CHAPTER II. THE MEANS FOR RADIATING AND INTERCEPTING ELECTRIC WAVES. AERIAL SYSTEMS. EARTH CONNECTION.Every radiotelegraphic station may be summed up as comprising these elements: first of all, certain appliances collectively forming the transmitter and serving to create the waves; secondly, the receiving apparatus, whose function is to detect the signals of some far-distant sending station, and lastly, an external organ called the aerial, or antenna, consisting of a huge system of wires elevated high in the air above all surrounding objects, either vertically or sloping, or partly horizontal and partly vertical, which radiates or intercepts the electromagnetic waves, accordingly as the station is transmitting or receiving.The antenna is at once both the mouth and the ear of the wireless station. Its site and arrangement will greatly determine the efficiency and range of the apparatus.The site selected is preferably such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smokestacks, telephone wires, etc., because such objects not only absorb an appreciable amount of energy when the station is transmitting messages, but also noticeably shield the aerial from the effects of incoming signals and limit its range.The nature of the ground over which the waves must travel also enters into the question, and is always considered in locating a station. In gliding over the surface of the earth, the waves generate weak currents in the earth itself. If the ground is very stony or dry, these earth currents encounter considerable resistance, and the possible distance of transmission over soil of this sort is very much less than if it were moist. Moist soil and water offer very little resistance, and the difference in the results obtainable at the receiving station when the waves travel over an area of this sort is very marked.FIG. 11.—An amateur aerial and station.FIG. 11.—An amateur aerial and station.A station which can only send 100 miles over land can send messages three or four hundred miles over the ocean.Forests exert a very decided effect upon the electric waves. Each individual tree acts as an antenna, reaching up into the air and absorbing part of the energy. The difference in the range of a station during the summer months and that of the same station in winter is considerable. In summer the trees are full of sap and, being much better conductors of electricity when in this condition, act in the capacity of innumerable aerials rising in the air, and able to absorb appreciable amounts of energy. During these same months the air becomes highlyionized, in which state the air molecules carry an electric charge, and are particularly opaque to the waves. This condition also usually exists in the presence of sunlight, the result being that the most favorable time for the wireless transmission of messages are the hours around midnight.FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.Locality is another factor which usually receives a fair share of attention in selecting the site. Certain sections of the country, for seemingly no apparent reason, are very hard to transmit messages, either to or from. Wireless stations located on the Pacific Coast, for instance, are more efficient than those situated along the Atlantic seaboard, while those in the tropical regions are only able to send short distances in comparison to those farther north or south. Messages seem to travel better in the direction of the lines of longitude than along the lines of latitude.FIG. 13.—Lightning discharge near Montclair, N. J.FIG. 13.—Lightning discharge near Montclair, N. J."Static," that "bugbear" of the wireless operator, is very much more in evidence in the eastern parts of the United States and in South America than it is on the western coast of the country. If any one should ask a wireless operator what "static" is, he would probably reply, "a nuisance." In reality, it is caused by atmospheric electricity. When atmospheric electricity "jumps," it is called "lightning." A lightning discharge sets up very powerful waves in the ether, which strike the aerial of the wireless station and produce a peculiar rumbling, scratching sound in the telephone receivers, and sometimes seriously interfere with a message. In fact, it is possible for a wireless operator to predict a thunder shower by many hours from the sounds he is able to hear in his telephone receivers.The cause of lightning is the accumulation of electric charges in the clouds. The electricity resides on the surface of the particles of water in the cloud. These charges grow stronger as the particles of water coalesce to form larger drops, because, as they unite, the surface increases proportionally less than the volume and, being forced to lodge on a smaller space, the electricity becomes more "concentrated," so to speak. For this reason the combined charge on the surface of the larger drop is more intense than were the charges on the separate particles, and the "potential" is increased. As the countless multitudes of drops grow larger and larger, in the process of forming rain, the cloud soon becomes heavily charged.Through the effects of a phenomenon called "induction," a charge of the opposite kind is produced on a neighboring cloud or some object of the earth beneath. These charges continually strive to burst across the intervening air and neutralize each other. As soon as the potential becomes sufficient to break down this layer of air, a lightning stroke from one to ten miles long takes place. The heated air in the path of the lightning expands with great force, but immediately other air rushes in to fill the partial vacuum, thus producing atmospheric waves, which impress the ear as the sound calledthunder.Wireless stations belonging to the United States navy and located on land are usually housed in a small building in the immediate neighborhood of the tall wooden mast which supports the aerial. Commercial stations are usually situated on the top floor of a high office building, or a hotel, and the aerials supported by a steel lattice-work tower. Amateurs place a small pole on the roof of the house, or in a tree, and locate their station in any convenient room near the top of the house.FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.Aerials are of numerous classes and forms, but the most prominent types can be divided into two main groups, called respectively, the "Flat-top" and "vertical" antenna.The vertical aerials are the older form, and are usually employed for long-distance work or ultra-powerful stations. The aerials intended for transmission from Europe to America, installed by Marconi, consisted of huge inverted pyramids, supported by four heavy lattice-work towers, over 200 feet high. Vertical aerials also sometimes take the form of an umbrella, or fan, where only one supporting pole is available. Iron pipe masts may be employed for the purpose, by setting on an insulating base. The umbrella aerial is used extensively in the army and portable sets.The flat-top aerials are gradually coming into very extended use. They are used to the exclusion of all others on shipboard. They need not be so high as a vertical type aerial in order to be as efficient. Flat-top aerials consist of a vertical portion and a nearly horizontal portion. The horizontal portion is practically useless, as far as its work in radiating waves is concerned, it being used for the purpose of increasing thecapacityof the aerial. An increase in capacity in an aerial means that more energy can be stored and radiated. Flat-top aerials have the objection, however, of possessing adirectiveaction; that is, they receive, or radiate waves, better in one direction than in the other. A flat-top aerial always receives or transmits better in the direction that the ends point than in a direction at right angles to the wires.FIG. 16.—A diagram showing pyramid aerial.FIG. 16.—A diagram showing pyramid aerial.The accompanying diagram is an illustration to show the effects of the directive action of a flat-top aerial. The black lines marked A B, and appearing very much like a little grating, represent an aerial of the inverted "L" type, looking down on it from above. B is thefreeend of the aerial, and A theclosedend, or end to which the wires leading down to the station are attached. If a snapshot of the lines of strain produced in the ether as the waves move away from the aerial could be taken, they would appear like the curved lines in the illustration. It can be readily seen that those passing outward from the aerial in a directionoppositeto that in which the free end points are the strongest, and that the radiation in that direction is the best.FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.FIG. 18.—Aerials of the "V" and inverted "L" types.FIG. 18.—Aerials of the "V" and inverted "L" types.The "V" aerial and also the inverted "L" type both receive waves much better when they come from a direction opposite to that in which the free end points.FIG. 19.—A diagram showing the arrangement of a "T" aerial.FIG. 19.—A diagram showing the arrangement of a "T" aerial.Probably the most interesting feature of the directive action of aerials lies in the fact that a land station is able to determine the approximate bearing of a ship signaling with a horizontal aerial.FIG. 20.—Flat top aerials of the inverted "U" and "T" types.FIG. 20.—Flat top aerials of the inverted "U" and "T" types.It is beyond the scope of the book to enter into all of the engineering details pertaining to the installation of a wireless station, but a few remarks and instructions for the benefit of those who may be interested in this phase of the subject may be appreciated.The flat-top "T" aerialgives the best "all around" results. The vertical and umbrella forms are close seconds.FIG. 21.—Umbrella aerial.FIG. 21.—Umbrella aerial.For the very best results, the top or horizontal portion of a "T" aerial should be slightly shorter than the vertical section.The umbrella typeof antenna is very efficient. Instead of a wooden mast, an iron pipe terminating above in a system of wires, inclining downward and serving both as part of the aerial and as guys to support the pole, is often used. The bottom of the pole is placed on an insulating base, protected from the rain by a small shelter. The wires are insulated near the lower ends by strain-insulators. The action of the wires is to serve as a capacity extension to the aerial.FIG. 22.—An amateur aerial (flat-top).FIG. 22.—An amateur aerial (flat-top).Vertical aerialsare not as efficient as either of those forms just mentioned. They require to be 50 per cent. higher than a flat-top aerial, in order to be of the same value.The "L" and "V" typesare somewhat directional. They are used where the highest point must be near the station, with a lower point some distance away. It is possible to secure excellent results with either type.The termsstraightawayandloopdenote the method of connecting the aerial wires. In the first form the upper or free ends of the wires terminate at the insulators. In the loop form they are all connected together, and divided into two sections, each of which is led separately into the operating room.FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.The straightaway aerial is the most efficient in most cases, but wherever great height cannot be obtained, or the aerial is necessarily short, the loop aerial will give the best results.Bare copper wire is the best, and is generally used for aerials. Wherever the stretch is 100 feet or over, however, so that the wires are subjected to considerable strain from their own weight, phosphor bronze is used because of its greater tensile strength. Commercial and navy stations employ stranded wire. High frequency currents have the peculiar property of traveling near the surface of wires and conductors. They do not permeate to the center of the wire, as do normal currents. The surface of a stranded wire is greater in comparison to its cross-section than a solid conductor of the same diameter, and therefore is often employed because it offers less resistance to currents of this sort.FIG. 24.—Showing how wires are arranged and insulated.FIG. 24.—Showing how wires are arranged and insulated.Aluminum wire is very light, and causes very little strain on the pole or cross-arms. It offers more resistance than copper, but some of the larger sizes may be used with equally good results.Iron wire must never be used, even if galvanized or tinned. It possesses a certain reactance tending to choke off the high frequency currents.FIG. 25.—Aerial insulator.FIG. 25.—Aerial insulator.The aerial is always very carefully insulated from its supports and surrounding objects by special insulators, capable of withstanding severe strains, made of a moulded material having an iron ring imbedded in each end.FIG. 26.—Leading-in insulator.FIG. 26.—Leading-in insulator.The wires leading from the aerial to the operating room are called the "rat-tail," or "lead-in." They must be very carefully insulated by leading through a bushing placed in the wall or window of the operating room.One of the most important factors in a wireless station is the proper earthing arrangement. The usual method is to use large copper plates buried in moist earth, or thrown in the sea. On shipboard it is merely necessary to connect the earth wire to the metallic plates of which the hull of the vessel is built. Amateurs employ the water or gas pipes in the house, the former being preferred. Connections are established by means of a ground clamp.In the country, where water-pipes are not available, the best way is to bury a sheet of copper three or four feet deep in moist earth.A very efficient earth can be formed by spreading a large area of chicken wire netting over the ground. This method is the best where the earth is very dry or sandy, and no other way is readily convenient.FIG. 27.—A side view of the aerial shown in Fig. 22.FIG. 27.—A side view of the aerial shown in Fig. 22.
CHAPTER II. THE MEANS FOR RADIATING AND INTERCEPTING ELECTRIC WAVES. AERIAL SYSTEMS. EARTH CONNECTION.Every radiotelegraphic station may be summed up as comprising these elements: first of all, certain appliances collectively forming the transmitter and serving to create the waves; secondly, the receiving apparatus, whose function is to detect the signals of some far-distant sending station, and lastly, an external organ called the aerial, or antenna, consisting of a huge system of wires elevated high in the air above all surrounding objects, either vertically or sloping, or partly horizontal and partly vertical, which radiates or intercepts the electromagnetic waves, accordingly as the station is transmitting or receiving.The antenna is at once both the mouth and the ear of the wireless station. Its site and arrangement will greatly determine the efficiency and range of the apparatus.The site selected is preferably such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smokestacks, telephone wires, etc., because such objects not only absorb an appreciable amount of energy when the station is transmitting messages, but also noticeably shield the aerial from the effects of incoming signals and limit its range.The nature of the ground over which the waves must travel also enters into the question, and is always considered in locating a station. In gliding over the surface of the earth, the waves generate weak currents in the earth itself. If the ground is very stony or dry, these earth currents encounter considerable resistance, and the possible distance of transmission over soil of this sort is very much less than if it were moist. Moist soil and water offer very little resistance, and the difference in the results obtainable at the receiving station when the waves travel over an area of this sort is very marked.FIG. 11.—An amateur aerial and station.FIG. 11.—An amateur aerial and station.A station which can only send 100 miles over land can send messages three or four hundred miles over the ocean.Forests exert a very decided effect upon the electric waves. Each individual tree acts as an antenna, reaching up into the air and absorbing part of the energy. The difference in the range of a station during the summer months and that of the same station in winter is considerable. In summer the trees are full of sap and, being much better conductors of electricity when in this condition, act in the capacity of innumerable aerials rising in the air, and able to absorb appreciable amounts of energy. During these same months the air becomes highlyionized, in which state the air molecules carry an electric charge, and are particularly opaque to the waves. This condition also usually exists in the presence of sunlight, the result being that the most favorable time for the wireless transmission of messages are the hours around midnight.FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.Locality is another factor which usually receives a fair share of attention in selecting the site. Certain sections of the country, for seemingly no apparent reason, are very hard to transmit messages, either to or from. Wireless stations located on the Pacific Coast, for instance, are more efficient than those situated along the Atlantic seaboard, while those in the tropical regions are only able to send short distances in comparison to those farther north or south. Messages seem to travel better in the direction of the lines of longitude than along the lines of latitude.FIG. 13.—Lightning discharge near Montclair, N. J.FIG. 13.—Lightning discharge near Montclair, N. J."Static," that "bugbear" of the wireless operator, is very much more in evidence in the eastern parts of the United States and in South America than it is on the western coast of the country. If any one should ask a wireless operator what "static" is, he would probably reply, "a nuisance." In reality, it is caused by atmospheric electricity. When atmospheric electricity "jumps," it is called "lightning." A lightning discharge sets up very powerful waves in the ether, which strike the aerial of the wireless station and produce a peculiar rumbling, scratching sound in the telephone receivers, and sometimes seriously interfere with a message. In fact, it is possible for a wireless operator to predict a thunder shower by many hours from the sounds he is able to hear in his telephone receivers.The cause of lightning is the accumulation of electric charges in the clouds. The electricity resides on the surface of the particles of water in the cloud. These charges grow stronger as the particles of water coalesce to form larger drops, because, as they unite, the surface increases proportionally less than the volume and, being forced to lodge on a smaller space, the electricity becomes more "concentrated," so to speak. For this reason the combined charge on the surface of the larger drop is more intense than were the charges on the separate particles, and the "potential" is increased. As the countless multitudes of drops grow larger and larger, in the process of forming rain, the cloud soon becomes heavily charged.Through the effects of a phenomenon called "induction," a charge of the opposite kind is produced on a neighboring cloud or some object of the earth beneath. These charges continually strive to burst across the intervening air and neutralize each other. As soon as the potential becomes sufficient to break down this layer of air, a lightning stroke from one to ten miles long takes place. The heated air in the path of the lightning expands with great force, but immediately other air rushes in to fill the partial vacuum, thus producing atmospheric waves, which impress the ear as the sound calledthunder.Wireless stations belonging to the United States navy and located on land are usually housed in a small building in the immediate neighborhood of the tall wooden mast which supports the aerial. Commercial stations are usually situated on the top floor of a high office building, or a hotel, and the aerials supported by a steel lattice-work tower. Amateurs place a small pole on the roof of the house, or in a tree, and locate their station in any convenient room near the top of the house.FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.Aerials are of numerous classes and forms, but the most prominent types can be divided into two main groups, called respectively, the "Flat-top" and "vertical" antenna.The vertical aerials are the older form, and are usually employed for long-distance work or ultra-powerful stations. The aerials intended for transmission from Europe to America, installed by Marconi, consisted of huge inverted pyramids, supported by four heavy lattice-work towers, over 200 feet high. Vertical aerials also sometimes take the form of an umbrella, or fan, where only one supporting pole is available. Iron pipe masts may be employed for the purpose, by setting on an insulating base. The umbrella aerial is used extensively in the army and portable sets.The flat-top aerials are gradually coming into very extended use. They are used to the exclusion of all others on shipboard. They need not be so high as a vertical type aerial in order to be as efficient. Flat-top aerials consist of a vertical portion and a nearly horizontal portion. The horizontal portion is practically useless, as far as its work in radiating waves is concerned, it being used for the purpose of increasing thecapacityof the aerial. An increase in capacity in an aerial means that more energy can be stored and radiated. Flat-top aerials have the objection, however, of possessing adirectiveaction; that is, they receive, or radiate waves, better in one direction than in the other. A flat-top aerial always receives or transmits better in the direction that the ends point than in a direction at right angles to the wires.FIG. 16.—A diagram showing pyramid aerial.FIG. 16.—A diagram showing pyramid aerial.The accompanying diagram is an illustration to show the effects of the directive action of a flat-top aerial. The black lines marked A B, and appearing very much like a little grating, represent an aerial of the inverted "L" type, looking down on it from above. B is thefreeend of the aerial, and A theclosedend, or end to which the wires leading down to the station are attached. If a snapshot of the lines of strain produced in the ether as the waves move away from the aerial could be taken, they would appear like the curved lines in the illustration. It can be readily seen that those passing outward from the aerial in a directionoppositeto that in which the free end points are the strongest, and that the radiation in that direction is the best.FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.FIG. 18.—Aerials of the "V" and inverted "L" types.FIG. 18.—Aerials of the "V" and inverted "L" types.The "V" aerial and also the inverted "L" type both receive waves much better when they come from a direction opposite to that in which the free end points.FIG. 19.—A diagram showing the arrangement of a "T" aerial.FIG. 19.—A diagram showing the arrangement of a "T" aerial.Probably the most interesting feature of the directive action of aerials lies in the fact that a land station is able to determine the approximate bearing of a ship signaling with a horizontal aerial.FIG. 20.—Flat top aerials of the inverted "U" and "T" types.FIG. 20.—Flat top aerials of the inverted "U" and "T" types.It is beyond the scope of the book to enter into all of the engineering details pertaining to the installation of a wireless station, but a few remarks and instructions for the benefit of those who may be interested in this phase of the subject may be appreciated.The flat-top "T" aerialgives the best "all around" results. The vertical and umbrella forms are close seconds.FIG. 21.—Umbrella aerial.FIG. 21.—Umbrella aerial.For the very best results, the top or horizontal portion of a "T" aerial should be slightly shorter than the vertical section.The umbrella typeof antenna is very efficient. Instead of a wooden mast, an iron pipe terminating above in a system of wires, inclining downward and serving both as part of the aerial and as guys to support the pole, is often used. The bottom of the pole is placed on an insulating base, protected from the rain by a small shelter. The wires are insulated near the lower ends by strain-insulators. The action of the wires is to serve as a capacity extension to the aerial.FIG. 22.—An amateur aerial (flat-top).FIG. 22.—An amateur aerial (flat-top).Vertical aerialsare not as efficient as either of those forms just mentioned. They require to be 50 per cent. higher than a flat-top aerial, in order to be of the same value.The "L" and "V" typesare somewhat directional. They are used where the highest point must be near the station, with a lower point some distance away. It is possible to secure excellent results with either type.The termsstraightawayandloopdenote the method of connecting the aerial wires. In the first form the upper or free ends of the wires terminate at the insulators. In the loop form they are all connected together, and divided into two sections, each of which is led separately into the operating room.FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.The straightaway aerial is the most efficient in most cases, but wherever great height cannot be obtained, or the aerial is necessarily short, the loop aerial will give the best results.Bare copper wire is the best, and is generally used for aerials. Wherever the stretch is 100 feet or over, however, so that the wires are subjected to considerable strain from their own weight, phosphor bronze is used because of its greater tensile strength. Commercial and navy stations employ stranded wire. High frequency currents have the peculiar property of traveling near the surface of wires and conductors. They do not permeate to the center of the wire, as do normal currents. The surface of a stranded wire is greater in comparison to its cross-section than a solid conductor of the same diameter, and therefore is often employed because it offers less resistance to currents of this sort.FIG. 24.—Showing how wires are arranged and insulated.FIG. 24.—Showing how wires are arranged and insulated.Aluminum wire is very light, and causes very little strain on the pole or cross-arms. It offers more resistance than copper, but some of the larger sizes may be used with equally good results.Iron wire must never be used, even if galvanized or tinned. It possesses a certain reactance tending to choke off the high frequency currents.FIG. 25.—Aerial insulator.FIG. 25.—Aerial insulator.The aerial is always very carefully insulated from its supports and surrounding objects by special insulators, capable of withstanding severe strains, made of a moulded material having an iron ring imbedded in each end.FIG. 26.—Leading-in insulator.FIG. 26.—Leading-in insulator.The wires leading from the aerial to the operating room are called the "rat-tail," or "lead-in." They must be very carefully insulated by leading through a bushing placed in the wall or window of the operating room.One of the most important factors in a wireless station is the proper earthing arrangement. The usual method is to use large copper plates buried in moist earth, or thrown in the sea. On shipboard it is merely necessary to connect the earth wire to the metallic plates of which the hull of the vessel is built. Amateurs employ the water or gas pipes in the house, the former being preferred. Connections are established by means of a ground clamp.In the country, where water-pipes are not available, the best way is to bury a sheet of copper three or four feet deep in moist earth.A very efficient earth can be formed by spreading a large area of chicken wire netting over the ground. This method is the best where the earth is very dry or sandy, and no other way is readily convenient.FIG. 27.—A side view of the aerial shown in Fig. 22.FIG. 27.—A side view of the aerial shown in Fig. 22.
Every radiotelegraphic station may be summed up as comprising these elements: first of all, certain appliances collectively forming the transmitter and serving to create the waves; secondly, the receiving apparatus, whose function is to detect the signals of some far-distant sending station, and lastly, an external organ called the aerial, or antenna, consisting of a huge system of wires elevated high in the air above all surrounding objects, either vertically or sloping, or partly horizontal and partly vertical, which radiates or intercepts the electromagnetic waves, accordingly as the station is transmitting or receiving.
The antenna is at once both the mouth and the ear of the wireless station. Its site and arrangement will greatly determine the efficiency and range of the apparatus.
The site selected is preferably such that the aerial will not be in the immediate neighborhood of any tall objects, such as trees, smokestacks, telephone wires, etc., because such objects not only absorb an appreciable amount of energy when the station is transmitting messages, but also noticeably shield the aerial from the effects of incoming signals and limit its range.
The nature of the ground over which the waves must travel also enters into the question, and is always considered in locating a station. In gliding over the surface of the earth, the waves generate weak currents in the earth itself. If the ground is very stony or dry, these earth currents encounter considerable resistance, and the possible distance of transmission over soil of this sort is very much less than if it were moist. Moist soil and water offer very little resistance, and the difference in the results obtainable at the receiving station when the waves travel over an area of this sort is very marked.
FIG. 11.—An amateur aerial and station.FIG. 11.—An amateur aerial and station.
FIG. 11.—An amateur aerial and station.
A station which can only send 100 miles over land can send messages three or four hundred miles over the ocean.
Forests exert a very decided effect upon the electric waves. Each individual tree acts as an antenna, reaching up into the air and absorbing part of the energy. The difference in the range of a station during the summer months and that of the same station in winter is considerable. In summer the trees are full of sap and, being much better conductors of electricity when in this condition, act in the capacity of innumerable aerials rising in the air, and able to absorb appreciable amounts of energy. During these same months the air becomes highlyionized, in which state the air molecules carry an electric charge, and are particularly opaque to the waves. This condition also usually exists in the presence of sunlight, the result being that the most favorable time for the wireless transmission of messages are the hours around midnight.
FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.
FIG. 12.—The Army wireless station at Fort Gibbons, Alaska, showing steel lattice work mast and aerial system.
Locality is another factor which usually receives a fair share of attention in selecting the site. Certain sections of the country, for seemingly no apparent reason, are very hard to transmit messages, either to or from. Wireless stations located on the Pacific Coast, for instance, are more efficient than those situated along the Atlantic seaboard, while those in the tropical regions are only able to send short distances in comparison to those farther north or south. Messages seem to travel better in the direction of the lines of longitude than along the lines of latitude.
FIG. 13.—Lightning discharge near Montclair, N. J.FIG. 13.—Lightning discharge near Montclair, N. J.
FIG. 13.—Lightning discharge near Montclair, N. J.
"Static," that "bugbear" of the wireless operator, is very much more in evidence in the eastern parts of the United States and in South America than it is on the western coast of the country. If any one should ask a wireless operator what "static" is, he would probably reply, "a nuisance." In reality, it is caused by atmospheric electricity. When atmospheric electricity "jumps," it is called "lightning." A lightning discharge sets up very powerful waves in the ether, which strike the aerial of the wireless station and produce a peculiar rumbling, scratching sound in the telephone receivers, and sometimes seriously interfere with a message. In fact, it is possible for a wireless operator to predict a thunder shower by many hours from the sounds he is able to hear in his telephone receivers.
The cause of lightning is the accumulation of electric charges in the clouds. The electricity resides on the surface of the particles of water in the cloud. These charges grow stronger as the particles of water coalesce to form larger drops, because, as they unite, the surface increases proportionally less than the volume and, being forced to lodge on a smaller space, the electricity becomes more "concentrated," so to speak. For this reason the combined charge on the surface of the larger drop is more intense than were the charges on the separate particles, and the "potential" is increased. As the countless multitudes of drops grow larger and larger, in the process of forming rain, the cloud soon becomes heavily charged.
Through the effects of a phenomenon called "induction," a charge of the opposite kind is produced on a neighboring cloud or some object of the earth beneath. These charges continually strive to burst across the intervening air and neutralize each other. As soon as the potential becomes sufficient to break down this layer of air, a lightning stroke from one to ten miles long takes place. The heated air in the path of the lightning expands with great force, but immediately other air rushes in to fill the partial vacuum, thus producing atmospheric waves, which impress the ear as the sound calledthunder.
Wireless stations belonging to the United States navy and located on land are usually housed in a small building in the immediate neighborhood of the tall wooden mast which supports the aerial. Commercial stations are usually situated on the top floor of a high office building, or a hotel, and the aerials supported by a steel lattice-work tower. Amateurs place a small pole on the roof of the house, or in a tree, and locate their station in any convenient room near the top of the house.
FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.
FIG. 14.— Photo of double lightning discharge passing to earth near the First Orange Mountain, Montclair, N. J.
FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.
FIG. 15.—Vertical aerials of the "grid," "fan" and "inverted pyramid" types.
Aerials are of numerous classes and forms, but the most prominent types can be divided into two main groups, called respectively, the "Flat-top" and "vertical" antenna.
The vertical aerials are the older form, and are usually employed for long-distance work or ultra-powerful stations. The aerials intended for transmission from Europe to America, installed by Marconi, consisted of huge inverted pyramids, supported by four heavy lattice-work towers, over 200 feet high. Vertical aerials also sometimes take the form of an umbrella, or fan, where only one supporting pole is available. Iron pipe masts may be employed for the purpose, by setting on an insulating base. The umbrella aerial is used extensively in the army and portable sets.
The flat-top aerials are gradually coming into very extended use. They are used to the exclusion of all others on shipboard. They need not be so high as a vertical type aerial in order to be as efficient. Flat-top aerials consist of a vertical portion and a nearly horizontal portion. The horizontal portion is practically useless, as far as its work in radiating waves is concerned, it being used for the purpose of increasing thecapacityof the aerial. An increase in capacity in an aerial means that more energy can be stored and radiated. Flat-top aerials have the objection, however, of possessing adirectiveaction; that is, they receive, or radiate waves, better in one direction than in the other. A flat-top aerial always receives or transmits better in the direction that the ends point than in a direction at right angles to the wires.
FIG. 16.—A diagram showing pyramid aerial.FIG. 16.—A diagram showing pyramid aerial.
FIG. 16.—A diagram showing pyramid aerial.
The accompanying diagram is an illustration to show the effects of the directive action of a flat-top aerial. The black lines marked A B, and appearing very much like a little grating, represent an aerial of the inverted "L" type, looking down on it from above. B is thefreeend of the aerial, and A theclosedend, or end to which the wires leading down to the station are attached. If a snapshot of the lines of strain produced in the ether as the waves move away from the aerial could be taken, they would appear like the curved lines in the illustration. It can be readily seen that those passing outward from the aerial in a directionoppositeto that in which the free end points are the strongest, and that the radiation in that direction is the best.
FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.
FIG. 17.–A diagram illustrating the directive action of a flat-top aerial.
FIG. 18.—Aerials of the "V" and inverted "L" types.FIG. 18.—Aerials of the "V" and inverted "L" types.
FIG. 18.—Aerials of the "V" and inverted "L" types.
The "V" aerial and also the inverted "L" type both receive waves much better when they come from a direction opposite to that in which the free end points.
FIG. 19.—A diagram showing the arrangement of a "T" aerial.FIG. 19.—A diagram showing the arrangement of a "T" aerial.
FIG. 19.—A diagram showing the arrangement of a "T" aerial.
Probably the most interesting feature of the directive action of aerials lies in the fact that a land station is able to determine the approximate bearing of a ship signaling with a horizontal aerial.
FIG. 20.—Flat top aerials of the inverted "U" and "T" types.FIG. 20.—Flat top aerials of the inverted "U" and "T" types.
FIG. 20.—Flat top aerials of the inverted "U" and "T" types.
It is beyond the scope of the book to enter into all of the engineering details pertaining to the installation of a wireless station, but a few remarks and instructions for the benefit of those who may be interested in this phase of the subject may be appreciated.
The flat-top "T" aerialgives the best "all around" results. The vertical and umbrella forms are close seconds.
FIG. 21.—Umbrella aerial.FIG. 21.—Umbrella aerial.
FIG. 21.—Umbrella aerial.
For the very best results, the top or horizontal portion of a "T" aerial should be slightly shorter than the vertical section.
The umbrella typeof antenna is very efficient. Instead of a wooden mast, an iron pipe terminating above in a system of wires, inclining downward and serving both as part of the aerial and as guys to support the pole, is often used. The bottom of the pole is placed on an insulating base, protected from the rain by a small shelter. The wires are insulated near the lower ends by strain-insulators. The action of the wires is to serve as a capacity extension to the aerial.
FIG. 22.—An amateur aerial (flat-top).FIG. 22.—An amateur aerial (flat-top).
FIG. 22.—An amateur aerial (flat-top).
Vertical aerialsare not as efficient as either of those forms just mentioned. They require to be 50 per cent. higher than a flat-top aerial, in order to be of the same value.
The "L" and "V" typesare somewhat directional. They are used where the highest point must be near the station, with a lower point some distance away. It is possible to secure excellent results with either type.
The termsstraightawayandloopdenote the method of connecting the aerial wires. In the first form the upper or free ends of the wires terminate at the insulators. In the loop form they are all connected together, and divided into two sections, each of which is led separately into the operating room.
FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.
FIG. 23.—Diagram showing the difference between "loop" and "straightaway" aerials.
The straightaway aerial is the most efficient in most cases, but wherever great height cannot be obtained, or the aerial is necessarily short, the loop aerial will give the best results.
Bare copper wire is the best, and is generally used for aerials. Wherever the stretch is 100 feet or over, however, so that the wires are subjected to considerable strain from their own weight, phosphor bronze is used because of its greater tensile strength. Commercial and navy stations employ stranded wire. High frequency currents have the peculiar property of traveling near the surface of wires and conductors. They do not permeate to the center of the wire, as do normal currents. The surface of a stranded wire is greater in comparison to its cross-section than a solid conductor of the same diameter, and therefore is often employed because it offers less resistance to currents of this sort.
FIG. 24.—Showing how wires are arranged and insulated.FIG. 24.—Showing how wires are arranged and insulated.
FIG. 24.—Showing how wires are arranged and insulated.
Aluminum wire is very light, and causes very little strain on the pole or cross-arms. It offers more resistance than copper, but some of the larger sizes may be used with equally good results.
Iron wire must never be used, even if galvanized or tinned. It possesses a certain reactance tending to choke off the high frequency currents.
FIG. 25.—Aerial insulator.FIG. 25.—Aerial insulator.
FIG. 25.—Aerial insulator.
The aerial is always very carefully insulated from its supports and surrounding objects by special insulators, capable of withstanding severe strains, made of a moulded material having an iron ring imbedded in each end.
FIG. 26.—Leading-in insulator.FIG. 26.—Leading-in insulator.
FIG. 26.—Leading-in insulator.
The wires leading from the aerial to the operating room are called the "rat-tail," or "lead-in." They must be very carefully insulated by leading through a bushing placed in the wall or window of the operating room.
One of the most important factors in a wireless station is the proper earthing arrangement. The usual method is to use large copper plates buried in moist earth, or thrown in the sea. On shipboard it is merely necessary to connect the earth wire to the metallic plates of which the hull of the vessel is built. Amateurs employ the water or gas pipes in the house, the former being preferred. Connections are established by means of a ground clamp.
In the country, where water-pipes are not available, the best way is to bury a sheet of copper three or four feet deep in moist earth.
A very efficient earth can be formed by spreading a large area of chicken wire netting over the ground. This method is the best where the earth is very dry or sandy, and no other way is readily convenient.
FIG. 27.—A side view of the aerial shown in Fig. 22.FIG. 27.—A side view of the aerial shown in Fig. 22.
FIG. 27.—A side view of the aerial shown in Fig. 22.