Also known as: upconverter

An upconverter is an external device that shifts HF signals up into the tuning range of a VHF/UHF SDR such as an RTL-SDR, letting radios that cannot tune HF directly receive shortwave.¹

An upconverter shifts HF signals up into the RTL-SDR's tunable range, since the dongle can't reach HF directly.

How it works

It mixes the incoming HF signal with a fixed local oscillator (commonly 100–125 MHz), so a 7 MHz signal appears around 107–132 MHz where the dongle can tune. Software subtracts the offset to show true frequencies.

Relevance to SDR

An upconverter is the budget route to HF on an RTL-SDR; a dedicated Airspy HF+ is the higher-performance alternative.

Sources

1. Frequency mixer — Wikipedia, on the mixing principle an upconverter uses to shift HF up into a VHF/UHF tuning range. ↩

See also

• RTL-SDR
• Airspy HF+
• Frequency bands (HF/VHF/UHF)
• Local oscillator

Learn it step by step

• Frequency, bands & the spectrum