A long lasting tropo event and then an aurora

After 3 April 2025 and the noticeable tropo duct mentioned in my last posting, there was a long lasting tropospheric event caused by a stable high pressure moist air system over the North Sea.

Long lasting stable high pressure systems are not always my favourite events, as it is normally alterations in pressure (usually downwards) which tend to produce openings. This was actually two systems, as when the first started to fill the second one moved in and merged. It appeared to be one high pressure system the whole time. 

I worked 53 stations on 144 and 432MHz between 1 and 11 April. This despite being absent at the GMDX convention on 5 and 6 April. The pressure was raised but not very high, peaking here at at 1026hpa on 10 April, but it had maintained a steady level above 1015hpa all the time since 30 March. In an area much given to storms arriving from the South West this long period of high pressure is unusual.

What constitutes "DX" for this purpose is debatable. Let us not have that debate here right now.

I have tried to plot contacts against barometric pressure as this event progressed over two weeks.

Week One - 

Barometric pressure at GM4FVM 31 March to 5 April 2025

As usual, click to enlarge images as required.

Where only a prefix is shown, just one station there was worked. Where a number is shown, e.g. 3xSM, this means three stations were reached in that prefix. A dotted line under the prefixes indicates that a contest was scheduled for one of the bands for a time during this period.

The barograph chart at GM4FVM shows the raised pressure during the week. Please have patience with me while I use up imperial measurement charts - I will properly calibrate the instrument once I have changed over to charts in hpa units.

The gentle rise in pressure up to the afternoon of 1 April produced no improved propagation. Then a very slight levelling out of the rise brought two OZ stations and a G who were all involved in the 144MHz NAC contest. The rise returned on the morning of 2 April but levelled out again in the evening. That level stretch brought a good opening to OZ during the 144MHz UKAC FT8 contest. Another slight dip in pressure coincided with the SM duct on 3 April (see last posting) and continued into an opening across the North Sea on the morning of 4 April. This ended with an short but steep rise in pressure, while the usual evening enhancement brought in mostly Gs and PAs towards the end of the day. On 4 April I worked 2 x LA, 3 x OZ and 3 x GM and one SM in the morning to afternoon period, plus 4xLA, 5 x G, 6 x PA and an OZ in the evening.

I was absent from the shack as I was away at GMDX on 5 April and almost all of 6 April. Actually I was home around lunchtime on the 6th but I then fell asleep - which must have shown the quality of the contributions I heard at the GM convention.

Week Two - 

Barometric pressure at GM4FVM 6 to 12 April 2025

During Week 2 the pressure gradually rose to a peak on 10 April and then fell steadily until 12 April. It was possible to work OZ on many days, and during the 432MHz NAC contest on 8 April I worked 6 OZ and 2 SMs. The 432MHz FT8 UKAC on 9 April produced a better than usual number of contacts. Once the steep decline set in at around 10:00 on 10 April I only worked one more DX station when the fall levelled up slightly.

Looking at these charts I would suggest that things depend on three factors for maximum DX for me on 144 and 432MHz (and probably 1296 too) 

EITHER

1) High pressure with moist air (ideally with gently declining pressure)

OR 

2) Evening cooling after a day of moist air high pressure

OR  Both

PLUS

3) A contest

It looks very much to me that either 1 or 2 or both is very desirable, but adding a contest really raises my DX performance. Not that I enter contests, but I do give away points. Mornings generally are not so good, and there are few morning contests except poorly supported ones at the weekends.

Basically, if the same opening had occurred at the end of the month when there are no contests on 2m and 70cm I think I would have fared much worse.

The fact that a contest makes so much difference was something I must have been aware of but I had never put into context. It seems to be a bigger influence than I would have expected.

By the way, the rather wobbly barometer trace is not due to the apparatus but due to my shaky hands. I went over the trace with a pen as the barometer leaves quite a faint mark. I am using a modern felt-tip pen on the barograph, but the line gets lost amongst the chart lines. Charts used to be in red ink so that you could see the trace more clearly ....

Dickson and Cargill Barograph at GM4FVM

Mind you, the barograph is 100 years old. It came to me via my father and it had not worked for at least 60 years. Although of no value I restored it recently. It is a useful thing to have for a VHF-er. I do have a modern weather station with a pressure readout but that will never be the same.

And then on 16 April came an impressive aurora. The K number at GM4PMK's magnetometer briefly reached a rather impressive K=9 and the VHF bands sounded amazing.

GM4PMK's magnetometer chart for 16 April 2025

I did a lot of listening. I did not work many stations compared to some others. I stuck to Q65 and contacted 12 stations, 7 on 50MHz, 1 on 70MHz and 4 on 144MHz. It would seem that the trend is continuing for Q65-15C to be common on 6m while Q65-30B is gaining ground on 2m where the going is rather more difficult.

Based on the present stage of the sunspot cycle many crystal-ball gazers are predicting more aurora activity for the coming months.

73 Jim

GM4FVM

A classic tropospheric duct

I really enjoy working tropo enhancements on VHF and UHF. Usually though they move around with the weather and can be quite wide, which makes them hard to identify against a complex background of other contacts.

However, on 3 April I stumbled across a long lasting and quite narrow duct on 70cm. The background is that a high pressure system had developed to the north of Scotland and was destined to affect our weather for ten days or more. Seeing the opportunity of the good weather, I had scheduled some antenna work. As barometric pressure was moderately high but not declining I though nothing much would emerge on the tropo front. Usually good conditions emerge only on the trailing edge of high pressure systems, when pressure is falling. However, even during long lasting highs it is possible to find good conditions.

With all this in mind, and while working on my 2m antenna, I passed the shack door on the way to collect some tools. I noticed a very strong station calling CQ. This was SM6VTZ in JO58.  I have worked Chris a dozen times on 23cm, 70cm and 2 metres over the past four years, but only during good conditions. The striking thing about seeing him on the waterfall this time was not only how strong he was, but that nobody else was to be seen. Apart from one station, conditions were normal.

Although he had finished calling CQ, I called Chris at 12:49 and gave him a +20 report, and he replied with +23dB. The path length is 879km. These are not unusual reports, the previous time we worked on 70cm was in September 2024 when the reports were +14/+29dB. It is worth bearing in mind that during normal conditions I cannot hear Chris at all and on a flat band I can usually work only about 300km with much lower reports.

What was different about this contact was the almost complete absence of any other station, not just on 70cm, but also on 23cm and 2m. Chris came on to KST chat room where other SM stations reported hearing nothing from me.

On KST Chris and I exchanged reports as the duct built over time, later reaching +24/+34dB. Having started before 12:49 this went on until after 16:50. I heard SM6CEN in JO57 at 15:19. I guess that Hakan is on the southern edge of the duct as signals to him were much lower at  -19/-16dB at a time when VTZ was reporting my signal via KST at 50dB higher than Hakan.

I also worked MM0INH who I think worked VTZ too, but at lower signal strengths than I did. Dale is 43km to the west of me. I was not aware of any other stations working Chris though he may have worked another station in North East England. It is clear that this duct was narrow.

Extract from station log at GM4FVM covering 3 April 2025

Click to enlarge images if you need to.

So how do I know that this was a narrow duct? Because it follows the general pattern for ducts:-

1) I did not work anybody else on 2m, 70cm or 23cm that day, and I would have expected to if this had been a general enhancement or a moving or wide duct.

2) It was extremely stable over a long time - several hours

3) Stations outside the duct did not get into it 

4) Signals were extremely strong as ducts pass signals very efficiently 

More usually ducts move with the weather. On this occasion, with a very stable weather pattern, it stayed in one place. I have experienced this before, but it is unusual.

Here is the best map I can do at the moment. In the absence of Log Analyser I have used K2DSL's "ADIF to Map" site. Once I had the map by this method I went back to the way I made maps years ago - passing the image through two pieces of software to add text and crop to size. I am still seeking a better solution.

Contacts at GM4FVM during 3 April 2025

Ducts are common. What was uncommon this time was finding such a narrow long lasting duct, with no other DX possible for the whole day. I like ducts, and after all it was a duct which allowed me to work EA8TJ on 5 August 2018, a distance of 3260km. But others in various parts of Scotland could access that duct, whereas this time it was very much narrower.

I shall look more carefully for such things in future. And next time I will try to remember to ask Chris to try 1296MHz too.

[EDIT. I should have mentioned that in contrast to this narrow duct, the next day I also worked SM6VTZ, this time on 144MHz. Unlike 3 April, contacts on 4 April were all round the compass and nothing like as strong. I worked 15 on 144MHz and 9 on 70cm, spread almost evenly around the North Sea. 5 x G, 4 x OZ, 5 x LA, 3 x GM, 6 x PA and one SM. That could hardly have been more different]

73 Jim

GM4FVM

Log Analyser de-activated.

[Edit - this may not be the final word on this - see update at the bottom]

Sad news from Mario DL4MFM that his excellent Log Analyser has been de-activated because Google no longer offers the map without charge.

This is an unfortunate development for me as Log Analyser was a very useful tool to use for this blog, as well as a very handy way of understanding QSO data.

I have written to Mario to thank him for a number of years of great work. Log Analyser developed over time and added some very useful features. He deserves our thanks for all his work.

It is a pity that another map source cannot be used - such as OpenStreetMap. In any case I would be willing to pay a subscription to a similar service if I could find one as good as Log Analyser.

Moving on, I am tinkering with GridTracker which is very good for all sorts of things but which does not quite match Log Analyser 3.2 for the functions I need. It may do for the meantime, and there are a couple of others around. We shall see.

I miss Log Analyser though.

73 Jim

GM4FVM

[Update - Mario has replied to me that he is hoping to bring Log Analyser back, perhaps with MapBox mapping. However, he has other commitments and this might take time. I am prepared to wait for such a useful aid. I have thanked Mario once again for his efforts to date. 73 Jim]