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