Intermodulation and a.m./p.m. distortion in f.m./f.d.m. radio systems during 2-path propagation

The total phase distortion on a path of an f.m./f.d.m. radio system under 2-path-propagation conditions consists of two components, intermodulation and amplitude/phase distortion which are not, in general, uncorrelated. It shown in the Appendix that the Taylor-series method of expanding a memoryless nonlinearity is, strictly, never valid in the case of 2-path propagation. The Fourier-series method of computing the path-intermodulation noise used previously is therefore extended to determine the power spectrum of the total phase-distortion noise. The analysis is confined to cases where the a.m./p.m.-conversion coefficient, expressed in degrees per decibel, is substantially constant and independent of frequency at low signal levels. Calculated results for total distortion noise in 1800- and 2700-channel systems are shown in the form of graphs which indicate that the values of the a.m./p.m. coefficient occurring in present receivers do not significantly degrade the system performance during 2-path propagation.