# Pico SDR

Using RP2040 / Raspberry Pi Pico as a software-defined radio receiver.

See the [blog post](https://blog.porucha.net/2024/pico-sdr/) for more information. Older code the article is mostly referring to can be found in the branch `old` and a more up-to-date approach in the branch `master`.

This branch contains code to use RP2040 with a 1:4 multiplexer and some passives as a quadrature sampling decoder receiver. It is still very much work in progress.

## Software

1. Clone using `git clone --recursive` as this package is using a custom USB
   stdio library for better throughput and to avoid deadlocks.

2. Build and flash the firmware as usual:

   ```bash
   export PICO_SDK_PATH=/path/to/pico-sdk
   cmake -B build src
   cmake --build build
   picotool load -f build/pico_sdr.uf2
   ```

3. Start the USB serial to TCP bridge:

   ```bash
   python util/bridge.py
   ```

   You need to have PySerial and Click packages installed.

4. Open `grc/PicoSDR-WBFM.grc` in GNU Radio Companion, adjust carrier frequency to match your favorite FM radio station and press `F6`.

5. Alternatively [gqrx](https://www.gqrx.dk/) works fine with `rtl_tcp` input mode. Maximum sample rate seem to be 400 ksps, above that the samples are dropped. Make sure to experiment with LNA gain. It might be digital, but it's supposed to be somewhere north of 12 dB.