This is a new one for me!!!
https://s3-us-west-2.amazonaws.com/pawlowski-01312016/flightaware/images/piaware-ballon.png
High altitude balloon with ADS-B out for conspicuity
Those are Google’s Project Loon. Expect to see more and more of them. Pretty crazy the first time I saw one. Right now we’ve got one near Little Rock that’s over 65kft.
Just watched the Google Loon project promo. Fascinating stuff. One scene shows ballon tracking from a laptop with multiple HBAL designations.
Great ADSB coverage n2mp.
Interesting thing is that google doesn’t have a motor to push the balloon around. Instead they figure out which altitude they need to fly to get the direction they want. Their altitude control is a balloon inside balloon design very much like a “cartesian diver” system. Not a lot that can go wrong, unless the balloon pops 
When google started the project they were only able to stay up about a month. They are up to many months now and looks definitely possible.
If you want to see the challenges of getting a ballon to work near the edge of space check out this video.
We Popped A Giant Internet Balloon! - YouTube)
Both SpaceX and Facebook have competing wide-area wifi systems in the works.
Haha that’s really cool. I had heard of people sending up balloons using a ham radio telemetry transmitter (basically transmits on a ham frequency) but it got me thinking it could be neat to do ADS-B since it will get picked up everywhere. Wonder how that works though, like if you need a special permit. I imagine they don’t want all sorts of people transmitting ADS-B signals.
We see them fairly often here on the Left Coast – HBAL013 at 58000 ft 20 kt, HBAL417 at 62500 feet 20 kt, HBAL380 50500 feet 36 kt.
They’re fun to track as they wander through the area.
My favourite for the last few months though was the U2 (AE094E) ID’ing as NCC1701A, 60000ft at 390 kt. That one brought both a smile to my face and tears to my eyes.
bob k6rtm
Would have made me smile more if didn’t have the A on the end but it still raised a chuckle from me 
HAMs generally use APRS or one of the HF digital modes to transmit location and weather information.
It doesn’t need to be very powerful as it is line of site(on VHF anyway) and the altitude gives you a huge range.
APRS: Automatic Packet Reporting System
aprs.org/
A transponder requires a lot more power. Not sure what the minimum is for balloon but even 10W should be enough at FL500+
@k6rtm,
That reminds me of the old SR71 joke(Urban legend) about the pilot asking ATC for clearance to FL600.
The quick witted controller said “And how do you plan to get up that high?”
The pilot responded “Permission to descend to FL600” (Above FL600 is not generally controlled by ATC)
Yeah APRS sounds interesting too, might have to read up more on it.
There are many premade GPS APRS transmitters that work on the amateur radio repeater network. Great way to track and follow your balloon before it pops since you don’t need to run base stations. I have seen APRS boards from $50-200 depending on features and quality.
For reference, ADSB transmitters are usually 5W to 500W. Most of the smaller GA planes are in the 50W-300W range. Bigger jets are 300W+.
PiAware with a prosticks can measure down to about -90dBm. So definitely sensitive enough to see a 5W ADSB transmitters if they are close enough.
There is a company trying to sell uncertified ADSB transmitters for $100-200. Uncertified means that it isn’t usable for passenger planes and even most GA aircraft. I don’t know anyone that has tried these for balloon tracking though.
uavionix.com
Also for reference, the ADSB satellite tracking will probably not see many planes with low power transmitters. The thought is that anything below 100W will not be able to be satellite tracked. We will know more once the satellite systems are operating.
APRS is a lot of fun, particularly for high altitude work. Also has a lot of uses on the ground.
My son and some of his friends did a number of balloon launches a number of years ago. The payload was a modified digital camera (Canon something or other with modified firmware to do a pic every -n- seconds) and 2 meter APRS for telemetry, mostly GPS position/altitude/speed, temperature on some flights.
The instrument package minus the camera was around $100 (GPS, APRS, controller, LiPo battery, antenna). Choosing an antenna and integrating that into the flight system is a challenge.
Operating range for a 2 watt APRS transmitter – remember, line of sight, which is pretty good above 40,000 feet!
Sitting at home watching the APRS network feed, some local stations are picking it up, it gets a little higher, and we have stations up and down the coast picking it up! Not only picking it up, but receiving more of the telemetry than closer-in stations, due to lack of competition (collisions). Stations in the boonies with not a lot of local traffic and a good view of the sky hear that little payload extremely well.
To do APRS on the 2 meter (144 MHz) ham band (in the United States – big caveat) requires a Technician class license or higher. The tech license is a 35 question multiple choice test. The set of questions and answers are fixed (updated periodically) and freely available. I’ve worked with groups that do single day study (cram) and test sessions with pass rates above 90% – short term memory. If you have any kind of aircraft certs, a college degree, or know that you shouldn’t stick your radio antenna in your ear, you can pass the Technician test with at most a couple of weeks of part time study.
If you are interested in ham radio, for APRS, emergency preparedness (when the * hits the fan, your cell phone won’t be good for much), or just out of nerdiness, PM me and I can give you pointers on studying for the test, getting a license, and what you can do with it once you have it.
My son got his Technician class license at 15 (he decided to do it for the balloon work), and surprised me enormously by upgrading to Extra (the highest US ham license) by the time he was 18.
I’ve worked aero mobile, in the mid 80’s in a friend’s 201 Mooney flying to Vegas for CES. 5 watts on 2 meters and I talked to folks in Oregon, Washington, Nevada, and all over California. Lots of fun and not even 15,000 feet.
bob k6rtm
Yeah been reading up a bit on ham radio actually. I’m in Canada but the rules seem to be fairly similar. They have “mock exams” for us too and I did one just for fun and got 50%, a fail but still gave me an idea of what kind of material I’d have to study further.
What is needed to simply receive APRS and contribute to tracking networks? I’d probably start with that just to check out what I see, as I imagine that does not require a license, just transmitting. Though I am toying with the idea of getting a license at some point, would be something cool to have under my belt.