It’s a crowdsourced set of antennas around the world that upload data to central server (think Flightradar24 for high altitude balloons). It’s been running for 15 years or so.
Various bits of more reading if you’re interested in this stuff: http://picospace.net/ https://ukhas.org.uk/
Btw how are they flying a circuit board in the raw without damaging environmental effect from water? I'm new to this part of the hobby.
P.S. - I've done a fair number of these flights and can speak in more detail about this hobby on request. Great fun!
Perhaps more reading will help me know the answer, but it doesn't seem like these are just off the shelf Mylar party balloons. Nor do they seem to be sized such that they can expand a lot as they rise.
The below linked article is kind of interesting in this area: it's about how Death Valley is littered with Mylar party balloons. According to the article...
"Mylar balloons do not go higher than about 3,000 feet to 7,000 feet before they either explode or lose their “lift.” This is because of their inability to expand to any great extent."
Read more here: https://www.sanluisobispo.com/news/weather/weather-watch/art...
In the referenced article, an SBS-13 balloon is used. It's made from a clear Mylar-like material and will fly at 40000ft+ when filled with helium (higher with hydrogen). This is the 'gold standard' of balloons and can fly for months at a time as it's over most weather. The downside is that they cost close to $200.
Another approach is to buy a cheaper 36" diameter balloon made of similar material from AliExpress that cost about $1. These are often pressurized to a certain differential pressure to 'stretch' the balloon before launch and gain some extra volume, as well as to QA the quality of the balloon (the QA on a $1 balloon isn't extensive). If filled with hydrogen, these can fly at 35000 ft+, a bit lower for helium. Usually two of these cheap balloons are used for a launch for more lift, though a single one can be used and a lower altitude reached.
A light payload is desirable as it will increase altitude. I've seen as light as 5 grams and the heavier ones are closer to 20g. One can calculate the free lift where the differential pressure of the balloon at altitude will pop it, but it's usually around 7g (so the balloon + payload + 7g will neither rise or fall before launching).
The balloons are standard mylar balloons, but slightly bigger than average. About 2.5 feet in diameter. In order to allow the balloon to climb to ~30k feet, you need to leave a lot of room for the gas to expand. I'd say our balloon was only about 15-20% full at launch. You put just enough helium in the ballon so that it has about 1 gram of lifting force.
These transmitters typically have geofencing routines that turn off the transmission when flying over these countries.
In reality, it's an almost unenforcable law to begin with. Most of the WSPR transmissions are on the order of 10mW (probably similar to the Bluetooth output of your cell phone). It's not unusual for these transmissions to be heard several thousand miles away, which is quite amazing!
I know for other amateur balloon experiments such as weather balloons, they often use the ISM bands instead in the UK.
I suppose having heard about the gas-powered model plane that crossed the Atlantic decades ago started my obsession. Then learning about the Japanese fire balloons that crossed the Pacific in WWII....
APRS is a line-of sight signal. In a balloon, you might be heard by transmitters 200 miles or so away. On a boat, I'd expect that range to drop to 50 or less. So if you're out at sea, it's unlikely you'd be heard when you're much outside the view of land.
WSPR has a very long range, but the density of information transmitted is very low. Each transmissison takes about 2 minutes and the tx rate is around 5 baud (not 5kb...5 baud!). The protocol was developed to test the range of ham radio antennae and it doesn't give you much more than the transmission voltage and the 'maidenhead' coordinates (which will give your location within a roughly 80 mile box depending on your latitude).
If that rough estimate of your position is good enough, WSPR may be useful to you for tracking a boat. Some balloon trackers also transmit a secondary signal under a different callsign with some more advanced telemetry information, such as altitude, speed, more granular position within a 2 or 3 mile box.
Also, you'll need an antenna of some length. My balloons transmit on the 20m bands, which means it has a 17 foot antenna both above and below the tracker constituting a half dipole (it's 36 gauge magnet wire so weights almost nothing. If your boats are big enough to cross oceans, you can likely mount them in a way where you'd be heard.