I have question about specifically FM radio receiver that use the heterodyne principle:
How Intermediate Frequency, that's fixed in one frequency (10.7 Mhz), works in FM receivers if FM radios need frequency modulation to pass a useful signal?
Does the mixer with local oscillator in a FM receiver pass a bandwidth or just one frequency?
Best Answer
The incoming radio signal isn't mixed down to exactly 10.7 MHz, that would be pointless. Rather, the incoming signal (which varies in frequency) is mixed with a stable local oscillator; the result is a signal that has the same frequency variations but centered around 10.7 MHz.
This intermediate frequency is filtered through either tuned LC circuits or a ceramic resonator, but these circuits are not so narrow-banded that the frequency deviation is lost. The frequency swing of commercial FM stations is +- 75 kHz anyway, or 0.075 MHz, less than 1% of the IF frequency.