Mixer Converter Circuits

In 2011, designing a frequency converter circuit consists in most cases of picking out an IC that has the characteristics you need from a gain and mixer spurious product standpoint, add a couple filters, and a power supply. In many cases the oscillator is part of the IC. Of course there are special cases where you have to use a basic mixer and do everything yourself, but even that is simpler than designing a tube circuit.
Mixer Converter Circuits - schematic

It really is amazing what engineers and hobbyists of yore were able to accomplish using point-to-point wiring and a slide rule. Here is a good article form the February 1941 QST magazine that discusses some of the considerations. Maybe you have an old radio that this knowledge will apply to. THE design of an efficient mixer or converter circuit is often the one thing that prevents the amateur from building his own communications receiver. In application the amateur usually is unable to tell whether or not the stage is giving normal performance and, lacking equipment for checking gain, no attempt is made to find out if it is doing the job efficiently. However, there are simple ways of determining whether or not a mixer or converter is operating efficiently, and it is the purpose of this discussion to explain these methods and to give some theory on the operation of converters. The general characteristics of the several mixers and converters now available are also given, with a general discussion of the performance characteristics of each. An elaborate mathematical theory of the operation of a converter or mixer1 is of no great importance for our particular problems. Roughly, a converter operates as follows: Within the tube there is developed a current at oscillator frequency which is modulated by the incoming signal to produce an intermediate frequency. The ability of the tube to develop a current at an intermediate...

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