Lightning scatter is one of those exotic propagation modes that sometimes get a mention in books and articles but there seems to be very few examples. I think most people would expect this mode to be perhaps seen in the VHF part of the spectrum so it was a surprise to read that VK7MO and VK3MAP in Australia claimed to have made an lightning scatter contact on 1296 MHz!
They report that on the 13th of February 2024, there was a severe lightning storm between them and they attempted to make contact on 1296 MHz using the MSK144 mode.
They write... "The distance between us is 505 km and we ran 33 & 36 element single yagis with power levels of 120 and 50 watts. We were surprised that at this distance it was also possible to receive MSK144 decodes on aircraft scatter. However, we found it was possible, by replaying the files and examining the MSK144, Fast Graph window, to clearly identify the difference between both types of propagation. While at the time we completed three QSOs on 1296 MHz using MSK144, examination of the files shows that only one QSO was completely on lightning scatter and the other two were partly on aircraft scatter. Still, we can report the completion of a QSO using lightning scatter on 1296 MHz."
After their tests, they came to the following conclusions...
- We are confident that we achieved 50 lightning scatter decodes and one QSO at 1296 MHz.
- We used 15 second periods and auto sequencing to respond quickly enough.
- If aircraft are present, it will be difficult to confirm that a QSO is completely via lightning scatter until files are subsequently decoded.
- The durations of lightning pings between 0.1 and 0.3 seconds are ideally suited to MSK144.
- We are somewhat surprised that no corresponding pings were detected on 2 metres but conclude that 1296 MHz is a better band. Even if lightning pings can be detected on 2 metres it will be difficult to discern them from meteor pings.
- We think 1296 MHz is probably the optimum band for lightning scatter.
- Stations in the tropics should have a much better chance of seeing such events.
Commentary: Aircraft scatter is a very common mode of propagation and its effects are often seen on signals in the VHF, UHF & Microwave bands.
At 10kms above the ground, an aircraft has a visible horizon of about 400kms (800km circle).
Looking at an airplane pilots forum, cloud to cloud lightning is most common at about 3kms above the ground. This means the visible horizon from that height is about 200kms (400km circle).
Doing a quick check, it seems that the lightning would need to be at least 4.5kms above the ground for it to be visible to both stations for a 500km path.
It would be interesting to see if others could replicate these results? Some locations in the Mediterranean or the SE of the United States are possible locations during the summer months?
I'd expect it won't be easy to stations to pick out any possible lightning scatter signals from the many aircraft scatter reflections and tropo-scatter signals present.
If you would like to read the article from VK7MO and VK3MAP, then click on this LINK
Addendum: In this video, VK7MO talks about the contact and some of the background information.
In the video, VK7MO makes the valid point that at lower frequencies like 144 MHz, the RF noise from the lightning discharge may actually interfere with the actual MSK144 signal that is being propagated.
Follow up video...
