FM Receiver Overview
There are many different types of radio receiver circuits, and all of them work in different ways. The primitive crystal radio receiver is so simple that it can be easily built by a child, while a more modern radio receiver needs to be carefully designed, built and tuned to work properly. The most common type of radio circuit in modern equipment is the superheterodyne receiver. It is very stable and has much better sound quality than simpler radio circuits.
Detection and Signal Amplification
FM signals are powerful electromagnetic waves traveling through the air. When these waves encounters an antenna, it gets converted into an electric signal in the antenna. Then, an amplifier is usually used to increase the strength of that signal. The radio signal only generates a very week current in the antenna. Before it can be processed, it needs to be amplified.
Mixing
A superheterodyne receiver has a built in oscillator, a device which produces an electromagnetic signal of its own. The signal produced by the oscillator and the original radio signal are mixed together by the mixer. This produces a signal at a certain special frequency, called the intermediate frequency (IF). The rest of the radio circuit is tuned to the intermediate frequency. It is easier to build circuits that work very well for just one frequency than circuits that work for a wide variety of different frequencies, which is part of the reason why a superheterodyne radio works so well.
Filtering and Demodulating
The new IF signal is run through a filter which removes any signals not at the correct frequency. This removes other bands of radio, and any other distortion that may have crept in. Then, the IF is amplified. After that, the signal goes to the demodulator. The demodulator detects tiny increases and decreases in the speed of the IF signal, and turns these into an audio signal. That signal is amplified one more time, and then fed into the speakers.
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