Computation of Interference into Angle-Modulated Systems Carrying Multichannel Telephone Signals

It is commonly known that, in order to calculate the demodulated noise power of the wanted frequency division multiplexedfrequency modulated (FDM-FM) signal due to interference, the convolution between the power spectra of the wanted FM signal and interference is required to be obtained. This concise paper shows a simple approach to calculate this convolution without direct calculation of the power spectrum of the FDMFM signal when the power spectrum of the interference is given (by measurements or calculation) and the highest and lowest channel frequencies of the baseband signal and rms frequency deviation of the wanted FDM-FM signal are known. Since the calculation of the FDM-FM signal power spectrum is not an easy problem in some cases, this approach makes much simpler an accurate evaluation of the output noise power due to interference.