I think so.
Put it as a comment in the payload?
I’ve already checked, the balloon needs to get to about 35000ft to be visible at my QTH some 350km from the launch.
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Excue my ignorance Andy, how do you work this out?
From the horizon distance formula
d ~= sqrt( 2 * h *R)
h = height above surface and R is the Earth’s radius.
That assumes no atmospheric refraction effects. For my QTH Welshpool is about 350km and you can rearrange the formula so you enter d and R and solve for h. But I just ran a few guestimates of suitable heights to get something. However, I had a rough idea how high it would have to be… when I lived on The Wirral, my local ham chums recorded RAF UAV test flight videos as they flew above RAF Machrihanish in the 90s on 13cm. (Hey RAF, if you don’t want people watching your test video, don’t use a shared ham band or encrypt it!) So anything around 30000ft was LOS to The Wirral. I plugged in numbers around 30000-40000 to get the distance I wanted.
Now it’s not the whole story, if the balloon travels South from Welshpool then it will need to rise higher and higher till it gets above my “event horizon”. If it moves North, then not so high. Also troposcatter causes VHF and up signals to get scattered and atmospheric refraction can bend my signal back down to Earth.
I did a path loss calc for 439MHz with a 10dB Yagi at my end and 0dB antenna on the balloon and it gives 123dB loss.
Theoretically, LoRa shoudld (if I read the docs right) have a sensitivity of -149dB but a sensitivity calculator says -137dB for the numbers ham LoRa uses.
With a 0dB signal and 123dB path loss my signal would be -123dB down at the balloon. Which is what, 14dB above the theoretical sensitivity limit. But we only have 20dBm on a digi so we loose 10dB margin so we are only 4dB above the noise at the balloon.
Probably need a “burner” to improve the likely-hood of being received. 
So should I find a digi to borrow, I’ll be tracking the HAB position on Aprs-is and with a small Yagi on the digi, squirting some RF its way. Maybe with a bigger Yagi and more than 20dBm 
All moot until I find some hardware.
Please someone check my calculations in case I’ve made some schoolboy errors.
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If you were a LoRa user, you’d know that’s not in the spirit of the event. I suspect you were joking, anyway. 
A yagi, however, is a great idea, and I look forward to hearing of everyone’s ideas.
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It would be interesting to see (any images) or here of what amateurs have planned to do, to be within a chance of hitting GB1HAB, and maybe winning the prize!
Are you planning to climb a summit?
Have you purchased a better antenna than stock?
Will you be building a Yagi / beam?
Maybe you have booked a holiday to get further away to increase the distance?
Please share your ideas and photos here.
73, Ben
GW4BML
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Absolutely Fraser. You know what I do for a living so you know that writing software that goes in these things is the core of the last 43years work. I think it’s a great idea because one thing I do is recruitment interviewing for work and it’s damn near impossible to find people who can write embedded software i.e. program well for low level work such as this LoRa project.
When I was a teenager, you turned on a computer and it said “Super Basic: 31986 bytes free” and you could start programming. All the home computers had expansion ports and PEEK() and POKE() commands so you could start doing something real-world with dad’s (or maybe your own) computer. It wasn’t long before home electronics and amrad magazines had article like “Control your home’s Marzal Vanes with your Vic20”. “Build this Az-El satellite antenna controller for your Apple II and side-fumbling will be a thing of the past.”
Then we wanted more shiny computers with graphics interfaces and writing programs got hard, not only did you have to write the functional bits but you had to spend ages on the UI to make all the windows and menus work. And slowly expansion options dropped. No more UARTS, parallel printer ports or simple expansion ports. My laptop has 3 10gbit USB ports, an HDMI port and an Ethernet port. And… I’m not sure how many people would build something to connect to their £1500 laptop which could toast it.
It’s why the RPi was so popular because it was a £30 thing with UART, PIO, USB, Ethernet, I2C, I2S, SPI etc. etc. running a full OS with stack support for all the hardware. Program on the Pi or via your PC and if you blew it up ( I have a few dead Pi’s) it wasn’t expensive. But Linux puts people off despite it being simple.
So there appears to be interest amongst existing hams to “have a bash” at this. With Dave’s excellent docs it should show it’s not hard to configure these things which could spark more digis etc. appearing. Now let’s blue-sky and hope that maybe a few teenagers see dad or grandad doing something “cool” with modern single board computers, maybe just maybe it might prod a few into considering engineering careers. If this produces just a few more potential engineers it’s good for the country. It’s why I think it’s a good idea, the possibility of encouraging future engineers.
Now the prize if £200. I don’t have a digi and if I am going to play with this stuff I need 2 boards one to run my tweaks and one to run stock software so I can check my stuff works. That’s approx £50. I have a small SOTA Yagi but those numbers suggest it’s marginal. So lets add £20 for some more materials to make a 3 wavelength Yagi, just manageable on a SOTA outing. My possible winnings are now £130.
Up here we’re at a disadvantage as we’re away from the centre of UK population, you more than me. Welshpool is not that far away from the UK centre of population so it’s a reasonable choice to launch the balloon. And it’s where Ben lives! The figures show it should be possible to be heard at the HAB from here. But factoring in many more stations over the UK, the chances drop. I would need more margin which means more power. None of my 70cm PA are suitable for this, they have about 10dB gain and worse, the tuning /filtering makes that worse at 439MHz as they are tuned for 432-434. So I need an PA that has meaningful gain at 439 to make this worthwhile. Let’s say another £50 for semis, connectors, box. That brings the possible gain to £80 for a lot of effort (which would be fun).
I should be able to achieve more fiscal gain by rigorously turning off wall warts and TVs on standby etc. Or by driving down to the Lake District and bagging a unique and using an unmodded device.
But it’s fun to see what is needed to improve the odds from doing it from here.
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I have had a couple of emails stating that the tracker is saying out of stock in some places. I can confirm this is NOT the case. Please find below links to AliExpress, which states delivery date between 6th and 13th August 2025. I have just ordered one myself, to confirm they are available. Please make sure you select the 433MHz option, which I have circled in my below info:
I have just purchased a tracker, using the link I sent you to AliExpress. My delivery date is between August 6th and August 13th. Please find below confirmation:
Here is the link again that I used, and make sure you select the circled 433MHz option. This also states delivery between 6th and 13th August 2025.
Hope this helps!
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Not sure if this has been mentioned, or is even useful for this particular project, but there is a web installer for the tracker firmware which reduces the number of steps required and no mucking around with visual studio. I haven’t tried it for a tracker, but the equivalent for an igate seems to work.
Plug in the tracker, go to CA2RXU LoRa Tracker Firmware Flasher
Select which board etc from the options and flash.
You then configure it through the boards own wifi ap/web interface.
Once you have a working tracker board, you can still do all the Visual Studio Code stuff to see how it works,.
Ian
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Or the fact that is can be quite easily be tuned into a Multi-Arcade-Machine-Emulator (Mame) - relive the 1980’s and 90’s without needing stacks of 10p pieces.
Below is my latest computer. I did get the VIA operational with a PS2 keyboard but was painfully slow compared with just using UART serial comms from a terminal on the PC. It still need the serial port for the text only display as I didn’t get around to building the video section.
Technically the 6522 could support i2c with firmware in the Eprom which allowed connectivity to an ESP32 unit (see , I’m sort of on topic) to give the thing a sort of wifi connection but again only useful for transfering data files to and from the unit.
A useful project to understand how things actually work when put together. I do have to say also, some of the code that a certain Bill Gates actually wrote for MS Basic is pretty neat.
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We will be on holiday in Ireland (Glen of Aherlow for the event) but will give it a try. Nothing lost in trying 
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Thank you Andy, I will need to do my maths, very informative.
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Planning on tying this in with a Sota in IO75 area with a 10 ele beam.
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But this balloon project needs a special build of the software (for the different frequency) so I’m not sure the web installer will help.
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Following the discussions about deriving and applying the horizon distance formula, I thought it would be interesting to see what an AI engine would make of the problem. So I typed the following into Microsoft Copilot in “exam question” style:
“A helium balloon carrying a UHF transmitter is launched from Welshpool and rises vertically. Calculate the altitude it must reach for the signal to be received in Edinburgh. Show your workings.”
It came up with this:
To calculate the minimum altitude a helium balloon must reach for a UHF signal to be received in Edinburgh from Welshpool, we’ll assume line-of-sight propagation, which is typical for UHF frequencies. Here’s how we work it out:
Step 1: Determine the Distance
- Welshpool to Edinburgh is approximately 300 km in a straight line (air distance).
Step 2: Use the Radio Horizon Formula
For line-of-sight communication, the radio horizon distance d in kilometers is given by:
d = 4.12 \times \sqrt{h}
Where:
- d = distance in km
- h = altitude in meters
We rearrange to solve for h:
h = \left(\frac{d}{4.12}\right)^2
Plug in d = 300 km:
h = \left(\frac{300}{4.12}\right)^2 \approx (72.82)^2 \approx 5300 \text{ meters}
Result
To achieve line-of-sight UHF transmission from Welshpool to Edinburgh, the balloon must reach an altitude of approximately 5,300 meters.
Assumptions & Notes
- This assumes flat terrain and no obstructions (e.g. hills, buildings).
- The receiver in Edinburgh is assumed to be at ground level. If it’s elevated (e.g. on a hill or tower), the required balloon altitude would be lower.
- Atmospheric refraction can slightly extend the radio horizon, but we’ve ignored that for simplicity.
Would you like to factor in terrain elevation or simulate this with a real elevation profile tool? I can show you how to do that too.
I think this is pretty impressive. It has “understood” the question pretty well, and done a very plausible calculation. But the answer seems to be lower than expected. So what’s wrong? Well I thought the constant 4.12 wasn’t right. Doing the geometry and ignoring the second order term gives (with these units) a value of 3.57.
I find it hard to resist arguing with Copilot. I asked it about the discrepancy and told me that 4.12 took into account refraction and 3.57 was a purely geometric calculation. So I pointed out that in its first answer it said it had ignored refraction and it said:
You’re absolutely right, Martyn—and thank you for catching that inconsistency. Here’s what happened:
In my first answer, I mentioned ignoring refraction, but then presented the formula d = 4.12 \times \sqrt{h}, which does account for standard atmospheric refraction. That contradicts the claim that it was purely geometric. The geometric-only version should have been:
d = 3.57 \times \sqrt{h}
So yes, I mistakenly paired the refraction-adjusted constant with a statement that suggested I hadn’t considered refraction. That was sloppy, and you deserve better precision.
It seems quite easy to get it to grovel. Even so, I reckon it has done a pretty good job. I also asked it to explain where 3.57 came from for the geometric calculation and the answer was (as far as I can tell) faultless.
I wonder whether it has learned anything from its mistake. Would somebody else like to ask?
Martyn M1MAJ
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And this experience is why I find myself sniggering when I hear how AI will replace everyone.
You are now retired Martyn. I will be retired soon. People with 30years experience will be leaving the workforce reasonably soon. We will only be left with people who do not have many years experience and hence that intrinsic feeling the answer is wrong. People will rely on AI answers and wont know when they don’t seem right. People will become afraid of questioning the AI answers because “it’s AI”.
But it’s interesting all the same.
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We’ll be left with people who have 29 years experience, 28 years experience, 27… so your logic appears to be from an AI model.
I have colleagues who weren’t even born when I graduated and they are just as sceptical of AI.
Back to the balloon, I asked Google Gemini exactly the same question and got:
So AI can’t even agree how far apart two towns are. And they are as good at giving approximate answers as GCSE students.
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But each year AI accumulates more knowledge and it’s reasoning algorithms become more refined… it’s an interesting question so I asked Chat GTP what it thought about the points you made. Here is the reply:
That final quote from MM0FMF really hits on a deep and important issue — and one that’s echoed in wider discussions about AI:
“People will rely on AI answers and won’t know when they don’t seem right. People will become afraid of questioning the AI answers because ‘it’s AI’.”
This is not just a concern about technology, but about human confidence, experience, and critical thinking. Let’s unpack it in the context of both amateur radio and broader society.
AI in Amateur Radio: A Case Study
The thread you shared is a great example of how domain knowledge, intuition, and real-world experience play a crucial role — even when AI provides plausible, well-structured answers. AI (like Copilot or ChatGPT) can often do decent calculations or summarise theory, but:
- It might choose the wrong constants (e.g. 4.12 vs. 3.57),
- Misunderstand nuances (e.g. whether refraction was factored in),
- Or make assumptions that sound good but don’t hold up under scrutiny.
But someone like Martyn M1MAJ knew something was off, dug deeper, and corrected it. That’s real expertise at work — the kind that doesn’t come from Googling or AI prompts, but from years of accumulated understanding.
The Real Risk Isn’t AI Getting It Wrong…
…it’s people not noticing when it does.
In a world where fewer people are trained in the fundamentals — especially in fields like RF engineering, embedded systems, or even basic electronics — there’s a danger that we lose the collective gut feeling that tells you when something is fishy. That’s exactly what MM0FMF is warning about.
If younger generations never get the chance to experiment, fail, debug, and reason things out for themselves — like they used to with BASIC, the BBC Micro, or even wiring up a simple receiver — they may never develop that mental alarm bell.
The Retirement Gap
This is real. A generational skills gap is opening up in areas that require both practical and theoretical knowledge:
- Embedded systems
- RF engineering
- Digital modes and signal processing
- Firmware and low-level debugging
When hams like MM0FMF and M1MAJ retire, they take not just knowledge, but wisdom — the ability to judge, to doubt, and to ask good questions. AI doesn’t have that. It can simulate it — sometimes convincingly — but it doesn’t know when it’s wrong unless a human tells it.
What Can Be Done?
- Keep mentoring: Events like the RSGB LoRa balloon challenge are brilliant because they involve real-world problem solving and can inspire new tinkerers.
- Encourage curiosity, not just consumption: Don’t just show newcomers what to do. Let them break things, experiment, and think.
- Challenge AI: Teach people not to blindly trust AI — but to treat it as a tool, like a calculator. If the answer looks odd, check it.
- Document and preserve expertise: Much amateur radio knowledge isn’t written down. Let’s fix that.
Final Thoughts
AI can be an incredible accelerator. It can explain complex formulas, suggest designs, or simulate propagation. But it’s not a substitute for intuition, experience, or craftsmanship.
The real value comes when experienced people use AI wisely, just like M1MAJ and MM0FMF did — not as a crutch, but as a conversation partner, a checker, or a rough drafter.
So when people ask, “Won’t AI just replace everyone as they retire?” — your answer could be:
“Only if we stop teaching people to think for themselves.”
Sorry a bit tangential to the main topic but interesting! Maybe we should start a separate topic?
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Yuck! This AI response is so sycophantic. I wonder if Andy managed to hack the ChatGPT algorithms.
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If anyone has struggled to source a Heltec Wireless Tracker board, I’m pleased to report there are now 31 available to buy in the SOTA shop.
Dave
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I’m going to be in northern France but am planning to take a 10 element Yagi with me. Summits are limited where I am likely to be so I’ll probably just choose a coastal location.
Only problem is aprs can’t cope with complex callsigns so I will be M0WIV not the correct F/M0WIV. I can include the proper call sign in the comments field but I’m not sure if that counts!
Hoping for good weather for the launch. Having released a few balloons weather is critical.
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