First District..............Boston, Mass.Second " ..............New York CityThird " ..............Baltimore, Md.Fourth " ..............Norfolk, Va.Fifth " ..............New Orleans, La.Sixth " ............. San Francisco, Cal.Seventh " ............. Seattle, Wash.Eighth " ............. Detroit, Mich.Ninth " ..............Chicago, Ill.
Kinds of Transmitters.--There are two general types of transmitters used for sending out wireless messages and these are: (1)wireless telegraphtransmitters, and (2)wireless telephonetransmitters. Telegraph transmitters may use either: (a) ajump-spark, (b) anelectric arc, or (c) avacuum tubeapparatus for sending out dot and dash messages, while telephone transmitters may use either, (a) anelectric arc, or (b) avacuum tubefor sending out vocal and musical sounds. Amateurs generally use ajump-sparkfor sending wireless telegraph messages and thevacuum tubefor sending wireless telephone messages.
The Spark Gap Wireless Telegraph Transmitter.--The simplest kind of a wireless telegraph transmitter consists of: (1) asource of direct or alternating current, (2) atelegraph key, (3) aspark-coilor atransformer, (4) aspark gap, (5) anadjustable condenserand (6) anoscillation transformer. Wheredry cellsor astorage batterymust be used to supply the current for energizing the transmitter a spark-coil can be employed and these may be had in various sizes from a little fellow which gives 1/4-inch spark up to a larger one which gives a 6-inch spark. Where more energy is needed it is better practice to use a transformer and this can be worked on an alternating current of 110 volts, or if only a 110 volt direct current is available then anelectrolytic interruptermust be used to make and break the current. A simple transmitting set with an induction coil is shown inFig. 2.
A wireless key is made like an ordinary telegraph key except that where large currents are to be used it is somewhat heavier and is provided with large silver contact points. Spark gaps for amateur work are usually of: (1) theplainorstationary type, (2) therotating type, and (3) thequenched gaptype. The plain spark-gap is more suitable for small spark-coil sets, and it is not so apt to break down the transformer and condenser of the larger sets as the rotary gap. The rotary gap on the other hand tends to preventarcingand so the break is quicker and there is less dragging of the spark. The quenched gap is more efficient than either the plain or rotary gap and moreover it is noiseless.
Condensers for spark telegraph transmitters can be ordinary Leyden jars or glass plates coated with tin or copper foil and set into a frame, or they can be built up of mica and sheet metal embedded in an insulating composition. The glass plate condensers are the cheapest and will serve your purpose well, especially if they are immersed in oil. Tuning coils, sometimes calledtransmitting inductancesandoscillation transformers, are of various types. The simplest kind is a transmitting inductance which consists of 25 or 30 turns of copper wire wound on an insulating tube or frame. An oscillation transformer is a loose coupled tuning coil and it consists of a primary coil formed of a number of turns of copper wire wound on a fixed insulating support, and a secondary coil of about twice the number of turns of copper wire which is likewise fixed in an insulating support, but the coils are relatively movable. Anoscillation transformer(instead of atuning coil), is required by government regulations unlessinductively coupled.
TheVacuum Tube Telegraph Transmitter.--This consists of: (1) asource of direct or alternating current, (2) atelegraph key, (3) avacuum tube oscillator, (4) atuning coil, and (5) acondenser. This kind of a transmitter sets upsustainedoscillations instead ofperiodicoscillations which are produced by a spark gap set. The advantages of this kind of a system will be found explained inChapter XVI.
The Wireless Telephone Transmitter.--Because a jump-spark sets upperiodic oscillations, that is, the oscillations are discontinuous, it cannot be used for wireless telephony. An electric arc or a vacuum tube sets upsustainedoscillations, that is, oscillations which are continuous. As it is far easier to keep the oscillations going with a vacuum tube than it is with an arc the former means has all but supplanted the latter for wireless telephone transmitters. The apparatus required and the connections used for wireless telephone sets will be described in later chapters.
Useful Information.--It would be wise for the reader to turn to theAppendix, beginning with page 301 of this book, and familiarize himself with the information there set down in tabular and graphic form. For example, the first table gives abbreviations of electrical terms which are in general use in all works dealing with the subject. You will also find there brief definitions of electric and magnetic units, which it would be well to commit to memory; or, at least, to make so thoroughly your own that when any of these terms is mentioned, you will know instantly what is being talked about.
As inferred in the first chapter, an aerial for receiving does not have to be nearly as well made or put up as one for sending. But this does not mean that you can slipshod the construction and installation of it, for however simple it is, the job must be done right and in this case it is as easy to do it right as wrong.
To send wireless telegraph and telephone messages to the greatest distances and to receive them as distinctly as possible from the greatest distances you must use for your aerial (1) copper or aluminum wire, (2) two or more wires, (3) have them the proper length, (4) have them as high in the air as you can, (5) have them well apart from each other, and (6) have them well insulated from their supports. If you live in a flat building or an apartment house you can string your aerial wires from one edge of the roof to the other and support them by wooden stays as high above it as may be convenient.
Should you live in a detached house in the city you can usually get your next-door neighbor to let you fasten one end of the aerial to his house and this will give you a good stretch and a fairly high aerial. In the country you can stretch your wires between the house and barn or the windmill. From this you will see that no matter where you live you can nearly always find ways and means of putting up an aerial that will serve your needs without going to the expense of erecting a mast.
Kinds of Aerial Wire Systems.--An amateur wireless aerial can be anywhere from 25 feet to 100 feet long and if you can get a stretch of the latter length and a height of from 30 to 75 feet you will have one with which you can receive a thousand miles or more and send out as much energy as the government will allow you to send.
The kind of an aerial that gives the best results is one whose wire, or wires, arehorizontal, that is, parallel with the earth under it as shown atAinFig. 3.If only one end can be fixed to some elevated support then you can secure the other end to a post in the ground, but the slope of the aerial should not be more than 30 or 35 degrees from the horizontal at most as shown atB.
(A) Fig. 3.--Flat top, or Horizontal Aerial. (B) Fig. 3.--Inclined Aerial.
Theleading-in wire, that is, the wire that leads from and joins the aerial wire with your sending and receiving set, can be connected to the aerial anywhere it is most convenient to do so, but the best results are had when it is connected to one end as shown atAinFig. 4, in which case it is called aninverted L aerial, or when it is connected to it at the middle as shown atB, when it is called aT aerial. The leading-in wire must be carefully insulated from the outside of the building and also where it passes through it to the inside. This is done by means of an insulating tube known as aleading-in insulator,orbulkhead insulatoras it is sometimes called.
(A) Fig. 4.--Inverted L Aerial. (B) Fig. 4.--T Aerial.
As a protection against lightning burning out your instruments you can use either: (1) anair-gap lightning arrester,(2) avacuum tube protector,or (3) alightning switch,which is better. Whichever of these devices is used it is connected in between the aerial and an outside ground wire so that a direct circuit to the earth will be provided at all times except when you are sending or receiving. So your aerial instead of being a menace really acts during an electrical storm like a lightning rod and it is therefore a real protection. The air-gap and vacuum tube lightning arresters are little devices that can be used only where you are going to receive, while the lightning switch must be used where you are going to send; indeed, in some localities theFire Underwritersrequire a large lightning switch to be used for receiving sets as well as sending sets.
How to Put Up a Cheap Receiving Aerial.--The kind of an aerial wire system you put up will depend, chiefly, on two things, and these are: (1) your pocketbook, and (2) the place where you live.
A Single Wire Aerial.--This is the simplest and cheapest kind of a receiving aerial that can be put up. The first thing to do is to find out the length of wire you need by measuring the span between the two points of support; then add a sufficient length for the leading-in wire and enough more to connect your receiving set with the radiator or water pipe.
You can use any size of copper or aluminum wire that is not smaller thanNo. 16 Brown and Sharpe gauge.When you buy the wire get also the following material: (1) twoporcelain insulatorsas shown atAinFig. 5; (2) three or fourporcelain knob insulators, seeB; (3) either (a) anair gap lightning arrester,seeC, or (b) alightning switchseeD; (4) aleading-in porcelain tube insulator,seeE, and (5) aground clamp, seeF.
Fig. 5.--Material for a Simple Aerial Wire System.
To make the aerial slip each end of the wire through a hole in each insulator and twist it fast; next cut off and slip two more pieces of wire through the other holes in the insulators and twist them fast and then secure these to the supports at the ends of the building. Take the piece you are going to use for the leading-in wire, twist it around the aerial wire and solder it there when it will look likeAinFig. 6. Now if you intend to use theair gap lightning arresterfasten it to the wall of the building outside of your window, and bring the leading-in wire from the aerial to the top binding post of your arrester and keep it clear of everything as shown atB. If your aerial is on the roof and you have to bring the leading-in wire over the cornice or around a corner fix a porcelain knob insulator to the one or the other and fasten the wire to it.
(A) Fig. 6.--Single Wire Aerial for Receiving.(B) Fig. 6.--Receiving Aerial with Air Gap Lightning Arrester.(C) Fig. 6.--Aerial with Lightning Switch.
Next bore a hole through the frame of the window at a point nearest your receiving set and push a porcelain tube 5/8 inch in diameter and 5 or 6 inches long, through it. Connect a length of wire to the top post of the arrester or just above it to the wire, run this through the leading-in insulator and connect it to the slider of your tuning coil. Screw the end of a piece of heavy copper wire to the lower post of the arrester and run it to the ground, on porcelain knobs if necessary, and solder it to an iron rod or pipe which you have driven into the earth. Finally connect the fixed terminal of your tuning coil with the water pipe or radiator inside of the house by means of the ground clamp as shown in the diagrammatic sketch atBinFig. 6and you are ready to tune in.
If you want to use a lightning switch instead of the air-gap arrester then fasten it to the outside wall instead of the latter and screw the free end of the leading-in wire from the aerial to the middle post of it as shown atCinFig. 6. Run a wire from the top post through the leading-in insulator and connect it with the slider of your tuning coil. Next screw one end of a length of heavy copper wire to the lower post of the aerial switch and run it to an iron pipe in the ground as described above in connection with the spark-gap lightning arrester; then connect the fixed terminal of your tuning coil with the radiator or water pipe and your aerial wire system will be complete as shown atCinFig. 6.
A Two-wire Aerial.--An aerial with two wires will give better results than a single wire and three wires are better than two, but you must keep them well apart. To put up a two-wire aerial get (1) enoughNo. 16, or preferablyNo. 14, solid or stranded copper or aluminum wire, (2) four porcelain insulators, seeBinFig. 5, and (3) two sticks about 1 inch thick, 3 inches wide and 3 or 4 feet long, for thespreaders, and bore 1/8-inch hole through each end of each one. Now twist the ends of the wires to the insulators and then cut off four pieces of wire about 6 feet long and run them through the holes in the wood spreaders. Finally twist the ends of each pair of short wires to the free ends of the insulators and then twist the free ends of the wires together.
For the leading-in wire that goes to the lightning switch take two lengths of wire and twist one end of each one around the aerial wires and solder them there. Twist the short wire around the long wire and solder this joint also when the aerial will look likeFig. 7. Bring the free end of the leading-in wire down to the middle post of the lightning switch and fasten it there and connect up the receiver to it and the ground as described under the caption ofA Single Wire Aerial.
Fig. 7.--Two Wire Aerial.
Connecting in the Ground.--If there is a gas or water system or a steam-heating plant in your house you can make your ground connection by clamping a ground clamp to the nearest pipe as has been previously described. Connect a length of bare or insulated copper wire with it and bring this up to the table on which you have your receiving set. If there are no grounded pipes available then you will have to make a good ground which we shall describe presently and lead the ground wire from your receiving set out of the window and down to it.
How to Put Up a Good Aerial.--While you can use the cheap aerial already described for a small spark-coil sending set you should have a better insulated one for a 1/2 or a 1kilowatttransformer set. The cost for the materials for a good aerial is small and when properly made and well insulated it will give results that are all out of proportion to the cost of it.
An Inexpensive Good Aerial.--A far better aerial, because it is more highly insulated, can be made by usingmidget insulatorsinstead of the porcelain insulators described under the caption ofA Single Wire Aerialand using a smallelectrose leading-in insulatorinstead of the porcelain bushing. This makes a good sending aerial for small sets as well as a good receiving aerial.
The Best Aerial that Can Be Made.--To make this aerial get the following material together: (1) enoughstranded or braided wirefor three or four lengths of parallel wires, according to the number you want to use (2) six or eightelectrose ball insulators, seeB,Fig. 8; (3) two 5-inch or 10-inchelectrose strain insulators, seeC; (4) six or eightS-hooks,see D; one largewithewith one eye for middle of end spreader, seeE; (6) two smallerwitheswith one eye each for end spreader, seeE; (7) two still smallerwithes, with two eyes each for the ends of the end spreaders, seeE(8) twothimbles, seeF, for 1/4-inch wire cable; (9) six or eighthard rubber tubesorbushingsas shown atG; and (10) twoend spreaders, seeH; onemiddle spreader, see I; and oneleading-in spreader, seeJ.
(A) Fig. 8--Part of a Good Aerial.(B) Fig. 8.--The Spreaders.
For this aerial any one of a number of kinds of wire can be used and among these are (a)stranded copper wire;(b)braided copper wire;(c)stranded silicon bronze wire,and (d)stranded phosphor bronze wire. Stranded and braided copper wire is very flexible as it is formed of seven strands of fine wire twisted or braided together and it is very good for short and light aerials. Silicon bronze wire is stronger than copper wire and should be used where aerials are more than 100 feet long, while phosphor bronze wire is the strongest aerial wire made and is used for high grade aerials by the commercial companies and the Government for their high-power stations.
The spreaders should be made of spruce, and should be 4 feet 10 inches long for a three-wire aerial and 7 feet 1 inch long for a four-wire aerial as the distance between the wires should be about 27 inches. The end spreaders can be turned cylindrically but it makes a better looking job if they taper from the middle to the ends. They should be 2-1/4 inches in diameter at the middle and 1-3/4 inches at the ends. The middle spreader can be cylindrical and 2 inches in diameter. It must have holes bored through it at equidistant points for the hard rubber tubes; each of these should be 5/8 inch in diameter and have a hole 5/32 inch in diameter through it for the aerial wire. The leading-in spreader is also made of spruce and is 1-1/2 inches square and 26 inches long. Bore three or four 5/8-inch holes at equidistant points through this spreader and insert hard rubber tubes in them as with the middle spreader.
Assembling the Aerial.--Begin by measuring off the length of each wire to be used and see to it that all of them are of exactly the same length. Now push the hard rubber insulators through the holes in the middle spreader and thread the wires through the holes in the insulators as shown atAinFig 9.
Next twist the ends of each wire to the rings of the ball insulators and then put the large withes on the middle of each of the end spreaders; fix the other withes on the spreaders so that they will be 27 inches apart and fasten the ball insulators to the eyes in the withes with the S-hooks. Now slip a thimble through the eye of one of the long strain insulators, thread a length of stranded steel wire 1/4 inch in diameter through it and fasten the ends of it to the eyes in the withes on the ends of the spreaders.
(A) Fig. 9.--Middle Spreader. (B) Fig. 9.--One End of Aerial Complete.(C) Fig. 9.--Leading in Spreader.
Finally fasten a 40-inch length of steel stranded wire to each of the eyes of the withes on the middle of each of the spreaders, loop the other end over the thimble and then wrap the end around the wires that are fixed to the ends of the spreaders. One end of the aerial is shown complete atBinFig. 9, and from this you can see exactly how it is assembled. Now cut off three or four pieces of wire 15 or 20 feet long and twist and solder each one to one of the aerial wires; then slip them through the hard rubber tubes in the leading-in spreader, bring their free ends together as atCand twist and solder them to a length of wire long enough to reach to your lightning switch or instruments.
Making a Good Ground.--Where you have to make agroundyou can do so either by (1) burying sheets of zinc or copper in the moist earth; (2) burying a number of wires in the moist earth, or (3) using acounterpoise. To make a ground of the first kind take half a dozen large sheets of copper or zinc, cut them into strips a foot wide, solder them all together with other strips and bury them deeply in the ground.
It is easier to make a wire ground, say of as many or more wires as you have in your aerial and connect them together with cross wires. To put such a ground in the earth you will have to use a plow to make the furrows deep enough to insure them always being moist. In the counterpoise ground you make up a system of wires exactly like your aerial, that is, you insulate them just as carefully; then you support them so that they will be as close to the ground as possible and yet not touch it or anything else. This and the other two grounds just described should be placed directly under the aerial wire if the best results are to be had. In using a counterpoise you must bring the wire from it up to and through another leading-in insulator to your instruments.
With a crystal detector receiving set you can receive either telegraphic dots and dashes or telephonic speech and music. You can buy a receiving set already assembled or you can buy the different parts and assemble them yourself. An assembled set is less bother in the beginning but if you like to experiment you canhook up, that is, connect the separate parts together yourself and it is perhaps a little cheaper to do it this way. Then again, by so doing you get a lot of valuable experience in wireless work and an understanding of the workings of wireless that you cannot get in any other way.
Assembled Wireless Receiving Sets.--The cheapest assembled receiving set [Footnote: The Marvel, made by the Radio Mfg. Co., New York City.] advertised is one in which the detector and tuning coil is mounted in a box. It costs $15.00, and can be bought of dealers in electric supplies generally.
This price also includes a crystal detector, an adjustable tuning coil, a single telephone receiver with head-band and the wire, porcelain insulators, lightning switch and ground clamp for the aerial wire system. It will receive wireless telegraph and telephone messages over a range of from 10 to 25 miles.
Another cheap unit receptor, that is, a complete wireless receiving set already mounted which can be used with a single aerial is sold for $25.00. [Footnote: The Aeriola Jr., made by the Westinghouse Company, Pittsburgh, Pa.] This set includes a crystal detector, a variable tuning coil, a fixed condenser and a pair of head telephone receivers. It can also be used to receive either telegraph or telephone messages from distances up to 25 miles. The aerial equipment is not included in this price, but it can be bought for about $2.50 extra.
Assembling Your Own Receiving Set.--In this chapter we shall go only into the apparatus used for two simple receiving sets, both of which have acrystal detector. The first set includes adouble-slide tuning coiland the second set employs aloose-coupled tuning coil, orloose coupler, as it is called for short. For either set you can use a pair of 2,000- or 3,000-ohm head phones.
The Crystal Detector.--A crystal detector consists of: (1)the frame, (2)the crystal, and (3)the wire point. There are any number of different designs for frames, the idea being to provide a device that will (a) hold the sensitive crystal firmly in place, and yet permit of its removal, (b) to permit thewire point, orelectrode, to be moved in any direction so that the free point of it can make contact with the most sensitive spot on the crystal and (c) to vary the pressure of the wire on the crystal.
A simple detector frame is shown in the cross-section atAinFig. 10; the crystal, which may begalena,siliconoriron pyrites, is held securely in a holder while thephosphor-bronze wire pointwhich makes contact with it, is fixed to one end of a threaded rod on the other end of which is a knob. This rod screws into and through a sleeve fixed to a ball that sets between two brass standards and this permits an up and down or a side to side adjustment of the metal point while the pressure of it on the crystal is regulated by the screw.
(A) Fig. 10.--Cross Section of Crystal Detector. (B) Fig. 10.--The Crystal Detector Complete.
A crystal of this kind is often enclosed in a glass cylinder and this makes it retain its sensitiveness for a much longer time than if it were exposed to dust and moisture. An upright type of this detector can be bought for $2.25, while a horizontal type, as shown atB, can be bought for $2.75. Galena is the crystal that is generally used, for, while it is not quite as sensitive as silicon and iron pyrites, it is easier to obtain a sensitive piece.
The Tuning Coil.--It is with the tuning coil that youtune inandtune outdifferent stations and this you do by sliding the contacts to and fro over the turns of wire; in this way you vary theinductanceandcapacitance, that is, theconstantsof the receiving circuits and so make them receiveelectric waves, that is, wireless waves, of different lengths.
The Double Slide Tuning Coil.--With this tuning coil you can receive waves from any station up to 1,000 meters in length. One of the ends of the coil of wire connects with the binding post markedainFig. 11, and the other end connects with the other binding post markedb, while one of the sliding contacts is connected to the binding postc, and theother sliding contactis connected with the binding postd.
(A) Fig. 11.--Schematic Diagram of Double Slide Tuning Coil. (B) Fig. 11.--Double Slide Tuning Coil Complete.
When connecting in the tuning coil, only the postaor the postbis used as may be most convenient, but the other end of the wire which is connected to a post is left free; just bear this point in mind when you come to connect the tuning coil up with the other parts of your receiving set. The tuning coil is shown complete atBand it costs $3.00 or $4.00. Atriple slidetuning coil constructed like the double slide tuner just described, only with more turns of wire on it, makes it possible to receive wave lengths up to 1,500 meters. It costs about $6.00.
The Loose Coupled Tuning Coil.--With aloose coupler, as this kind of a tuning coil is called for short, veryselective tuningis possible, which means that you can tune in a station very sharply, and it will receive any wave lengths according to size of coils. The primary coil is wound on a fixed cylinder and its inductance is varied by means of a sliding contact like the double slide tuning coil described above. The secondary coil is wound on a cylinder that slides in and out of the primary coil. The inductance of this coil is varied by means of a switch that makes contact with the fixed points, each of which is connected with every twentieth turn of wire as shown in the diagramAinFig. 12. The loose coupler, which is shown complete atB, costs in the neighborhood of $8.00 or $10.00.
(A) Fig. 12.--Schematic Diagram of Loose Coupler. (B) Fig. 12.--Loose Coupler Complete.
Fixed and Variable Condensers.--You do not require a condenser for a simple receiving set, but if you will connect afixed condenseracross your headphones you will get better results, while avariable condenserconnected in theclosed circuit of a direct coupled receiving set, that is, one where a double slide tuning coil is used, makes it easy to tune very much more sharply; a variable condenser is absolutely necessary where the circuits areinductively coupled, that is, where a loose coupled tuner is used.
A fixed condenser consists of a number of sheets of paper with leaves of tin-foil in between them and so built up that one end of every other leaf of tin-foil projects from the opposite end of the paper as shown atAinFig. 13. The paper and tin-foil are then pressed together and impregnated with an insulating compound. A fixed condenser of the exact capacitance required for connecting across the head phones is mounted in a base fitted with binding posts, as shown atB, and costs 75 cents. (Paper ones 25 cents.)
(A) Fig. 13.--How a Fixed Receiving Condenser is Built up. (B) Fig. 13.--The Fixed Condenser Complete.(C) and (D) Fig. 13.--The Variable Rotary Condenser.
A variable condenser, seeC, of the rotating type is formed of a set of fixed semi-circular metal plates which are slightly separated from each other and between these a similar set of movable semi-circular metal plates is made to interleave; the latter are secured to a shaft on the top end of which is a knob and by turning it the capacitance of the condenser, and, hence, of the circuit in which it is connected, is varied. This condenser, which is shown atD, is made in two sizes, the smaller one being large enough for all ordinary wave lengths while the larger one is for proportionately longer wave lengths. These condensers cost $4.00 and $5.00 respectively.
About Telephone Receivers.--There are a number of makes of head telephone receivers on the market that are designed especially for wireless work. These phones are wound toresistancesof from 75ohmsto 8,000ohms, and cost from $1.25 for a receiver without a cord or headband to $15.00 for a pair of phones with a cord and head band. You can get a receiver wound to any resistance in between the above values but for either of the simple receiving sets such as described in this chapter you ought to have a pair wound to at least 2,000 ohms and these will cost you about $5.00. A pair of head phones of this type is shown inFig. 14.
Fig. 14.--Pair of Wireless Head Phones.
Connecting Up the Parts--Receiving Set No. 1.--For this set get (1) acrystal detector, (2) atwo-slide tuning coil, (3) afixed condenser, and (4) a pair of 2,000 ohm head phones. Mount the detector on the right-hand side of a board and the tuning coil on the left-hand side. Screw in two binding posts for the cord ends of the telephone receivers ataandbas shown atAinFig. 15. This done connect one of the end binding posts of the tuning coil with the ground wire and a post of one of the contact slides with the lightning arrester or switch which leads to the aerial wire.
Fig. 15.--Top View of Apparatus Layout for Receiving Set No. 1.(B) Fig. 15.--Wiring Diagram for Receiving Set No. 1.
Now connect the post of the other contact slide to one of the posts of the detector and the other post of the latter with the binding posta, then connect the binding postbto the ground wire and solder the joint. Next connect the ends of the telephone receiver cord to the postsaandband connect a fixed condenser also with these posts, all of which are shown in the wiring diagram atB, and you are ready to adjust the set for receiving.
Receiving Set No. 2.--Use the same kind of a detector and pair of head phones as forSet No. 1, but get (1) aloose coupled tuning coil, and (2) avariable condenser. Mount the loose coupler at the back of a board on the left-hand side and the variable condenser on the right-hand side. Then mount the detector in front of the variable condenser and screw two binding posts,aandb, in front of the tuning coil as shown atAinFig. 16.
Fig. 16.--Top view of Apparatus Layout for Receiving Set No. 2.(B) Fig. 16.--Wiring Diagram for Receiving Set No. 2.
Now connect the post of the sliding contact of the loose coupler with the wire that runs to the lightning switch and thence to the aerial; connect the post of the primary coil, which is the outside coil, with the ground wire; then connect the binding post leading to the switch of the secondary coil, which is the inside coil, with one of the posts of the variable condenser, and finally, connect the post that is joined to one end of the secondary coil with the other post of the variable condenser.
This done, connect one of the posts of the condenser with one of the posts of the detector, the other post of the detector with the binding posta, and the postbto the other post of the variable condenser. Next connect a fixed condenser to the binding postsaandband then connect the telephone receivers to these same posts, all of which is shown in the wiring diagram atB. You are now ready to adjust the instruments. In making the connections use No. 16 or 18 insulated copper wire and scrape the ends clean where they go into the binding posts. See, also, that all of the connections are tight and where you have to cross the wires keep them apart by an inch or so and always cross them at right angles.
Adjusting the No. 1 Set--The Detector.--The first thing to do is to test the detector in order to find out if the point of the contact wire is on a sensitive spot of the crystal. To do this you need abuzzer, aswitchand adry cell. An electric bell from which the gong has been removed will do for the buzzer, but you can get one that is made specially for the purpose, for 75 cents, which gives out a clear, high-pitched note that sounds like a high-power station.
Connect one of the binding posts of the buzzer with one post of the switch, the other post of the latter with the zinc post of the dry cell and the carbon post of this to the other post of the buzzer. Then connect the post of the buzzer that is joined to the vibrator, to the ground wire as shown in the wiring diagram,Fig. 17.Now close the switch of the buzzer circuit, put on your head phones, and move the wire point of the detector to various spots on the crystal until you hear the sparks made by the buzzer in your phones.
Fig. 17.--Adjusting the Receiving Set.
Then vary the pressure of the point on the crystal until you hear the sparks as loud as possible. After you have made the adjustment open the switch and disconnect the buzzer wire from the ground wire of your set. This done, be very careful not to jar the detector or you will throw it out of adjustment and then you will have to do it all over again. You are now ready to tune the set with the tuning coil and listen in.
The Tuning Coil.--To tune this set move the slideAof the double-slide tuner, seeBinFig. 15, over to the end of the coil that is connected with the ground wire and the slideBnear the opposite end of the coil, that is, the one that has the free end. Now move the slideAtoward theBslide and when you hear the dots and dashes, or speech or music, that is coming in as loud as you can move theBslide toward theAslide until you hear still more loudly. A very few trials on your part and you will be able to tune in or tune out any station you can hear, if not too close or powerful.
Adjusting the No. 2 Set.--First adjust the crystal detector with the buzzer set as described above withSet No. 1,then turn the knob of your variable condenser so that the movable plates are just half-way in, pull the secondary coil of your loose-coupled tuner half way out; turn the switch lever on it until it makes a contact with the middle contact point and set the slider of the primary coil half way between the ends.
Now listen in for telegraphic signals or telephonic speech or music; when you hear one or the other slide the secondary coil in and out of the primary coil until the sounds are loudest; now move the contact switch over the points forth and back until the sounds are still louder, then move the slider to and fro until the sounds are yet louder and, finally, turn the knob of the condenser until the sounds are clear and crisp. When you have done all of these things you have, in the parlance of the wireless operator,tuned inand you are ready to receive whatever is being sent.
A wireless telegraph transmitting set can be installed for a very small amount of money provided you are content with one that has a limited range. Larger and better instruments can, of course, be had for more money, but however much you are willing to spend still you are limited in your sending radius by the Government's rules and regulations. The best way, and the cheapest in the end, to install a telegraph set is to buy the separate parts and hook them up yourself.
The usual type of wireless telegraph transmitter employs adisruptive discharge,orspark,as it is called, for setting up the oscillating currents in the aerial wire system and this is the type of apparatus described in this chapter. There are two ways to set up the sparks and these are: (1) with aninduction coil,orspark-coil,as it is commonly called, and (2) with analternating current transformer, orpower transformer, as it is sometimes called. Where you have to generate the current with a battery you must use a spark coil, but if you have a 110-volt direct or alternating lighting current in your home you can use a transformer which will give you more power.
A Cheap Transmitting Set (No. 1).--For this set you will need: (1) aspark-coil, (2) abatteryof dry cells, (3) atelegraph key, (4) aspark gap, (5) ahigh-tension condenser, and (6) anoscillation transformer. There are many different makes and styles of these parts but in the last analysis all of them are built on the same underlying bases and work on the same fundamental principles.
The Spark-Coil.--Spark coils for wireless work are made to give sparks from 1/4 inch in length up to 6 inches in length, but as a spark coil that gives less than a 1-inch spark has a very limited output it is best to get a coil that gives at least a 1-inch spark, as this only costs about $8.00, and if you can get a 2- or a 4-inch spark coil so much the better. There are two general styles of spark coils used for wireless and these are shown atAandBinFig. 18.
(A) and (B) Fig. 18.--Types of Spark Coils for Set. No. 1.(C) Fig. 18.--Wiring Diagram of Spark Coil
A spark coil of either style consists of (a) a softiron coreon which is wound (b) a couple of layers of heavy insulated wire and this is called theprimary coil, (c) while over this, but insulated from it, is wound a large number of turns of very fine insulated copper wire called thesecondary coil; (d) aninterrupter, orvibrator, as it is commonly called, and, finally, (e) acondenser. The core, primary and secondary coils form a unit and these are set in a box or mounted on top of a hollow wooden base. The condenser is placed in the bottom of the box, or on the base, while the vibrator is mounted on one end of the box or on top of the base, and it is the only part of the coil that needs adjusting.
The vibrator consists of a stiff, flat spring fixed at one end to the box or base while it carries a piece of soft iron called anarmatureon its free end and this sets close to one end of the soft iron core. Insulated from this spring is a standard that carries an adjusting screw on the small end of which is a platinum point and this makes contact with a small platinum disk fixed to the spring. The condenser is formed of alternate sheets of paper and tinfoil built up in the same fashion as the receiving condenser described under the caption ofFixed and Variable Condensers, inChapter III.
The wiring diagramCshows how the spark coil is wired up. One of the battery binding posts is connected with one end of the primary coil while the other end of the latter which is wound on the soft iron core connects with the spring of the vibrator. The other battery binding post connects with the standard that supports the adjusting screw. The condenser is shunted across the vibrator, that is, one end of the condenser is connected with the spring and the other end of the condenser is connected with the adjusting screw standard. The ends of the secondary coil lead to two binding posts, which are usually placed on top of the spark coil and it is to these that the spark gap is connected.
The Battery.--This can be formed of dry cells or you can use a storage battery to energize your coil. For all coils that give less than a 1-inch spark you should use 5 dry cells; for 1-and 2-inch spark coils use 6 or 8 dry cells, and for 3 to 4-inch spark coils use 8 to 10 dry cells. The way the dry cells are connected together to form a battery will be shown presently. A dry cell is shown atAinFig, 19.
Fig. 19.--Other parts for Transmitting Set No. 1
The Telegraph Key.--You can use an ordinary Morse telegraph key for the sending set and you can get one with a japanned iron base for $1.50 (or better, one made of brass and which has 1/8-inch silver contact points for $3.00. A key of the latter kind is shown atB).
The Spark gap.--It is in thespark gapthat the high tension spark takes place. The apparatus in which the spark takes place is also called thespark gap. It consists of a pair of zinc plugs, calledelectrodes, fixed to the ends of a pair of threaded rods, with knobs on the other ends, and these screw into and through a pair of standards as shown atc. This is called afixed, orstationary spark gapand costs about $1.00.
The Tuning Coil.--Thetransmitting inductance, orsending tuning coil, consists of 20 to 30 turns ofNo. 8 or 9hard drawn copper wire wound on a slotted insulated form and mounted on a wooden base. It is provided withclipsso that you can cut in and cut out as many turns of wire as you wish and so tune the sending circuits to send out whatever wave length you desire. It is shown atd, and costs about $5.00. See alsoOscillation Transformer, page 63 [Chapter IV].
The High Tension Condenser.--High tension condensers, that is, condensers which will stand up underhigh potentials, or electric pressures, can be bought in units or sections. These condensers are made up of thin brass plates insulated with a special compound and pressed into a compact form. Thecapacitance[Footnote: This is the capacity of the condenser.] of one section is enough for a transmitting set using a spark coil that gives a 2 inch spark or less and two sections connected together should be used for coils giving from 2 to 4 inch sparks. It is shown ate.
Connecting Up the Apparatus.--Your sending set should be mounted on a table, or a bench, where it need not be moved. Place the key in about the middle of the table and down in front, and the spark coil to the left and well to the back but so that the vibrator end will be to the right, as this will enable you to adjust it easily. Place the battery back of the spark coil and the tuning coil (oscillation transformer) to the right of the spark coil and back of the key, all of which is shown in the layout atAinFig. 20.
(A) Fig. 20.--Top View of Apparatus Layout for Sending Set No. 1.(B) Fig. 20.--Wiring of Diagram for Sending Set No. 1.
For thelow voltage circuit, that is the battery circuit, useNo. 12or14insulated copper wire. Connect all of the dry cells together inseries, that is, connect the zinc of one cell with the carbon of the next and so on until all of them are connected up. Then connect the carbon of the end cell with one of the posts of the key, the zinc of the other end cell with one of the primary posts of the spark coil and the other primary post of the spark coil with the other post of the key, when the primary circuit will be complete.
For thehigh tension circuits, that is, theoscillation circuits, you may use either bare or insulated copper wire but you must be careful that they do not touch the table, each other, or any part of the apparatus, except, of course, the posts they are connected with. Connect one of the posts of the secondary coil of the spark coil with one of the posts of the spark gap, and the other post with one of the posts of the condenser; then connect the other post of the condenser with the lower spring clip of the tuning coil and also connect this clip with the ground. This done, connect the middle spring clip with one of the posts of the spark gap, and, finally, connect the top clip with the aerial wire and your transmitting set is ready to be tuned. A wiring diagram of the connections is shown atB. As this set is tuned in the same way asSet No. 2which follows, you are referred to the end of this chapter.
A Better Transmitting Set (No. 2).--The apparatus for this set includes: (1) analternating current transformer, (2) awireless telegraph key, (3) afixed, arotary, or aquenched spark gap, (4) acondenser, and (5) anoscillation transformer. If you have a 110 volt direct lighting current in your home instead of 110 volt alternating current, then you will also need (6) anelectrolytic interrupter, for in this case the primary circuit of the transformer must be made and broken rapidly in order to set up alternating currents in the secondary coil.
The Alternating Current Transformer.--An alternating current, or power, transformer is made on the same principle as a spark coil, that is, it has a soft iron core, a primary coil formed of a couple of layers of heavy wire, and a secondary coil wound up of a large number of turns of very fine wire. Unlike the spark coil, however, which has anopen magnetic coreand whose secondary coil is wound on the primary coil, the transformer has aclosed magnetic core, with the primary coil wound on one of the legs of the core and the secondary wound on the other leg. It has neither a vibrator nor a condenser. A plain transformer is shown atAinFig. 21.
Fig. 21.--Parts for Transmitting Set No. 2.
A transformer of this kind can be bought either (a)unmounted, that is, just the bare transformer, or (b)fully mounted, that is, fitted with an iron stand, mounted on an insulating base on which are a pair of primary binding posts, while the secondary is provided with asafety spark gap. There are three sizes of transformers of this kind made and they are rated at 1/4, 1/2 and 1 kilowatt, respectively, they deliver a secondary current of 9,000, 11,000 and 25,000 volts, according to size, and cost $16.00, $22.00 and $33.00 when fully mounted; a reduction of $3.00, $4.00 and $5.00 is made when they are unmounted. All of these transformers operate on 110 volt, 60 cycle current and can be connected directly to the source of alternating current.
The Wireless Key.--For this transmitting set a standard wireless key should be used as shown atB. It is made about the same as a regular telegraph key but it is much heavier, the contact points are larger and instead of the current being led through the bearings as in an ordinary key, it is carried by heavy conductors directly to the contact points. This key is made in three sizes and the first will carry a current of 5amperes[Footnote: SeeAppendixfor definition.] and costs $4.00, the second will carry a current of 10 amperes and costs $6.50, while the third will carry a current of 20 amperes and costs $7.50.
The Spark Gap.--Either a fixed, a rotary, or a quenched spark gap can be used with this set, but the former is seldom used except with spark-coil sets, as it is very hard to keep the sparks from arcing when large currents are used. A rotary spark gap comprises a wheel, driven by a small electric motor, with projecting plugs, or electrodes, on it and a pair of stationary plugs on each side of the wheel as shown atC. The number of sparks per second can be varied by changing the speed of the wheel and when it is rotated rapidly it sends out signals of a high pitch which are easy to read at the receiving end. A rotary gap with a 110-volt motor costs about $25.00.
A quenched spark gap not only eliminates the noise of the ordinary gap but, when properly designed, it increases the range of an induction coil set some 200 per cent. A 1/4 kilowatt quenched gap costs $10.00. [Footnote: SeeAppendixfor definition.]
The High Tension Condenser.--Since, if you are an amateur, you can only send out waves that are 200 meters in length, you can only use a condenser that has a capacitance of .007microfarad. [Footnote: SeeAppendixfor definition.] A sectional high tension condenser like the one described in connection withSet No. 1can be used with this set but it must have a capacitance of not more than .007 microfarad. A condenser of this value for a 1/4-kilowatt transformer costs $7.00; for a 1/2-kilowatt transformer $14.00, and for a 1-kilowatt transformer $21.00. SeeE, Fig. 19.
The Oscillation Transformer.--With an oscillation transformer you can tune much more sharply than with a single inductance coil tuner. The primary coil is formed of 6 turns of copper strip, or No. 9 copper wire, and the secondary is formed of 9 turns of strip, or wire. The primary coil, which is the outside coil, is hinged to the base and can be raised or lowered like the lid of a box. When it is lowered the primary and secondary coils are in the same plane and when it is raised the coils set at an angle to each other. It is shown atDand costs $5.00.
Connecting Up the Apparatus. For Alternating Current.--Screw the key to the table about the middle of it and near the front edge; place the high tension condenser back of it and the oscillation transformer back of the latter; set the alternating current transformer to the left of the oscillation transformer and place the rotary or quenched spark gap in front of it.
Now bring a pair ofNo. 12or14insulated wires from the 110 volt lighting leads and connect them with a single-throw, double-pole switch; connect one pole of the switch with one of the posts of the primary coil of the alternating power transformer and connect the other post of the latter with one of the posts of your key, and the other post of this with the other pole of the switch. Now connect the motor of the rotary spark gap to the power circuit and put a single-pole, single-throw switch in the motor circuit, all of which is shown atAinFig. 22.
(A) Fig. 22.--Top View of Apparatus Layout for Sending Set No. 2.(B) Fig. 22.--Wiring Diagram for Sending Set No. 2.
Next connect the posts of the secondary coil to the posts of the rotary or quenched spark gap and connect one post of the latter to one post of the condenser, the other post of this to the post of the primary coil of the oscillation transformer, which is the inside coil, and the clip of the primary coil to the other spark gap post. This completes the closed oscillation circuit. Finally connect the post of the secondary coil of the oscillation transformer to the ground and the clip of it to the wire leading to the aerial when you are ready to tune the set. A wiring diagram of the connections is shown atB.
For Direct Current.--Where you have 110 volt direct current you must connect in an electrolytic interrupter. This interrupter, which is shown atAandBinFig. 23, consists of (1) a jar filled with a solution of 1 part of sulphuric acid and 9 parts of water, (2) a lead electrode having a large surface fastened to the cover of surface that sets in a porcelain sleeve and whose end rests on the bottom of the jar.
Fig. 23.--Using 110 Volt Direct Current with an Alternating Current Transformer.
When these electrodes are connected in series with the primary of a large spark coil or an alternating current transformer, seeC, and a direct current of from 40 to 110 volts is made to pass through it, the current is made and broken from 1,000 to 10,000 times a minute. By raising or lowering the sleeve, thus exposing more or less of the platinum, or alloy point, the number of interruptions per minute can be varied at will. As the electrolytic interrupter will only operate in one direction, you must connect it with its platinum, or alloy anode, to the + orpositivepower lead and the lead cathode to the - ornegativepower lead. You can find out which is which by connecting in the interrupter and trying it, or you can use a polarity indicator. An electrolytic interrupter can be bought for as little as $3.00.
How to Adjust Your Transmitter. Tuning With a Hot Wire Ammeter.--A transmitter can be tuned in two different ways and these are: (1) by adjusting the length of the spark gap and the tuning coil so that the greatest amount of energy is set up in the oscillating circuits, and (2) by adjusting the apparatus so that it will send out waves of a given length.
To adjust the transmitter so that the circuits will be in tune you should have ahot wire ammeter, or radiation ammeter, as it is called, which is shown inFig. 24. It consists of a thin platinum wire through which the high-frequency currents surge and these heat it; the expansion and contraction of the wire moves a needle over a scale marked off into fractions of an ampere. When the spark gap and tuning coil of your set are properly adjusted, the needle will swing farthest to the right over the scale and you will then know that the aerial wire system, or open oscillation circuit, and the closed oscillation circuit are in tune and radiating the greatest amount of energy.
Fig. 24.--Principle of the Hot Wire Ammeter.
To Send Out a 200 Meter Wave Length.--If you are using a condenser having a capacitance of .007 microfarad, which is the largest capacity value that the Government will allow an amateur to use, then if you have a hot wire ammeter in your aerial and tune the inductance coil or coils until the ammeter shows the largest amount of energy flowing through it you will know that your transmitter is tuned and that the aerial is sending out waves whose length is 200 meters. To tune to different wave lengths you must have awave-meter.
The Use of the Aerial Switch.--Where you intend to install both a transmitter and a receptor you will need a throwover switch, oraerial switch, as it is called. An ordinary double-pole, double-throw switch, as shown atAinFig. 25, can be used, or a switch made especially for the purpose as atBis handier because the arc of the throw is much less.
Fig. 25.--Kinds of Aerial Switches.
Aerial Switch for a Complete Sending and Receiving Set.--You can buy a double-pole, double-throw switch mounted on a porcelain base for about 75 cents and this will serve forSet No. 1. Screw this switch on your table between the sending and receiving sets and then connect one of the middle posts of it with the ground wire and the other middle post with the lightning switch which connects with the aerial. Connect the post of the tuning coil with one of the end posts of the switch and the clip of the tuning coil with the other and complementary post of the switch. This done, connect one of the opposite end posts of the switch to the post of the receiving tuning coil and connect the sliding contact of the latter with the other and complementary post of the switch as shown inFig. 26.
Fig. 26.--Wiring Diagram for Complete Sending and Receiving Set No. 1.
Connecting in the Lightning Switch.--The aerial wire connects with the middle post of the lightning switch, while one of the end posts lead to one of the middle posts of the aerial switch. The other end post of the lightning switch leads to a separate ground outside the building, as the wiring diagramsFigs. 26and27show.
Fig. 27.--Wiring Diagram for Complete Sending and Receiving Set No. 2.
It is easy to understand how electricity behaves and what it does if you get the right idea of it at the start. In the first place, if you will think of electricity as being a fluid like water its fundamental actions will be greatly simplified. Both water and electricity may be at rest or in motion. When at rest, under certain conditions, either one will develop pressure, and this pressure when released will cause them to flow through their respective conductors and thus produce a current.
Electricity at Rest and in Motion.--Any wire or a conductor of any kind can be charged with electricity, but a Leyden jar, or other condenser, is generally used to hold an electric charge because it has a much largercapacitance, as its capacity is called, than a wire. As a simple analogue of a condenser, suppose you have a tank of water raised above a second tank and that these are connected together by means of a pipe with a valve in it, as shown atAinFig. 28.
Fig. 28.--Water Analogue for Electric Pressure.
Now if you fill the upper tank with water and the valve is turned off, no water can flow into the lower tank but there is a difference of pressure between them, and the moment you turn the valve on a current of water will flow through the pipe. In very much the same way when you have a condenser charged with electricity the latter will be underpressure,that is, adifference of potentialwill be set up, for one of the sheets of metal will be charged positively and the other one, which is insulated from it, will be charged negatively, as shown atB. On closing the switch the opposite charges rush together and form a current which flows to and fro between the metal plates. [Footnote: Strictly speaking it is the difference of potential that sets up the electromotive force.]
The Electric Current and Its Circuit.--Just as water flowing through a pipe hasquantityandpressureback of it and the pipe offers friction to it which tends to hold back the water, so, likewise, does electricity flowing in a circuit have: (1)quantity, orcurrent strength, or justcurrent, as it is called for short, oramperage, and (2)pressure, orpotential difference, orelectromotive force, orvoltage, as it is variously called, and the wire, or circuit, in which the current is flowing has (3)resistancewhich tends to hold back the current.
A definite relation exists between the current and its electromotive force and also between the current, electromotive force and the resistance of the circuit; and if you will get this relationship clearly in your mind you will have a very good insight into how direct and alternating currents act. To keep a quantity of water flowing in a loop of pipe, which we will call the circuit, pressure must be applied to it and this may be done by a rotary pump as shown atA in Fig. 29;in the same way, to keep a quantity of electricity flowing in a loop of wire, or circuit, a battery, or other means for generating electric pressure must be used, as shown atB.
Fig. 29.--Water Analogues for Direct and Alternating Currents.
If you have a closed pipe connected with a piston pump, as atC, as the piston moves to and fro the water in the pipe will move first one way and then the other. So also when an alternating current generator is connected to a wire circuit, as atD, the current will flow first in one direction and then in the other, and this is what is called analternating current.
Current and the Ampere.--The amount of water flowing in a closed pipe is the same at all parts of it and this is also true of an electric current, in that there is exactly the same quantity of electricity at one point of the circuit as there is at any other.
The amount of electricity, or current, flowing in a circuit in a second is measured by a unit called theampere, [Footnote: For definition ofampereseeAppendix.] and it is expressed by the symbol I. [Footnote: This is because the letterCis used for the symbol ofcapacitance] Just to give you an idea of the quantity of current anampereis we will say that a dry cell when fresh gives a current of about 20 amperes. To measure the current in amperes an instrument called anammeteris used, as shown atAinFig. 30, and this is always connected inserieswith the line, as shown atB.
Fig. 30.--How the Ammeter and Voltmeter are Used.
Electromotive Force and the Volt.--When you have a pipe filled with water or a circuit charged with electricity and you want to make them flow you must use a pump in the first case and a battery or a dynamo in the second case. It is the battery or dynamo that sets up the electric pressure as the circuit itself is always charged with electricity.
The more cells you connect together inseriesthe greater will be the electric pressure developed and the more current it will move along just as the amount of water flowing in a pipe can be increased by increasing the pressure of the pump. The unit of electromotive force is thevolt, and this is the electric pressure which will force a current of1 amperethrough a resistance of1 ohm; it is expressed by the symbolE. A fresh dry cell will deliver a current of about 1.5 volts. To measure the pressure of a current in volts an instrument called avoltmeteris used, as shown atCinFig. 30, and this is always connected across the circuit, as shown atD.
Resistance and the Ohm.--Just as a water pipe offers a certain amount of resistance to the flow of water through it, so a circuit opposes the flow of electricity in it and this is calledresistance. Further, in the same way that a small pipe will not allow a large amount of water to flow through it, so, too, a thin wire limits the flow of the current in it.
If you connect aresistance coilin a circuit it acts in the same way as partly closing the valve in a pipe, as shown atAandBinFig. 31. The resistance of a circuit is measured by a unit called theohm, and it is expressed by the symbolR. A No. 10, Brown and Sharpe gauge soft copper wire, 1,000 feet long, has a resistance of about 1 ohm. To measure the resistance of a circuit an apparatus called aresistance bridge is used. The resistance of a circuit can, however, be easily calculated, as the following shows.
Fig. 31.--Water Valve Analogue of Electric Resistance. A- a valve limits the flow of water. B- a resistance limits the flow of current.
What Ohm's Law Is.--If, now, (1) you know what the current flowing in a circuit is inamperes, and the electromotive force, or pressure, is involts, you can then easily find what the resistance is inohmsof the circuit in which the current is flowing by this formula: