At a receiving station four electromagnets are placed in series in the main rthe circuit. The armatures of these instruments are iron reeds, fastened at one end, and attuned to vibrate at rates corresponding with their respective vibrat ing forks at the transmitting station. Hence, each reed will select and respond only to the pulsatiqns of current transmitted by its respec tive vibrating fork. Contact points controlling a local current are also ,attached to the arma tures , of the receiving magnets and by this mean3 the transmitted dots and dashes are re ceived by a Morse telegraph sounder in prac tically the usual way.
Obviously, when all of these differing rates of current impulses are being transmitted at one time over one wire the resultant com posite wave must be complex to a degree. Yet the Gray Harmonic telegraph system was in successful operation for several years between New York and Chicago on the lines of the Postal Telegraph Company. Indeed the degree of complexity of the resultant current referred to did not end with the operation of the func tions outlined in the foregoing remarks. For, in addition to the four pulsatory circuits men tioned, an ordinary Morse duplex system was superposed on the vibrating system, this giving a sixtuplex telegraph system capable of trans mitting six messages over one wire simul taneously.
The Heising Multiplex Wirekss Telephone System.—In this system an arrangement meas urably analogous to the foregoing is employed for setting up electric oscillations of different frequencies, which differing rates of oscilla tions are simultaneously radiated as a com pound wave in space from .the aerials of nearby transmitting stations and .are selected and received at the receiving stations by suit ably attuned wireless apparatus, in a mariner to be described.
This system was installed experimentally on three or more ships of the United States navy, but owing to the declaration of war with Ger many the tests were prematurely discontinued. The transmitting apparatus on one ship is out lined in Fig. 11. The apparatus on all the ships was similar, but certain of the tuning circuits on each ship were adjusted to different rates of oscillation. The plan employed is to trans mit from the three ships a carrier wave of say Z000,000 cycles (150 meters). Then on one ship to modulate this frequency with an intermediate wave of 25,000 cycles, which fre quency in turn is modulated with the waves due to speech. On another ship the satne pro
cedure is followed except that an intermediate wave of 35,000 cycles is employed and on the third ship an intermediate wave of 45,000 cycles is utilized.
Let Fig. 11 crepresent the ship (A) using wave modulates at R the amplitude of the 25,000 cycle frequency set up by the oscillator-tube VT'. In turn this modulated 25,000 cycle fre quency after amplification in power tube VT' is, through transformer P caused, at condenser C, to modulate the 2,000,000 cycle carrier wave developed by oscillator VT'. This doubly modified earner wave after increased power amplification by the tube VT' is delivered by the transformer r to the antenna A. The batteries and other devices used in this system are not shown in the figure.
To avail of this arrangement each of the three ships or other stations equipped with this apparatus will transmit a carrier wave of Z000,000 cycles. But one ship, say A, will modulate this wave with a 25,000-cycle wave. B will modulate it with a wave, and C with a 45,000-cycle wave. The receiving ship A' will tune his apparatus to a 2,000,000 cycle wave and to an intermediate frc-quency of 25,000 cycles. Ship B' will tune his appara tus to a 2,000,000-cycle wave and to an inter mediate wave of 35,000 cycles, and ship C' to a 2,000,000-cycle wave and to an intertnediate wave of 45,000 cycles. The receiving apparatus is indicated in Fig. 12. A is the aerial. The bracket m encloses the 2,000,000-wave detector tube and the appropriate tuning coils TC, trans formers RC and condensers C. Bracket x en closes the intermediate frequency and voice detector tube VT', the telephone receiver R and the usual filament and potential batteries. It is plain then that the receiving apparatus of the ships A' B' C' will only respond to the 25,000, 35,000 and 45,000 speech modulated radio waves, respectively, while all three will receive and detect the 2,000,000 carrier wave, practically as the vibrating reeds in the Gray Harmonic Telegraph system respond only to he speec'h modulated wave of 25,000 fre quency. T is a microphone transmitter. The speech waves set up by this transmitter is repeated by the transformer or repeater coil RC into an amplifier VT. This amplified s-peech the particular train of impulses to whidi theY are attuned.