Intermodulation distortion in f.m. f.d.m. trunk-radio systems in 2-path fading situations

The intermodulation-noise performance of f.m. f.d.m. trunk-radio systems is examined in conditions of 2-path fading. By using a convolution series expansion for the demodulated-baseband output corresponding to the CCIR noise-test-signal input modulation, it is possible to calculat both the noise/power ratio and the baseband enhancements to be expected in systems of 960 and 1800 audio-channel capacity. Numerical results are presented representative of calculations made for a range of echo-delay times from 1 to 10ns, and relative echo amplitudes up to 0.99 (40dB maximum fade depth), showing the effect of intermodulation on the total system noise in this type of fading condition.