Raspberry Pi SDR
What it is
A small, self-contained device that receives radio signals and plots their IQ data live on a touchscreen — and demodulates the same signal to audio so you can hear what you’re looking at. It’s built entirely from off-the-shelf parts and open-source software:
- Raspberry Pi 5 mounted behind a touchscreen (on a touchscreen stand)
- RTL-SDR v5 USB dongle as the receiver
- USB soundcard / speaker for the demodulated audio
The signal processing is a GNU Radio flow graph: it takes IQ samples from the USB dongle, selects the region of interest from the captured bandwidth, plots the IQ, demodulates to audio, and sends that audio to the speaker.
Why I built it
IQ is the foundation of every modern software-defined radio, but it’s usually buried inside the software and never seen. I wanted a physical object I could put on a table in front of people — tune it to a real signal and let them watch the constellation move while hearing the audio at the same time. Seeing an AM carrier trace a line, an FM signal ride a circle, and FT8 hop between eight tones does far more than a slide ever will.
It’s a demonstration tool for the IQ talk more than an instrument, which is why it’s deliberately built from cheap, easily-sourced components that anyone could copy.
Current status & goals
- Built and working, and used live as part of the Making the invisible visible talk.
- Plots IQ and demodulates to audio simultaneously from a single RTL-SDR.
- Also used with a range of other SDR hardware during development: an SDRplay RSPdx-R2, a LibreSDR (Ettus B210 clone), and a FlexRadio 8400.
- Goals: tidy the flow graph for general use and publish it, so anyone can build the same device from the parts list.
Key links
- sdrplay-gnuradio-examples — my GNU Radio flow graphs
- Setup guide for IQ visualisation — how to get started with this yourself
- GNU Radio — the DSP environment
- Radioconda — pre-packaged GNU Radio with SDR driver support
- RTL-SDR — the receiver dongle
The flow graph for this specific device is still being tidied for release — in the meantime it’s available on request, get in touch.
