Rca1948FrequencyModu.. - The New Jersey Antique Radio Club

256 FREQUENCY MODULATION, Volume Ithe frequency drift is proportional to the intermediate frequency. Thisinfluence of intermediate-frequency value on frequency and regenerationstability is the principal difficulty involved in the use of a highintermediate frequency and must be weighted against the advantageof high intermediate frequency in reducing spurious responses. Designexpedients, such as impedance distribution or neutralization may beused to minimize the regeneration stability influence and expedientssuch as cathode degeneration used to minimize frequency-stabilityproblems.ConclusionsIt has been shown that the use of an intermediate-frequency valuehigher than 4 megacycles materially reduces the probability of spuriousresponses, but at the same time may entail some sacrifice in gain andfrequency stability.It would appear therefore, that for receivers designed to operateon weak signals, where spurious responses are unlikely, a relativelylow intermediate frequency of 4.3 megacycles or 5.38 megacycles ispreferable. However for a considerable part of the service area, wheresignal intensities are high and spurious responses likely, high sensitivityis not required and an intermediate frequency of 8.26 megacyclesor even 11.45 megacycles has much to recommend it. Where a receiveris designed to operate over a wide range of signal intensities, it maybe preferable to use a relatively high intermediate-frequency value tominimize spurious responses, using impedance distribution or neutralizationprinciples, and if necessary an additional stage to obtain therequired high gain with stability.