August 29, 2025
This week saw a change in HF propagation with a perceptible move towards more autumnal conditions.
The 10 and 12m bands have started opening up to the USA, at least on FT8. As we move into
September this will improve further. Also, as we head towards the autumnal equinox, we can expect better conditions on north-south paths, such as the UK to South Africa.
The week saw the solar flux index climb to 226 on Thursday, the 28th, thanks to a host of sunspots, mainly in the Sun’s southern hemisphere.
Over the last seven days the Sun also provided us with 12 M-class solar flares. Any associated coronal mass ejections (CMEs) were not Earth-directed, so these had little effect and the Kp index stayed firmly at 3 or below. The latest updates suggest that there is only a 10 percent chance for a strong X-class solar flare.
FT8 continues to be the preferred HF mode, or so it seems, with stations in China, Japan, Indonesia and Cameroon making their way into UK logs on the 12m band.
The 10m band has also been humming, with South America rolling in during late afternoon and early evening. This can only get better as we move into September and October.
NOAA predicts that the coming week will start with a solar flux index of 155 on Monday, 1 September. This may be a little pessimistic, but we’ll see. It also predicts that the solar flux index will drop off as the week progresses, ending the week at 125.
Geomagnetic conditions are forecast to be good for the first half of the week, but then decline from 4 September. Batten down the hatches as a Kp index of 6 is forecast for 5 September, with unsettled conditions lasting until 10 September. Check for auroral HF signals on 5 September, or even the possibility of visible aurora from the UK.
We recommend you get your HF DXing in early next week!
VHF and up propagation news from G3YLA and G4BAO:
Last week saw some lovely late season sporadic E on the 6 and 4m bands, including Spain, Italy, and east into Ukraine. There was an opening to Brazil on the 24th that reached as far as East Anglia but, as usual, stations on the south coast and west of the country had the best of the transatlantic QSOs.
This is the last bulletin in the nominal 2025 sporadic E season, which lasts from May to August. However, last week was a good reminder not to give up too soon as there were several CW and SSB paths showing up, particularly on the 10 and 6m bands. There were also a few reports on the 4m band.
The daily sporadic E blogs on propquest.co.uk come to an end Sunday, 31 August, but the site will continue to provide the maps as usual. To help you, notes on how to interpret the maps are available on the website. Thanks to all the sporadic E operators who have submitted logs to the various clusters this year.
The change over to unsettled weather is now complete and we will see rain and thunderstorms in most areas from time to time. It’s a good period to check out rain scatter propagation if you are set up for the gigahertz bands.
The heavier rain is well-captured by the many online rain radar displays to help you track the most active scattering volumes, which move with the stronger winds quite high up in the atmosphere. Speeds of 30 to 60 miles per hour are common.
There is one note of contrast with the model evolution after midweek. One branch sticks with low pressure to the following weekend, while another outcome tries to bring in a ridge of high pressure and a chance of tropo propagation. If the latter turns out to be the actual evolution, it may prove useful for the 144MHz Trophy and Backpackers Contest next weekend. However, it may not have arrived in time for the 144MHz UK Activity Contest on Tuesday.
The solar conditions are still providing some interest for auroral propagation, but with a Kp index less than 3, nothing of use radio-wise. Look for a Kp index increase beyond 7 for that. Meteor activity is currently between major showers so expect random activity, which suggests early mornings for checking out meteor scatter prospects.
Moon declination is negative, reaching a minimum on Monday, 1 September. So, it’s a week to check out your equipment rather than to operate. With the Sun still high in the sky, it’s easy to check system performance with Sun noise. Path losses started to fall after apogee on Friday, 29 August. 144MHz sky noise is close to 3,000 Kelvin on Monday, dropping back to moderate on Wednesday.
(Mike Terry/BDXC)
