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gr-bruninga

This project evolved out of several interests. Primarily, I wanted to understand exactly what was happening inside an APRS modem, and design the the best demodulator out there with GNU Radio.

To my surprise, several excellent projects exist which already have this capability. Direwolf (by WB2OSZ) and APRSdroid/javAPRS (algorithm by 4X6IZ) feature extellent demodulation algorithms, tested with the TNC Test CD (WA8LMF).

While this project has 1/10th the functionality of the above programs, it does present an easy to understand and modular approach to demodulating AFSK signals -- particularly in the signal processing realm.

Installing

This package requires GNU Radio 3.7.4 for the HDLC Deframer block. Follow the standard install procedure for other out of tree modules.

git clone https://github.com/tkuester/gr-bruninga
cd gr-bruninga 
mkdir build
cd build
cmake ..
make -j8
make install

If you are using a version of GNU Radio installed via your distribution's repository, you may need to tell cmake.

cmake -DCMAKE_INSTALL_PREFIX=/usr ..

Usage

The easiest way to get started is to hook up a handheld radio (like the UV-5R) to your computer's input, and run examples/aprs-wav.grc

However, you can easily hook a UV-5R (or other radio) to your microphone port, and run examples/aprs-wav.grc.

TODO

  • Separate the TNC/KISS interface into separate blocks
  • Clean up the initial bandpass filter / resampler?
  • Play with bit twiddling to save packets
  • Do BER testing on the demodulator
  • MOAR DOCUMENTATION
  • Add AXPORT input (AX25 to HDLC? Possible modification of string-to-aprs?)
  • Add option for zeros or mute to FSK modulator

Known Issues

  • The ALSA Audio Sink (as of 3.7.5) does not like it when you stop sending it samples. As a work around, the modulator block spits out 0's when no packets are available. This does cause a little lag