Harmonic Distortion of Wideband (Television) FM Transmission Links Due to Predetection Filtering

An analysis of the distortion contributed by RF predetection filtering in the transmission of a frequency modulated signal has been performed. Test signals of two types were employed in the analysis, namely, single and multiple sinusoidal test tones. This combination of signals was used to provide a repeatable, tractable signal model, useful for characterizing video transmission in a band-limited communications link. Two RF predetection filter characteristics, the Bessel and the Butterworth, were analyzed by computer-aided techniques. Plots of single and multiple test tone distortion were generated for a variety of vital link parameters, including modulation index, bandwidth/baseband ratio, and filter center frequency/bandwidth ratio for the two filter characteristics. The analysis is summarized in this paper, in terms of these variables, for single tone only.