This, my first flight of the season, will test a few new things:

  • LoRa Calling Mode
  • 3G Modem functions:
    • Upload of balloon position to habitat
    • Upload of full-size photographs to a web server
    • Streaming of launch and landing/recovery to Youtube
  • Landing Prediction
  • Standalone GSM/GPS Tracker

LoRa Calling Mode

“Calling Mode” is where the tracker periodically sends out a special message, on a standard frequency using standard settings, announcing the particular frequency and other settings that it is using.  This allows for unattended receivers to be set up on the calling channel, where they can be expected to automatically switch to any balloons using that channel.

To see how this works, see this page that I wrote last year.

The calling frequency is 433.650MHz, chosen as the quietest part of the 433/434MHz ISM band.


The tracker for this flight has a Huawei 3G USB modem, connected to the O2 network via GiffGaff, using the Sakis3G script.  The tracker runs a Python program that knows the current GPS altitude (passed to it from the PITS C software using a named pipe) so that it knows when it is worth attempting to connect to the internet via 3G (i.e. below 2000m).  That same script controls the various functions that operate over 3G – video streaming, ftp image upload, and direct habitat telemetry upload.

Direct Habitat Upload

As well as the usual ISM (LoRa) radio telemetry, this flight will upload telemetry more directly whilst it has a 3G connection.   Most usefully, assuming it lands in an area with 3G coverage via O2, this will mean that the landing position is uploaded automatically.

Photograph Uploads

Again most useful on landing, the tracker will upload full-sized images (taken by the Pi camera) to a web server via ftp.  That server ( will automatically build thumbnails of the uploaded images.

Youtube Streaming

For both launch and landing, live video will be streamed to my Youtube channel, at this URL.

Landing Prediction

The tracker will predict its own landing position, sending the result out over LoRa as a “XX” which then appears on the map as a large red “X” (marks the spot).  The prediction is only useful after burst, and uses both the measured wind speeds/directions on the way up and the effectiveness of the parachute on the way down.

Standalone GSM/GPS Tracker

These are inexpensive devices that use SMS or GPRS to automatically send out their position.  They don’t have a good track record for HAB, partly because they tend to use cheap and rather deaf GPS and GSM hardware, and also because HABs tend to land in remote areas away from GSM coverage.  Regardless of the above, they have some use as a backup device to a regular radio tracker.

For this flight, I’ve set up a TK102 tracker to connect to the internet via GPRS and to send its position to a traccar server.  traccar is an open-source tracking system which displays multiple car tracking devices on a map.  Here, I’m using a small Python script to extract data from traccar (via its log file) and to then send the position of my particular tracker on to the habitat system so the TK102 appears on the usual HAB map.


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