Wireless Telegraphy and Telephony/Wireless Telephony
Wireless Telephony
Since wireless telegraphy has become so successful, it is but natural that wireless telephony should follow, just as the telephone followed the telegraph. In the ordinary wire telephone a transmitter is employed which varies the intensity of the electric current in the wire in direct ratio to the changes in the intensity of the sound waves set up by the human voice. All the undulations and tones of the voice are, therefore, transformed into complicated electric currents which, in passing through the telephone receiver, cause the diaphragm of the receiver to vibrate in unison with these complex currents, thereby reproducing articulate speech.
The high-frequency oscillations employed in wireless telegraphy are so rapid that the human ear cannot detect their presence in a telephone receiver. Therefore it is plain that if means be employed to vary the intensity of these high-frequency oscillations by a telephone transmitter actuated by the human voice, the received waves may be made to so operate a telephone receiver connected to a regular wireless detector, that articulate speech may be reproduced in the telephone receiver.
The first problem was to find means for generating a continuous flow of electromagnetic waves, without sufficient interruptions to cause a sound in the telephone receiver, excepting that caused by speech. It will be recalled that the sound heard in the telephone receiver employed in wireless telegraphy is due to the interruption of the waves; hence the sound heard at the receiving wireless telegraph station corresponds to the sound of the interrupted “spark” at the transmitting station.
The principal method employed for producing a continuous wave train is obtained by the use of an arc light. In this case, however, one carbon and a rod of copper are employed instead of the usual two carbons. The electric arc is connected to a condenser which produces the high-frequency oscillations. By these means a nearly continuous train of waves is radiated from the antenna.
A regular transmitter is connected in the antenna circuit as shown in Fig. 27, which when spoken into varies the strength of the high-frequency oscillatory current passing through it, thus varying or damping the electromagnetic waves. Almost any type of wireless telegraph receiver can be used as a wireless telephone receiver.
Communication cannot be carried on over so great distances by the wireless telephone as by the wireless telegraph, owing to the fact that the best results in wireless telegraphy are obtained by using sustained uniform waves, whereas mn wireless telephony the waves are damped, or, in other words, their form is changed by the effects of speech in the transmitter. Moreover, so great
Fig. 27.—Wireless Telephone Transmitter Connections
an amount of energy cannot be handled with the wireless telephone, as with the wireless telegraph.
While wireless telegrams have been successfully transmitted and received over a distance exceeding 3000 miles, the wireless telephone has only been successfully used up to distances barely exceeding 20 miles, and those used in the U. S. Navy are only guaranteed to operate five miles.
It is particularly adapted for service between the vessels constituting fleets, and for use on ferry-boats, tugs, etc., in harbors.
However, the art is young, and no doubt the distance will be increased after we have obtained a better knowledge of the ether.