SondeChase weather balloons with a phone and an SDR.
SondeFox turns an OTG-capable Android phone and an Airspy SDR into a complete radiosonde chase rig — scan the 400–406 MHz band, decode telemetry, and follow the flight on a live map all the way to recovery. No root, no drivers: the app talks to the Airspy directly over USB-OTG.
Live interactive preview — tap the bottom tabs
Everything between the first peak and the recovered sonde
One app covers the whole chase: detection, decoding, navigation, the on-foot search, and reporting back to the community.
Band scan & decode
Sweep the full 400–406 MHz radiosonde band and auto-lock when a sonde header correlates. Vaisala RS41 decodes today — serial, GPS, PTU, and Reed–Solomon error correction — with DFM and M10/M20 decoders in validation.
Chase map
A real MapLibre map with markers for you, the sonde, and the predicted landing point, plus the flight track. Tiles cache for offline use, so the chase keeps going when coverage drops.
Compass pointer
A Find-My-style arrow to the sonde: declination-corrected to true north, with live distance and bearing, color-coded as you close in — green under 100 m, amber under 1 km.
Signal Hunt heat-map
For the last few hundred meters on foot: your receiver position and signal strength are painted onto the map as a heat-map, so you can triangulate a sonde in a cornfield. Auto-activates within about 1 km.
SondeHub, both directions
See what other stations hear before you decode anything locally, pull community landing predictions, and — strictly opt-in — contribute telemetry and recovery reports. Uploads are off by default.
Open source core
One portable C++17 decoder core, libsonde, powers the Android app, a host replay CLI, and a desktop SDR++ plugin. GPL-3.0, built on the shoulders of the radiosonde and SDR communities.
The full chase loop
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Scan the band
Plug in the Airspy over OTG, open Spectrum, and watch peaks appear across 400–406 MHz. Auto-lock engages when a sonde header correlates.
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Lock & decode
Frames flow through error correction into the Sondes list: type, serial, position, altitude, climb rate, and signal quality, updating live.
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Drive with map and compass
Start Chase for GPS-guided navigation — the map shows the track and predicted landing, and the compass pointer keeps the bearing in view.
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Signal-hunt on foot
Inside roughly a kilometer, the Signal Hunt heat-map takes over. Walk the field, watch the hot spots build, and home in on the strongest samples.
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Mark it recovered
Sonde in hand, tap Mark Recovered to file a SondeHub recovery report so the next chaser knows this one is already off the board.
A whole chase rig in your pocket
An honest word about the beta
The Vaisala RS41 is the working decoder: validated end-to-end against synthetic signals, with live over-the-air reception from a real Airspy the next thing to prove — which is exactly what the beta is for. DFM06/09/17 and M10/M20 decoders are implemented but still in validation against real signals, and iMet, LMS6, Meisei, MRZ, and MTS01 are roadmap only. A few conveniences, like tapping a spectrum peak to tune, aren't wired up yet.
The honest, per-type breakdown lives in decoder support — and if that page reads like your kind of project, the beta program is open for testers.
Foxes wanted.
We're inviting a small group of sonde chasers with an Airspy Mini or R2 and a launch site within driving range to help validate SondeFox in the field. Free, open source, and honest about what works.