RSGB
GB2RS News Team | September 19, 2025
Last week we said that it looked like someone had thrown a switch on the Sun and all the sunspots had vanished. Well, this week we’re pleased to report they’re back!
We have eight sunspot groups, spread evenly throughout the Sun’s hemispheres. Interestingly, the northern hemisphere sunspots are close to the equator, which is what you would expect at this point in the latter part of the solar cycle. The southern spots are somewhat higher in latitude, perhaps indicating that there might still be the potential for a double peak.
On Thursday 18 September, the solar flux index stood at 147 and the Kp index at 2. This suggests that HF conditions might be pretty good, at least until the next geomagnetic disturbance.
There have been no M- or X-class solar flares over the past week.
The solar wind speed dropped from a high of 800 kilometres per second on Tuesday 16 September, to a more reasonable 538 kilometres per second on Thursday 18 September. However, the Bz has been pointing south at times, which can cause problems with a raised Kp index.
The maximum useable frequency, or MUF, over a 3,000km path generally allows for operation between 21 and 24MHz during daylight and 7 and 10.1MHz at night. At 0845UTC on Thursday 18 September, a quick check of the NCDXF beacons on 21.150MHz showed reception of CS3B in Madeira and 4X6TU in Israel.
On 24.930MHz, 4S7B in Sri Lanka, ZS6DN in South Africa, and CS3B in Madeira could be heard. On 28.200MHz the only audible beacon was 4X6TU in Israel.
The NCDXF beacons are a quick way to check worldwide HF propagation in just three-minutes per band, from 20 to 10m. For more details visit ncdxf.org/beacon
HF DX this week has included FP5KE on St Pierre and Miquelon, which is operating until 26 September. PJ7K on St. Maarten, which is active until 22 September, was worked; and VK9NT on Norfolk Island, which is operating until 27 September, also made it into UK logbooks. Check the DX cluster for the latest spots.
Next week NOAA predicts the solar flux index will remain in the range of 125 to 135. The Kp index is forecast to remain low at 2 all week. A coronal hole threatens to push the Kp index higher, perhaps late today, 21 September, or tomorrow, 22 September.
VHF and up:
The first part of the coming week will be under the influence of the unsettled weather pattern with lows and fronts affecting the British Isles. So, it feels like there will be a few more days for the GHz rain scatter folk to play.
Be aware that even among low-pressure systems there can be fleeting moments of good Tropo. On Friday 19 September there were ideal Tropo conditions over southern Britain and south across Biscay to Spain as well as east across the North Sea.
The big change takes place on Wednesday 24 September as an area of high pressure starts to build over the UK. This could last through to the end of the week. So, there is plenty of time to develop some good Tropo conditions over large parts of the UK and near-continent.
There will probably be an elevated inversion some 1 or 2km above the surface. This will be caused by the high itself and may provide ducting conditions throughout the 24-hour period. This may be supported by temporary surface inversions overnight due to the ground cooling.
These features tend to take a while to establish, which suggests that the latter part of the coming week may be the best time to operate. The effect will only just be starting to influence conditions over the western side of the UK for the SHF UK Activity Contest on Tuesday 23 September.
Regarding the aurora prospects, it feels like we should be keeping a watch throughout this autumn period when the Earth’s magnetic field couples with the solar wind more effectively. Earlier last week the Kp reached 5, which is a good trigger to get interested in beaming north for those fluttery auroral signals.
Meteor scatter remains in between events at the moment with no major showers in the period. So, it’s random meteors only which, as we know, tend to favour the early morning, pre-dawn hours.
We are outside the traditional Sporadic-E season now but, as you may have noticed on the Propquest graphs, there has been the occasional spike on the foEs plot up to 5MHz or so. This is plenty to generate some strong short-skip European signals on the HF bands, especially 10m.
In the morning on Wednesday 17 September, Sporadic-E was probably triggered by the powerful jet stream moving east over the near continent. There may well be further occasions with strong jet streams during the next week, so keep checking the NVIS tab at propquest.co.uk to see if the foEs trace spikes again.
Now for an EME update. Moon declination is decreasing, from its maximum on 14 September. The Moon’s distance from Earth is also increasing until apogee on the 27-28 September. This means path losses are growing over the next week. Sky noise will remain low until 29-30 September.
https://rsgb.org/main/blog/news/gb2rs/propagation-news/2025/09/19/propagation-news-21-september-2025/
(Mike Terry, UK/BDXC)
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