Filter which separates pilot frequency from carrier wave - by adding two phase shifted signals obtained by demodulation at zero phase and 90-degree phase

摘要

The filter produces an interference frequency Fm roughly equal to Fp + DELTA F, where Fp is the pilot frequency and DELTA F = Fs + Fp where Fs is the sideband transmission frequency. Two waves shifted in phase by 90 deg. are derived from the interference frequency. Demodulation is accomplished for the 0 deg. phase wave and for the 90 deg. phase wave. The two signals obtained from these two demodulation processes are shifted by 90 deg. w.r.t. one another and added. The signal of frequency DELTA F is filtered from this sum. The system comprises an oscillator, two demodulators, a phase shifter, a summation circuit and a filtering circuit.