An open-source, console (no-GUI) RTL-SDR receiver for ITC — the 220 MHz Positive Train Control radio system used by North American railroads.

OpenITC captures I/Q directly from an RTL-SDR (with bias tee support for inline LNAs), tunes to ITC channels, and fully decodes the ITC air interface in-process: demodulation, sync, forward error correction, and link-layer packets such as base beacons (type 0x02). No external binaries are required.

This is a clean-room reimplementation. It is an independent, unofficial project and is not affiliated with or endorsed by any railroad, ITC, or vendor.

• Native RTL-SDR capture: tuner, gain, ppm, and bias tee.
• Channelizer: mix a 25 kHz ITC channel to baseband and decimate (HR 96 kHz, FR 192 kHz).
• π/4-DQPSK differential demodulation with 64-bit unique-word sync.
• K=7 rate-1/2 convolutional (Viterbi) header FEC.
• Block de-interleave, RS(16,12) Reed–Solomon over GF(2^8), CRC-16/ARC.
• Packet decode, including full 0x02 base-beacon fields.
• monitor: wideband scan of the whole band, listing packets live until stopped.
• openitc-gui: a desktop dashboard (Dear ImGui + GLFW) with a live beacon map, dual local/ITC clocks, an active-WIU board, and a syntax-highlighted frame log. Built as a Windows GUI app (no console window).

• M0 — native RTL-SDR capture with bias tee, tuner/gain/ppm
• M1 — decimation + channelizer (960 kSa/s → 192 kSa/s baseband)
• M2 — π/4-DQPSK demodulator + 64-bit sync
• M3 — K=7 Viterbi header FEC
• M4 — RS(16,12) + CRC-16/ARC + header/packet decode
• M5 — 0x02 base beacon decode & display
• M6 — all-channel monitor

frequency = 217587500 + channel * 25000 (Hz). Channel 102 (220.1375 MHz) is the national/common channel; bases beacon there announcing their local channel. The 27 on-air channels span 220.1125–221.9875 MHz (1.875 MHz).

• Modulation: π/4-DQPSK, 12 samples/symbol (HR 8 ksym/s, FR 16 ksym/s).
• 64-bit unique word: ASCII f337eeb637660672 (hex, MSB-first).
• Header: 48 coded bits → K=7 rate-1/2 Viterbi → 24 bits (length 9b, mode 4b, type 8b, 3b LFSR check, poly 0xb).
• Data: block de-interleave → RS(16,12) (GF(2^8), poly 0x11d, fcr 0, 4 roots) → CRC-16/ARC (0xA001) → payload.

Full details, including the reverse-engineering notes, are in docs/reverse-engineering.md.

pacman -S --needed mingw-w64-x86_64-gcc mingw-w64-x86_64-cmake \
    mingw-w64-x86_64-ninja mingw-w64-x86_64-rtl-sdr mingw-w64-x86_64-zeromq
cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release
cmake --build build

The runtime DLLs (librtlsdr, libusb-1.0, libzmq, libsodium, GNU runtime) must sit next to openitc.exe or on PATH. On Windows the RTL-SDR dongle also needs a WinUSB driver (e.g. via Zadig).

# List RTL devices
./build/openitc -l

# Monitor the whole PTC band: channelize + decode every channel, list packets
# live until Ctrl-C.
./build/openitc monitor -g 40.2 -b 1

# Decode one channel live (FR or HR):
./build/openitc demod -c 142 -m FR -s 960000 -g 40.2 -b 1 -n 3840000

# Decode an offline baseband capture (interleaved complex float32):
./build/openitc demod -f ch142.cf32 -m HR -E 4

monitor prints, as packets arrive:

[15:09:15] ch142 FR  type=05 5       len=12  38282dbd00004040c0000000
[15:09:17] ch142 FR  type=34 34      len=11  a5e904ce44820ac7c58440
[15:09:32] ch142 FR  type=02 beacon  len=27  id=38282d lat=41.831817 lon=-80.768800 ch=142 rate=1 util=17 list=167,166,165,153,142,127

monitor options: -t <ms> chunk size (default 250), -C <s> per-packet repeat cooldown (default 8), -E <n> max sync errors (default 8), plus -d/-s/-g/-e/-b.

Each line shows time, channel, rate (FR/HR), the link type, and decoded fields. Link types: 0x01 QSTAT, 0x02 beacon, 0x03 ACK, 0x04 ACQ, 0x05 CNTL (TID + Seq# + data), 0x06 TIME (UTC date/time), 0x07 T07, 0x33/0x34 WIU status, 0x70 unicast. Beacons show radio id, lat/lon, local channel and channel list; TIME shows the base's UTC clock; CNTL shows the transmitter TID, sequence number and payload; WIU (0x33/0x34) shows the wayside unit ID plus a best-effort switch/signal indicator decode (the exact per-WIU layout is normally configured in ITCMon, so the raw indicator bytes are always shown too).

# Launch the desktop dashboard (no console window)
./build/openitc-gui.exe

The dashboard has a header (SDR status chips and dual local / ITC (UTC) clocks with drift), a sidebar (session state, active WIUs, latest beacon), a live beacon map and a colorized raw frame log with type/text filters and pause/clear/export.

• The map uses Esri World Imagery (satellite) tiles, cached under %LOCALAPPDATA%\OpenITC\tiles. Override the provider with environment variables: OPENITC_TILE_URL (supports {z}/{x}/{y} or {z}/{y}/{x} and {key}), OPENITC_TILE_UA (User-Agent), and OPENITC_TILE_KEY.
• The SDR selector lists detected RTL-SDR devices; gain/AGC, ppm, bias tee and chunk are configurable (restart to apply).
• Decoded packets are recorded to %LOCALAPPDATA%\OpenITC\openitc.db (SQLite).

# Capture raw I/Q on channel 102 with bias tee enabled
./build/openitc -c 102 -s 960000 -g 40.2 -b 1 -n 960000 -o ch102.iq

# Channelize a channel to baseband (complex float32)
./build/openitc -c 142 -s 960000 -R 192000 -n 19200000 -o ch142.cf32

openitc decode is a legacy path that shells out to a reference binary; the native demod/monitor commands above are self-contained.

GPL-2.0-or-later (see LICENSE).