SondeFox

Closed beta

Getting started

From a sealed Airspy box to your first decoded RS41 frame. This guide takes you through installing the beta build, the five settings that matter on first run, and a start-to-finish chase.

Who this guide is for

SondeFox is in closed beta. If you're reading this, you're probably one of a small group of radiosonde chasers helping us validate the app against real launches — thank you. The RS41 decode chain is validated end-to-end against synthetic signals; what the beta exists to prove is live over-the-air performance across real launches, phones, antennas, and sites. Expect rough edges, and please report them to beta@sondefox.com.

Not in the beta yet? Request an invite, or poke around the live demo in your browser — no hardware needed.

What you need

  • An Android 10+ phone or tablet with USB-OTG support (no root required)
  • An Airspy Mini or Airspy R2 — these are the only supported receivers; RTL-SDR is not supported
  • A USB-OTG cable — a powered OTG hub is recommended, since the Airspy draws significant current
  • An antenna for 400–406 MHz: a quarter-wave whip (~17 cm) is fine to start; a small Yagi helps on the ground

For the full parts list, gain-preset details, and antenna notes, see the hardware guide.

Install the beta build

Because the beta is closed, SondeFox isn't in an app store. Testers receive a signed APK directly from the beta coordinator — if a build is due and you haven't got one, email beta@sondefox.com.

To install from your phone:

  1. Open the APK from your downloads or the email attachment.
  2. Android will ask you to allow installs from that app ("Install unknown apps") — this is the standard prompt for anything outside an app store. Allow it for your browser or file manager.
  3. Confirm the install. Updates install over the previous build; your settings are kept.

Prefer the command line? With USB debugging enabled, install over adb instead:

adb install -r sondefox-beta.apk

The -r flag reinstalls over an existing build, preserving app data.

First-run setup

Do this once in Settings before your first chase — it takes about two minutes.

  1. Pick a gain profile

    Under Airspy settings, choose the preset that matches your environment: Quiet rural (maximum sensitivity), Urban / interference, External LNA, or full Manual if you know your LNA/mixer/VGA numbers. When in doubt, start with Quiet rural.

  2. Leave the sample rate at 3 MSPS

    3 MSPS is the default and the stable, recommended mode for chasing. 6 MSPS widens the scan window at the cost of more CPU — treat it as an experiment, not a default.

  3. Set your callsign and choose your SondeHub opt-ins

    Fetching nearby sondes from SondeHub is passive and always on. Uploading your decoded telemetry is off by default and requires both the opt-in toggle and a callsign. Chase-car position sharing is a separate toggle, also off by default — it's the only thing in the app that ever transmits your location. Details in the SondeHub guide.

  4. Plug in the Airspy and grant USB permission

    Connect the Airspy via your OTG cable or powered hub. Android shows a USB permission prompt the first time — accept it, and SondeFox takes the radio from there. No drivers, no root.

Your first chase

With the radio connected and an antenna attached, the loop looks like this:

  1. Scan. Open the Spectrum screen. SondeFox sweeps the worldwide radiosonde band, 400–406 MHz, and lists the peaks it finds above the noise floor.
  2. Auto-lock. When a peak correlates with a known sonde header, the app classifies it, tunes to it, and starts decoding — no manual tuning needed.
  3. Watch the Sondes list. Decoded frames fill the Sondes screen with type, serial, frequency, altitude, and SNR. You'll also see sondes other stations are already reporting via SondeHub, often before you decode anything locally.
  4. Chase. Pick your sonde and open the Chase screen: a live map with your position, the sonde, its track, and the predicted landing point. Press Start Chase for the compass pointer with live distance and bearing. Within roughly 1 km, the Signal Hunt heat-map takes over for the final on-foot search — walk toward green, then tap Mark Recovered to file a SondeHub recovery report.
Beta limitation: tap-to-tune isn't wired yet

In the current beta, tapping a peak on the Spectrum screen does not retune the radio — the screen shows the band scan, but manual peak-tap tuning is still being built. Auto-lock does the tuning for you when a sonde header is detected, so in practice you rarely need it. It's a known gap, not a bug worth reporting.

When to expect launches

Weather services launch radiosondes on a synchronized worldwide schedule: roughly 00:00 and 12:00 UTC, every day. Sondes typically go up 30–60 minutes before the synoptic hour, so plan to be scanning a little early. That's two chase opportunities a day, every day — and the Sondes screen will show what nearby stations are hearing even before your own antenna picks anything up.

Troubleshooting

The Airspy isn't detected when I plug it in

This is almost always power. The Airspy Mini draws significant current, and many phones can't supply it over a bare OTG cable — use a powered OTG hub. Also check that your cable actually supports OTG (some are charge-only) and that you accepted the USB permission prompt. If the prompt never appeared, unplug, wait a moment, and re-plug.

The app says the Airspy needs to be re-plugged

Occasionally the Airspy's USB control endpoint wedges — the device enumerates but stops answering commands, which would otherwise show up as a silently dead spectrum. SondeFox probes for this on connect and shows a clear banner instead: unplug the Airspy, wait a second, and plug it back in. That resets the device and capture resumes.

Scanning works but I decode nothing

Check the launch schedule first — outside the ~00/12 UTC windows there may simply be nothing in the air near you. If a launch should be up, try a different gain profile (a too-hot front end in an urban environment can bury the signal), confirm your antenna is connected and roughly cut for 400–406 MHz, and compare against the Sondes list: if SondeHub stations hear a sonde you don't, it's a reception problem, not a decoding one.

Stuck on something else? Email beta@sondefox.com — beta reports directly shape what gets fixed next.

Hardware guide →