he Superheterodyne receiver (or to give it its full name, The Supersonic Heterodyne Receiver – usually these days shortened to superhet) was invented by Edwin Armstrong in 1918.

The Super Heterodyne principle, as used in radio receivers, allows certain obstacles in high performance radio design to be overcome. Tuned radio frequency (TRF) receivers suffered from poor frequency stability, and poor selectivity, as even filters with a high Q factor have a wide bandwidth at radio frequencies. Regenerative and super-regenerative receivers offer better sensitivity but suffer from stability and selectivity problems.

In radios using the principle, all signal frequencies are converted typically to a constant lower frequency before detection. This constant frequency is called the intermediate frequency, or IF. In typical AM (Medium Wave) home receivers, that frequency is 455 kHz, for FM VHF receivers, it is usually 10.7 MHz.

Super Heterodyne receivers "beat" or heterodyne a frequency from a local oscillator (within the receiver) with the incoming signal. The user tunes the radio by adjusting the set's oscillator frequency and/or the tuning of the incoming signals. This heterodyning results in a higher and a lower frequency than that of the incoming frequency. Either the higher or the lower (typically) is chosen as the IF, which is amplified and then demodulated (reduced to just audio frequencies through a speaker).

Almost all receivers in use today utilize this method. The diagram below shows the basic elements of a single conversion superhet receiver. In practice not every design will have all these elements, nor does this convey the complexity of other designs, but the essential elements of a local oscillator and a mixer followed by a filter and IF amplifier are common to all superhet circuits.