Also known as: superheterodyne receiver, superhet

A superheterodyne receiver uses a mixer driven by a local oscillator to shift a chosen band down to a fixed intermediate frequency (IF) — or to baseband — where it is easier to filter and detect.¹

A superheterodyne receiver mixes the wanted signal down to a fixed intermediate frequency for easier filtering.

How it works

Tuning is just changing the local-oscillator frequency so the wanted band lands at the fixed IF. SDR quadrature front-ends apply the same idea, mixing to baseband as IQ before the ADC.

Relevance to SDR

Understanding the mixer/LO explains why “tuning” an SDR is simply setting a number, and how a digital down-converter does it in software.

Sources

1. Superheterodyne receiver — Wikipedia, on mixing a band down to a fixed intermediate frequency. ↩

See also

• Local oscillator
• Digital down-converter (DDC)
• Analog-to-digital converter (ADC)
• Software-defined radio (SDR)

Learn it step by step

• How an SDR receiver works