SondeFox
The fine print

License, privacy & legal

Everything worth knowing about how SondeFox is licensed, what data leaves your phone (short answer: nothing you decode, and never your position, unless you opt in), what's legal to receive, and whose shoulders this project stands on.

Jump to: License · Privacy policy · Legality & safety · Acknowledgements · Trademarks

License — GPL-3.0-or-later

SondeFox is free software, licensed under the GNU General Public License, version 3.0 or (at your option) any later version. That covers the whole project: the Android app, the portable libsonde C++ decoder core, the Airspy USB bridge, the host-side replay CLI, and the desktop SDR++ plugin.

In practical terms, the GPL means:

  • You can run it — for any purpose, with no fees and no strings.
  • You can study and modify it — the source code is part of the deal, not an afterthought.
  • You can share it — copies and modified versions alike, as long as they stay under the same license (copyleft).
  • Nobody can close it — improvements that are distributed must remain free software.

The choice of license isn't accidental. SondeFox reimplements and takes reference from GPL-family work across the radiosonde and SDR communities (see the acknowledgements below), so GPL-3.0 across the whole project is both an obligation and a thank-you.

Source availability during the closed beta

SondeFox is currently in a closed beta: there is no public download and no public repository yet. That doesn't suspend the license — the app is GPL-3.0, and every distributed build comes with its corresponding source. Beta testers receive the complete source code for each APK they're sent, along with the full GPL rights that attach to it. Third-party provenance is documented in the THIRD_PARTY_NOTICES file that ships with that source.

No warranty

SondeFox is distributed in the hope that it will be useful, but without any warranty — not even the implied warranties of merchantability or fitness for a particular purpose. The full terms are in the license text included with every build.

Privacy policy

Short version

No analytics, no ads, no accounts, no tracking — in the app or on this site. Decoding happens entirely on your phone, and nothing you decode leaves it unless you explicitly opt in. Your own location is never uploaded unless you turn on a separate, clearly labelled chase-car toggle, which is off by default.

The app

  • No analytics, no accounts. The app contains no analytics or advertising SDKs, requires no sign-up, and phones nothing home.
  • Decoding is local. All signal processing and telemetry decoding runs on your device. Location and sensor permissions are used on-device for chase guidance and the compass pointer.
  • SondeHub, reading: the app fetches the public list of active sondes and landing predictions from the SondeHub API. These are ordinary HTTPS requests, so the SondeHub servers see standard request metadata (such as your IP address) — but no account and no identity.
  • SondeHub, writing: strictly opt-in — see the table below.
  • Map tiles: when you're online, the chase map fetches tiles from the map tile provider; like any web request, the provider sees your IP address and which map areas you request. Tiles are cached on-device so chases keep working offline.

SondeHub uploads — all opt-in

Everything you upload to SondeHub joins a public telemetry stream and may be redistributed by SondeHub and downstream projects. The in-app opt-in flow says the same thing before you enable anything.

Upload Default What it contains
Sonde telemetry Off opt-in + callsign required The sonde's position and telemetry, your callsign, and your station metadata (radio/antenna description). Never your own position.
Chase-car position Off separate opt-in Your GPS position, shared as a mobile station. This toggle is the only part of the app that ever transmits your location.
Recovery report Only when you tap “Mark recovered” The sonde's serial, the recovery position, and your notes.

This website

  • Static pages only. No cookies, no trackers, no analytics, no third-party scripts or fonts.
  • Hosting: the site is served through Cloudflare, which — like any host — sees standard request logs (IP address, user agent, requested URL) as part of serving and protecting the site. We add nothing on top.
  • Email: if you write to [email protected], your message is handled like ordinary email and used only to respond and to run the beta program.

Reception legality & field safety

Radiosonde telemetry in the 400–406 MHz band is unencrypted and broadcast as part of the public meteorological service. Receiving it is legal in most jurisdictions — and SondeFox is a receive-only tool; it never transmits.

Check your local law

Legality of reception is the norm, not a guarantee. Rules vary by country, and uploading telemetry or operating radio equipment may have separate local requirements. Know your regulations before you go further than listening.

  • Never transmit without authorization. SondeFox won't do it for you — don't do it yourself either, unless you hold the appropriate license.
  • Never trespass to recover a sonde. Get the landowner's permission first, and let a recovery go rather than take a risk. A dead RS41 in a field is not worth a confrontation, an injury, or a fine.
  • Chirp monitor: authorized signals only. The experimental chirp-spread-spectrum (CSS) monitor is off by default and scoped strictly to signals you're authorized to receive — your own devices, amateur-radio telemetry under your license, and ISM-band experiments. It performs PHY-level bit recovery only: no key extraction, no payload decryption, no private-network interception.

Acknowledgements

SondeFox exists because the radiosonde and SDR communities did the hard work first, in the open. Our sincere thanks to:

  • rs1729 / RS — the definitive open radiosonde decoders, and the protocol and algorithm reference behind our entire RS41 chain: demodulation, Reed–Solomon error correction, CRC, whitening, and geodesy.
  • Project Horus — radiosonde_auto_rx & SondeHub — auto_rx shaped our scanning and detection strategy, and SondeHub is the community tracker that turns sonde chasing into a shared, worldwide sport.
  • Airspy — airspyone_host — the authoritative reference for the Airspy USB protocol that our Android bridge speaks.
  • demantz / airspy_android — the proof, and the design template, that an Airspy can be driven from Android over USB OTG without root.
  • SDR++ — the excellent desktop SDR host our sonde_decoder plugin lives in.
  • MapLibre — the open map renderer behind the chase map and its offline tile cache.

Full third-party provenance — what was referenced, what was reimplemented, and under which licenses — is documented in the THIRD_PARTY_NOTICES file distributed with the source.

Trademarks

Vaisala, Graw, Meteomodem, Intermet, Meisei, and other manufacturer names are trademarks of their respective owners, used here solely to identify the radiosonde models SondeFox can decode or plans to decode. Airspy is a trademark of its owner. Android is a trademark of Google LLC. SondeHub and SDR++ are independent community projects.

SondeFox is an independent project and is not affiliated with, endorsed by, or sponsored by any of the organizations or projects named above.

Questions about the license, this policy, or anything else on this page? Write to [email protected].