Variable capacitors are used in tuning many circuits of radios. I read the theory of basic tuning and resonance frequency. What I understand by changing the capacitor we change the resonance frequency of the radio tuner and select a particular frequency. My question is:
1) What is selected here? Carrier frequency or signal e.g audio frequency? They have totally different frequency bands. If carrier wave is selected, why the modulated lower freq. audio also pass through the circuit. Isn't it contradicting to the theory?
2) If one tunes a receiver circuit to a frequency how can a band of frequencies like audio signals pass through. I mean tuning seems to let pass only 1 particular frequency not a band.
I'm afraid I lost the route at points when trying to understand and confused.
Best Answer
Tuning a radio to a particular station using a tuning capacitor or any other method selects the carrier frequency.
The frequency-selective circuits in a radio are not "perfect" - they allow a band of frequencies to pass, not just a single discrete frequency, so the carrier and the sidebands generated by the modulating signal (audio) can apss through the RF and IF stages of the receiver.