Publisher's Synopsis
Excerpt from Operation of the Modulator Tube in Radio Telephone Sets
The function of a modulating device in radio communication is to vary the output current of a radio generator at a frequency or at frequencies lower than the radio frequency involved. Ih' a certain sense practically all radio communication using Single wave-length signals is by a modulation method. In continuous wave transmission, the keying by which the Signals are conveyed constitutes a dot-and-dash modulation of the antenna current. In the operation of spark and other tone transmitters, the radio frequency Wave trains are sent 'out at more of less regular inter vals at an'audio frequency, SO that an audible note is heard upon rectification with a detecting device. In addition to this audio modulation, a second order of dot-and-'dash modulation is required for conveying the telegraph signal. In radio telephony the mes sage which is conveyed depends upon the first Order modulation itself. The antenna current is made to vary, not at a 'single tone frequency, but with frequencies and in degrees corresponding to the pitches and intensities Of the sound waves produced. By the voice of the speaker. In consequence, upon rectification of the received radio Signals, there' are produced in the receiving tele phones electrical currents which are of precisely the same nature as would be produced by communication by wire telephony.
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