A radio receiver selects and detects an incoming radio wave; its frequency selection affects which signals reach its output.
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As well put by Wikipedia, a radio receiver has to perform three functions on the signal from the antenna:
- filtering, so you can tune the station you care about. This filters based on the frequency of the carrier wave you want. I.e. you use a bandpass filter.
- amplification: otherwise you won't be able to hear anything if the emitter is too far away
- demodulation: this means decoding the signal based on whatever way it was encoded, notably e.g. AM/FM