ARLA/CLUSTER: UK HF Propagation charts for August 2012

[João Costa > CT1FBF]

Steve G0KYA has published his UK HF propagation charts for August 2012 at
www.g0kya.blogspot.com.

He says:

It may be summer, and the Olympics are in full swing, but we can’t
really expect to see record-breaking propagation on the HF bands in
the Northern hemisphere.

This often puzzles new (and not so new) hams. After all, HF
propagation relies on sunlight and we have that in abundance in the
summer.

Unfortunately, life is not that simple. While increased UV in the
summer is guaranteed, as the angle the sun makes with the ionosphere
in the northern hemisphere is increased, you actually get less overall
ionisation of the all-important F2 layer.

This is due to a chemical change in the composition of the F2 layer in
the summer compared with the winter. There is an increase in the
molecular-to-atomic composition of this layer in the summer, which
makes it harder to ionise. As a result the F2 critical frequencies in
June can be half what it they are in January.

This effect is called the Winter Anomaly.

At the same time D-layer absorption is very high in the summer,
especially around local noon, which gives us a double whammy – lots of
absorption and low F2 critical frequencies.

The net effect is that the bands much above 18MHz can remain
stubbornly closed, apart from Sporadic E (Es) openings, which by
August are less prevalent. And the lower bands are also less useful
during the day due to absorption.

For this reason stay away from 80m (3.5MHz) in the daytime – 40m will
be better around the UK as long as the critical frequency stays up
near 7MHz. Twenty metres (14MHz) will probably remain the most
reliable DX band both during the day and night, although don’t write
off 18MHz (17m).

Better HF conditions will start to re-appear in September – sunspots,
solar flares and coronal mass ejections (CMEs) willing.

Don’t forget there is also a free book about HF propagation available
to download at www.g0kya.blogspot.com

73 Steve G0KYA


• All propagation reports can be found at:
http://www.southgatearc.org/propagation