Faults on frequency-changer circuits
In the average circuit diagram the frequency-changer (FC) stage appears to be the most complicated part of the radio receiver. This is due mainly to the waveband switching arrangements, which are only too often drawn in a spidery fashion with lines crisscrossing each other all over the place. It is much more helpful initially to regard the FC as a single waveband device, as in Figure 23.1, with the items in the broken line boxes being those which are concerned purely with tuning. Note that the two coils in the local oscillator circuit (extreme right) are shown as having variable iron-dust cores, and that the padder, C11, is shown as a semivariable condenser. This is to illustrate both possible arrangements; ...
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