Sunday, November 19, 2023

Inter UK contacts on 14 MHz possible as skip distance shortens to 500kms - Nov 2023

Most weeks, I skip through the news bulletin from the RSGB and I found this item of interest.

RSGB News... "Propquest shows that the F2-layer critical frequency is still maxing out at more than 12MHz around noon. The F2-layer critical frequency is the highest at which radio waves are returned back to Earth when sent directly up into the ionosphere.

This gives us a maximum usable frequency, or MUF, over a 3,000km path of more than 40MHz. Interestingly, it also gives us an MUF over a 500km path of more than 14.7MHz. So, look out for long-distance inter-G signals around noon, or thereabouts, on the 20m band. 

The 30m band remains a pretty solid inter-G band from late morning to mid-afternoon."

On the face of it, it should come as no great surprise. If a signal can go straight up (90 deg) to the F2 layer of the ionosphere and come back down at 12-MHz then a skip distance of about 500kms on 14-Mhz sounds about right.

The diagram above shows the path of the signals. The 14-MHz signal will eventually reach a low enough angle... i.e. the critical angle so that it can return to point B.

Back in February of 2017, I was working some Spanish special event stations during what was then the minimum of the sunspot cycle. The shortest path back then on 14 MHz then was around 1500kms.

Now in November 2023, we're near the peak of the sunspot cycle with a higher solar flux and the skip distance on 14 MHz has reduced to about 500kms at midday. This 'short skip' distance on 14 MHz should apply to other stations as well in say North America or Europe if they're located below say 60 deg latitude.

From my perspective here on the south coast of Ireland, the whole of the UK is generally within my skip distance on the higher HF bands. On bands like 14-MHz, it's normal to hear stations from say Germany but not the UK.

There are times during the summer Sporadic-E season when short paths are possible but usually not in November.

28 MHz... The shorter skip distances also applies to the higher bands. The minimum distance now on the 28 MHz (10m) band should be around the 1500km mark, maybe a little less.

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