Also known as: digital down-converter, DDC

A digital down-converter (DDC) shifts a chosen channel within a wideband IQ stream to baseband using a numerically controlled oscillator (a software local oscillator), then filters and decimates it.¹

A digital down-converter shifts a channel to baseband (NCO), filters it, and decimates — the heart of channelising.

How it works

Multiplying the IQ by a rotating tone centres the target channel at zero frequency; a low-pass filter isolates it and decimation lowers the rate. Many DDCs can run in parallel from one capture.

Relevance to SDR

The DDC is how GopherTrunk extracts a control channel and multiple voice channels from a single wideband capture.

Sources

1. Digital down converter — Wikipedia, for the NCO/filter/decimate channelization architecture. ↩

See also

• Local oscillator
• Decimation
• Digital filter
• IQ data
• Demodulation

Learn it step by step

• Filtering & decimation

From the blog

• SDR Internals, Part 5: Tuning & channelization