Intermodulation (IM) occurs whenever one or more radio frequencies are combined in a non-linear device. This produces sum and difference frequencies which are known as IM products. The non-linear device may be a transmitter, a receiver, an isolator, a bad connector or any number of other items. Sometimes the condition is desirable, as in the mixer stage of a superheterodyne receiver where signals are combined and selected to produce the familiar "Intermediate Frequencies" (I.F.). Most of the time however, intermodulation is undesirable and steps must be taken to prevent or eliminate the conditions which give rise to intermodulation. Such measures usually include the use of circulators and cavities to prevent signals from entering the final amplifier stages of transmitters, and the use of band-pass cavities at the inputs of receivers. These factors are of special concern at mountain top repeater sites The number of receivers and transmitters at most repeater sites can vary anywhere between a dozen to a few hundred. The number of intermodulation products which can be generated could be in the thousands A site manager may be able to exert total control over the conditions at a particular site, or only nominal influence over the activities of other users of the site. In either case, a site manager faced with an intermodulation problem would be faced with the formidable problem of tracking down the one combination out of possibly tens of thousands which might be the source of the problem This program is designed to make that task easier. Even though the number of intermodulation products is theoretically infinite, only a limited number of them are significant for a given set of receivers The products which we are mainly interested in are only those which will fall on or near a receiver frequency, and are of low enough order to be of significant amplitude
