Paul,
Good info and results!
LWPC is acknowledged as having a rather poor terminator model; no suggested
workaround that I know of, other than customized LWPC or other customized
EIW modeler.
Do you know offhand what field strength (fT) corresponds to your 30nV 4e-
received signal level?
At this location in northern Virginia I can run 10uW ERP at 8820 Hz for ~ 12
hour periods; oscillator stability may be ~100uHz. Do I need more power and
better stability for a T/A attempt?
Thanks also to Dex for displacing the four electrons, they went to good use.
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Thursday, December 4, 2014 1:01 PM
To: [email protected]
Subject: Re: VLF: W4DEX in Europe at 8820 Hz
Examining W4DEX at Todmorden overnight on 1st/2nd Dec...
S/N dB in 278uHz and signal phase in 1 hour steps:
From dB phase
22:30 7.6 80.4
23:00 8.9 90.9
23:30 9.1 115.6
00:00 6.3 106.2
00:30 7.9 30.6
01:00 7.9 60.4
01:30 11.8 88.8
02:00 10.1 78.6
02:30 10.8 62.7
03:00 10.0 77.3
The effect of the terminator is lasting a bit longer than LWPC predicts and
it doesn't really settle down until 01:00.
But the phase doesn't go too wild, just a bit of a wobble and it could still
be usable if the S/N was a bit higher.
From 01:00 to 04:00 is very good but not long enough for a worthwhile
message.
Some calculation shows that with a rate 1/8 K=25 FEC code a 5 character
message could be sent between 23:20 and 04:00 using
30 second symbols with reasonable chance of success if the S/N was averaging
around 10.0 dB during the night.
There's a very steep cliff effect with this coding, an extra
dB would make it almost certainly successful. We could
probably do that with a bit of extra antenna current and a low background
night.
Background noise for European receivers over four recent nights
http://abelian.org/vlf/tmp/141204-vlf1.png
http://abelian.org/vlf/tmp/141204-vlf6.png
http://abelian.org/vlf/tmp/141204-vlf15.png
Some nights are 3dB better than others, and a good night at one site is not
necessarily good at the others.
At Bielefeld the estimated signal strength is around 30nV.
With antenna capacitance of say 20pF, that's an alternating charge of
amplitude around 6e-19 Coulombs which is about 4 electron charges.
We don't actually have 4 electrons oscillating between ground and antenna.
Instead there is an oscillating displacement of the average position of all
the free electrons in the antenna wire with amplitude of around about 15 or
so proton diameters.
--
Paul Nicholson
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