A method for intermodulation noise calculations in a cable television network with HD-MAC, PAL and FM radio signals

A statistical method for calculation of intermodulation noise is developed for CATV systems whose traffic can be characterized as a sum of a large number of independent signals. The Central Limit Theorem leads to a method of calculating the intermodulation noise power spectrum, given the degree of nonlinearity of the transmission system. The method is demonstrated by calculating the signal to intermodulation noise ratio in the various channels of a prototype cable network supporting HD-MAC, PAL and FM radio signals. The spectra of these individual signals are simplified in order to perform part of the calculation analytically. As expected, the signal to intermodulation noise ratio decreases when the total signal power is increased. This method can be used to calculate the necessary back-off of a cable network for a given frequency plan, and thus to determine suitable plans for loading and controlling CATV networks.