Re: Number of tuned circuits in a set
You need to differentiate *where* these tuned-circuits are.
A typical medium/long-wave broadcast/entertainment radio will have one signal-frequency tuned-circuit [ahead of the frequency-changer] and then usually four IF tuned-circuits [between the mixer/IF-amp/detector].
That's just fine on medium/long-waves, for receiving AM broadcasts.
When you move to short-wave reception you need additional selectivity - first, ahead of the mixer [to cut down on 'image' signals] and secondly, in the IF stages to give better exclusion of 'adjacent channel' signals.
So a receiver optimised for short-wave 'communications' service may have three or four signal-frequency tuned-circuits [and two RF-amplifier stages], and six, or maybe even eight, intermediate-frequency tuned-circuits [with two or three IF-amplifier stages].
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