Propagation News – 18 November 2018
The predicted bad geomagnetic conditions forecast for last weekend didn’t turn out to be quite so bad after all. The Kp index only rose to four on the 10th and then conditions settled again, despite a large coronal hole on the Sun’s surface. However, reports did come in of poor conditions on 80 metres on Monday evening during the RSGB 80m Autumn Series contest. A good guide to conditions for inter-G, or near vertical incidence skywave propagation, is always the ionosonde data at propquest.co.uk. The site showed that the critical frequency, which is the maximum frequency at which signals launched vertically into the ionosphere are returned, dropped as low as 3.16MHz on Monday evening. This so-called critical frequency, or FoF2, meant the ionosphere couldn’t support close-in 80 metre signals—they basically carried on out into space rather than being returned to Earth. This may be a trend we see in the evenings throughout the winter, especially with a solar flux index as low as 67 as we have been seeing. The only answer is to move to Top Band or make do with VHF and UHF.
Next week, NOAA predicts more of the same, with an SFI of around 68-70. Geomagnetic conditions are predicted to be more settled though with a maximum Kp index of two. This means daytime maximum useable frequencies are likely to be around 18 or 19MHz over a 3,000km path. There have been the occasional openings during the day up to 21 and even 28MHz, but these are likely to be fleeting and generally unreliable.
Night-time MUFs over a 3,000km path may struggle to reach 9-12MHz at times, with 40, or more likely 80 metres, being the highest reliable band for DX.
VHF and up
It looks like a good tropo spell coming up, especially over the eastern side of the country with some good paths across the North Sea to northern Europe and Scandinavia. This is due to a strong temperature inversion set up by a large area of high pressure over Scandinavia. As this high drifts away towards Iceland, the tropo will decline and low pressure will take over for southern areas by mid-week. This could introduce some coastal showers, especially along the English Channel and over the southern North Sea, which may bring some chance of rain scatter for the microwave bands.
This Sunday we should still be in the tail end of last night’s Leonid meteor shower so look for enhanced meteor scatter paths.
Moon declination goes positive tomorrow so the week will see increasingly long Moon windows and path losses will fall as the week progresses.
Category: GB2RS Propagation News
