Also known as: IF, intermediate frequency

The intermediate frequency (IF) is the fixed, lower frequency that a superheterodyne receiver shifts the wanted signal down to before filtering and digitising.¹ Mixing the variable input frequency to a constant IF lets the receiver use one well-designed filter regardless of the tuned channel.

Mixing the tuned signal to a constant intermediate frequency lets one filter handle any channel.

Overview

Many SDRs use a low-IF or zero-IF (baseband) architecture, where the IF is at or near 0 Hz — convenient for the ADC but introducing a DC offset artefact to manage.

Sources

1. Intermediate frequency — Wikipedia, on superheterodyne downconversion to a fixed IF. ↩

See also

• Superheterodyne receiver
• Local oscillator
• Baseband
• Analog-to-digital converter (ADC)

Learn it step by step

• How an SDR receiver works