Thursday, October 26, 2023

Tracking the AF6IM Pico-Balloon on 28 MHz from the USA to China - Oct 2023

For the last 12-months or so, I have been being monitoring the WSPR beacon frequency of 28.1246 MHz nearly every day and uploading the reception reports to the WSPRNet site.

I noticed recently an unusual signal out in the Mid-Atlantic.. AF6IM. I thought at first it was a bogus WSPR report but then I noticed that I had heard the signal several times and it was moving!

After some checking, I discovered that the signal was actually from a Pico-Balloon with a 13-milliwatt WSPR transmitter underneath it. It was launched by Mark, AF6IM in California at the end of Sept 2023 and it has been slowly drifting eastwards since. At the time of writing on the 26th of October, it is over China.

The map above shows my reception reports of the 13mW beacon. It only operates for a few hours every day as it is solar powered and has no battery. That's why the signal is shown as small batches of signal locations in a row.

The pictured is further complicated by the fact that Mark actually had two 28 MHz Pico-Balloons in the air over the last few weeks.

The design of the WSPR transmitter is shown above and you can find more information about it HERE

The antenna for this 28-MHz transmitter is a very thin wire which is 2.54 metres long which is a quarter wave on 10m.

This photo by AF6IM shows the pico-balloon at launch. As the balloon gains altitude and the pressure reduces, the size of the balloon will get larger.

The solar cells are not shown.

Even though the original balloon looks very small, it's still able to keep a very small payload aloft at a high altitude. The chart above shows the launch of the balloon and floating along at an altitude of about 12,500m or 40,000ft. This is well into the Jet Stream and this is what is now carrying it  around the world.

The temperatures at this altitude are well below zero as can be seen in this image above. One obvious advantage in not carrying a battery other than additional weight is that there are no problems with a battery trying to survive at these low temperatures.

In conclusion... There have been plenty of other pico-balloons operating on lower frequencies in the past like on 14 MHz but I really don't have much interest in those bands. This is the first time I recall seeing one operating on 28 MHz.

What I find fascinating is that I have heard the little 13-milliwatt 28 MHz transmitter over 450 times over the last few weeks while it was hanging below a little balloon up in the Jet-Stream.

If you want to track it, you can follow it HERE


Mark AF6IM said...

Thanks for the great writeup John. I’ve got to give massive credit to Kevin AD6Z who did the hard work on these balloons. I hugely enjoy combining ham radio with aviation.

Anonymous said...

Great work from two smart guys!! Tom K

Anonymous said...

Not sure how to enter tracking data, but I copied the beacon today in NH from 1900-2000z at signal strengths of -11 to -20dB. Pretty amazing for 10mW to some wire! It was reporting its position as BL72.

Anonymous said...

Thanks for posting your reception report. I too am astonished at how far this micropower xmtr can be heard. All credit for my balloon successes belongs to AD6Z.