PHASE LOCKED LOOP

摘要

An oscillator in a spacecraft transponder or repeater is frequency stabilized by a phase locked loop with reference signal therefor having a frequency (N/M) F being received in the repeater from a ground station. The reference signal is processed in the repeater and returned to the ground station where it is monitored to detect when the pull-in range of the loop is exceeded. When this condition is detected, the frequency of the reference signal is swept in the ground station until the frequency of the reference signal and frequency of the signal of the oscillator in the repeater is within said pull-in range. The oscillator frequency F is divided by M and the phase comparator includes a first tuned input circuit to respond to a frequency (N/M) F, a second turned input circuit to respond to the nth harmonic of the frequency F/M and a phase error detecting circuit to produce a control signal used to stabilize the frequency of the oscillator.