Study of Adaptive Processes Applied to Phase-Locked Loops

摘要

The phase-locked loop is a form of FM detector that is being widely used in space communication systems. This is probably the circuit most responsible for the success of low-data rate, extremely long-range space communication links. There are two important uses of phaselocked loops. One is as a Doppler tracking filter and the other is as a demodulator. The transfer function of the optimum tracking filter is a function of the rate of Doppler shift and the signal-to-noise ratio. If a form is assumed for the modulation, the optimum filter is a function only of the signal strength. This report is a summary of the current progress of a study of adaptive phase-locked loops. Measurements of the rate of Doppler shift and/or signal strength are made automatically and the loop is adjusted to near optimum. The study is divided into two main parts. The first is primarily theoretical. It concerns the synthesis of the optimum filters when the measured data are known and the optimum means for taking the measurements. The second phase is an experimental study of the hardware.