By Courtesy of the Propagation team
G3YLA JIM
G0KYA STEVE
G4BAO JOHN
Its all about the weather
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Jim Bacon G3YLA
NARC club member
and Nick Henwood
RSGB President.
Propogation News
11th July 2025
HF
3
Last week was characterised by settled geomagnetic conditions, but a relatively-low solar flux index.
The Kp index hit 5.33 on the 6th and 7th of July, but was otherwise rummaging around one or two for the rest of the week. These settled conditions were helpful to HF propagation, although the maximum usable frequency over a 3,000km path didn’t really get much above 21MHz.
This is likely to be due to the HF summer doldrums and we are unlikely to see it rise much more until September, once the F2 layer has switched to Autumnal propagation conditions.
Meanwhile, the solar flux index remained steadfastly in the range of 115-120 – enough to provide fair propagation, but not enough to set new DX records!
But there was DX to be worked, including T30TT, Western Kiribati, on 20m and 15m FT8 Fox and Hounds; ZD7FT St Helena Island on 17m SSB; and C94RRC on 10m FT8 from Mozambique.
Laurie G3UML, on the CDXC Slack group, commented that there was a lot of DX about, including FP/KV1J via 17m SSB on Miquelon; TY5AD on 17m CW from Benin and FY4JI on 17m SSB from French Guiana.
Now the bad news. A very large solar coronal hole will begin to face Earth this weekend. A solar wind stream flowing from this zone is expected to reach Earth beginning July 12th with the main influence by July 13/14.
If the Bz of the plasma cloud points south we can expect disturbed geomagnetic conditions and a reduction in the MUF.
NOAA predicts that the Kp index could reach four on the 12th. It also predicts unsettled conditions, with a Kp index of four between July 15th and 19th. The solar flux index is expected to be in the range 105 and 125 for the next week.
And finally, during this weekend’s IARU HF World Championship (on July 12-13), five stations – GB0WR, GB2WR, GB5WR, GB8WR and GB9WR – will be active on 80-10 metres SSB and CW and tested under field conditions. They will be using the exact planned equipment for the WRTC 2026 event as a trial.
The operating location will be a cluster of sites within Suffolk and there will be two awards available for chasers during the event so keep an eye open – 40m during the day and 80m in the evening will probably be the best bands.
VHF and up
The hot weather continues to set the agenda in the short term, at least through this first weekend into the start of the new week. Something to note is that for VHF and UHF Tropo ducting, the ideal is for warm dry air to sit on top of cool moist air.
These conditions are commonplace over the nearby seas as hot dry air moves out across the coast to overlay the cool, moist air near the sea surface. Think North Sea, English Channel, Irish Sea and Biscay as being very good Tropo paths in high summer, but the award goes to the Mediterranean where very strong ducting conditions are pretty much a given if you happen to be sitting on some exotic holiday beach.
Back at home if you live inland, then you will be out of luck during the heat of the day since there is no cool, moist surface air, but in the evening as the ground cools and perhaps cool sea air moves inland you could find yourself coupled into the Tropo conditions that those on the coast have been enjoying all day!
In other words, for most of the country, Tropo will be better overnight and early morning.
The other modes are worth checking of course, especially Sporadic-E which is continuing to give some paths on most days, at least for digital modes, but also for those using SSB or CW.
Most days there will be some direction available from the UK on 10m and perhaps on 6m with many online clusters to show you where the current paths are located.
We really must get used to the idea that Sporadic-E can be very localised, and you will only know about it if someone calls CQ; so if you do that, you may be surprised by how good conditions have been all along!
Disturbed solar conditions should keep aurora as a possibility and meteor scatter is often worth checking in this month with two showers peaking later in the month. The middle part of the coming week looks like turning more unsettled for a time, so rain scatter is also an option for the GHz bands.
Moon declination is increasing again reaching maximum on Tuesday and path losses are falling so time to put the feed back in the dish. 144MHz sky noise is moderate to start the week but decreasing to low after the weekend.
G3YLA JIM
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G0KYA STEVE
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