Propagation News – 16 August 2015

Long-range HF propagation showed signs of picking up this week. Whether this was due to the slow change to better autumnal propagation, or from having a short period of fairly settled geomagnetic conditions, is debatable.

The settled conditions didn’t last long though as the Kp index was up to four on Thursday due to plasma from a high-speed solar wind stream. The interplanetary magnetic field had a strong south-facing component meaning it coupled with the earth’s magnetic field and plasma flooded in. This brought poor HF conditions once again, with little being heard outside of Europe on Thursday morning.

Next week the solar flux index is predicted to be in the range 90-100, with more periods of unsettled geomagnetic conditions at times. Optimum working frequencies on 3,000km paths during daylight are now about 18 or 21MHz on southerly routes, such as UK to South Africa. On easterly paths to the US, 14 or 18MHz are more likely to bring contacts. It is similar story on the short path to Japan, where 18MHz remains favourite, with occasional openings on 21MHz.

The Chilton Ionosonde indicated a critical frequency of 6.425MHz at midday on Wednesday, showing that 40 metres is not really a viable option for inter-G communications. 80 metres may be better, but suffers badly from daytime absorption.

VHF and up propagation

After last week’s excitement of the Perseids meteor shower it’s back to more normal VHF conditions, with just the tail end of the shower enhancing meteor scatter paths on the low VHF bands.

Early in the week there will be a weak ridge of high pressure over the UK, so some enhancement of tropo conditions is possible, chiefly overnight. There are two main high pressure centres this week; one over Scandinavia and the other near the Azores, and these are likely to persist through the week. This could mean some slightly enhanced tropo conditions up and down the North Sea as well as down towards the Azores.

The trough of low pressure between these two highs may produce some heavy showers resulting in possible GHz bands rain-scatter paths within the UK.

It’s still worth checking for sporadic-E on 50 and 70MHz in both the late morning and late afternoon peak operating windows and, with jet stream activity over the Pyrenees, the first paths to look at should probably be those towards EA and CT.

Category: GB2RS Propagation News