Fig. 6 AM-1 Transmitter
Frequency ranges from 1.5 to 9mc can be employed with the AM-1. The modulation of the AM-1 is effected by use of a triode modulator (2-3A5) tubes) connected in series with the plate supply of a class "C" RF amplifier. Variation of the plate supply voltage of the RF amplifier caused by change in tube resistance gives amplitude modulation linear with plate voltage of the amplifier. By use of this system modulation from DC to several hundred cycles is obtained.
The receiver for this transmitter was a Hammerlund SP 400X with several modifications. In order to increase the signal to noise ratio a crystal filter was introduced into the IF amplifier circuit to narrow the bandwidth. Bandwidth was also reduced by