As we are now at the peak of the solar cycle, some radio amateurs are using WSPR on the 28 MHz band for their Pico-Balloons as they travel around the world.

Back in April of 2024, I had a post about reception of the KD9NGV pico-balloon as it made its way off the west coast of Ireland to the North Sea. See post HERE

I often see these pico-balloon on my receive list for 28 MHz WSPR but they're nearly all somewhere far away and the propagation mode is via the ionosphere. What I find interesting about the rare really close passes is that there is no propagation mode as such, the balloon is essentially line of sight to my location.

KJ7VBX-11... On the 8th of May 2024, I noticed that I was hearing the KJ7VBX-11 pico-balloon early in the morning just as it had woken up with the sun shining on it's solar panels. I was able to hear it pretty much all day from 07:40 UTC until 18:20 UTC.

During this time, it travelled from a spot off the west coast of Ireland, over the northern counties of Donegal, Derry and Antrim in Ireland, over the south-west of Scotland and then over Cumbria in England before falling silent for the night.

On the 9th of May, it woke up over the English Channel and then headed over the Netherlands.

The balloon is at an altitude of about 13,500 metres or 44,000 feet. The WSPR transmitter is supposed to be 20-milliwatts. As far as I know, it was launched on the 2nd of May 2024 but there seems to be very little information about it.

Format... Early on the morning of the 8th, I was the only person reporting it and it was the only signal I was hearing so I was able to do some tests without any confusion from other signals.

The WSPR transmitter on the balloon seems to have two formats. The first one is shown above. The transmitter turns on as a plain carrier for 30-seconds and then sends one WSPR transmission. I presume this carrier is to warm up the transmitter which is at or below 0 deg C and the 30 second carrier stops any drifting of the following WSPR signal.

The second format is shown below...

This time, there is a second WSPR transmission after the first one.

This is a sample of the decodes that I got in the space of about an hour...

The short format results in just a KJ7VBX decode.

The longer format results in an additional decode which are shown above in red.

At first sight, they look wrong. The callsign, locator and power levels seem to be nonsense. However note that the callsign field starts with a zero. This is a special data WSPR signal and contains the information about the location, altitude, temperature and battery voltage. It's just the WSJT-X receive software shows it in a format that doesn't seem to make any sense.

In conclusion... The balloon is currently heading over Europe so it's going to be line of sight to a lot of stations. Just listen on WSPR on 28 MHz and see if you can hear it.

On the 28th of November 2023, Perri Moore KD9NGV launched a Pico-Balloon from Illinois in the United States with a solar powered payload that transmits a WSPR beacon on 28.1246 MHz.

Most of the Pico-Balloons launched from the USA tend to take a path closer to about 30 degrees north of the equator and cross areas like the north of Africa and south Asia. In contrast,  the KD9NGV balloon seems to have covered a much wider area and has been reported at more northerly latitudes as shown on the map above.

By the 16th of December 2023, it had gone around the world once! By the 19th of February, it had gone around the world three times. By mid April 2024, it has gone around the globe multiple times and the red dots on the map show where it was when I received some of the WSPR signals over the last few weeks.

It then went silent as darkness fell. Once daylight broke again on the 8th of April, it was over the North Sea and GM4WJA started to report it.

At the time of the screen grab, LA3FY/2 in Norway was hearing it and it continued then over Scandinavia. It has since crossed over Russia and at the time of writing is up over the far north of Canada.

KD9NGV Payload... The actual payload pre-launch is shown below.

The 28 MHz WSPR signal is generated by a Si5351 clock generator and the power output is just 9 milliwatts... 0.009 watts!

The antenna is a vertical half-wave dipole made of #36 enamelled wire.  The top half is from the balloon to the U4B tracker (QRP Labs) and the lower half hangs below the tracker.  Three Powerfilm MPT 3.6-75  in a vertical triangle provide the power.  The complete payload weighs 12 grams.

The balloon is described as a "silver SAG Balloon with Helium.".

In conclusion... I have noticed these WSPR pico-balloons many times on the 28 MHz band before but they are nearly always flying over some exotic location. It was just unusual to have one pass so close and be line of sight.