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9-2: Superheterodyne Receivers
Superheterodyne receivers convert all incoming signals to a lower frequency, known as the intermediate frequency (IF), at which a single set of amplifiers is used to provide a fixed level of sensitivity and selectivity.
Gain and selectivity are obtained in the IF amplifiers.
The key circuit is the mixer, which acts like a simple amplitude modulator to produce sum and difference frequencies.
The incoming signal is mixed with a local oscillator signal.