CHAPTER V. TUNING AND COUPLING, DIRECTIVE WAVE TELEGRAPHY.Tuning has been mentioned in several places but not explained in any greater measure than was necessary to render a conception which would enable the reader to follow the text intelligently in order not to depart from the subjects under discussion there and consequently defeat the purpose of clearness.The great importance and value of properly "tuning" the circuit of radiotelegraphic apparatus cannot be overestimated and for that reason the subject can hardly be passed without some further explanation. Its effects are two-fold. In the first place it is always desirable and highly important that wireless messages should be, so far as is possible,selective, inasmuch as there are often several stations in the same immediate neighborhood operating at the same time. This result is reached by tuning and it is possible for them all to transmit different messages at the same time without confusion by the proper arrangement of thewave length. The second effect is the transmission of messages over long distances with the comparative consumption of small amount of power by adjusting the "period" or electrical length of the circuits until the oscillations "flow in harmony" with each other and resonance is secured.Perhaps the only way that these results may be made clearly intelligible is by resort to a graphical example. Suppose that a very heavy weight were suspended from a chain as shown in the illustration and that it is struck at regular intervals,once every second, with a hammer.Every time that the hammer strikes the ball it will give it an impulse and cause it to swing slightly. If the chain is short, the ball will swing faster, while if it is long it will swing more slowly. We will suppose that the ball is struck from such a direction that it starts to swing over toward A. The ball is so heavy and the hammer so light in comparison however that the ball does not swing very far and soon commences a return journey. If it should return to the point B just as the hammer delivers another blow the force of the blow will be expended in stopping the ball rather than adding to its motion because they are both traveling inopposite directions. However if the chain is lengthened so that it has a period of swing lasting one second, the succeeding blow will strike the ball after it has reached the point C and is on its return journey, thus imparting fresh energy because both the ball and hammercome together at the right timewhen they are both swinging together. Proper adjustment of the length of the chain will make it possible for the hammer to always descend at the right moment to add its energy and motion to that previously given the ball. The result will be considerable increase in the amplitude of the swing.FIG. 86.—Chain and ball arranged to illustrate effect of tuning.FIG. 86.—Chain and ball arranged to illustrate effect of tuning.From this we may easily perceive how it is possible by shortening or lengthening the period of an electrical circuit to so adjust it that resonance is secured and each succeeding oscillation will take place at the proper time to assist the previous one, not dying away after one or two surges and becoming what is known in technical language as rapidly "damped."FIG. 87.—Loose coupled helix.FIG. 87.—Loose coupled helix.The instruments for accomplishing these things consist as previously explained, in the case of a transmitter, of thehelixand in the receiving station of varioustuning coilsand condensers.FIG. 88.—Hot-wire ammeter.FIG. 88.—Hot-wire ammeter.Helix and tuning coils are divided into the "inductive" or "loose" and the "direct" or close coupled types. Inductive tuning coils are known as "loose-couplers" and "receiving transformers." Inductive helixes consist simply of two helixes, separated from one another as shown in the accompanying illustration. The upper helix, called the secondary, can be raised or lowered upon a central support. Varying the distance between the primary and secondary is varying the "coupling." There are several advantages derived by using loose coupled sending helixes, the chief of which lie in the fact that it is possible to radiate larger amounts of energy and also decrease the "damping."FIG. 89.—The principle of the hot-wire ammeter.FIG. 89.—The principle of the hot-wire ammeter.In order to tune a transmitter, the "hot-wire" ammeter is necessary. This instrument makes use of the property which electrical conductors possess to become heated and expand when a current is passed through them.The accompanying diagram serves to illustrate the principle of the "hot-wire" meter. A piece of platinum wire is stretched tightly between two rigidly fixed posts. A thread leads from the center of the "hot wire" to a small spindle around which it passes once or twice. The spindle is also connected to a spring which exerts a continual tendency to turn the spindle but is prevented from so doing by the thread attaching to the hot wire. Any tendency on the part of the string to slacken a little, however, will immediately permit the spring to turn the spindle. When a high frequency current is passed through the platinum wire it becomes heated and expands. The expansion of the wire allows the thread to slacken slightly with the immediate result that the spindle turns. The spindle carries a pointer at the upper end which shows the amount of turning. It is therefore easy to tell the comparative strength of current flowing accordingly as the deflection is great or small.FIG. 90.—Diagram showing loose coupled helix in circuit.FIG. 90.—Diagram showing loose coupled helix in circuit.The meter is placed in series with the aerial and when the high frequency currents pass through it they heat and expand a fine wire, causing the needle to move over a graduated scale and indicate the amount of current passing. The apparatus is "tuned" or in resonance when the length of the spark gap, the condenser and the helix have been so adjusted that the oscillations flow freely through the system and the maximum amount of current is indicated by the ammeter.FIG. 91.—Loose coupled tuning coil.FIG. 91.—Loose coupled tuning coil.FIG. 92.—Loose coupled tuner.FIG. 92.—Loose coupled tuner.The loose coupled tuning coil consists of two windings wound over two concentric cylinders, forming a primary and a secondary. The secondary is the smaller winding and slides in and out of the primary so that the "coupling" is variable. The primary is adjustable by means of a slider and the secondary by means of a multi-pointed switch. The slider is usually connected to the aerial and one end of the coil to the ground. The detector, etc., are connected to the terminals of the secondary. Variable condensers may be added with good results to both the primary and secondary circuits.FIG. 93.—Diagram showing position of loose coupler in circuit.FIG. 93.—Diagram showing position of loose coupler in circuit.Loose couplers also take the form of doughnut tuners in which the secondary revolves instead of slides. The coupling is variable in such an instrument by simply turning the secondary.The wave emitted from a transmitter is in reality made up of two waves of different lengths. The variation in the lengths of these two waves is dependable upon a factor known as the coefficient of coupling. It is almost impossible to clearly explain the phenomenon and in order not to confuse and complicate by a rather lengthy explanation it may be well to simply state that its effect is to make selective tuning difficult unless the coupling of the receiving station can be varied to correspond with that of the transmitter and ask the reader to take it for granted. Varying the coupling adjusts the difference in the two wave lengths and when properly accomplished renders the apparatus highly selective.FIG. 94.–Fort Gibbons, Alaska, wireless station.FIG. 94.–Fort Gibbons, Alaska, wireless station.FIG. 95.—Transmitting condenser (molded dielectric).FIG. 95.—Transmitting condenser (molded dielectric).Directive Wireless Telegraphy is an interesting phase of this new art which is receiving considerable attention in the hands of investigators and has resulted in the devisement of several successful systems for confining the propagation of the electric waves to certain directions.FIG. 96.—Braun's method for directing wireless telegraph signals.FIG. 96.—Braun's method for directing wireless telegraph signals.A general diffusion of waves is often very undesirable for the reasons that the message may be received by an unfriendly neighbor or enemy and also because it is wasteful of energy. By so directing the waves that they may be sent over the earth to any desired point of the compass and only in that direction, it is possible to communicate without disturbing another station and also for a vessel at sea to secure its bearings and position by tuning its apparatus to respond to electric waves from two different known stations.The manner in which the problem has been solved varies considerably according to the inventor. All are interesting and ingenious.It will be remembered that electric waves possess all the characteristics and properties of light waves, etc., and may be reflected, refracted and polarized.Ferdinand Braun has devised a system consisting of a number of metallic strips arranged to compose a parabolic surface. Another similar set of strips below the first set completes the arrangement. The two sets are connected to the terminals of a spark gap and induction coil. This apparatus acts as a huge reflector and sends out waves in one direction only, but however interesting and ingenious it may be is not entirely practical.FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.Another method devised by Braun employs two or more aerials at certain distances apart. The alternating currents used to excite the oscillations differ inphase, i. e. are so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennae suitably differing in their phase of excitation and situated at the vertices of a triangle it is possible to send strong signals in certain directions only.FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are incoming and to the condenser, spark gap and coil when the signals are to be transmitted.Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.FIG. 99.—Complete receiving and transmitting outfit.FIG. 99.—Complete receiving and transmitting outfit.By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.
CHAPTER V. TUNING AND COUPLING, DIRECTIVE WAVE TELEGRAPHY.Tuning has been mentioned in several places but not explained in any greater measure than was necessary to render a conception which would enable the reader to follow the text intelligently in order not to depart from the subjects under discussion there and consequently defeat the purpose of clearness.The great importance and value of properly "tuning" the circuit of radiotelegraphic apparatus cannot be overestimated and for that reason the subject can hardly be passed without some further explanation. Its effects are two-fold. In the first place it is always desirable and highly important that wireless messages should be, so far as is possible,selective, inasmuch as there are often several stations in the same immediate neighborhood operating at the same time. This result is reached by tuning and it is possible for them all to transmit different messages at the same time without confusion by the proper arrangement of thewave length. The second effect is the transmission of messages over long distances with the comparative consumption of small amount of power by adjusting the "period" or electrical length of the circuits until the oscillations "flow in harmony" with each other and resonance is secured.Perhaps the only way that these results may be made clearly intelligible is by resort to a graphical example. Suppose that a very heavy weight were suspended from a chain as shown in the illustration and that it is struck at regular intervals,once every second, with a hammer.Every time that the hammer strikes the ball it will give it an impulse and cause it to swing slightly. If the chain is short, the ball will swing faster, while if it is long it will swing more slowly. We will suppose that the ball is struck from such a direction that it starts to swing over toward A. The ball is so heavy and the hammer so light in comparison however that the ball does not swing very far and soon commences a return journey. If it should return to the point B just as the hammer delivers another blow the force of the blow will be expended in stopping the ball rather than adding to its motion because they are both traveling inopposite directions. However if the chain is lengthened so that it has a period of swing lasting one second, the succeeding blow will strike the ball after it has reached the point C and is on its return journey, thus imparting fresh energy because both the ball and hammercome together at the right timewhen they are both swinging together. Proper adjustment of the length of the chain will make it possible for the hammer to always descend at the right moment to add its energy and motion to that previously given the ball. The result will be considerable increase in the amplitude of the swing.FIG. 86.—Chain and ball arranged to illustrate effect of tuning.FIG. 86.—Chain and ball arranged to illustrate effect of tuning.From this we may easily perceive how it is possible by shortening or lengthening the period of an electrical circuit to so adjust it that resonance is secured and each succeeding oscillation will take place at the proper time to assist the previous one, not dying away after one or two surges and becoming what is known in technical language as rapidly "damped."FIG. 87.—Loose coupled helix.FIG. 87.—Loose coupled helix.The instruments for accomplishing these things consist as previously explained, in the case of a transmitter, of thehelixand in the receiving station of varioustuning coilsand condensers.FIG. 88.—Hot-wire ammeter.FIG. 88.—Hot-wire ammeter.Helix and tuning coils are divided into the "inductive" or "loose" and the "direct" or close coupled types. Inductive tuning coils are known as "loose-couplers" and "receiving transformers." Inductive helixes consist simply of two helixes, separated from one another as shown in the accompanying illustration. The upper helix, called the secondary, can be raised or lowered upon a central support. Varying the distance between the primary and secondary is varying the "coupling." There are several advantages derived by using loose coupled sending helixes, the chief of which lie in the fact that it is possible to radiate larger amounts of energy and also decrease the "damping."FIG. 89.—The principle of the hot-wire ammeter.FIG. 89.—The principle of the hot-wire ammeter.In order to tune a transmitter, the "hot-wire" ammeter is necessary. This instrument makes use of the property which electrical conductors possess to become heated and expand when a current is passed through them.The accompanying diagram serves to illustrate the principle of the "hot-wire" meter. A piece of platinum wire is stretched tightly between two rigidly fixed posts. A thread leads from the center of the "hot wire" to a small spindle around which it passes once or twice. The spindle is also connected to a spring which exerts a continual tendency to turn the spindle but is prevented from so doing by the thread attaching to the hot wire. Any tendency on the part of the string to slacken a little, however, will immediately permit the spring to turn the spindle. When a high frequency current is passed through the platinum wire it becomes heated and expands. The expansion of the wire allows the thread to slacken slightly with the immediate result that the spindle turns. The spindle carries a pointer at the upper end which shows the amount of turning. It is therefore easy to tell the comparative strength of current flowing accordingly as the deflection is great or small.FIG. 90.—Diagram showing loose coupled helix in circuit.FIG. 90.—Diagram showing loose coupled helix in circuit.The meter is placed in series with the aerial and when the high frequency currents pass through it they heat and expand a fine wire, causing the needle to move over a graduated scale and indicate the amount of current passing. The apparatus is "tuned" or in resonance when the length of the spark gap, the condenser and the helix have been so adjusted that the oscillations flow freely through the system and the maximum amount of current is indicated by the ammeter.FIG. 91.—Loose coupled tuning coil.FIG. 91.—Loose coupled tuning coil.FIG. 92.—Loose coupled tuner.FIG. 92.—Loose coupled tuner.The loose coupled tuning coil consists of two windings wound over two concentric cylinders, forming a primary and a secondary. The secondary is the smaller winding and slides in and out of the primary so that the "coupling" is variable. The primary is adjustable by means of a slider and the secondary by means of a multi-pointed switch. The slider is usually connected to the aerial and one end of the coil to the ground. The detector, etc., are connected to the terminals of the secondary. Variable condensers may be added with good results to both the primary and secondary circuits.FIG. 93.—Diagram showing position of loose coupler in circuit.FIG. 93.—Diagram showing position of loose coupler in circuit.Loose couplers also take the form of doughnut tuners in which the secondary revolves instead of slides. The coupling is variable in such an instrument by simply turning the secondary.The wave emitted from a transmitter is in reality made up of two waves of different lengths. The variation in the lengths of these two waves is dependable upon a factor known as the coefficient of coupling. It is almost impossible to clearly explain the phenomenon and in order not to confuse and complicate by a rather lengthy explanation it may be well to simply state that its effect is to make selective tuning difficult unless the coupling of the receiving station can be varied to correspond with that of the transmitter and ask the reader to take it for granted. Varying the coupling adjusts the difference in the two wave lengths and when properly accomplished renders the apparatus highly selective.FIG. 94.–Fort Gibbons, Alaska, wireless station.FIG. 94.–Fort Gibbons, Alaska, wireless station.FIG. 95.—Transmitting condenser (molded dielectric).FIG. 95.—Transmitting condenser (molded dielectric).Directive Wireless Telegraphy is an interesting phase of this new art which is receiving considerable attention in the hands of investigators and has resulted in the devisement of several successful systems for confining the propagation of the electric waves to certain directions.FIG. 96.—Braun's method for directing wireless telegraph signals.FIG. 96.—Braun's method for directing wireless telegraph signals.A general diffusion of waves is often very undesirable for the reasons that the message may be received by an unfriendly neighbor or enemy and also because it is wasteful of energy. By so directing the waves that they may be sent over the earth to any desired point of the compass and only in that direction, it is possible to communicate without disturbing another station and also for a vessel at sea to secure its bearings and position by tuning its apparatus to respond to electric waves from two different known stations.The manner in which the problem has been solved varies considerably according to the inventor. All are interesting and ingenious.It will be remembered that electric waves possess all the characteristics and properties of light waves, etc., and may be reflected, refracted and polarized.Ferdinand Braun has devised a system consisting of a number of metallic strips arranged to compose a parabolic surface. Another similar set of strips below the first set completes the arrangement. The two sets are connected to the terminals of a spark gap and induction coil. This apparatus acts as a huge reflector and sends out waves in one direction only, but however interesting and ingenious it may be is not entirely practical.FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.Another method devised by Braun employs two or more aerials at certain distances apart. The alternating currents used to excite the oscillations differ inphase, i. e. are so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennae suitably differing in their phase of excitation and situated at the vertices of a triangle it is possible to send strong signals in certain directions only.FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are incoming and to the condenser, spark gap and coil when the signals are to be transmitted.Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.FIG. 99.—Complete receiving and transmitting outfit.FIG. 99.—Complete receiving and transmitting outfit.By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.
Tuning has been mentioned in several places but not explained in any greater measure than was necessary to render a conception which would enable the reader to follow the text intelligently in order not to depart from the subjects under discussion there and consequently defeat the purpose of clearness.
The great importance and value of properly "tuning" the circuit of radiotelegraphic apparatus cannot be overestimated and for that reason the subject can hardly be passed without some further explanation. Its effects are two-fold. In the first place it is always desirable and highly important that wireless messages should be, so far as is possible,selective, inasmuch as there are often several stations in the same immediate neighborhood operating at the same time. This result is reached by tuning and it is possible for them all to transmit different messages at the same time without confusion by the proper arrangement of thewave length. The second effect is the transmission of messages over long distances with the comparative consumption of small amount of power by adjusting the "period" or electrical length of the circuits until the oscillations "flow in harmony" with each other and resonance is secured.
Perhaps the only way that these results may be made clearly intelligible is by resort to a graphical example. Suppose that a very heavy weight were suspended from a chain as shown in the illustration and that it is struck at regular intervals,once every second, with a hammer.
Every time that the hammer strikes the ball it will give it an impulse and cause it to swing slightly. If the chain is short, the ball will swing faster, while if it is long it will swing more slowly. We will suppose that the ball is struck from such a direction that it starts to swing over toward A. The ball is so heavy and the hammer so light in comparison however that the ball does not swing very far and soon commences a return journey. If it should return to the point B just as the hammer delivers another blow the force of the blow will be expended in stopping the ball rather than adding to its motion because they are both traveling inopposite directions. However if the chain is lengthened so that it has a period of swing lasting one second, the succeeding blow will strike the ball after it has reached the point C and is on its return journey, thus imparting fresh energy because both the ball and hammercome together at the right timewhen they are both swinging together. Proper adjustment of the length of the chain will make it possible for the hammer to always descend at the right moment to add its energy and motion to that previously given the ball. The result will be considerable increase in the amplitude of the swing.
FIG. 86.—Chain and ball arranged to illustrate effect of tuning.FIG. 86.—Chain and ball arranged to illustrate effect of tuning.
FIG. 86.—Chain and ball arranged to illustrate effect of tuning.
From this we may easily perceive how it is possible by shortening or lengthening the period of an electrical circuit to so adjust it that resonance is secured and each succeeding oscillation will take place at the proper time to assist the previous one, not dying away after one or two surges and becoming what is known in technical language as rapidly "damped."
FIG. 87.—Loose coupled helix.FIG. 87.—Loose coupled helix.
FIG. 87.—Loose coupled helix.
The instruments for accomplishing these things consist as previously explained, in the case of a transmitter, of thehelixand in the receiving station of varioustuning coilsand condensers.
FIG. 88.—Hot-wire ammeter.FIG. 88.—Hot-wire ammeter.
FIG. 88.—Hot-wire ammeter.
Helix and tuning coils are divided into the "inductive" or "loose" and the "direct" or close coupled types. Inductive tuning coils are known as "loose-couplers" and "receiving transformers." Inductive helixes consist simply of two helixes, separated from one another as shown in the accompanying illustration. The upper helix, called the secondary, can be raised or lowered upon a central support. Varying the distance between the primary and secondary is varying the "coupling." There are several advantages derived by using loose coupled sending helixes, the chief of which lie in the fact that it is possible to radiate larger amounts of energy and also decrease the "damping."
FIG. 89.—The principle of the hot-wire ammeter.FIG. 89.—The principle of the hot-wire ammeter.
FIG. 89.—The principle of the hot-wire ammeter.
In order to tune a transmitter, the "hot-wire" ammeter is necessary. This instrument makes use of the property which electrical conductors possess to become heated and expand when a current is passed through them.
The accompanying diagram serves to illustrate the principle of the "hot-wire" meter. A piece of platinum wire is stretched tightly between two rigidly fixed posts. A thread leads from the center of the "hot wire" to a small spindle around which it passes once or twice. The spindle is also connected to a spring which exerts a continual tendency to turn the spindle but is prevented from so doing by the thread attaching to the hot wire. Any tendency on the part of the string to slacken a little, however, will immediately permit the spring to turn the spindle. When a high frequency current is passed through the platinum wire it becomes heated and expands. The expansion of the wire allows the thread to slacken slightly with the immediate result that the spindle turns. The spindle carries a pointer at the upper end which shows the amount of turning. It is therefore easy to tell the comparative strength of current flowing accordingly as the deflection is great or small.
FIG. 90.—Diagram showing loose coupled helix in circuit.FIG. 90.—Diagram showing loose coupled helix in circuit.
FIG. 90.—Diagram showing loose coupled helix in circuit.
The meter is placed in series with the aerial and when the high frequency currents pass through it they heat and expand a fine wire, causing the needle to move over a graduated scale and indicate the amount of current passing. The apparatus is "tuned" or in resonance when the length of the spark gap, the condenser and the helix have been so adjusted that the oscillations flow freely through the system and the maximum amount of current is indicated by the ammeter.
FIG. 91.—Loose coupled tuning coil.FIG. 91.—Loose coupled tuning coil.
FIG. 91.—Loose coupled tuning coil.
FIG. 92.—Loose coupled tuner.FIG. 92.—Loose coupled tuner.
FIG. 92.—Loose coupled tuner.
The loose coupled tuning coil consists of two windings wound over two concentric cylinders, forming a primary and a secondary. The secondary is the smaller winding and slides in and out of the primary so that the "coupling" is variable. The primary is adjustable by means of a slider and the secondary by means of a multi-pointed switch. The slider is usually connected to the aerial and one end of the coil to the ground. The detector, etc., are connected to the terminals of the secondary. Variable condensers may be added with good results to both the primary and secondary circuits.
FIG. 93.—Diagram showing position of loose coupler in circuit.FIG. 93.—Diagram showing position of loose coupler in circuit.
FIG. 93.—Diagram showing position of loose coupler in circuit.
Loose couplers also take the form of doughnut tuners in which the secondary revolves instead of slides. The coupling is variable in such an instrument by simply turning the secondary.
The wave emitted from a transmitter is in reality made up of two waves of different lengths. The variation in the lengths of these two waves is dependable upon a factor known as the coefficient of coupling. It is almost impossible to clearly explain the phenomenon and in order not to confuse and complicate by a rather lengthy explanation it may be well to simply state that its effect is to make selective tuning difficult unless the coupling of the receiving station can be varied to correspond with that of the transmitter and ask the reader to take it for granted. Varying the coupling adjusts the difference in the two wave lengths and when properly accomplished renders the apparatus highly selective.
FIG. 94.–Fort Gibbons, Alaska, wireless station.FIG. 94.–Fort Gibbons, Alaska, wireless station.
FIG. 94.–Fort Gibbons, Alaska, wireless station.
FIG. 95.—Transmitting condenser (molded dielectric).FIG. 95.—Transmitting condenser (molded dielectric).
FIG. 95.—Transmitting condenser (molded dielectric).
Directive Wireless Telegraphy is an interesting phase of this new art which is receiving considerable attention in the hands of investigators and has resulted in the devisement of several successful systems for confining the propagation of the electric waves to certain directions.
FIG. 96.—Braun's method for directing wireless telegraph signals.FIG. 96.—Braun's method for directing wireless telegraph signals.
FIG. 96.—Braun's method for directing wireless telegraph signals.
A general diffusion of waves is often very undesirable for the reasons that the message may be received by an unfriendly neighbor or enemy and also because it is wasteful of energy. By so directing the waves that they may be sent over the earth to any desired point of the compass and only in that direction, it is possible to communicate without disturbing another station and also for a vessel at sea to secure its bearings and position by tuning its apparatus to respond to electric waves from two different known stations.
The manner in which the problem has been solved varies considerably according to the inventor. All are interesting and ingenious.
It will be remembered that electric waves possess all the characteristics and properties of light waves, etc., and may be reflected, refracted and polarized.
Ferdinand Braun has devised a system consisting of a number of metallic strips arranged to compose a parabolic surface. Another similar set of strips below the first set completes the arrangement. The two sets are connected to the terminals of a spark gap and induction coil. This apparatus acts as a huge reflector and sends out waves in one direction only, but however interesting and ingenious it may be is not entirely practical.
FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.
FIG. 97.—Bellini-Tosi radio-goniometer for directive wireless telegraphy.
Another method devised by Braun employs two or more aerials at certain distances apart. The alternating currents used to excite the oscillations differ inphase, i. e. are so arranged that they have different comparative values at the same moment. It is possible to send very strong signals in a direction lying in the same plane as the aerials. By the use of three or more antennae suitably differing in their phase of excitation and situated at the vertices of a triangle it is possible to send strong signals in certain directions only.
FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.
FIG. 98.—Arrangement of Bellini and Tosi for directive wireless telegraphy.
Messrs. Bellini and Tosi have devised a very ingenious method of directively transmitting and receiving electric waves as shown in the accompanying diagrams. The antenna consists of two closed or nearly closed circuits of triangular shape arranged in two perpendicular planes. The two aerials each contain a circular coil of wire perpendicular to each other with their windings in the planes of the antenna circuits respectively. A third coil is connected to the receiving apparatus when the messages are incoming and to the condenser, spark gap and coil when the signals are to be transmitted.
Waves coming in from any particular direction produce oscillations in the two aerial circuits whose intensity varies according to the direction in which the waves These currents passing through the coils generate a magnetic field having a direction perpendicular to that from which the waves come. The strength of the currents in the movable coil will depend upon its position in the resultant magnetic field and will be at a maximum when the coil embraces as many as possible of the lines of magnetic force.
FIG. 99.—Complete receiving and transmitting outfit.FIG. 99.—Complete receiving and transmitting outfit.
FIG. 99.—Complete receiving and transmitting outfit.
By providing the movable coil with a pointer it is possible to thereby determine the plane in which the station producing the signals lies. Any ambiguity regarding the final position of the station, whether it is located in the same direction indicated by the pointer or in the opposite one, is only removed by general knowledge of the location of existing stations.
The processes involved in sending messages are the reverse of those entering into the receiving apparatus. The movable coil being connected with the condenser, gap and transformer or induction coil creates a magnetic field which induces oscillating currents in the other two coils and consequent waves in the aerial whose strongest exertions will lie in a plane determined by the third coil. Changing the position of the latter will send the messages in any direction desired.