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9-2: Superheterodyne Receivers
Mixers and Local Oscillators
The output of the RF amplifier is applied to the input of the mixer.
The mixer also receives an input from a local oscillator or frequency synthesizer.
The mixer output is the input signal, the local oscillator signal, and the sum and difference frequencies of these signals.
A tuned circuit at the output of the mixer selects the difference frequency, or intermediate frequency (IF).
The local oscillator is made tunable so that its frequency can be adjusted over a relatively wide range.