood and provided with pulleys so that the wires may be lowered any time it may be necessary. The mast should be thoroughly braced with stays or guys so as to counteract the strain of the aerial.The aerial should not be hoisted up perfectly tight, but should be allowed to hang somewhat loose, as it will then put less strain on the ropes and poles that support it.When an aerial is to be fastened in a tree, it is best to attach it to a pole placed in the top of the tree, so that it will come well above any possible interference from the branches.The wires leading from the aerial to the instruments should be very carefully insulated throughout their length. This part of the aerial is called the "rat-tail" or lead-in.The illustrations in Figure 199 show the proper place to attach the “lead-in" form of aerial. The wires should gradually converge.Fig. 200.—A Ground Clamp for Pipes.Fig. 200.—A Ground Clamp for Pipes.It is very important that a good ground connection be secured for wireless instruments. A good ground is absolutely necessary for the proper working of the apparatus. Amateur experimenters usually use the water or gas-pipes for a ground, and fasten the wires by means of a ground clamp such as shown in Figure 200. In the country, where such pipes are not available, it is necessary to bury a sheet of copper, three or four feet square, in a moist spot in the earth and connect a wire to it.The Receiving ApparatusThe receiving instruments form the most interesting part of a wireless station and usually receive first attention from the amateurs. They are the ears of the wireless station and are wondrously sensitive, yet are very simple and easy of construction.The instruments necessary for receiving are:A Detector,A Tuning Coil or a Loose Coupler,A Fixed Condenser,A Telephone Receiver.Other devices, such as a test buzzer, variable condenser, etc., may be added and will improve the outfit.After the aerial has been properly erected, the first instrument necessary to construct will be either a tuning coil or a loose coupler. It is a good plan to make a tuning coil first, and a loose coupler after you have had a little experience with your apparatus.A Tuning Coilis a very simple arrangement making it possible to receive messages from greater distances, and also somewhat to eliminate any messages not desirable and to listen without confusion to the one wanted.A tuning coil consists of a single layer of wire wound upon a cylinder and arranged so that connection may be had with any part of it by means of sliding contacts.The cylinder upon which the wire is wound is a cardboard tube six and three-quarters inches long and two and seven-eighths inches in diameter outside. It should be given two or three coats of shellac both inside and out so that it is thoroughly impregnated, and then laid away until dry. This treatment will prevent the wire from becoming loose after the tube is wound, due to shrinkage of the cardboard.Fig. 201.—Details of the Tuning Coil.Fig. 201.—Details of the Tuning Coil.After having become dry, the tube is wound with a single layer of No. 25 B. & S. gauge green silk or cotton-covered magnet wire. The wire must be wound on very smoothly and tightly, stopping and starting one-quarter of an inch back from each end. The ends of the wire are fastened by weaving back and forth through two small holes punched in the cardboard tube with a pin.The winding should be given a single coat of clear varnish or white shellac and allowed to dry.The coil heads or end pieces are cut from one-half-inch wood according to the plan and dimensions shown in the accompanying illustration.The top corners are beveled and notched to receive the slider-rods. A circular piece of wood two and five-eighths inches in diameter and three-eighths of an inch thick is nailed to the inside of each of the coil heads to support the ends of the cylinder.The wooden parts should be stained mahogany or some other dark color and finished with a coat of shellac or varnish.The slider-rods are square brass 3-16 x 3-16 inches and seven and three-quarters inches long. A small hole is bored near the ends of each, one-quarter of an inch from the edge, to receive a round-headed brass wood screw which holds the rod to the tuner end.The sliders may be made according to the plan shown in Figure 201.The slider is made from a small piece of brass tubing, three-sixteenths of an inch square. An 8-32 flat-headed brass screw is soldered to one face, in the center. A small strip of phosphor bronze sheet or spring copper soldered to the bottom of the slider forms a contact for making connection to the wire on the cylinder. A small "electrose" knob screwed to the slider makes a neat and efficient handle.Two sliders are required, one for each rod.The tuning coil is assembled as shown in Figure 203. The cardboard tube is held in place by several small brass nails driven through it into the circular pieces on the coil heads.A slider is placed on each of the slider-rods and the rods fastened in the slots in the coil ends by a small round-headed brass screw, passing through the holes bored near the ends for that purpose.Fig. 202.—Side and End Views of the Tuning Coil.Fig. 202.—Side and End Views of the Tuning Coil.Two binding-posts are mounted on one of the coil ends. One should be connected to each of the slider-rods. A third binding-post is placed below in the center of the head and connected to one end of the wire wound around the cylinder.A small, narrow path along the coil, directly underneath each slider and to which the copper strip can make contact, must be formed by scraping the insulation off the wire with a sharp knife. The sliders should make contact with each one of the wires as they pass over, and should slide smoothly without damaging or disarranging any of the wires.Fig. 203.—Complete Double-Slider Tuning Coil.Fig. 203.—Complete Double-Slider Tuning Coil.When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.A Loose Coupleris a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.Fig. 204.—A Simple Loose Coupler.Fig. 204.—A Simple Loose Coupler.The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.The primary should be wound with a single layer of No. 22 single-silk-covered magnet wire. The secondary is wound with No. 29 single-silk.The head supporting the secondary is smaller than that used for the same purpose on the primary. The round boss to which the tube is fastened, however, is much thicker.The secondary slides on a "guide-rod" supported at one end by passing through the primary head and at the other by a brass upright. The upright may also be made of wood.If the secondary is "offset," that is, placed out of center slightly to one side, it will leave room so that the secondary slider will possibly pass inside of the primary without striking.Both the primary and the secondary must be fitted with "sliders" to make contact with the various turns of wire.The method of constructing a slider has already been described.The ends of the slider-rods are bent at right angles and fastened to the coil heads by two small screws passing through holes bored near the ends. A small narrow path must be scraped in the insulation under each so that the slider will make contact with each turn. The secondary head may be provided with a small electrose handle to facilitate sliding it back and forth.Two binding-posts are mounted on each of the coil heads.One post on each is connected to the end of the coil farthest from the head, and the other posts are each connected to the slider-rods.Figure 220 shows how to connect the loose coupler in the receiving set.In order to tune with a loose coupler, first adjust the slider on the primary until the signals are the clearest. Then set the secondary slider in the best place and move the secondary in and out of the primary until the signals are clearest.How to Build the Junior Loose CouplerA loose coupler of the sort just described is simple and quite easily constructed, but will not be found to work as well as one in which the secondary may be varied by means of a switch while it is inside of the primary.The base of the instrument measures twelve by three and five-eighths inches. The primary is composed of a single layer of No. 24 B. & S. gauge single-silk-covered wire wound on a cardboard tube two and three-quarter inches in diameter and three and three-quarter inches long. The winding is laid on in a single layer and should comprise about 150 turns. After winding on tightly, it should be given a coat of clean white shellac and allowed to dry. The shellac is for the purpose of fastening the wire down tightly to the tube so that it will not loosen when the slider is moved back and forth.The primary is mounted between two heads, the details of which are shown in Figure 205. One of the heads,B, has a flanged hole two and three-quarter inches in diameter cut through the center so as to receive the end of the tube and permit the secondary to pass inside.Fig. 205.—Details of the Wooden Parts.Fig. 205.—Details of the Wooden Parts.The secondary winding is composed of a single layer of No. 28 B. & S. gauge silk-covered wire and divided into six equal sections. The secondary is supported by two circular wooden pieces,CandF, and slides back and forth on two guide-rods. The guide-rods should be brass. Iron or steel rods running through the center of a loose coupler will seriously weaken the signals, and such practice must by all means be avoided.Fig. 206.—Side View of the Loose Coupler.Fig. 206.—Side View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.The secondary sections are connected to six contacts and a switch-arm mounted on the end of the secondary so that by turning the switch either one, two, three, four, five, or six sections of the winding may be connected.Fig. 208.—End Views of the Loose Coupler.Fig. 208.—End Views of the Loose Coupler.Fig. 209.—Complete Loose Coupler.Fig. 209.—Complete Loose Coupler.The two binding-posts near the secondary end of the coupler are connected to the terminals of the secondary winding by means of two flexible wires. They have not been shown in several of the illustrations because they would be liable to confuse the drawing.The primary is provided with a slider moving back and forth over a narrow path scraped through the insulation so that it may make contact with each wire independently.DetectorsDetectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.Fig. 210.—A Crystal Detector.Fig. 210.—A Crystal Detector.The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.The mineral is contained in a small brass cup mounted on the base below the end of the knob.Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.Fig. 211.—Details of the Crystal Detector.Fig. 211.—Details of the Crystal Detector.The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral.It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena.A Double Slider Tuning Coil.A Double Slider Tuning Coil.A Junior Loose Coupler.A Junior Loose Coupler.Crystal Detectors.Crystal Detectors.Crystal Detectors.Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler."Fig. 212 Details of the "Cat Whisker" Detector.Fig. 212 Details of the "Cat Whisker" Detector.The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth.A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip.The detector shown in Figure 214 is more elaborate than any of the others described so far.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.The base is a wooden block, three and one-half by one and three-quarters inches by one-half inch. The binding-posts are of the type commonly used on electrical instruments. One of the posts is pivoted so that it will swing from side to side. A short piece of brass rod fitted with a rubber or fiber knob passes through the wire hole in the post. A piece of No. 30 B. & S. gauge bronze wire is soldered to the end of the rod. A small brass cup contains the mineral, which may be eithergalena, orsilicon. By twisting the post and sliding the rod back and forth, any portions of the mineral surface may be selected.Fixed Condenser.The construction of the condenser is illustrated in Figure 205. Take twenty-four sheets of thin typewriter paper, three by four inches, and twenty-three sheets of tinfoil, two by four inches. Pile them up, using first a sheet of paper then a sheet of tinfoil, then paper, and so on, so that every two sheets of tinfoil are separated by a sheet of paper. Each sheet of tinfoil must, however, project out beyond the edge of the paper. Connect all the tinfoil projections on one end of the condenser together and and attach a small wire. Connect all those on the opposite side in a similar manner. Then fasten a couple of rubber bands around the condenser to hold it together.Fig. 215.—Building up a Fixed Condenser.Fig. 215.—Building up a Fixed Condenser.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.If it is desired to give the condenser a finished appearance, it may be placed in a brass tube fitted with two wooden or fiber ends. The ends are provided with binding-posts to which the terminals of the condenser are connected.Telephone Receiversfor use with wireless instruments must be purchased. Their construction is such that they cannot be made by the experimenter.Fig. 217.—A Telephone Head Set.Fig. 217.—A Telephone Head Set.A seventy-five ohm, double-pole telephone receiver will do for stations not wishing to receive farther than fifty miles.In order to secure the best results from wireless instruments, it is necessary to have receivers especially made for wireless. Each receiver should have 1000 ohms resistance. Some boys may find it necessary to purchase one receiver at a time. Two receivers, a double headband, and a double cord, forming a complete head set as shown in Figure 217, should be secured as soon as possible.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Connecting the Receiving ApparatusFigure 218 shows how to connect a double-slide tuner, a detector, a fixed condenser and a pair of telephones to the aerial and ground. The same instruments with a loose coupler in place of the double-slide tuner are shown in Figure 219.The diagrams in Figure 220 are the same circuits as those shown in Figures 218 and 219, but show different instruments.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.After the instruments are connected, place a piece of galena or silicon in the cup of the detector and bring the wire down on it. Then move the sliders on the tuning coil or loose coupler and adjust the detector until you can hear a message buzzing in the telephones. It may require a little patience and practice, but if you persist you will soon learn how to adjust the apparatus so as to receive the signals loudly and clearly with very little trouble.The Transmitting ApparatusSpark coils have already been described in Chapter XII. They may be used to transmit wireless messages simply by connecting to a spark-gap and a key.Spark coils which are especially made for wireless telegraphy will usually send farther than an ordinary spark coil used for experimental purposes.Fig. 221.—A Wireless Spark Coil.Fig. 221.—A Wireless Spark Coil.A good one-inch coil costs from $4.50 to $5.00 and will send from three to five miles if used with a fair aerial.A spark coil requires considerable current for its successful operation and will give the best results if operated on storage cells, dry cells, or bichromate cells. If dry cells are used, it is a good plan to connect them in series multiple as shown in Figure 69.Spark-gaps may be made by mounting two double binding-posts on a wooden base as shown in Figure 222.Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.Fig. 222.—Small Spark Gaps.Fig. 222.—Small Spark Gaps.The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.Fig. 223.—Diagram showing how to connect a Simple Transmitter.Fig. 223.—Diagram showing how to connect a Simple Transmitter.If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.Several tubes may be arranged in a rack as shown in Figure 225.A helix consists of a spiral of brass ribbon set in a wooden frame. The two strips composing the frame are each nine inches long. The spiral consists of eight turns of brass ribbon, three-eighths of an inch wide, set in saw-cuts made in the frame. A binding-post is connected to the outside end of the ribbon.Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap.The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end.Fig. 224.—A Test-Tube Leyden Jar.Fig. 224.—A Test-Tube Leyden Jar.In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading.The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest.Anoscillation transformeris sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time.Fig. 226.—A Helix and Clip.Fig. 226.—A Helix and Clip.An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226.Fig. 227.—An Oscillation Transformer.Fig. 227.—An Oscillation Transformer.The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put.AN OSCILLATION HELIX.AN OSCILLATION HELIX.AN OSCILLATION CONDENSER.AN OSCILLATION CONDENSER.An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230.Fig 228.—Circuit showing how to connect a Helix and a Condenser.Fig 228.—Circuit showing how to connect a Helix and a Condenser.The aerial should be connected to the postAand the ground toB. The postsEandFlead to the transmitter, andCandDto the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench.A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.Fig 230.—An Aerial Switch.Fig 230.—An Aerial Switch.Two or three months’ steady practice with a chum should enable the young experimenter to become a very fair wireless telegraph operator. Then by listening for some of the high power wireless stations which send out the press news to ships at sea during the evening it should be possible to become very proficient. The press news is sent more slowly than ordinary commercial wireless messages, and is therefore easy to read and a good starting point for the beginner learning to read.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig. 232.—The Continental Alphabet.Fig. 232.—The Continental Alphabet.A Coherer OutfitA Coherer Outfitis usually capable of only receiving messages coming from a distance of under one mile. In spite of this fact, however, it is an exceedingly interesting apparatus to construct and experiment with, and for this reason is found fully described below.A coherer set will ring a bell or work a sounder for short distances and therefore is the best sort of an arrangement for demonstrating the workings of your wireless apparatus to your friends.The first thing that you need for a coherer is a pair of double binding-posts. Mount these about an inch and three-quarters apart on a wooden base, six inches long and four inches wide as shown in Figure 233.Fig. 233.—A Coherer and a Decoherer.Fig. 233.—A Coherer and a Decoherer.Get a piece of glass tubing about an inch and one-half long and about one-eighth of an inch inside diameter. You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space.The filings must be very carefully prepared, and in order to make them, first use a coarse-grained file on the edge of a five-cent piece. Do not use the fine dust and powder, but only the fairly coarse filings. Mix a few silver filings from a ten-cent piece with the nickel in such proportion that the mixture is 90% nickel and 10% silver.Fig. 234.—Details of the Coherer.Fig. 234.—Details of the Coherer.You will have to experiment considerably to find out just the right amount of filings to place in the tube, and how far apart to place the brass rods or plugs.Remove the gong from an old electric bell and mount the bell on the base as shown in Figure 233. It should be in such a position that the bell hammer will touch the coherer very lightly when the bell is ringing.The two binding-posts, tube rods, and filings constitute thecoherer. The bell is thedecoherer.The next thing required in order to complete the apparatus is a relay. You may use the relay described in Chapter X or build one according to the plan shown in Figure 235. This relay consists of a single electro-magnet mounted on a wooden base, two inches wide and four inches long. The armature is a piece of soft iron rod one-quarter of an inch in diameter and one-eighth of an inch long, riveted to the end of a thin piece of spring brass, about No. 34 B. & S. gauge in thickness.Fig. 235.—The Relay.Fig. 235.—The Relay.The other end of the spring is fitted to a bracket and provided with a thumbscrew to adjust the tension of the spring.The under side of the armature and the upper side of the magnet core are each fitted with a small silver contact.The contacts should meet squarely when the armature is drawn down on to the core by a current of electricity passing through the electro-magnet.By turning the adjusting screw, the armature can be raised or lowered. It should be adjusted so that it almost touches the core and is only just far enough away to slip a piece of thick paper under.The terminals of the magnet are connected to the two binding-posts on the base markedSandS. One of the binding-posts,P, is connected to the brass upright, and the other is connected to the core of the magnet.Figure 236 shows how to connect up the outfit. It will require some very nice adjusting before you will be able to get it to working properly.Fig. 236.—The Complete Coherer Outfit.Fig. 236.—The Complete Coherer Outfit.If you wish to use the outfit for demonstration purposes or for sending messages for very short distances, as for instance across a room, you do not need an aerial but merely a pair of "catch-wires."The "catch-wires" are two pieces of stiff copper wire, about two feet long, placed in the lower holes in the double binding-posts forming part of the coherer.In order to set the apparatus for operation, raise the adjusting screw of the relay until the armature is quite far away from the core. Then push the armature down against the contact on the core. The decoherer should then immediately operate and begin to tap the coherer. Then turn the thumbscrew until the armature is brought down to the core in such a position that it is as close as it is possible to get it without ringing the bell.The transmitter should consist of a spark coil, battery, key, and a spark-gap. The gap should be connected to the secondary of the coil and adjusted so that the electrodes are only about one-eighth of an inch apart. The key is placed in series with the primary of the coil and the battery, so that pressing the key will send a stream of sparks across the gap. Fit the spark-gap with two catch-wires similar to those on the coherer and place the transmitter about four or five feet away from the coherer outfit.You are now likely to find that if you press the key of the transmitter, the decoherer will ring. It is possible that it will continue to ring after you have stopped pressing the key. If such is the case, it will be necessary to turn the adjusting screw on the relay so as to move the armature upward a short distance away from the core.If the decoherer will not operate each time when you press the key, the brass plugs in the coherer need adjusting. You must not be discouraged if you have some difficulty in making the apparatus work at first. After you learn how to adjust it properly, you will find that you can move the transmitter quite a distance away from the coherer and it will still operate very nicely.After you manage that, you can place the apparatus in separate rooms and find it possible to work it just the same, because ordinary walls will not make any difference to wireless waves.Bear in mind that the nearer the coherer plugs are to each other, the more sensitive the coherer will be, but that if too close, the decoherer will not be able to shake the filings properly and will not stop when you stop pressing the key.The operation of the apparatus depends upon the fact that when properly adjusted the resistance of the filings between the two brass plugs is too great to allow sufficient battery current to flow to attract the armature of the relay. As soon as any wireless waves from the transmitter strike the catch-wires of the coherer, they cause the filings to cling together or cohere. When in this state, they have a low resistance and permit the current to flow in the relay circuit and draw down the armature. The armature closes the second circuit and sets the decoherer into operation. The decoherer shakes the filings and causes them to decohere or fall apart and so makes them ready again for the next signal.A coherer set of this sort may be used on an aerial and ground by substituting the coherer for the detector, but otherwise following any of the receiving circuits which have already been shown.A WIRELESS TELEPHONE

The Aerial

Every wireless station is provided with a system of wires elevated high in the air, above all surrounding objects, the purpose of which is to radiate or intercept the electromagnetic waves, accordingly as the station is transmitting or receiving. This system of wires is, as already has been stated, called theaerialorantenna.

The arrangement of the aerial will greatly determine the efficiency and range of the apparatus.

The aerial should be as long as it is reasonably possible to make it, that is from 50 to 150 feet.

It will be necessary for most amateurs to put up their aerial in some one certain place, regardless of what else may be in the vicinity, but whenever possible the site selected should preferably be such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smoke-stacks, telephone wires, etc., because such objects will interfere with the aerial and noticeably decrease the range of the station, both when transmitting and receiving.

Bare copper wire makes the best aerials. Aluminum wire is very often used and on account of its light weight causes very little strain on the poles or cross arms. Iron wire should never be used for an aerial, even if galvanized or tinned, because it tends to choke the currents which must flow up and down the aerial when the station is in operation.

Fig. 196.—Molded Aerial InsulatorFig. 196.—Molded Aerial Insulator

Fig. 196.—Molded Aerial Insulator

The aerial must be very carefully insulated from its supports and all surrounding objects. The insulation must be strong enough to hold the weight of the aerial and able to withstand any strain caused by storms.

Special aerial insulators made of molded insulating material and having an iron ring imbedded in each end are the best.

Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.

Fig. 197.—A Porcelain Cleat will make a Good Insulator for Small Aerials.

Ordinary porcelain cleats may be used on small aerials where the strain is light.

One insulator should be placed at each end of each wire close to the spreader or spar.

Most aerials are made up of four wires. The wires should be placed as far apart as possible.

There are several different forms of aerials, the principal ones of which are shown in Figure 199. They are known as the grid, “V," inverted “L,” and “T” types.

Most amateurs support their aerials from a pole placed on the top of the house, in a tree, or erected in the yard. Many use two supports, since such an aerial has many advantages. The facilities to be had for supporting the aerial will largely determine which form to use.

Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.

Fig. 198.—Method of Arranging the Wires and Insulating them from the Cross Arm or Spreader.

The grid aerial has no particular advantages or disadvantages.

The “V” aerial receives waves much better when they come from a direction opposite to that in which the free end points. The "free" end of the aerial is the one not leading into the station.

The inverted “L” aerial possesses the same characteristics as the “V” type.

The “T” aerial is the best “all around" and is to be recommended whenever it is possible to put up an aerial of this sort.

Much of the detail of actually putting up an aerial or antenna must be omitted, because each experimenter will usually meet different conditions.

It should be remembered, however, that the success of the whole undertaking will rest largely upon the construction of a proper aerial. The most excellent instruments will not give very good results if connected to a poor aerial, while, on the other hand, inferior instruments will often give fair results when connected to a good aerial.

Fig. 199.—Various Types of Aerials.Fig. 199.—Various Types of Aerials.

Fig. 199.—Various Types of Aerials.

The aerial should be at least thirty feet high.

The wire should not be smaller than No. 14 B. & S.

The masts which support the aerial should be of wood and provided with pulleys so that the wires may be lowered any time it may be necessary. The mast should be thoroughly braced with stays or guys so as to counteract the strain of the aerial.

The aerial should not be hoisted up perfectly tight, but should be allowed to hang somewhat loose, as it will then put less strain on the ropes and poles that support it.

When an aerial is to be fastened in a tree, it is best to attach it to a pole placed in the top of the tree, so that it will come well above any possible interference from the branches.

The wires leading from the aerial to the instruments should be very carefully insulated throughout their length. This part of the aerial is called the "rat-tail" or lead-in.

The illustrations in Figure 199 show the proper place to attach the “lead-in" form of aerial. The wires should gradually converge.

Fig. 200.—A Ground Clamp for Pipes.Fig. 200.—A Ground Clamp for Pipes.

Fig. 200.—A Ground Clamp for Pipes.

It is very important that a good ground connection be secured for wireless instruments. A good ground is absolutely necessary for the proper working of the apparatus. Amateur experimenters usually use the water or gas-pipes for a ground, and fasten the wires by means of a ground clamp such as shown in Figure 200. In the country, where such pipes are not available, it is necessary to bury a sheet of copper, three or four feet square, in a moist spot in the earth and connect a wire to it.

The Receiving Apparatus

The receiving instruments form the most interesting part of a wireless station and usually receive first attention from the amateurs. They are the ears of the wireless station and are wondrously sensitive, yet are very simple and easy of construction.

The instruments necessary for receiving are:

A Detector,

A Detector,

A Tuning Coil or a Loose Coupler,

A Tuning Coil or a Loose Coupler,

A Fixed Condenser,

A Fixed Condenser,

A Telephone Receiver.

A Telephone Receiver.

Other devices, such as a test buzzer, variable condenser, etc., may be added and will improve the outfit.

After the aerial has been properly erected, the first instrument necessary to construct will be either a tuning coil or a loose coupler. It is a good plan to make a tuning coil first, and a loose coupler after you have had a little experience with your apparatus.

A Tuning Coilis a very simple arrangement making it possible to receive messages from greater distances, and also somewhat to eliminate any messages not desirable and to listen without confusion to the one wanted.

A tuning coil consists of a single layer of wire wound upon a cylinder and arranged so that connection may be had with any part of it by means of sliding contacts.

The cylinder upon which the wire is wound is a cardboard tube six and three-quarters inches long and two and seven-eighths inches in diameter outside. It should be given two or three coats of shellac both inside and out so that it is thoroughly impregnated, and then laid away until dry. This treatment will prevent the wire from becoming loose after the tube is wound, due to shrinkage of the cardboard.

Fig. 201.—Details of the Tuning Coil.Fig. 201.—Details of the Tuning Coil.

Fig. 201.—Details of the Tuning Coil.

After having become dry, the tube is wound with a single layer of No. 25 B. & S. gauge green silk or cotton-covered magnet wire. The wire must be wound on very smoothly and tightly, stopping and starting one-quarter of an inch back from each end. The ends of the wire are fastened by weaving back and forth through two small holes punched in the cardboard tube with a pin.

The winding should be given a single coat of clear varnish or white shellac and allowed to dry.

The coil heads or end pieces are cut from one-half-inch wood according to the plan and dimensions shown in the accompanying illustration.

The top corners are beveled and notched to receive the slider-rods. A circular piece of wood two and five-eighths inches in diameter and three-eighths of an inch thick is nailed to the inside of each of the coil heads to support the ends of the cylinder.

The wooden parts should be stained mahogany or some other dark color and finished with a coat of shellac or varnish.

The slider-rods are square brass 3-16 x 3-16 inches and seven and three-quarters inches long. A small hole is bored near the ends of each, one-quarter of an inch from the edge, to receive a round-headed brass wood screw which holds the rod to the tuner end.

The sliders may be made according to the plan shown in Figure 201.

The slider is made from a small piece of brass tubing, three-sixteenths of an inch square. An 8-32 flat-headed brass screw is soldered to one face, in the center. A small strip of phosphor bronze sheet or spring copper soldered to the bottom of the slider forms a contact for making connection to the wire on the cylinder. A small "electrose" knob screwed to the slider makes a neat and efficient handle.

Two sliders are required, one for each rod.

The tuning coil is assembled as shown in Figure 203. The cardboard tube is held in place by several small brass nails driven through it into the circular pieces on the coil heads.

A slider is placed on each of the slider-rods and the rods fastened in the slots in the coil ends by a small round-headed brass screw, passing through the holes bored near the ends for that purpose.

Fig. 202.—Side and End Views of the Tuning Coil.Fig. 202.—Side and End Views of the Tuning Coil.

Fig. 202.—Side and End Views of the Tuning Coil.

Two binding-posts are mounted on one of the coil ends. One should be connected to each of the slider-rods. A third binding-post is placed below in the center of the head and connected to one end of the wire wound around the cylinder.

A small, narrow path along the coil, directly underneath each slider and to which the copper strip can make contact, must be formed by scraping the insulation off the wire with a sharp knife. The sliders should make contact with each one of the wires as they pass over, and should slide smoothly without damaging or disarranging any of the wires.

Fig. 203.—Complete Double-Slider Tuning Coil.Fig. 203.—Complete Double-Slider Tuning Coil.

Fig. 203.—Complete Double-Slider Tuning Coil.

When scraping the insulation, be very careful not to loosen the wires or remove the insulation from between them, so that they are liable to short-circuit between adjacent turns.

A Loose Coupleris a much more efficient tuning device than a double-slider tuner, and sooner or later most amateur wireless operators install one in their station.

The loose coupler shown in the figure given on the next page is a very simple one and is both easy and inexpensive to build. Its simplicity is a disadvantage in one respect, however. Owing to its construction, it is impossible to move the slider on the secondary when the latter is inside the primary. The reason that I have chosen this sort of loose coupler to describe is to acquaint my young readers with the methods of making a loose coupler.

The "Junior" loose coupler described farther on is a more elaborate instrument of greater efficiency, but much harder to build.

Fig. 204.—A Simple Loose Coupler.Fig. 204.—A Simple Loose Coupler.

Fig. 204.—A Simple Loose Coupler.

The base of the loose coupler is of wood and measures twelve by four inches. The head supporting the primary is of the same size as those used on the "Junior" double-slide tuning coil just described. It may be made in the same manner, and fitted with a circular block to support the tube. The primary tube is of the same diameter as that on the tuning coil but is only four inches long. It is fastened to the primary head with glue and then secured with a number of small tacks. One or two coats of shellac liberally applied will render it non-shrinkable, so that the wire will not be apt to loosen after the loose coupler has been in use a while.

The secondary is of the same length as the primary, but of smaller diameter, so that it will easily slip inside. It also is treated with shellac.

The primary should be wound with a single layer of No. 22 single-silk-covered magnet wire. The secondary is wound with No. 29 single-silk.

The head supporting the secondary is smaller than that used for the same purpose on the primary. The round boss to which the tube is fastened, however, is much thicker.

The secondary slides on a "guide-rod" supported at one end by passing through the primary head and at the other by a brass upright. The upright may also be made of wood.

If the secondary is "offset," that is, placed out of center slightly to one side, it will leave room so that the secondary slider will possibly pass inside of the primary without striking.

Both the primary and the secondary must be fitted with "sliders" to make contact with the various turns of wire.

The method of constructing a slider has already been described.

The ends of the slider-rods are bent at right angles and fastened to the coil heads by two small screws passing through holes bored near the ends. A small narrow path must be scraped in the insulation under each so that the slider will make contact with each turn. The secondary head may be provided with a small electrose handle to facilitate sliding it back and forth.

Two binding-posts are mounted on each of the coil heads.

One post on each is connected to the end of the coil farthest from the head, and the other posts are each connected to the slider-rods.

Figure 220 shows how to connect the loose coupler in the receiving set.

In order to tune with a loose coupler, first adjust the slider on the primary until the signals are the clearest. Then set the secondary slider in the best place and move the secondary in and out of the primary until the signals are clearest.

How to Build the Junior Loose Coupler

A loose coupler of the sort just described is simple and quite easily constructed, but will not be found to work as well as one in which the secondary may be varied by means of a switch while it is inside of the primary.

The base of the instrument measures twelve by three and five-eighths inches. The primary is composed of a single layer of No. 24 B. & S. gauge single-silk-covered wire wound on a cardboard tube two and three-quarter inches in diameter and three and three-quarter inches long. The winding is laid on in a single layer and should comprise about 150 turns. After winding on tightly, it should be given a coat of clean white shellac and allowed to dry. The shellac is for the purpose of fastening the wire down tightly to the tube so that it will not loosen when the slider is moved back and forth.

The primary is mounted between two heads, the details of which are shown in Figure 205. One of the heads,B, has a flanged hole two and three-quarter inches in diameter cut through the center so as to receive the end of the tube and permit the secondary to pass inside.

Fig. 205.—Details of the Wooden Parts.Fig. 205.—Details of the Wooden Parts.

Fig. 205.—Details of the Wooden Parts.

The secondary winding is composed of a single layer of No. 28 B. & S. gauge silk-covered wire and divided into six equal sections. The secondary is supported by two circular wooden pieces,CandF, and slides back and forth on two guide-rods. The guide-rods should be brass. Iron or steel rods running through the center of a loose coupler will seriously weaken the signals, and such practice must by all means be avoided.

Fig. 206.—Side View of the Loose Coupler.Fig. 206.—Side View of the Loose Coupler.

Fig. 206.—Side View of the Loose Coupler.

Fig. 207.—Top View of the Loose Coupler.Fig. 207.—Top View of the Loose Coupler.

Fig. 207.—Top View of the Loose Coupler.

The secondary sections are connected to six contacts and a switch-arm mounted on the end of the secondary so that by turning the switch either one, two, three, four, five, or six sections of the winding may be connected.

Fig. 208.—End Views of the Loose Coupler.Fig. 208.—End Views of the Loose Coupler.

Fig. 208.—End Views of the Loose Coupler.

Fig. 209.—Complete Loose Coupler.Fig. 209.—Complete Loose Coupler.

Fig. 209.—Complete Loose Coupler.

The two binding-posts near the secondary end of the coupler are connected to the terminals of the secondary winding by means of two flexible wires. They have not been shown in several of the illustrations because they would be liable to confuse the drawing.

The primary is provided with a slider moving back and forth over a narrow path scraped through the insulation so that it may make contact with each wire independently.

Detectors

Detectors are very simple devices and consist merely of an arrangement for holding a small piece of certain minerals and making a contact against the surface.

The crystal detector shown in Figure 210 is a very efficient form that may be easily and quickly made. When finished, it will make a valuable addition to almost any amateur experimenter's wireless equipment.

Fig. 210.—A Crystal Detector.Fig. 210.—A Crystal Detector.

Fig. 210.—A Crystal Detector.

The bracket is bent out of a piece of strip brass about one-eighth of an inch thick and five-eighths of an inch wide, according to the shape shown in the illustration. The bracket is mounted on a circular wooden base about three inches in diameter. The circular wooden blocks used by electricians in putting up chandeliers, called “fixture blocks,” will make a satisfactory base. An electrose knob of the typewriter type may be purchased from any good dealer in wireless supplies. It should be fitted with a threaded shank which will screw into a hole in the upper part of the bracket.

The mineral is contained in a small brass cup mounted on the base below the end of the knob.

Contact with the mineral in the cup is made by means of a fine wire spring soldered to the end of the adjusting screw.

Moving the screw up or down will vary the pressure of the spring on the mineral and permit the most sensitive adjustment to be secured. The bracket is connected to one of the binding-posts and the cup to the other.

Fig. 211.—Details of the Crystal Detector.Fig. 211.—Details of the Crystal Detector.

Fig. 211.—Details of the Crystal Detector.

The detector shown in Figure 212 is of the type often termed a "cat-whisker," because of the long, fine wire resting on the mineral.

It consists of a small clip, formed by bending a strip of sheet-brass, which grips a piece of galena.

A Double Slider Tuning Coil.A Double Slider Tuning Coil.

A Double Slider Tuning Coil.

A Junior Loose Coupler.A Junior Loose Coupler.

A Junior Loose Coupler.

Crystal Detectors.

Crystal Detectors.Crystal Detectors.

Crystal Detectors.

Galena may be obtained from any dealer in radio supplies. A piece of No. 30 phosphor bronze wire is soldered to the end of a short length of brass rod supported by a binding post. The other end of the rod is fitted with an electrose knob. This part of the detector is called the "feeler."

Fig. 212 Details of the "Cat Whisker" Detector.Fig. 212 Details of the "Cat Whisker" Detector.

Fig. 212 Details of the "Cat Whisker" Detector.

The detector is fitted with binding posts and may be mounted upon any suitable small base. The mineral clip is connected to one post and the binding-post supporting the "feeler" to the other. The tension or pressure of the end of the fine wire upon the mineral may be regulated by twisting the electrose knob so as to twist the rod. The different portions of the crystal may be "searched" for the most sensitive spot by sliding the rod back and forth.

A somewhat similar form of cat-whisker detector is shown in Figure 213. It is provided with a cup to hold the mineral in place of a clip.

The detector shown in Figure 214 is more elaborate than any of the others described so far.

Fig. 213.—Another Form of the "Cat-Whisker" Detector.Fig. 213.—Another Form of the "Cat-Whisker" Detector.

Fig. 213.—Another Form of the "Cat-Whisker" Detector.

Fig. 214.—"Cat-Whisker" Detector.Fig. 214.—"Cat-Whisker" Detector.

Fig. 214.—"Cat-Whisker" Detector.

The base is a wooden block, three and one-half by one and three-quarters inches by one-half inch. The binding-posts are of the type commonly used on electrical instruments. One of the posts is pivoted so that it will swing from side to side. A short piece of brass rod fitted with a rubber or fiber knob passes through the wire hole in the post. A piece of No. 30 B. & S. gauge bronze wire is soldered to the end of the rod. A small brass cup contains the mineral, which may be eithergalena, orsilicon. By twisting the post and sliding the rod back and forth, any portions of the mineral surface may be selected.

Fixed Condenser.

The construction of the condenser is illustrated in Figure 205. Take twenty-four sheets of thin typewriter paper, three by four inches, and twenty-three sheets of tinfoil, two by four inches. Pile them up, using first a sheet of paper then a sheet of tinfoil, then paper, and so on, so that every two sheets of tinfoil are separated by a sheet of paper. Each sheet of tinfoil must, however, project out beyond the edge of the paper. Connect all the tinfoil projections on one end of the condenser together and and attach a small wire. Connect all those on the opposite side in a similar manner. Then fasten a couple of rubber bands around the condenser to hold it together.

Fig. 215.—Building up a Fixed Condenser.Fig. 215.—Building up a Fixed Condenser.

Fig. 215.—Building up a Fixed Condenser.

Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.

Fig. 216.—A Fixed Condenser enclosed in a Brass Case made from a Piece of Tubing fitted with Wooden Ends.

If it is desired to give the condenser a finished appearance, it may be placed in a brass tube fitted with two wooden or fiber ends. The ends are provided with binding-posts to which the terminals of the condenser are connected.

Telephone Receiversfor use with wireless instruments must be purchased. Their construction is such that they cannot be made by the experimenter.

Fig. 217.—A Telephone Head Set.Fig. 217.—A Telephone Head Set.

Fig. 217.—A Telephone Head Set.

A seventy-five ohm, double-pole telephone receiver will do for stations not wishing to receive farther than fifty miles.

In order to secure the best results from wireless instruments, it is necessary to have receivers especially made for wireless. Each receiver should have 1000 ohms resistance. Some boys may find it necessary to purchase one receiver at a time. Two receivers, a double headband, and a double cord, forming a complete head set as shown in Figure 217, should be secured as soon as possible.

Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.

Fig. 218.—A Circuit showing how to connect a Double-Slider Tuning Coil.

Connecting the Receiving Apparatus

Figure 218 shows how to connect a double-slide tuner, a detector, a fixed condenser and a pair of telephones to the aerial and ground. The same instruments with a loose coupler in place of the double-slide tuner are shown in Figure 219.

The diagrams in Figure 220 are the same circuits as those shown in Figures 218 and 219, but show different instruments.

Fig. 219.—Circuit showing how to connect a Loose Coupler.Fig. 219.—Circuit showing how to connect a Loose Coupler.

Fig. 219.—Circuit showing how to connect a Loose Coupler.

Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.

Fig. 220.—A Diagram showing how to connect some of the Instruments described in this Chapter.

After the instruments are connected, place a piece of galena or silicon in the cup of the detector and bring the wire down on it. Then move the sliders on the tuning coil or loose coupler and adjust the detector until you can hear a message buzzing in the telephones. It may require a little patience and practice, but if you persist you will soon learn how to adjust the apparatus so as to receive the signals loudly and clearly with very little trouble.

The Transmitting Apparatus

Spark coils have already been described in Chapter XII. They may be used to transmit wireless messages simply by connecting to a spark-gap and a key.

Spark coils which are especially made for wireless telegraphy will usually send farther than an ordinary spark coil used for experimental purposes.

Fig. 221.—A Wireless Spark Coil.Fig. 221.—A Wireless Spark Coil.

Fig. 221.—A Wireless Spark Coil.

A good one-inch coil costs from $4.50 to $5.00 and will send from three to five miles if used with a fair aerial.

A spark coil requires considerable current for its successful operation and will give the best results if operated on storage cells, dry cells, or bichromate cells. If dry cells are used, it is a good plan to connect them in series multiple as shown in Figure 69.

Spark-gaps may be made by mounting two double binding-posts on a wooden base as shown in Figure 222.

Zinc possesses some peculiar property which makes it very efficient for a spark-gap, and for this reason the electrodes of a spark-gap are usually zinc.

Fig. 222.—Small Spark Gaps.Fig. 222.—Small Spark Gaps.

Fig. 222.—Small Spark Gaps.

The figure shows two different forms of electrodes. In one, they are made of zinc rods and provided with “electrose” handles. In the other gap, the zinc electrodes are in the shape of "tips" fitted on the ends of two short brass rods.

A one-inch spark coil will give very good results by connecting the spark-gap directly across the secondary of the coils. The aerial is connected to one side of the gap and the ground to the other.

The transmitter may be "tuned" and the range sometimes increased by using a condenser and a helix.

A condenser is most easily made by coating the inside and outside of a test-tube with tinfoil so as to form a miniature Leyden jar. The end of the tube is closed with a cork through which passes a brass rod connecting to the inner coating of tinfoil.

Fig. 223.—Diagram showing how to connect a Simple Transmitter.Fig. 223.—Diagram showing how to connect a Simple Transmitter.

Fig. 223.—Diagram showing how to connect a Simple Transmitter.

If such a condenser is connected directly across the spark-gap, the spark will become very white and crackling.

Several tubes may be arranged in a rack as shown in Figure 225.

A helix consists of a spiral of brass ribbon set in a wooden frame. The two strips composing the frame are each nine inches long. The spiral consists of eight turns of brass ribbon, three-eighths of an inch wide, set in saw-cuts made in the frame. A binding-post is connected to the outside end of the ribbon.

Figure 228 shows how to connect a helix and a condenser to a coil and a spark-gap.

The two clips are made by bending a strip of sheet brass and connecting a piece of flexible wire to one end.

Fig. 224.—A Test-Tube Leyden Jar.Fig. 224.—A Test-Tube Leyden Jar.

Fig. 224.—A Test-Tube Leyden Jar.

In large stations, the best position for the clips is found by placing a "hot-wire ammeter" in the aerial circuit and then moving the clips until the meter shows the highest reading.

The young experimenter will have to tune his set by moving the helix clips about until the best results are obtained in sending.

Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.

Fig. 225.—Eight Test-Tube Leyden Jars mounted in a Wooden Rack.

If the spark coil is a good one and capable of giving a good hot spark, it may be possible to tell when the set is in proper tune by placing a small miniature tungsten lamp in series with the aerial and changing the clips, the condenser, and the length of the spark-gap until the lamp lights the brightest.

Anoscillation transformeris sometimes used to replace an ordinary helix when it is desirable to tune a station very closely so that its messages shall not be liable to be confused with those of another station when both are working at the same time.

Fig. 226.—A Helix and Clip.Fig. 226.—A Helix and Clip.

Fig. 226.—A Helix and Clip.

An oscillation transformer consists of two helixes arranged so that one acts as a primary and the other as a secondary. An oscillation helix may be made by making two sets of helix frames similar to that in Secondary Figure 226.

Fig. 227.—An Oscillation Transformer.Fig. 227.—An Oscillation Transformer.

Fig. 227.—An Oscillation Transformer.

The primary should be provided with eight turns of brass ribbon and the secondary with twelve. The primary supports a stiff brass rod upon which the secondary is mounted. The secondary should slide up and down on the rod but move very stiffly so that it will stay where it is put.

AN OSCILLATION HELIX.AN OSCILLATION HELIX.

AN OSCILLATION HELIX.

AN OSCILLATION CONDENSER.AN OSCILLATION CONDENSER.

AN OSCILLATION CONDENSER.

An ordinary double-throw, double-pole knife switch having a porcelain base will make a very good aerial switch in a small station. It is used to connect the aerial and ground to either the transmitting or receiving apparatus at will. Such a switch is shown in Figure 230.

Fig 228.—Circuit showing how to connect a Helix and a Condenser.Fig 228.—Circuit showing how to connect a Helix and a Condenser.

Fig 228.—Circuit showing how to connect a Helix and a Condenser.

The aerial should be connected to the postAand the ground toB. The postsEandFlead to the transmitter, andCandDto the receptor, or vice-versa according to which is the more convenient from the location of the apparatus on the table or operating bench.

A suitable table should be arranged to place the wireless instruments upon so that they may be permanently connected together.

Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.

Fig 229.—Circuit showing how to connect an Oscillation Transformer and a Condenser.

The Continental Code is the one usually employed in wireless telegraphy. It differs slightly from Morse as it contains no space letters. It will be found easy to learn and somewhat easier to handle than Morse.

Fig 230.—An Aerial Switch.Fig 230.—An Aerial Switch.

Fig 230.—An Aerial Switch.

Two or three months’ steady practice with a chum should enable the young experimenter to become a very fair wireless telegraph operator. Then by listening for some of the high power wireless stations which send out the press news to ships at sea during the evening it should be possible to become very proficient. The press news is sent more slowly than ordinary commercial wireless messages, and is therefore easy to read and a good starting point for the beginner learning to read.

Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.

Fig 231.—A Complete Wiring Diagram for both the Transmitter and the Receptor.

Fig. 232.—The Continental Alphabet.Fig. 232.—The Continental Alphabet.

Fig. 232.—The Continental Alphabet.

A Coherer Outfit

A Coherer Outfitis usually capable of only receiving messages coming from a distance of under one mile. In spite of this fact, however, it is an exceedingly interesting apparatus to construct and experiment with, and for this reason is found fully described below.

A coherer set will ring a bell or work a sounder for short distances and therefore is the best sort of an arrangement for demonstrating the workings of your wireless apparatus to your friends.

The first thing that you need for a coherer is a pair of double binding-posts. Mount these about an inch and three-quarters apart on a wooden base, six inches long and four inches wide as shown in Figure 233.

Fig. 233.—A Coherer and a Decoherer.Fig. 233.—A Coherer and a Decoherer.

Fig. 233.—A Coherer and a Decoherer.

Get a piece of glass tubing about an inch and one-half long and about one-eighth of an inch inside diameter. You will also need some brass rod which will just slide into the tube tightly. Cut off two pieces of the brass rod each one and three-quarters inches long and slip these through the upper holes in the binding-posts and into the glass tube as shown in Figure 234. Before putting the second rod in place, however, you must put some nickel and silver filings in the tube, so that when the rods are pushed almost together, with only a distance of about one-sixteenth of an inch between them, the filings will about half fill the space.

The filings must be very carefully prepared, and in order to make them, first use a coarse-grained file on the edge of a five-cent piece. Do not use the fine dust and powder, but only the fairly coarse filings. Mix a few silver filings from a ten-cent piece with the nickel in such proportion that the mixture is 90% nickel and 10% silver.

Fig. 234.—Details of the Coherer.Fig. 234.—Details of the Coherer.

Fig. 234.—Details of the Coherer.

You will have to experiment considerably to find out just the right amount of filings to place in the tube, and how far apart to place the brass rods or plugs.

Remove the gong from an old electric bell and mount the bell on the base as shown in Figure 233. It should be in such a position that the bell hammer will touch the coherer very lightly when the bell is ringing.

The two binding-posts, tube rods, and filings constitute thecoherer. The bell is thedecoherer.

The next thing required in order to complete the apparatus is a relay. You may use the relay described in Chapter X or build one according to the plan shown in Figure 235. This relay consists of a single electro-magnet mounted on a wooden base, two inches wide and four inches long. The armature is a piece of soft iron rod one-quarter of an inch in diameter and one-eighth of an inch long, riveted to the end of a thin piece of spring brass, about No. 34 B. & S. gauge in thickness.

Fig. 235.—The Relay.Fig. 235.—The Relay.

Fig. 235.—The Relay.

The other end of the spring is fitted to a bracket and provided with a thumbscrew to adjust the tension of the spring.

The under side of the armature and the upper side of the magnet core are each fitted with a small silver contact.

The contacts should meet squarely when the armature is drawn down on to the core by a current of electricity passing through the electro-magnet.

By turning the adjusting screw, the armature can be raised or lowered. It should be adjusted so that it almost touches the core and is only just far enough away to slip a piece of thick paper under.

The terminals of the magnet are connected to the two binding-posts on the base markedSandS. One of the binding-posts,P, is connected to the brass upright, and the other is connected to the core of the magnet.

Figure 236 shows how to connect up the outfit. It will require some very nice adjusting before you will be able to get it to working properly.

Fig. 236.—The Complete Coherer Outfit.Fig. 236.—The Complete Coherer Outfit.

Fig. 236.—The Complete Coherer Outfit.

If you wish to use the outfit for demonstration purposes or for sending messages for very short distances, as for instance across a room, you do not need an aerial but merely a pair of "catch-wires."

The "catch-wires" are two pieces of stiff copper wire, about two feet long, placed in the lower holes in the double binding-posts forming part of the coherer.

In order to set the apparatus for operation, raise the adjusting screw of the relay until the armature is quite far away from the core. Then push the armature down against the contact on the core. The decoherer should then immediately operate and begin to tap the coherer. Then turn the thumbscrew until the armature is brought down to the core in such a position that it is as close as it is possible to get it without ringing the bell.

The transmitter should consist of a spark coil, battery, key, and a spark-gap. The gap should be connected to the secondary of the coil and adjusted so that the electrodes are only about one-eighth of an inch apart. The key is placed in series with the primary of the coil and the battery, so that pressing the key will send a stream of sparks across the gap. Fit the spark-gap with two catch-wires similar to those on the coherer and place the transmitter about four or five feet away from the coherer outfit.

You are now likely to find that if you press the key of the transmitter, the decoherer will ring. It is possible that it will continue to ring after you have stopped pressing the key. If such is the case, it will be necessary to turn the adjusting screw on the relay so as to move the armature upward a short distance away from the core.

If the decoherer will not operate each time when you press the key, the brass plugs in the coherer need adjusting. You must not be discouraged if you have some difficulty in making the apparatus work at first. After you learn how to adjust it properly, you will find that you can move the transmitter quite a distance away from the coherer and it will still operate very nicely.

After you manage that, you can place the apparatus in separate rooms and find it possible to work it just the same, because ordinary walls will not make any difference to wireless waves.

Bear in mind that the nearer the coherer plugs are to each other, the more sensitive the coherer will be, but that if too close, the decoherer will not be able to shake the filings properly and will not stop when you stop pressing the key.

The operation of the apparatus depends upon the fact that when properly adjusted the resistance of the filings between the two brass plugs is too great to allow sufficient battery current to flow to attract the armature of the relay. As soon as any wireless waves from the transmitter strike the catch-wires of the coherer, they cause the filings to cling together or cohere. When in this state, they have a low resistance and permit the current to flow in the relay circuit and draw down the armature. The armature closes the second circuit and sets the decoherer into operation. The decoherer shakes the filings and causes them to decohere or fall apart and so makes them ready again for the next signal.

A coherer set of this sort may be used on an aerial and ground by substituting the coherer for the detector, but otherwise following any of the receiving circuits which have already been shown.

A WIRELESS TELEPHONE

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