High Altitude Balloons and a DIY Radio Tracker

[DBK]

In my continuing quest to avoid growing old I've been playing with a small homemade radio tracker. I haven't been doing this with a MH application in mind though in theory it might be used, though probably as a backup to a more conventional tracker. If someone wants to try that angle then feel free to go ahead!

What I've made is this:

The thing in the middle is a Raspberry Pi Zero and is about 3" long. The little board on the left is a GPS module with built in antenna. The thing on the right attached by a ribbon cable is a Raspberry Pi camera, its pointing at the bench so you can't see the lens. The small board inside the red case on the right of the Pi Zero main board with the wires going to it is a radio transceiver module, that is it can both transmit and receive. The orange wire you can see going off to the right is the antenna for the radio. It is only about 6" long.

The other half of this setup is this:

This is a normal Raspberry Pi but the green board you can see with the antenna sticking out is a ready made radio gadget which uses exactly the same transceiver module as I've attached to the Pi Zero. This board just fits on top of the Pi.

The radio system uses a system called LoRa, which stands for Long Range. In theory with suitable antenna a range of two or three hundred kilometres is possible, but it only works line of site. In a built up area a range of only one or two kilometres might be possible. The radio uses very little power and operates at around 434MHz. No license is required to use. LoRa is a very clever system and if you want to really stretch your brain cells I suggest trying to read a description of how it works! I've watch a video of someone describing it and my brain melted about a quarter of the way through.

The software I've used is available from the Pi In The Sky project, which is about using Raspberry Pi devices to track high altitude balloons. The description how to make both the tracker and the ground station can be found on this website:

DIY Lightweight Pi Tracker with SSDV – Dave Akerman

www.daveakerman.com

The output is shown on this screenshot.

The lines of text on the bottom are the individual packets of data which includes the GPS location, altitude and almost at the end temperature - 22.9. I've edited the image as it was of course showing my exact location. The software also takes a picture with the camera every 30 seconds and uploads that too.

There is a high altitude balloon community who run a website where in theory your balloon shows on a map with data uploaded from your own ground station but also other ground stations around Europe.

I'm very tentatively planning to fly a balloon myself but it won't be until much later this year. I want to do a lot more testing of my equipment and almost certainly build a second tracker and ground station so there is redundancy in case one link fails. Balloons typically carry two trackers for this very reason.

I should say this isn't the easiest of projects. Nothing worked when I first turned it on but after a few days head scratching and experimentation I think it is working now. I also need to investigate the best types of antenna to use.

If anyone has any expertise in any of this, the radio uses what is called the 70cm band, then all advice will be gratefully received.

It will all keep me out of mischief for a while...

 

[Spriddler]

Fascinating widgetry.
Presumably it's sent up with the balloon so that you can find the balloon after it has 'landed' in someone's back garden?
Do they land under control or just keep going up til they burst?

 

[DBK]

Fascinating widgetry.
Presumably it's sent up with the balloon so that you can find the balloon after it has 'landed' in someone's back garden?
Do they land under control or just keep going up til they burst?

It is fascinating. The radio module is just 15mm square and cost about £15.

The balloons just go up until they burst then the radio payload will descend under a small parachute. A typical balloon might be only a metre or so in diameter at launch but it will expand as it rises and might be nearly five metres across when it bursts. Altitudes of 25 km or even more are not unusual. There is a website where you can enter details of your balloon and it will predict where it might land. One account I read described the descending radio kept giving locations until it got to within a hundred metres of the ground. Providing it lands in a field it should be possible to find it but you have to accept there is always a risk it might be lost. There was a launch yesterday from Ipswich which hoped to get across the Channel to France but sadly it went down into the sea about twenty miles short. It was their second attempt. Perhaps third time lucky?

 

[tonyidle]

The aerial design will be determined by how much room you have but should preferably designed for circular polarisation with a wide beam pattern - possibly a simple phased crossed dipole against an aluminium reflector. Even that is going to be 12+" in diameter x 6" deep unless loaded elements are used.

 

[The Wino]

What happens if your balloon strays into the airways?

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[andy63]

are these balloons any sort of hazard to aircraft John... just wondering
Andy

 

[Spriddler]

I guess there's regulation wrt balloons being flown near airports, and at up to 25,000' wouldn't they be a hazard to commercial aircraft?

Could've done with one of those early 60's when I was flying free-flight aircraft. Radio Tx/Rx kit was very expensive, bulky, unreliable and so heavy (batteries, valve receivers, motorised relays/actuators) that you needed about 42" wingspan minimum to install and carry the gear. Anyway, the kit only received signals.
A two minute engine run would take it up to a couple of hundred feet and after that it just glided in large circles to wherever it wanted. My pals and I ran miles all over the Sussex Downs chasing them but too often the planes caught a thermal and went high or behind trees and out of sight. Few lost ones were ever returned in spite of having our addresses on them.
Lunchtimes my colleagues used to spend their lunchtimes in W H Smith reading 'MAD' magazines but being a bit of a nerd I went to a Gov't Surplus Aladdin's Cave and lusted after the radio gear and military widgetry.

 

[DBK]

What happens if your balloon strays into the airways?

are these balloons any sort of hazard to aircraft John... just wondering
Andy

You have to contact the CAA I understand and a NOTAM or warning is issued to pilots. I haven't looked at this side in detail but yes, there are regulations and no doubt restrictions where balloons can be launched. For example, not near airports I guess.

Weather balloons are being launched all the time so it is an established procedure.

 

[The Wino]

Just had a quick look at the CAA it looks like it may need some research it's not just near airports but under controlled airspace.

 

[DBK]

The aerial design will be determined by how much room you have but should preferably designed for circular polarisation with a wide beam pattern - possibly a simple phased crossed dipole against an aluminium reflector. Even that is going to be 12+" in diameter x 6" deep unless loaded elements are used.

That's the side I know nothing about. A directional Yagi can be used on the ground although most folk seem to use a simple short rod on a magnetic base in their "chase" car - or MH in my case.

I had expected on the balloon just a dangly bit of wire would suffice, and this is used but the balloon which ditched in the Channel yesterday had a rigid antenna which was mounted vertically through the neck of the balloon!

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[tonyidle]

If you are receiving GPS co-ordinates then the chase aerial isn't being used for direction-finding. If that is the case then a chase Yagi is a bit irrelevant and maybe too directional depending on the distance you expect to receive over. A dangly wire isn't making the most of your transmitter. A tuned length of dangly wire would be considerably better. If you can cope with a metre of dangly wire there's a simple design that would suffice.

 

[DBK]

If you are receiving GPS co-ordinates then the chase aerial isn't being used for direction-finding. If that is the case then a chase Yagi is a bit irrelevant and maybe too directional depending on the distance you expect to receive over. A dangly wire isn't making the most of your transmitter. A tuned length of dangly wire would be considerably better. If you can cope with a metre of dangly wire there's a simple design that would suffice.

Thanks, I was thinking a directional antenna at the receiving end might have a longer range.

The wire on the balloon end is tuned at the moment to a quarter of a wavelength. Making it a half or full wavelength should be better. You can also use a dipole with an identical bit of wire stretching in the opposite direction connected to the receiver's ground terminal.
I just need to do more reading and experimentation.

 

[tonyidle]

Thanks, I was thinking a directional antenna at the receiving end might have a longer range.

The wire on the balloon end is tuned at the moment to a quarter of a wavelength. Making it a half or full wavelength should be better. You can also use a dipole with an identical bit of wire stretching in the opposite direction connected to the receiver's ground terminal.
I just need to do more reading and experimentation.

A directional aerial will have longer range if you know which way to point. What is the frequency and power output at the transmitter - I've assumed 446MHz & under 0.5W? Is it most important to receive whilst the balloon is flying or when it is on the ground? If as I assume it's whilst flying range should be pretty good even at low power levels. I've seen a You Tube video of simple line-of-sight tests that achieved 30+ kilometres using PRM446 handhelds.

 

[DBK]

A directional aerial will have longer range if you know which way to point. What is the frequency and power output at the transmitter - I've assumed 446MHz & under 0.5W? Is it most important to receive whilst the balloon is flying or when it is on the ground? If as I assume it's whilst flying range should be pretty good even at low power levels. I've seen a You Tube video of simple line-of-sight tests that achieved 30+ kilometres using PRM446 handhelds.

The frequency I'm planning to use is 434MHz and the radio module has a power according to the spec of 20dBm which equates to 100mW according to a website I found. This is a tiny power of course which is why they don't really work at ground level but when the balloon is umpteen kilometres high then with the right receiving equipment they can be picked up at ranges of even a few hundred kilometres. However, the usual trick is to follow the balloon in a chase car so it should be possible to keep it within a range of tens of kilometers. You can get relatively inexpensive (~£50) pre-amps which give something like a 19dB gain at the receiver and these seem like the way to go.

Being able to receive the data packets from the balloon when it is in flight is critical as it allows the path and landing site to be predicted. After bursting and descending under the parachute the balloon won't be able to communicate any distance once the tracker hits the ground. This is where a second backup tracker can be useful and I'm thinking my Rewire Tracker might be ideal. These have been used successfully. They don't work in the air as there is no phone signal at altitude but once they land they should be able to pick up a phone signal and with their GPS advertise their location. In theory.

 

[hilldweller]

but you have to accept there is always a risk it might be lost.

There is always the risk it will hit a motorcyclist and kill him ( just to come up with one possible disaster ) -- Then What ?

What do the CAA say about this ?

PS.... Now I worked my way through the rest, I see you have considered the CAA. But I guess not the biker with open face helmet whacked in the face at 70 mph.

I know, 0.00000001% chance, BUT !

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[tonyidle]

A mobile tracker makes sense although there are likely to be some occasions when there's no mobile signal. A simple beam might be useful for receiving - maybe a DF design?

 

[DBK]

There is always the risk it will hit a motorcyclist and kill him ( just to come up with one possible disaster ) -- Then What ?

What do the CAA say about this ?

PS.... Now I worked my way through the rest, I see you have considered the CAA. But I guess not the biker with open face helmet whacked in the face at 70 mph.

I know, 0.00000001% chance, BUT !

The payload is installed into a lightweight box, typically made of expanded polystyrene or closed cell foam. Probably a significantly great chance by many decimal points of the biker being hit by a pheasant. I'm not belittling the risk but in the greater scheme of things the risk is negligible but I probably need to look at third party insurance.

 

[hilldweller]

but I probably need to look at third party insurance.

I think so. It's your liability. You could lose everything if your luck runs out. Even if it just dropped down a chimney, that could cost a fortune, depending on the chimney.

Sorry to be negative, just trying to protect you.

 

[tonyidle]

There is always the risk it will hit a motorcyclist and kill him ( just to come up with one possible disaster ) -- Then What ?

What do the CAA say about this ?

PS.... Now I worked my way through the rest, I see you have considered the CAA. But I guess not the biker with open face helmet whacked in the face at 70 mph.

I know, 0.00000001% chance, BUT !

As a motorcyclist I was more concerned about hedge-hopping blackbirds.

 

[DBK]

I think so. It's your liability. You could lose everything if your luck runs out. Even if it just dropped down a chimney, that could cost a fortune, depending on the chimney.

Sorry to be negative, just trying to protect you.

Not being negative at all, I hadn't considered insurance. I'll ask around and see what folk do.

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[two]

methinks some folk worry too much.

 

[DBK]

On a more positive note I've got my test payload now appearing on the balloon tracking map. That's me in the south west as Swall-1. On the downside the radio module keeps cutting out. I may have a dry joint or a duff module. They only cost £9 not the £15 I mentioned earlier so I think I'll get a spare or two as I want to build a backup model. The other balloons on the map are actual flying ones but all from yesterday or Friday. No one seems to be doing anything today. Bad weather I suspect.

 

[Spriddler]

To digress a bit on this fascinating subject but as an example of how far technology has advanced.........
Back in the 70's I used to sail to France frequently in my 23 footer. For navigation most boats only had a compass and a crude 'Seafix' hand-held Radio Direction Finder (RDF) which was just a basic receiver with internal ferrite rod aerial and a compass on the top which was dial-tuned in turn to the 'Null' from various coast radio beacons transmitting a Morse i.d. for about ten seconds, then a continuous tuning tune for about 20 secs. after which It would shut down for 6 minutes. Each beacon transmitted on a different frequency. Tuning to the chosen transmitter was a very hit-n-miss process involving waving it about on deck listening through headphones for the beacon to come up, then listening for the 'Null'. An almost impossible task whilst being buffeted about on a pitching and yawing deck in all the noise of bad weather.
On one occasion in very bad weather I picked up a distress call on my VHF radio from a desperate sailor lost with his wife and two young kids after setting out from Portsmouth. He said his RDF bearing and his estimated position by dead reckoning put him to the East of St Vaast on the Cherbourg Peninsular but he had been sailing towards it for 5 hours (!) with still no sight of land. The coastguard at Barfleur Lighthouse and the Alderney Airport Aero staff took bearings on his transmission and found he had strayed in the bad weather to the West of the peninsular and he was plotting his position on the reciprocal of the Barfleur beacon that was not directly ahead but directly behind him. Next landfall the U.S.A.
Seafix RDF

 

[DBK]

To digress a bit on this fascinating subject but as an example of how far technology has advanced.........
Back in the 70's I used to sail to France frequently in my 23 footer. For navigation most boats only had a compass and a crude 'Seafix' hand-held Radio Direction Finder (RDF) which was just a basic receiver with internal ferrite rod aerial and a compass on the top which was dial-tuned in turn to the 'Null' from various coast radio beacons transmitting a Morse i.d. for about ten seconds, then a continuous tuning tune for about 20 secs. after which It would shut down for 6 minutes. Each beacon transmitted on a different frequency. Tuning to the chosen transmitter was a very hit-n-miss process involving waving it about on deck listening through headphones for the beacon to come up, then listening for the 'Null'. An almost impossible task whilst being buffeted about on a pitching and yawing deck in all the noise of bad weather.
On one occasion in very bad weather I picked up a distress call on my VHF radio from a desperate sailor lost with his wife and two young kids after setting out from Portsmouth. He said his RDF bearing and his estimated position by dead reckoning put him to the East of St Vaast on the Cherbourg Peninsular but he had been sailing towards it for 5 hours (!) with still no sight of land. The coastguard at Barfleur Lighthouse and the Alderney Airport Aero staff took bearings on his transmission and found he had strayed in the bad weather to the West of the peninsular and he was plotting his position on the reciprocal of the Barfleur beacon that was not directly ahead but directly behind him. Next landfall the U.S.A.
Seafix RDF
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I first sailed in the late 70s in the Baltic and from memory we had no aids other than a compass. I sailed again in the 80s and though this was pre-GPS (I think) there were systems around which plotted your position but I can't remember what they were.

 

[Spriddler]

I first sailed in the late 70s in the Baltic and from memory we had no aids other than a compass. I sailed again in the 80s and though this was pre-GPS (I think) there were systems around which plotted your position but I can't remember what they were.

Yes, it was superseded, I think in the late 70's, by what was known as the 'Decca' nav system which was used for marine and aero navigation. It was a rather large and fixed box with a mast-top aerial. It picked up several land and/or 'Decca' beacons simultaneously and triangulated their bearings to display a 'Fix' and also show the bearings of the individual beacons on an LED screen which could then be plotted on a chart. One could pre-determine an entire route by inputting several Waypoints and it would give a continuous 'Course to steer' from one Waypoint to the next. However, this 'Rhumb Line' course was not generally the fastest, shortest or safest course due to wind direction and the effect of tides and currents (and any land that existed between the current waypoint and the next one!!).
Like most 'new' technology the kit was very expensive and when it first came out it was mainly used by commercial rather than leisure craft. It was a right PITA when I navigated on offshore races as the nosey Crew and the Skipper could all read the course to steer displayed on the Decca and frequently questioned why I had given a different one!! My next boat, a 27 footer had one already fitted by the P.O. but Decca had a fairly short life (10 to 15 years?) before the far superior GPS was introduced (in the early 90's?) and the Decca beacons were taken out of service.

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[DBK]

Not the most exciting of photographs, an image of the sky, part of a garden chair and a bit of my fence. The system takes a small format image at low altitude then switches to full format above 1000m, or whatever altitude to configure it to change over at. But it still took 22 packets of data to send this image, which I downloaded from the server it was uploaded to.

I've had intermittent problems of losing the radio signal and it seems it might be due to using certain battery power banks. I'm now using an Anker pack, which are reported to produce less interference, on a 70cm long USB cable and it appears stable now. I was using cheaper packs on much shorter cables earlier not knowing battery packs can produce radio interference! For actual flights four non-rechargeable Energizer Lithium AA batteries are widely favoured. They need to work at down to -50C which is the temperature at about 13,000m. Above that the temperature of the air increases due to UV absorption I've learned today!