Split loop AFC system for a SSB receiver

摘要

An automatic frequency control circuit for a single side band receiver employing a split-loop phase locked loop system is disclosed. Initially, both a first and second voltage controlled oscillator lock to a received pilot taken after the IF strip of the SSB receiver. Once lock is achieved, a sample is taken of the control line voltage of the first VCO whereafter the first VCO control line is held at the sampled voltage and will no longer track the received pilot until such time as the second VCO deviates from a predetermined range. Simultaneous to switching the first VCO, the loop filter of the second VCO is adapted to maintain identical loop dynamics both before and after switching control of the first VCO.