FIG. 141.–Wireless telephone receiving apparatus (induction method).
FIG. 142.—Fessenden wireless telephone transmitting phonograph music.
It may now readily be realized that there are long pauses between the sparks when there are no oscillations in the aerial, and, consequently, no electromagnetic waves passing between the transmitter and receptor during those periods.
The wavy line, C, represents the vibrations of the human voice when producing speech. Part of it has been represented by a continuous line, and part by a dotted line. The portions represented by the dotted line occur when there are no oscillations in the aerial, and consequently these portions are not transmitted. The continuous portions are the only ones reaching the receptor. Literally, there are "holes in the voice," and the result is a jumble of sounds, sometimes bearing a resemblance to speech, but usually untranslatable.
FIG. 143.—Diagram illustrating the reason why damped oscillations will not carry the voice.
The fault lies in the method of producing the oscillations which are damped and therefore do not exist continuously. If they could be made to keep on swinging and at a sufficiently high speed so that their tone would be inaudible and not confuse the speech, the problem would be solved. In other words, three things are necessary for the successful operation of a wireless telephone.
- A means of producing and radiating a stream of undampened electrical waves sufficiently continuous to transmit the upper harmonics of the voice, on which the quality and recognition of the speech depends.
- Means for varying or modulating the stream of electrical waves in accordance with the sound waves.
- A receiver, continuously responsive and capable of corresponding with sufficient rapidity to the speech harmonics.
In order to obtain the desired result, recourse is had to an arc lamp as a generator of undamped high frequency oscillations.