How does a superheterodyne receiver work?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

A superheterodyne receiver, introduced by Edwin Armstrong around 1918, mixes the incoming RF with a tunable LO to a fixed intermediate frequency (IF), where fixed high-selectivity filters and most of the gain are applied. Tuning changes only the LO. Its principal design issue is the image frequency, 2·f_IF away from the wanted signal.^[1]^[2]

How is the IF chosen?

High IF: image far from the signal, easy RF image filtering; harder IF channel filtering.
Low IF: easier channel selectivity; image close in and hard to filter.
Dual conversion resolves this: high first IF, low second IF. Classic broadcast receivers used 455 kHz (AM) and 10.7 MHz (FM) IFs.

What spurs must a frequency plan avoid?

Besides the image, the half-IF spur (f_RF ± f_IF/2 mixing via second harmonics), LO harmonics mixing with out-of-band signals, and IF feedthrough. Spur charts and frequency-planning tools check m×n products across the tuning range.^[3]

Where are superheterodynes still used?

Spectrum analyzers and test receivers, satellite and radar receivers, high-dynamic-range communications receivers and many microwave links, often with digital IF sampling as the last stage.^[4]

Frequently asked questions

Who invented the superheterodyne?

Edwin H. Armstrong is usually credited, with related work by Lucien Lévy and Walter Schottky.

Why is IF gain easier?

A fixed frequency allows optimized narrowband amplifiers and filters.

What is a pre-selector?

A tunable or fixed RF filter before the mixer to reject the image and strong signals.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“RF Microelectronics, 2nd ed.”. B. Razavi, Prentice Hall. 2012.
“The ARRL Handbook for Radio Communications”. ARRL. annual editions.
“Mixer and amplifier application notes (e.g., 'Understanding Mixers — Terms Defined, and Measuring Performance')”. Mini-Circuits. application note.
“Spectrum Analysis Basics (Application Note 150)”. Keysight Technologies. application note.

Categories: Receivers and systems

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