RSGB
RadCom Assistant Editor
December 5, 2025
The prediction made for last week was for the solar flux index to increase, possibly reaching 155 by 1 December and 175 by 6 December.
In fact, it hit 196 on 1 December and 200 on 2 December. This was no doubt aided by three large sunspot groups in the Sun’s southern hemisphere.
We also said that the Kp index could hit 5 on 3 December and it actually hit 6.67. So well done to the Space Weather Prediction Centre for its forecast.
On Thursday, 4 December, the solar wind speed gradually increased from around 360 kilometres per second to 475 kilometres per second, thanks to the onset of an enhanced solar wind from a very large coronal hole.
The Bz component of the interplanetary magnetic field has also been pointing sharply south at times, which means it more easily couples with the Earth and the Kp index goes up as solar plasma floods in.
Maximum useable frequencies, or MUFs, have been affected, but not too much. The MUF over a 3,000km path was still above 28MHz on 3 December, at least until sunset. Night-time MUFs are now characteristically below 14MHz, leaving only 10MHz and below open to DX.
As reported by CDXC’s Slack group this week, recent DX included the YJ0GC DXpedition to Vanuatu and OX7AM in Greenland on the 10m band using CW. 5R8IC in Madagascar was noted on the 15m band using FT4. And SU8YOTA in Egypt was worked on the 20m band using SSB.
Next week, NOAA predicts that the solar flux index will stay in the 180 to 190 range and the good news is that the Kp index is predicted to remain low, at least until Saturday, 13 December, when it is forecast to rise once again to 5.
So, get your HF DXing in during the daytime over this coming week.
VHF and up propagation news from G3YLA and G4BAO:
The weather charts for the coming week or more show a very unsettled pattern with some deep areas of low pressure, strong winds and heavy rain at times.
Tropo is unlikely in the traditional high-pressure sense, but sometimes a strong maritime south-westerly wind can bring a brief slight improvement for parts of southeast Britain in the windy warm sector of the depression. Watch out for this on Tuesday, 9 December.
Rain scatter remains a good option since there will be numerous bands of rain and showers available as scatter elements. The Margate 24GHz WebSDR has seen the Flanders beacon ON0HVL for a number of days due to rain over the southern North Sea, but the lack of active 24GHz stations on the east coast made this a frustrating watch on a WebSDR.
Aurora is a possibility during the coming week. Look for a Kp index above 5 to generate a good radio response. The evening of 3 December saw classic fluttery HF signals on the 80m and 40m bands, supported by a Kp index of 6.67 and reported auroral QSOs on 70, 144 and 50MHz.
Lastly, a consideration of the meteor scatter prospects is more promising as we are now in the broader period for the Geminids, which is due to peak on Sunday, 14 December. This shower has a maximum hourly rate of 120, so ranks as a joint second after the August Perseids.
For EME operators, Moon declination reached a maximum yesterday, 6 December, meaning long Moon windows and high peak elevation. Path losses are at their lowest but increasing during the week. 144MHz sky noise is low for the coming week.
Mike Terry, UK/BDXC)
