superhet

A superheterodyne receiver, or superhet, is a radio receiver architecture that converts a received radio frequency signal to a fixed intermediate frequency (IF) by mixing it with a locally generated signal from a local oscillator. The mixer yields sum and difference frequencies, and the difference frequency is selected as the IF, which is then amplified and filtered. By keeping the IF fixed, highly selective, stable amplification stages can be used, improving selectivity and sensitivity across a wide tuning range.

One challenge of the superhet is the image frequency problem: a signal at a different RF frequency can produce the same IF after mixing. Image rejection is achieved with a strong RF front end, selective prefilters, and, in many designs, by choosing high-side or low-side injection or by using a second conversion stage to improve separation.

Typical signal flow includes an RF front end with a preselector, a mixer with a local oscillator, an IF filter and amplifier chain, and a detector or demodulator followed by audio or baseband processing. For AM, envelope detection or product detectors are common; for FM, dedicated demodulators are used after the IF. Some configurations employ double conversion to enhance image rejection, while modern implementations may incorporate digital signal processing or software-defined radio techniques after the IF or at the baseband.

The superheterodyne design dominated mainstream radio receivers in the 20th century due to its reliable tuning, stable selectivity, and ease of implementation. It is associated with Edwin Howard Armstrong, who developed and refined the concept in the early days of radio, laying the foundation for many contemporary receiver architectures.