msdr

Signal discovery, decoding and listening tools for SDRconnect.

msdr runs alongside SDRconnect and connects through its WebSocket API. No build step.

• Discover and decode signals, track satellites
• Keep a journal of what you hear, and save receiver setups to return to
• Passive Wi-Fi, BLE and drone Remote ID, with separate hardware, not the SDR (Optional software)

Every label shows its source: DSP measurement, decoded payload, schedule, band allocation or your note. A schedule or band-plan match is a hint, not proof of reception. Levels are relative, not calibrated. msdr never transmits.

Tested on macOS with SDRconnect 1.0.10 and an RSPdx-R2.

Quick start

Requirements: Python 3.11+, SDRconnect 1.0.9+ (WebSocket API 1.0.3), macOS. Windows and Linux are untested.

1. In SDRconnect, enable Primary SP “…” → Preferences → WebSocket Server on port 5454.

2. Clone, install and start msdr:

   git clone https://github.com/gdamdam/msdr && cd msdr
   pip install .        # or: pipx install .
   msdr

3. Open 127.0.0.1:8765 and press Play in SDRconnect.

4. Follow the Getting Started checklist at the top of the page. Press S to save the current receiver state. Cmd/Ctrl-K tunes by typed frequency (e.g. 145.800 or 1090M); search results appear once you have saved signals or imported catalogs.

msdr --no-browser runs it headless. Your library stays browsable and editable while SDRconnect is closed.

Optional software

msdr runs with SDRconnect alone. Each item below only switches on the feature named; the app shows it as missing, with an install hint, until it is found. Command-line tools are looked up on PATH and in ~/.local/bin.

For	Install
POCSAG, FLEX, EAS, APRS 1200/9600, DTMF, CW	multimon-ng: build from source, copy to ~/.local/bin
AX.25 300 baud packet	brew install direwolf
RTTY cross-check	brew install minimodem (the built-in RTTY decoder needs nothing)
DMR, P25, NXDN, D-STAR, YSF, dPMR, M17	dsd-fme: build from source (mbelib, itpp, libsndfile, ncurses from Homebrew), copy to ~/.local/bin
ISM sensors, wireless M-Bus	brew install rtl_433
FreeDV 700D/700E/1600 (text and sync only)	brew install codec2 (provides freedv_rx)
DFM, M10, M20, RS92 radiosondes	dfm09mod, m10mod, m20mod, rs92mod: build demod/mod from radiosonde_auto_rx with make, copy to ~/.local/bin
FT8	WSJT-X (jt9 on PATH or inside wsjtx.app)
Wi-Fi networks	An ALFA AWUS036ACH and the msdr-wifi-capture helper: docs/wifi.md
BLE advertisements	A Bluetooth 4 USB dongle (brew install libusb) or a SONOFF ZBDongle-P with Sniffle firmware, plus pip install '.[ble]': docs/ble.md
Satellite passes	nextpass: pip install git+https://github.com/gdamdam/nextpass
IQ recording analysis	iqscan: pip install git+https://github.com/gdamdam/iqscan
JS8Call, Winlink, FreeDATA messages	The JS8Call, Pat or FreeDATA application, running (Setup → Integrations)

Built in, nothing to install: LoRa (Meshtastic and MeshCore headers), ADS-B / Mode S, ACARS, AIS, RS41 radiosondes, Orbcomm satellite downlinks (synthetic-validated only), DSC, WEFAX, SSTV, NAVTEX, RTTY, PSK31, HF ALE, WWV/WWVB/DCF77/MSF/JJY/CHU time codes, End-of-Train, VOR and ILS.

Features

msdr is organised into nine workspaces.

Workspace	What it does
Listen	Live survey beside the Listen panel (recent, favourites, nearby, suggestions, channel watch, log), decode deck, IQ recording, antenna and mode locks.
Discover	Live survey, Discovery inbox, saved signals and decodes, Wi-Fi, BLE, Remote ID, Timeline, watch rules and NCDXF/NDB beacons.
Map	Aircraft, vessels, radiosondes, APRS and DSC traffic with a position.
Band scans	The list of range scans with each report: coverage, findings, session comparisons and exports.
Review	Recordings, replay, Scope, messages and observations.
Satellites	Pass predictions, sky tracks and Doppler tracking.
Library	Memories, profiles, notes, tags, lists, favourites, recordings and tune history.
Catalog	Imported station schedules and reference directories: search, on-air first, sort by frequency, time, name or distance, tune.
Allocations	The US Table of Frequency Allocations as a zoomable chart and list.

A few things that are less common elsewhere:

• Channel watch follows a list of frequencies and captures activity with a pre-roll IQ recorder, so the start of a burst is on disk before you press record.
• Band scans keep a report of what was found and what was actually covered, so a quiet frequency and an unscanned one are not confused.
• Any saved signal can be exported as an evidence ZIP: observations, claims, decoder versions, notes and a short IQ clip when one exists.

The user guide covers every workspace in detail.

Decoders

Raw-IQ decoders (ADS-B / Mode S, RS41, FT8, DSC, End-of-Train, VOR, ILS, LoRa) run on the live channel and on recordings in Review. Audio decoders run beside them, including Radiofax (WEFAX) and SSTV. Open Decode setup (⚙) to pick decoders; Messages shows the decoded history.

A decoder shows Ready when its code or tool is installed. That does not mean it has been validated on real signals; see decoder scope and evidence.

Lawful use. msdr is receive-only: it never transmits, and its Wi-Fi and BLE features only listen to frames that devices broadcast. Laws on monitoring radio traffic, and on recording or disclosing what is received, differ by country and by service (for example pager, land-mobile and digital-voice systems). You are responsible for complying with the law where you operate.

Per-decoder notes: ADS-B · LoRa / mesh · FT8 · RS41 · DSC · SSTV · user guide → Decoders

Configuration

• Data and settings live in ~/Library/Application Support/msdr/.
• CLI flags: --host (SDRconnect host), --port, --web-port, --db, --settings, --no-browser, --debug (also log every HTTP request). See msdr --help.
• Access: the web UI listens on 127.0.0.1 only.
• Live data needs SDRconnect playing. Satellite features need your location and orbital elements (↻ TLE in the app).
• Device history (Wi-Fi/BLE) is off by default; enable it with "history": {"enabled": true} in settings.json.
• Theme: the ◐ button in the instrument strip cycles Default, Midnight, Blueprint, Avionics and Monochrome (remembered per browser).

Keyboard shortcuts

Key	Action
Cmd/Ctrl-K	Search and tune
Cmd/Ctrl-Z	Undo settings, tuning and library edits
Cmd/Ctrl-Shift-Z	Redo the last undone change
S	Save current receiver state
Cmd/Ctrl-[ / Cmd/Ctrl-]	Back / Forward
E / I	Edit memory / identify
F	Edit VFO frequency
R	Start or stop pre-roll recording
← / →	Step VFO; Shift for ×10, Alt for ×0.1
,	Open Setup
Esc	Close palette, drawer or frequency editor

Frequency input accepts 137.9, 137900k, or 14.230 MHz.

Docs

• User guide: every feature in detail
• Catalog sources · Reference catalogs · Frequency allocations
• Passive Wi-Fi · Passive BLE · Device history and timeline · Remote ID
• Integrations: JS8Call, Winlink, FreeDATA · Receiver DSP · Discover map
• Architecture: how the code is organised

Development

python3 -m venv .venv
.venv/bin/pip install -e ".[dev]"
.venv/bin/python scripts/dev_fake.py      # fake receiver on port 5455
.venv/bin/msdr --port 5455                # in another terminal
.venv/bin/pytest -q -W error && .venv/bin/ruff check msdr tests scripts

One Python process: a RadioAdapter boundary to the receiver, SQLite storage with numbered migrations, a FastAPI backend and a no-build Lit UI. See Architecture.

How it's built

msdr is a free, non-commercial project, built out of love for radio. It was developed with AI coding tools; every change was designed, reviewed and tested by a human, on real hardware (RSPdx-R2).

Credits and license

msdr's original code is licensed under GPL-3.0-only. Third-party code, models and data keep their own terms; see THIRD_PARTY_NOTICES.md.

Receiver and platform

• SDRplay's SDRconnect WebSocket API (the receiver msdr drives).
• Python dependencies: FastAPI, Uvicorn, websockets, Pydantic, Skyfield and NumPy.

Bundled code

• Lit 3.2.1 (BSD-3-Clause) and Leaflet 1.9.4 (BSD-2-Clause) in the UI.
• Decoder and demodulator code adapted from SDRangel and gr-lora_sdr (GPL-3.0); authors and details in THIRD_PARTY_NOTICES.md.

Separately installed tools (not bundled)

• Decoders: WSJT-X jt9, multimon-ng, minimodem, direwolf, dsd-fme; FlightAware dump1090-fa as an alternative ADS-B backend in the code (the built-in decoder is the default).
• Satellite passes: nextpass; IQ analysis: iqscan.
• Passive Wi-Fi: the rtl8812au-macos userspace driver (GPL-2.0-only, derived from aircrack-ng/rtl8812au and Realtek code), run as its own program; msdr only reads its PCAP output.

Data

• Orbital elements: CelesTrak. Map tiles: © OpenStreetMap contributors.
• Frequency allocations: NTIA Table of Frequency Allocations and 47 CFR §2.106 (US government works).
• Broadcast and signal catalogs: EiBi, HFCC, Aoki, NDXC, NOAA radiofax, SigIDWiki, Priyom and SatNOGS, under each source's terms.
• Reference catalogs: NIST time stations, FAA NASR navaids, IOOS HFRNet radar sites and SuperDARN radar hardware tables (identifiers and locations only; SuperDARN data use is governed by its PI agreement).
• Test fixtures: "SSTV sunset audio" by Mysid, CC BY 2.5, via Wikimedia Commons.
• SSTV mode timings follow JL Barber (N7CXI), "Proposal for SSTV Mode Specifications" (2000).