Tetra demodulator plugin for SDR++

Designed to provide output to tetra-rx from osmo-tetra-sq5bpf

Signal chain:

VFO->Demodulator(RRC->AGC->Maximum Likelihood(y[n]y'[n]) timing recovery->Costas loop)->Constellation diagram->Symbol extractor->Differential decoder->Bits unpacker->Output UDP sender

Building:

0. If you have arch-like system, just install package sdrpp-tetra-demodulator-git with all dependencies

1. Install SDR++ core headers to /usr/include/sdrpp_core/, if not installed (sdrpp-headers-git package for arch-like systems)

   git clone https://github.com/AlexandreRouma/SDRPlusPlus.git
   cd "SDRPlusPlus/core/src"
   sudo mkdir -p "/usr/include/sdrpp_core"
   sudo find . -regex ".*\.\(h\|hpp\)" -exec cp --parents \{\} "/usr/include/sdrpp_core" \;
   

2. Build:

   mkdir build
   cd build
   cmake ..
   make
   sudo make install
   

3. Enable new module by adding

   "Tetra demodulator": {
     "enabled": true,
     "module": "tetra_demodulator"
   }
   

   to config.json, or add it via Module manager

Usage:

1. Find TETRA frequency you want to receive

2. Move demodulator VFO to the center of it

3. After some time, it will sync to the carrier and you'll likely see 4 constellation points(sync requires at least ~10dB of signal)

4. To use osmo-tetra-sq5bpf with it, you need:

   Build osmo-tetra-sq5bpf itself (you can use my version with fixed compilation issues for latest GCC: https://github.com/cropinghigh/osmo-tetra-sq5bpf)

   Configure network address and port, or leave them default.

   Start decoder listening on the required port, for example:

   socat - udp-listen:8355 | ./tetra-rx -s -r -e /dev/stdin
   

   Start network in the module

   If everything was done right, you will see decoded BURSTs from tetra-rx