Propagation News – 21 October 2018
The sun remained pretty well spotless in the latter half of this week, with a solar flux index of 70 at the time this report was being prepared. But after an email from a GB2RS listener it is probably a good idea to recap how sunspot numbers are calculated. We count each sunspot as one, but each group as 10. So a single sunspot in what is obviously one group is 11, and two in two different groups becomes 22. So while the leap from zero to 11 may sound like a big jump, it may mean that only a single, solitary, and probably tiny, sunspot has appeared. This is precisely what happened earlier in the week, although the spot probably had little real effect on HF propagation. The best guide is the smoothed, or averaged sunspot number, which is what prediction programs like VOACAP use.
Geomagnetic conditions were more settled on Tuesday and Wednesday after last weekend, but we did have a planetary K-index of five on the 13th thanks to our old friend, a solar coronal hole. This may have generated a pre-auroral positive phase on Saturday, when the HF station at the RSGB Convention managed to work the USA and South America, although a beam did help. This week NOAA predicts the solar flux will remain around 70 and geomagnetic conditions will be reasonably settled, with a maximum Kp index of three.
Fingers crossed that better HF conditions continue for next weekend’s CQ Worldwide DX SSB contest.
VHF and up
The coming week will be dominated by high pressure and indeed looks like being in control over most of the country. This is a typical pattern for autumn with misty nights and early morning fog indicating a sharp temperature inversion. This can occur at the Earth’s surface and is often joined by a second inversion at a height of 1km to 3km. These temperature inversions set up sharp changes in the refractive index of the air over short vertical distances and can form important ducts for the propagation of VHF, UHF and microwave signals. These effects often last for extended periods and cover long distances, similar in scale to the dimensions of the high pressure system itself. So don’t just sit on the repeaters and complain about co-channel interference, get onto the simplex channels or down into the CW, SSB or data mode segments and spread out a bit. You’d be amazed what these modes can bring you with only a modest directional antenna.
The Moon’s declination rises all this week, going positive on Tuesday, so combined with falling path losses, it’s time to start looking for EME contacts again.
Meteor showers to look for this week are the Orionids, peaking this Sunday, plus the smaller Leonis Minorids on Wednesday.
Category: GB2RS Propagation News
