Hi all, there have be several queries in the past about the nature of fading
seen on the 136kHz band. As a result of a "classic" plot made by Brian of
DCF39 on the 13th/14th of August 2003 I decided to try and analyse the
causes for the deep troughs in the night-time signal strength.
I have used some simple school level algebra, and a rather "naive" model of
the ionosphere, to calculate the path differences between, in this case, a
one-hop and a two-hop signal paths, relating that to a phase difference at
138.83khz. I some ways the results pose as many new questions as they
answer. The full analysis is posted on my web site under the Propagation
section. The direct URL of the page is
http://www.alan.melia.btinternet.co.uk/fading.htm
The equations, and spreadsheet, could be applied to other combinations of
paths, such as ground-wave and one-hop at distances greater than 700kms
where the night-time "skywave" becomes stronger than the ground-wave
component. Multiple simultaneous observations at different locations might
make it possible to calculate the actual height of the "reflecting" layer.
Cheers de Alan G3NYK
[email protected]
www.alan.melia.btinternet.co.uk
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