Abstract: A received radio signal is demodulated by applying it to a coherent demodulator loop for detection of a modulated input signal. The loop has a variable gain control capability. A gain control voltage dependent upon variations of amplitude of the input signal is then generated and is applied to control the gain within the loop.In one aspect, a received radio signal is demodulated by multiplying the signal with a local oscillator signal to produce two product voltages the first of which reflects exponential (EM frequency or phase) variations and may reflect amplitude variations in said radio signal and the second of which reflects only amplitude variations.

Abstract: Digitally controlled tuning by storing a digital code representative of the frequency of a selected channel and generating successive digital counts, each proportional to the number of cycles of an oscillator signal in each of a plurality of successive uniform sample intervals. The digital code is then compared with a digital count to generate a first output when equal, a second output when the code exceeds the count, and a third output when the count exceeds the code. The frequency of the oscillator is varied in response to one of the second and third outputs to increase or decrease the frequency, respectively, and to permit the frequency of the oscillator to lock in response to the first output signal.