RSGB
October 17, 2025
Conditions over the past week have been reasonable with a relatively high solar flux and lower Kp indices. This resulted in a maximum usable frequency (MUF) over a 3,000km path, in excess of 35MHz. This is just what October was meant to be like!
But all good things come to an end, and there are a few flies in the ointment coming up.
On the 14th, the latest coronal mass ejection (CME) tracking model from NOAA and the Space Weather Prediction Testbed showed three weak CMEs possibly passing Earth over the next few days.
Although none of them is expected to deliver a large impact to the Earth’s geomagnetic field, a combined passage could generate minor G1 to isolated moderate G2 geomagnetic storming.
We are now well and truly into autumn and—with a daytime critical frequency of more than 9 to 10MHz—the 40m band is ideal for QSOs around the UK during the daylight hours. At night, the critical frequency is generally around 5MHz in the early part of the evening, dropping to 3.5 to 3.6MHz as the night progresses.
This means that the 80m band is remaining open around the UK for longer, but it may fade out, perhaps towards midnight.
October is a great month for HF with the potential for worldwide openings on the higher bands.
Next week, NOAA predicts that the solar flux index will be in the 140 to 150 range. Unsettled geomagnetic conditions with reduced MUFs are forecast for 20 October and then again on the 25th and 26th, when the Kp index could hit 5. Incidentally, these are the same dates as the CQ Worldwide SSB contest.
VHF and up propagation news from G3YLA and G4BAO:
This next period offers a marked contrast to our recent spell of tropo weather under high pressure.
This Sunday, the 19th, sees a change to a much more unsettled weather type with rain, areas of low pressure, strong winds and showers.
This will take tropo off the agenda for the coming week and its replacement is likely to be rain scatter for those on the GHz bands. There is no point in trying to time each individual low and front coming through this far ahead, and there is no real scope for any significant intervening areas of high pressure between the lows. So, there is no hint of tropo next week.
The recent solar conditions have again suggested that it’s worth looking at the Kp index for signs of aurora, should it go above 5.
Next, a few words about meteor scatter, which is gearing up for the Orionids, peaking on Tuesday, the 21st. However, they can have a broad spread, with a minor peak preceding the main event. Either way, it’s worth checking up on meteor scatter techniques and frequencies before the shower, rather than wondering what to do when it happens.
For EME operators, the Moon’s declination is falling again, and becomes negative on Sundy, the 19th, so Moon window lengths and peak elevation follow suit by falling. Path losses are still rising as we approach apogee early on the morning of the 24th.
As we move through 2026 we reach a sweet spot in June where perigee and the highest declination coincide. This means the lowest path losses occur when we have the longest Moon windows. This cyclic event last occurred in 2018 and will not occur again until 2035.
144MHz sky noise starts the week low until Tuesday, the 21st, when the Sun and Moon are close in the sky. This brings noise problems for Yagi-type antennas with their high beam width. After that, the noise rises to high again for the weekend beginning 25 of October.
(Mike Terry, UK/BDXC)
