A Crude Method of Amplitude Modulation

Author: J.B. Hoag

Fig. 16 E. A crude method of amplitude modulation

In Fig. 16 E, a microphone is connected directly in series with the antenna circuit. Sound waves which vibrate the diaphragm of the microphone change its resistance periodically at the frequency of the sound waves, and in proportion to the intensity of the sound waves. Since the microphone is in series with the high-frequency current, its amplitude, and that of the radiated wave, is caused to fluctuate. However, the radio frequency currents tend to " pack " the carbon granules in the microphone so that it ceases to function. There are numerous other difficulties which make this method impracticable.