Tuesday, 23 June 2020

Summer peak of VHF propagation

I can see a lot of stations on 6m trying very hard to work Japan (though it seems that China or India would do). There seems to be a lot of frustration. The God of Propagation does not listen to prayers, and is playing hard to get. So far.

Me? I have not got involved in that pursuit so far. I doubt very much if I can make a QSO like that and I am not willing to devote the hours of activity necessary to find out. Anyway, it is early morning activity so that is not appealing to lazy old me.

I would have thought that working Kazakhstan on 4m would be an early morning thing until I heard somebody mention that it is more likely in the afternoon. I am not yet too old to learn so I kept a watch on the DX Maps page and when I saw that UN7MBH was active at what looked like a suitable time I gave him a try.
4m (70MHz) stations worked at GM4FVM on 5 June 2020
I worked him first on 5 June 2020 at 16:44. He is in LO51 square and the distance is 3478km (which would be a 4m record for me if I had not worked 4X1TI at 3956km on 18 May). Needless to say that is a new square.

Calling CQ AS (or whatever) repeatedly as done by the 6m DX hunters is not in my style. I prefer to hang around and work people by stealth. I like the long game. Instant gratification is not necessary here. That meant that I missed Cyprus on 4m last year, but worked it this year. And my approach has probably put off working Kazakhstan for two years, but I like it this way. Maybe if I was chasing awards or entering contests things would be different. On the other hand, maybe I work this way because I am not doing those things.

I am not the type of operator who only comes on for Tuesday and Thursday evening between 20:00 and 22:30. I am not against contests; I think that they are "a good thing". I just think that there is more to radio than just that. I hear it said that there is "no activity" outside contest hours - well my experience seems to disprove that. I know some people actually take their antennas down outside those contest hours. They do their thing and I do mine. However, I find it is true that activity is definitely low during periods I have taken my antenna down.

Likewise, I cannot imagine just coming on for the Es season, or only for 2m for meteor scatter during shower periods. I cannot see the point in limiting myself by excluding large parts of the operating year. We have all these different bands for a reason. What I do works for me.

Not content with my first Kazakhstan station on 4m, on 16 June I worked both UN7MBH and UN3M (LO61) and then went on to work UN7IZ and UN9L (MO12) plus UN3GX (MN83) on 6m for one new country and two new squares there. Things like that tend not to happen during contests on Tuesday or Thursday nights, and they were all between 14:00 and 15:00.

You do not need a very big antenna to make contacts like this. Worst report from UN was -14dB so I could have done it on a dipole, though maybe not as easily.

Looking at the map of the first contact on 5 June, we can see that I then worked YL2CA (KO06, 1478km). This was at 16:53. Apart from G1CEY, which at 108km is a bit more "run of the mill" (though still welcome), these were the only two stations I worked all day on 4m. Thus you can see a distinct shape of one hop propagation to YL2CA and two hop to UN7MBH. Often there is so much activity that the pattern is lost amongst other QSOs.

The distances do not quite match 1478 and 3478, but the QSOs were nine minutes apart so propagation may have shifted slightly. I would not expect the distances to be exactly 50% and 100% anyway, as even with the low height of Es propagation and the limited area of ionisation effective at 70MHz, there will be some area of land half way between the maximum which will be "illuminated" by my signal even during a chordal hop. Although we represent radio signals by straight thin lines, radio energy spreads out into space and would be better represented by a cone. 

There are a lot of variables here, so it is good to see the pattern so clearly. The map projection means that the paths will not be shown as straight lines. This is because the Earth is curved but the map is flat. Despite this we can use the maps as a guide to propagation prediction and I may write something about this later. Also, the area covered at the end of the first hop is generally unknown to us, and may be in the sea or somewhere where there are no amateur activity, so we do not always see it. 

Then again, the signal may not actually touch down at all. For best DX there is no "reflection" of the signal off the ground at the mid point. The usual drawing we see in text books of two hop propagation is misleading. All the best DX paths are what is sometimes called "chordal hop" where the mid point may pass quite high over the ground, though for a near-maximum path length such as this one it will be quite low. The conical nature of propagation into free space will tend to bring the signal to ground at mid point, but the idea of it "bouncing" off the Earth to produce great DX, as we read in books, is fanciful. Sure it happens, but you don't work very far using it.

The remarkable thing about double hop Es, or even more amazing for multi-hop Es with more than two hops, is that it is possible at all. It becomes a big advantage that our signals spread out into free space in a conical fashion. The narrow straight lines we see in the books would never make it. The inverse square law makes it weak, but also makes it possible. As the frequency goes up, the ionised area we can hit gets smaller. Getting two roughly in a line is very difficult. When I studied for my licence it was thought to be impossible. I would like to say that we were taught that even single hop Es was possible, but they did not think Es was worth mentioning. Once I was licensed I looked it up and this revealed only single hop Es was covered by the books. 

Those guys spending hours calling CQ AS on 6m are proof of how hard multihop Es really is, but it is possible.

I write this two days after the Summer solstice. "The nights are drawing in". The next two weeks or so tend to produce the best of Summer Es. Whilst no doubt there will still be some Summer Es in September, these are the days to capitalise on it at its best.

73
Jim
GM4FVM

2 comments:

  1. Hello Jim, interesting article like always actually. I like to read what others do on 6m/4m. Yes, it is possible for you to work Japan/Korea if you are at the radio at the right time. You need to have some luck. Propagation could be there for 5 minutes in a whole year. Last year we had some excellent propagation to JA. It was so strong there were multiple stations replying to my signal. Others from the Netherlands did report they worked Japan with just a V2000 vertical and 100W. I've seen Japan/Korea last Sunday, they were strong. But unfortunately my signal was not seen there. I worked UN3M for a new one on 6m this year. Hope to work him or someone else from his country on 4m as well. As a matter of fact, I hope to work you on 4m, would be a new DXCC for me on that band. 73, Bas

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    1. Sorry, it was not UN3M but UN7ZO I worked on6m for a new one. 73, Bas

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