Ionoscatter opening on 144MHz?

I am not very familiar with ionoscatter propagation. My knowledge has been limited to 

a) it is a forward scatter mode from the D layer

b) it peaks with D layer ionisation, so high summer at mid-day is a good time

c) it does not depend on atmospheric pressure like tropo

d) distances achievable are around 900 to 2000km

e) best frequencies are 30 to 60MHz, though up to 100MHz is sometimes quoted

f) it needs a lot of effective radiated power to work

The interplay between (e) and (f) tends to rule it out for me. At 50MHz I have 200W at the antenna, and on 70MHz it is 50-100W. On the other hand, at 144MHz I can put 200W to the antenna which has a lot more gain than is available on the lower bands. My ERP on 2m is twice what I have on 6m, even with the same power at the antenna.

So the only band I put out a reasonable ERP is above the ideal frequency for working Ionoscatter. I have read about it but I did not think it was for me. So, basically, I have ignored Ionoscatter so far.

As you may gather from this post, this period of overlooking Ionoscatter is now over. Yesterday was 20 June, almost at the Summer Solstice when the day length was 17 hours and 35 minutes here. Not a bad date for Ionoscatter. Mid Summer, mid day, a handy time to be looking for this.

There is an interesting article here  

https://www.qsl.net/oz1rh/ionoscatter/ionoscatter_lecture_2002.htm#_Toc10594132

The first sign I had that something odd was happening was hearing DK1FG working a local station. Now Gerhard is an EME operator with an antenna array with 10dB more gain than mine.  Also he has an linear amplifier with about 6 or 7 dB more than mine so his ERP will be tens of kilowatts more than mine, and probably a lot more. With the benefits of his much taller mast he will have several more dB over me there too, plus he has a superb site. With the advantage of antenna elevation he can also set his antennas to the optimum angle for ionoscatter. Despite all of this, I normally cannot hear him because under normal conditions no path exists. Hearing him yesterday was something of a surprise, working him was a greater surprise.

These were not "normal conditions". The distance between DK1FG and GM4FVM is 1128km, an ideal distance for ionoscatter. To achieve a contact like this we are exploiting one of ionoscatter's key characteristics. Whilst there is a ideal frequency range of 30 to 100MHz, this is not a strict limit. In fact as you exceed those values the losses rise but the propagation continues to work with more path loss until you reach the noise level. So by using an EME capable station at one end of the QSO it becomes possible to generate the sort of power budget which would make ionoscatter possible at 144MHz. Much lower ERP should work at 70 or 50MHz.

DK1FG's mast and antennas (DK1FG's QRZ.com site)

I do not have that sort of station but the path loss arithmetic suggests that a more modest station at one end of the QSO should be able to make ionoscatter work at 2m. From my point of view I decided to treat ionoscatter like moonbounce - I could not work a station like mine at 1000km range, but I might be able to work a superstation.

Actually using ionoscatter on 144MHz proved a bit tricky. Stations were on great circle bearings (unlike meteor scatter or aurora) but signals were patchy with what looked like steep QSB. It took a while to get a complete QSO. In line with the idea that around mid day would be best, I worked DK1FG at 11:55 and then worked four stations up to 14:22. I also failed to complete with one station and worked another one which may have been tropo.

144MHz contacts at GM4FVM on 20 June 2023

I have put 100km circles on this map to show what happened next. The following QSO was with F5RZC. Jean-Francois also runs a powerful station but he is "only" 642km away and I can work him under slightly raised tropo conditions. I am pretty sure that this was a tropo contact, and although not very strong, it did not show the peaky QSB shown by the other contacts.

After that I worked SM5DIC (JO89 1197km), OH6KTL (KP02 1506), SM1HOW (JO97 1270) and SM0DJW (JO88 1240). I failed to complete with OH2FNR (KP20 1641). These are all good VHF stations with better antennas, receive pre-amps and power levels than I have.

So why am I rambling on about how much better stations these are? Because that is what is needed for ionoscatter. It would not be required for a tropo contact during a tropo lift at these distances. All the signs are there for ionoscatter, and this is reinforced by the operators sending postings to the cluster indicating that this was ionoscatter. 

I suspect that the contact with F5RZC was tropo. There was no other tropo around and it did stand out as unusual. However, it appears to be too close for ionoscatter. The others look more certain.

Could I do this again? Can I use it on 6m and 4m where is might be more effective outside the mid-Summer mid-day window?

P.S. During similar conditions today I caught this screen grab which shows the distinctive patterns on the waterfall. Tropo would have shown long slow QSB and strong signals, this shows patchy weak signals.

Set against this, I seem to have forgotten several days of nice tropo since the last posting. The high pressure collapsed, the tropo went away and that is why I noticed the ionoscatter.

73 Jim

GM4FVM