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Re: LF: Alert CFS NDB

from [Alan Melia] [Permanent Link][Original]
To: <[email protected]>
Subject: Re: LF: Alert CFS NDB
From: "Alan Melia" <[email protected]>
Date: Sun, 30 Nov 2014 21:03:34 -0000
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Hi Roelof, I had not registered the time.....it is possible that two hop and the one hop (which is possible, the range is extended by diffraction/scatter at the ends, so somewhat attenuated) may be in antiphase when the 2nd hop is in darkness. Then as the daylight washes out the second hop the 1 hop signal is left as the sole path. Another option is that the final 2000km is by 2 hops of 1000km from the daytime D-layer at an altitude of 50km. Although this is usually weak it could due to the increased path reinforce the one hop before the daylight reaches mid Atlantic. When I has monitoring for Joe some years back now I did copy him quite long after sunrise when he forgot to kill the TX in the morning. In summer the first ray illuminate the D-layer from underneath and this gives a very high absorbtion leading to the "morning dip" but in winter it is possible the radiation is not strong enough to produce high level of absorption.
 
Its all fascinating stuff, a lot of "hand-waving", no real proof, but its stimulating to think up reasons why it might occur. I think if you use the "paid-for" version of GeoClock (is it still around?) you can define the altitude at which the sun rise shadow display is formed. It is interesting to look at the plot as this passes through the "reflection" points for the different hop modes. The ideal would be a constant phase signal and monitor for the phase changes. This would have been possible with Markus's software on Loran C but unfortunately all the N. American stations closed down. I am sure I have these isolated peaks at dawn on some of the old plots I used to make of CFH Newport Corner, Halifax NS on 137.00kHz ten years or so ago.
 
Best Wishes
Alan
G3NYK
 
 
 
----- Original Message -----
Sent: Sunday, November 30, 2014 8:23 PM
Subject: Re: LF: Alert CFS NDB

Hello Alan,

Thank you for the information.
That implies at least two hops and the second reflection point in full daylight.
However, at this time of the year "full daylight" is something different than in June.
I gather that in December/January the density of the D-layer is less than in June.

There is also daytime reception, up to the daily solstice of the sun, over a much longer path than 4000 km.
YQ-305, Churchil, Canada Manitoba, is about 5700 km away and YEK-329, Arivat/Eskimo Point, Canada, Nunavit 5500 km.
This should be all multi-hop propagation.

73,
Roelof, PA0RDT 
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