Thursday, 4 May 2017

Making the best of Es on VHF.

With the coming of May, on this Northern Hemisphere anyway, the annual Summer Sporadic E season ("Es") cannot be far away.

There have been a couple of openings on 10 metres, with Gianfranco IU1DZZ heard here for several hours each day. So I thought it might be time to set out how I manage it. I am not going to talk about the science of the process much, and instead concentrate on the operations.

The Annual Season Starts ...
The exact start of the season varies from place to place. Being located at 56 degrees North it tends to come a bit later here than nearer the Equator. But, broadly, it runs for 8 weeks or so on either side of the Summer Solstice (22 June). I am dealing with the Summer Es season here, though there are openings around Christmas and the odd day at other times, including after auroras.

Although there have been several weak openings, my first VHF Es contact during the 2017 season was today as I write this (4 May 2017). That was a JT65 contact with EA4WO in IN80 square, at 1734km. It was followed by a QSO with CT1FJC in IM57 (2142km). Both EA and CT were showing up on 10m WSPR, which gives me a clue to where to point my 6m beam.

What follows are a series of these clues plus some hints and tips. They work for me, but of course you can just sit back and work VHF Es as it comes. Most of this has appeared in this blog before, but I am pulling it together for this posting.

It all depends which band of frequencies you use ...
The level of ionisation in the E layer will affect the degree in which any particular frequency is refracted back towards the Earth.

When ionisation rises sufficiently to bend your signal back to reach ground the band "opens". This can be quite sudden with loud signals where moments before there was nothing. Hopefully during the day the ionisation will increase and signals will get stronger. And as that happens the ionisation may rise further to allow the next band up in frequency to open. This is a "rising MUF".

As the ionisation and the MUF rise futher, this most distant contact may disappear as other closer stations are heard instead. So the A to B path is present only at a certain level of ionisation, which will vary with the frequency used. Click to enlarge the image below if that would help.
 The same thing happens in reverse, with the higher frequency bands closing in turn as the "maximum usable frequency" (MUF) falls.

At a certain frequency the signal just gets refracted back to the ground and above that frequency the higher frequency bands will be closed. It is therefore the maximum usable frequency at that time.

Since the higher frequencies require stronger ionisation, they tend to open less often. My own experience is that my favourite bands tend to open during the Es season as follows:-

10 metres - almost every day
6 metres - every 2 to 3days
4 metres - every 3 to 4 days
2 metres - two or three days per year

So, if Es occurs more often on the lower bands, why go up in frequency to wait for an opening to arrive? The answer to that question is next.

Es is always better when ionisation is weakest ...
Yes, I know. It depends what you mean by "best". If you want to fill in lots of squares in countries which are well within the longest distance possible, then "best" would mean working loads of stations. On the other hand, "best" in this sense means working the longest distance.

Rather like F-layer propagation, Es gets to the best dx when the signal is radiated as close to horizontal as possible and it is then reflected by the furthest away ionised cloud near the horizon, and reaches a similarly distant station as it completes its travel (in other words, when the transmitted frequency is just on the MUF). This path is favoured when the band has just opened or is about to close as it is then that the bending is least and you can reach maximum DX. Generally there is only one station to work then, whereas if you want loads of stations to work then pick periods when there is stronger ionisation, though paths will generally be shorter.

So longer distance is definitely "best", and shorter distances are also "best". Marvin the Paranoid Andoid would appreciate that statement. As usual, click to enlarge the photos if that would help.
But this diagram is at one frequency, what if we use that information to bad hop?

Doing the treble ...
I use the information I gather on 28MHz WSPR to look for a 50MHz opening, then if things are good there, look for 70MHz and eventually 2m. It certainly beats sitting on 2m for 363 days a year waiting for the rare openings there. It is also possible to gather information from broadcast stations on the 88 to 108MHz band.
Doing the treble for me means following the Es opening up from 50MHz to 70MHz to 144MHz, making contacts as I go. This is usually only possible in the week or so on either side of the Solstice when ionisation is at its strongest.

As, by definition, the ionisation is weaker on the higher band, you often stumble across the "best" conditions as you move up the bands. And as it 2m there are only occasional short openings then they are often "good" if you can follow them - for instance contacts from here to Belarus and Italy. Not bad for 144MHz.

Moving down the bands after the higher ones have closed produces similar effects, usually with more DX around as they have been on the lower band all along (and missing the action).

Splitting the difference ...
DXMaps is an important resource for me. However, it depends on stations reporting contacts made. PSK Reporter is similar. If everybody sits around watching blank maps and nobody calls CQ then the maps stay blank.

However, if you see an interesting contact on DXMaps, how should you proceed? Well, I try "splitting the difference". Lets us suppose that I see an Es contact reported between an OH station in Finland and an EA station in Spain. Great. I need new squares in both Finland and Spain.
Imaginary contact similar to what might be seen on DX Maps.
If I beam at LA or EA I will almost certainly hear nothing. The signal is being refracted by a cloud of ionisation in the E layer midway between the two stations. So, I need to split the distance between the stations and try to work someone off that patch of E layer.
Likely path available (white line) based on the reported contact (red line)
Maybe I do not need Italian squares so much, but that is the likely path to open.

If you doubt this idea, here is some proof ...
Actual example from 70MHz DX Maps on 3 May 2017.
If you study DX Maps you will see these points where the cloud is located on a regular basis.

You can find the estimated ionised regions during an Es opening, by square, by clicking on DX Maps MUF ES tab.

It all depends of course as to how close to me to Es patch is. In my imaginary case it is nicely positioned for a good contact into Italy. If it was closer, I might hear nothing. Ideal spacing for Es clouds for best DX is about 1000km from me, which is an arc from SE Norway through to NW France.

Do the Es clouds move ...
Who knows?

If you look at DX Maps or PSK Reporter you will see the propagation move around. It is often said that the Es clouds appear to "move" North and West. I have never seen much evidence for this. The Sun is moving relative to the Earth (actually a product of the Earth spinning once a day) and it is the energy from the Sun which causes the ionisation. This would suggest that the patches of ionisation should "move" Westward. Look for yourself, but I find that most clouds tend to be pretty well fixed.

What does move is that the variation in the ionisation causes the path you can work to change, lengthening and shortening (and widening and narrowing in the process) , and that looks pretty much like the clouds moving from our perspective.

Then again, some clouds fade and others are made as the Sun appears to move in the sky, but the new clouds are not always to the west of the earlier ones, and may be to the north or south.

What sets it off? Now there is an issue for further discussion (but not here please). It certainly is not thunderstorms over the Alps, as we once read.

Are there two peaks of propagation during the day ...
Who knows?

A couple of years ago I tried to plot out all my contacts to see if there was a two peak pattern. I found no pattern at all.

For me it is, to use the famous Scottish jury verdict, "not proven" (other countries have just guilty and not guilty, but we place people we don't like but who cannot be found guilty into a nether land of doubt and suspicion for the rest of their lives).

If it exists, I sense a vague effect between the first peak at about 11:00 to 13:00 and the second from 16:00 to 20:00 (an hour later for clock time in the UK for Summer time). I would say that this is less noticeable at the start and end of the season.

The best I could say given my experience is that during most of the season VHF Es occurs after about 10:00 and rarely after 20:00. Near the peak at the Summer Solstice Es can occur almost all day and most of the night. This is especially true towards polar regions (where it does not get dark at that time of year).

I recently saw a suggestion in a magazine that the second peak only occurs at higher ionisation levels, so for example, might occur on 6m but not on 4m when 4m is only slightly open. For a weak event it suggested that only the morning peak would occur. I see the point they are making, I just find that sometimes I only get the later one!

It is very difficult to be certain because on 6m and 4m there are many countries which do not have the bands, and there might be various phases which open into desert or ocean.

What about multi-hop Es ...
A glorious thing if you can find it. With Es being pretty rare and irregular, we all thought that multi-hop Es was more or less incredible when I was first licensed. Then came some terrible dips in the sun-spot cycle and it emerged that what we passed off as F-layer propagation now turns out to be multi-hop Es. Some of the distances can be phenomenal. Some research suggests that up to 5 hops can be involved.

 It is bound to be less prevalent as you go higher in frequency, as Es is less common. However, at 6m I have worked trans-Atlantic paths. On 4m I have been heard in Asia. I am hoping one day to work into central Asia and Japan, but those things have not occurred yet. It depends where your station is situated. You can always hope.

What about the strange openings I can hear ...
10m and 2m are world-wide amateur bands. Generally you do hear only amateur traffic on them. On 6m and 4m things are different. On 6m you can sometimes hear TV timebase signals, mostly from Russia. On 4m there are wideband FM broadcast stations from Russia, and all sorts of sounds and FM signals from countries which do not have amateur allocations there.

These are useful indications that the band is open to somewhere and perhaps the path will shorten or lengthen to bring in an amateur station.

Expect the unexpected ...
The band noise seems to fall when the band is open for Es. This can be a useful sign. Sadly it often signifies that the band is open for a single hop into somewhere with few amateurs (like the North Atlantic).

Thinking about this, and the fact that for 180 degrees round me I am surrounded by sea at the key 2000km distance, I called CQ beaming West and was answered by a station on the Azores Islands. If you look at the huge size of the Atlantic and the tiny relative size of the Azores group, you might be surprised that it was possible at all, never mind that a station would be there, tuned to 70MHz, at the time I was trying. But it happened.

Next stop, Madeira and Capo Verde? Please.

You just never know. Which is the joy of the thing.

And finally ...
Post your result to the cluster, please, so that we can see it all on DX Maps.

Have a happy Es season.





  1. Excellent and informative (and Marvin too!) Why is this man not writing for Radcom?

    Bri G0MJI

  2. Thanks Bri

    Radcom could not afford my salary.

    Perhaps I should write a book?


  3. Definitely. You have enough material for more than one ;)