Thanks to Robbie, EI2IP putting a post up on Facebook, I noticed that a high altitude balloon was crossing over Ireland due to the easterly winds over the country and it was transmitting on the 432-440 MHz 70cms band.
I remembered that I had managed to decode RTTY signals from a balloon over the UK a few years ago and I found it fascinating. It was always something on my 'to do list' to try again but I forgot all about it. When I checked today, that reception report was back in in July of 2018!
So there was no time like the present, I followed the links and started reading about it.
Part 1 of 2... The high altitude with the amateur radio payload was named Flybag-2 and had been launched from Maastricht in the Netherlands. It was transmitting on two frequencies on the 70cms band with data on it's location, height and internal temperature.
The payload was transmitting using the Horus Binary (v1/v2) modulation format which is a digital signal that is way superior to the old RTTY mode.
I downloaded the software to decode the Horus Binary signals, starting to mess about with the various settings, tuned the radio to 437.600 MHz USB and listened....silence.
The balloon had just cross over the east coast of Ireland and was heading west. I was using a homemade vertical colinear in the attic of my house which wasn't the best for listening for weak signals from a tiny transmitter 120kms away.
I also had the WSJT-X software running as well and I could make out weak traces in the waterfall. I tuned the radio down about 500 Hz to 437.5995 MHz. Eventually I could hear the signal weakly but still no decodes. Time to read the instructions.
The instructions said the audio level needed to be near -5dB. I had the volume well down and the software said it was 'good'? I tried turning the volume of the radio way up and success!
The stats show that I managed to get 20 decodes in total which is 20 more than I thought I'd get. The attic antenna is really blocked a lot in that direction so I was delighted to get anything.
Part 2 of 2... A few hours after Flybag-2, another balloon named Flybag-4FSK crossed to the south of Ireland. I had a lot more success with this one getting 71 decodes in total with my attic antenna.
The first decode was when the balloon was about 300kms away over the Bristol Channel and just below the horizon. My view to the east is pretty good and this resulted in a lot of decodes.
It was interesting to note that the signal was reasonably consistent up to about 00:24 UTC and then it dropped suddenly and the last decode was at 00:40.
This is the location of the balloon relative to my location. The balloon is slowly moving to the left (left).
This is the horizon from my location. The balloon from my point of view would have been moving slowly from roughly east to the south of me and then to the south west.
When the balloon was to the south-east, I was getting a lot of decodes as my horizon is close to 0-degrees in that direction. Once it got to 00:24 UTC, the local hill had an elevation of 1-degree. Beyond that, the signal dropped as the elevation of the hill got higher.
After 00:40, the local hill had an elevation of about 3.5-degrees and it was now blocking the signal.
I knew my take-off in that direction was poor but it was interesting to see conformation of it.
High altitude balloon... There are generally two types of balloons. The one I heard back in 2018 was like a weather balloon, it went up to an altitude of about 20kms and then the balloon burst.
This time, the balloon reached a height of about 4kms where it levelled off. Unless the hydrogen/helium gas escapes or it hits rough weather, it should stay up for quite some time.
STEM... It also strikes me that this would make a great STEM project. Schools and colleges can't afford microsats but a low budget balloon could teach a lot about tracking, propagation, layers in the atmosphere, weather, etc.
For more information, go to https://amateur.sondehub.org/
