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Saturday, January 8, 2011

Summer Daytime African Mode appears

Each summer, here in Melbourne, a propagation event occurs, where strong
signals from Southern Africa are audible in our early afternoons, across the
window between 0300 and 0500 on 6 MHz, 7 MHz, and 9 MHz.

These signals appear mysteriously and suddenly, often rising to great
strength, and then disappear just as quickly, after staying for varying
durations, some for a few seconds, others for everal minutes.

The actual propagation mode has never been determined, and the event
generally is best during years of low, or decreasing sunspot activity.

It's been observed since the 1950s - my first reception of this mode was the
service of the South African Broadcasting Corporation, on 7295, with strong
signals at 0515 (3.15 pm here) on January 10, 1959. I recall that was a very
hot day - my receiver was a five-valve dual wave set - my location was the
inner east suburb of Auburn.

This propagation mechanism defies any simple solutions, at least where
attempts are made to explain it using classical propagation theory!

For the particular case of South Africa (Meyerton), Great Circle path
distances are:

10,287 km shortpath
27,713 km long path

Shortpath is across the Indian Ocean, in total daylight. Longpath is over
West Africa, the Atlantic, North America, the North Pacific - about 16,000
km of that route is night - about 11,000 km is in total daylight.

"Normal" propagation in total daylight on 7 MHz and 9 MHz over 10,000 km is
difficult to reconcile with conventional transmission theory!

There is little professional technical documentation available on this
propagation phenomenon - it continues to remain an enigma!

This is my summary of January 7, 2011, from a monitoring location on Firth
Hill, Warrandyte State Park, 20 km from central Melbourne, using the
little Eton E5 and a five metre random antenna:

7230 S. AFRICA Channel Africa, Meyerton, English, *0400
7255 ASCENSION BBC English 0415
7305 S. AFRICA BBC Meyerton Portuguese *0430
7340 BOTSWANA VOA Kinyarwanda to 0430*
9430 ZAMBIA CVC English *0400
9450 RWANDA DW-Kigali *0400
9460 S. AFRICA BBC-Meyerton 0430 English
9885 BOTSWANA VOA English to 0430*
" SAO TOME VOA English from *0430

Other monitoring observations of technical interest, from the same location
and date:

7260 VANUATU Vila, audible from as early as 0400
9405 USA WINB English 0400
9560 CHINA PBS-Xinjiang, Urumqi, Uyghur 0430
9685 CHINA CNR5 Chinese 0415
9730 N. KOREA VOK English 0420
9755 CANADA RCI-Sackville Arabic 0400
11685 CHINA CURL Mongolian 0420
11810 S. KOREA ABS-Kimjae 0400 Korean
11815 CHINA CAR Mongolian 0430

Comments and reactions would be appreciated!

Regards from Melbourne!

Bob Padula

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