Relationship of Noise Power Ratio to FM/FM Data Quality

Abstract

The IRIG (Inter-Range Instrumentation Group) 118 series "Test Methods for Telemetry Systems and Subsystems" has standardized the notch-noise loading test for frequency division systems. This paper presents a practical method for predicting subcarrier output SNR (signal-to-noise ratio) from NPR (noise power ratio) measurements at the video output of a telemetry receiver. A laboratory test is described in which NPR test data and FM (frequency modulation) subcarrier output SNR data were measured using the same FM radio link and modulation level. The test data show satisfactory agreement between predicted and measured subcarrier output signal-to-noise ratios. In addition, the data show that a flat NPR test spectrum is adequate for predicting performance of frequency division systems using the normal 6 dB/octave and 9 dB/octave tapers.