Raspberry Pi SDR
What it is
A small, self-contained device that receives radio signals and plots their IQ data live on a touchscreen, then 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 and 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 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, which covers getting 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, so do get in touch.
