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Re: LF: EbNaut from Todmorden

To: [email protected]
Subject: Re: LF: EbNaut from Todmorden
From: Gary - G4WGT <[email protected]>
Date: Mon, 14 Mar 2016 18:55:09 +0000
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Hi Paul & All,

Paul wrote :-
I was about to fire up the tx but it looks like somebody is
on or near 137.465 already.

That was probably Mike G3XDV running Opera "Op32" mode (32 minutes Tx).

See :-

https://www.dropbox.com/s/7t1tuy1iuuglvqj/Screenshot%202016-03-14%2018.41.52.png?dl=0

73, de Gary - G4WGT
MF-LF-VLF Grabber : http://myweb.tiscali.co.uk/wgtaylor/grabber2.html
Web : http://myweb.tiscali.co.uk/wgtaylor/index.html

.

On 13/03/2016 21:34, Paul Nicholson wrote:
Thanks all very much indeed for the reports and decodes.

I've downloaded Domenico's wav files for a closer look.
It was a good result for EbNaut.  The best decode by Domenico
corresponds to about -46dB in a 2.5kHz bandwidth and it seems
that I made a good guess of the symbol period to use.

The phase is clearly a lot steadier at LF than MF.  In almost
all cases the BER was lower than expected from the measured
carrier S/N which I think tends to indicate that other signals
or interference are present in the ebnaut-rx input file but
outside the bandwidth of the transmission.

It looks like I could have dropped to 24W input and still
get at least one decode from Markus and Domenico. At a BER
corresponding to 13dB S/N with the 03:00, the constellation
is beginning to show some axis and the two phases for a time
almost separate completely.

I am completely impressed by Reolof's reception capability at
both LF and MF.  If I connected the multiplier output to the
antenna I wouldn't be surprised to be received in Middelburg.

It was most unexpected to find that the transmission at LF
didn't affect the VLF receivers at all.  This enabled me to
leave the tx on overnight and not miss any of the VLF activity
that was going on last night.

Before I dismantle the tx and antenna, I'll aim to do another
run this evening with the signal 10Hz higher to avoid the
interference Stefan mentioned.  Maybe 22:00 to 00:30.  I only
wish there were some more distant coherent receivers to aim
for using longer symbol periods.  It would be nice to know if
LF could support, say, 8 second symbols for a two hour message
at very long range.

An unresolved mystery are those periodic glitches showing
up on Gary's spectrogram.   I'll be having another look at
those later.

I was about to fire up the tx but it looks like somebody is
on or near 137.465 already.

 http://myweb.tiscali.co.uk/wgtaylor/grabber2.html

--
Paul Nicholson
--


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