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Tracking Pico Balloons Using Ham Radio [pdf] (harc.net)
95 points by jah 32 days ago | hide | past | favorite | 33 comments

Whenever I see things like this in light of the various threats to amateur radio (usually from various interests who would like to get the frequencies sold at FCC auction for commercial use), I'm reminded of the tremendous value this hobby adds to engineering education. So many of the engineers I know who work with radio got started by tinkering with amateur gear.

Related discussion from yesterday:


The tracker is very cool: http://habhub.org/

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/

Wow, that's amazing. 22 laps around the world over the course of one year. And HF data rx in Australia from this tiny circuit board attached to a tiny balloon over the mid-atlantic. Worth a read. Also bonus Windows XP points.

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.

At the altitudes these are flying at (10km+), the air is bone dry. Unless moisture is encountered on the ascent, there is no need for conformal coating.

P.S. - I've done a fair number of these flights and can speak in more detail about this hobby on request. Great fun!

It amazes me that the balloon can last that long. That it's not losing it's loft over time.

Maybe they just put on a thin layer of conformal coating?

What about clear coat paint you would get from a hardware store just before launch?

fwiw You can get urethane and silicone conformal coating in a spray can and it's not that expensive.

Agreed, and your wife won't be upset when she discovers all the nailpolish is gone :)

I've always used clear nailpolish as a hacky version of conformal coating.

As fascinating as the electronics tech is, I'm perhaps more interested in the balloon tech.

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... https://www.sanluisobispo.com/news/weather/weather-watch/art...

There are several approaches that can be taken with balloons. By design, they do not expand like a weather balloon does. One wants to put in enough lifting gas to make it fly high (mostly to avoid clouds that will bring down a balloon with such little free lift), but not enough that it will burst.

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).

I've launched one of these balloons before. Made it from Colorado to the Gulf of Mexico and started making the turn up the coast before losing contact overnight.

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.

Why is the UK (in the unusual company of Yemen and North Korea) an important "do not transmit zone"?

Airborne transmissions of this sort are not legal over the UK, North Korea, or Yemen. Guessing it's a leftover rule from WW2 in the case of the UK, not sure.

These transmitters typically have geofencing routines that turn off the transmission when flying over these countries.

But in my brief attempt to answer my own question I only found pages detailing pico balloon launches from the UK.

I'm sure people in the UK are doing launches, but it's illegal for them to transmit when flying in UK airspace.

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!

If I remember right is the reason is that it’s illegal do use amateur radio bands on something that is flying, so that excludes APRS. However, using the ISM bands are fine so that’s what people in the UK tend to use, but it means no APRS and you have to have people tracking you in other ways (e.g. sending your telemetry over LoRa or RTTY)

Yeah unfortunately the uk amateur radio licence (at all levels) prohibits airborne use of the licence.

I know for other amateur balloon experiments such as weather balloons, they often use the ISM bands instead in the UK.

This is the coolest thing I have seen this year. I think I always wanted to do such a thing, circle the earth with a balloon — had no idea it was within reach. I love all the ways in which they shaved weight on the payload.

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....

How are these ballons flights managed, in relation to airspace? Given the increasing restrictions on drone flight, I’m surprised such balloons are allowed to wander and descend Without any control.

In the US, a balloon with a total payload weight of less than 4 pounds doesn't require any kind of clearance or approval.

Can this frequency/protocol be used from sea level? I have some boats offshore that I would like to track. We currently use a combination of AIS and SPOT trackers.

You can, but you may not get the results you're looking for.

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.

I’m guessing it’s possible. I think WSPR supports a wide selection of bands so you can have over the horizon comms. APRS is usually VHF/UHF so it’s mostly line of sight. On land, there are APRS repeaters that rebroadcast your signal at higher power so I’m guessing it’s more suited for land.

Do these balloons transmit any weather data along with their telemetry? Or at the altitude they fly, maybe there's not much weather to report?

I love Leo Bodnar's stuff. I made a 'flight sim' joystick and pedals from one of his boards

What's the purpose of that capacitor?

These are run by solar panels that only transmit during the day. The capacitor just gives a half a minute or so in the event of brief cloud cover, panel not facing the sun at a good angle, etc. Not strictly necessary, but since a WSPR message takes almost two minutes to send, a good idea to not have it abort in the middle of the transmission due to lack of power for a couple of seconds.

As the other person responded, basically a battery back-up.

This kind of reminds me of CubeSats. I love the simple little design with the side solar panel wings.

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