Desensitization in transistorized PM/FM-receivers

An analysis of the mechanism of desensitization - or blocking - in the RF- and mixer stage of a transistorized PM/FM receiver is given, and it is shown, that noise figure degradation because of noise conversion is the principal source of receiver desensitization. A simple expression for the noise factor increase as a function of the level of the interfering signal is derived. Using this result an expression for the overall blocking level of a receiver, where blocking may take place in the RF-stage and/or in the mixer stage, is developed, and the influence of RF-stage and mixer stage parameters on the overall receiver blocking level is analyzed. The theoretical results are supported by results of measurements on practical receiver circuits.