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Propagation News – 15 September 2019

It was a quiet week, geomagnetically speaking, with the Kp index generally not rising above two. But a lack of sunspots didn’t help HF propagation, which was decidedly uninspiring. There were some highlights though, mostly on FT8. Columbia was decoded on Wednesday evening on 15 metres at a time when CW and SSB users might have thought the band was dead. FT8’s ability to dig out signals that are below the noise level is saving the day in terms of DX being workable.

On a brighter note, in a new paper, scientists predict that the current solar cycle 24 will end in the first half of 2020, kicking off the growth of solar cycle 25 very shortly after. The paper, from the US National Center for Atmospheric Research, is based on a new theory that tsunamis of plasma race through the Sun’s interior and trigger the birth of the next sunspot cycle.

Meanwhile NOAA predicts that next week the solar flux index will remain low with an estimate of 68-70. A total lack of Earth-facing coronal holes is good news, with the Kp index remaining at around two.

Finally, we are starting to see the gradual change to autumnal HF conditions, which will bring better DX working over the next couple of months. The Propquest site shows that the maximum usable frequency is now hitting more than 18MHz over a 3,000km path at times, so 17m is becoming quite usable as we exit the summer doldrums. It is also still showing an uplift in the critical frequency after dark on most days, which could bring some DX surprises.

VHF and up:
The coming week will suit VHFers who like to rise early, so set those alarms to get the best DX opportunities. The week will start with high pressure over the country and, except for a brief period when low pressure moves across the far north of Britain this Saturday, the 14th, it’s pretty much a tropo story all the way. When there is still summer warmth around, it’s worth noting that the strong lift conditions in the early morning usually fade as the temperature rises. So it’s really an early bird that catches the worm for tropo!

Last Friday saw Moon apogee, when it is at its furthest point from Earth, and Moon declination goes positive this Sunday, so EME conditions will improve as the week progresses. The Moon will rise higher in the sky at zenith and will be above 50 degrees elevation in southern England in the early hours of Thursday. Sky noise on 144MHz starts the week at a low of around 250 kelvin, and path losses will fall.

There are no major meteor showers this week, but the September Epsilon-Perseids minor shower, though past its peak, continues to be active until around 21 September. Check the early hours before dawn for the best random meteors.

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