README.md

sdrpp-tetra-demodulator

Tetra demodulator plugin for SDR++

Designed to fully demodulate and decode TETRA downlink signals

Thanks to osmo-tetra authors for their great library

Signal chain:

VFO->Demodulator(AGC->FLL->RRC->Maximum Likelihood(y[n]y'[n]) timing recovery->Costas loop)->Constellation diagram->Symbol extractor->Differential decoder->Bits unpacker->Osmo-tetra decoder->Sink

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" \;
   

   Download and patch ETSI TETRA codec(in this repository):

   cd src/decoder/etsi_codec-patches
   ./download_and_patch.sh
   

   Install libosmocore via package manager

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 ~20dB of signal)

4. If the channel is unencrypted, just wait for the voice activity and listen to it!