Performance prediction method for communications and tracking channels of Apollo unified S-band telecommunications and tracking system.

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Excessive telemetry error rates caused by baseband voice interference occur in several modes of the Apollo communication system. Demodulation, using essentially nonlinear quadrature phase detection, causes voice terms to appear in the telemetry spectrum. In this report, two methods which effectively linearize the demodulation process are used to reduce the voice interference. One method uses a negative feedback loop incorporated around the present nonlinear phase detector. The other method uses a frequency-modulation demodulator preceded by a composite filter containing three band-pass filters in parallel. The theoretical development, construction, and testing of both methods are presented. Significant improvement in telemetry performance is obtained. Results show that voice interference to both the 1.6- and 51.2-kbps telemetry data is negligible for all spacecraft/ground-station conditions when using either of the two methods. It is recommended that the negative-feedback-loop method be implemented in the Manned Space Flight Network ground stations as a result of its relative simplicity and superior performance.