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Re: VLF: W4DEX in Europe at 8820 Hz

To: [email protected]
Subject: Re: VLF: W4DEX in Europe at 8820 Hz
From: Markus Vester <[email protected]>
Date: Tue, 2 Dec 2014 12:24:03 -0500
Cc: [email protected], [email protected], [email protected]
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once more, very impressive work! I'm tempted to call that a TA first for Dex and Wolf, and Renato at even larger distance is getting very close. But most of all, I think it's the cooperative effort between you guys which really deserves congratulations!
Markus (DF6NM)
Von: Paul Nicholson <[email protected]>
An: rsgb_lf_group <[email protected]>
Cc: wolf_dl4yhf <[email protected]>
Verschickt: Di, 2 Dez 2014 5:47 pm
Betreff: Re: VLF: W4DEX in Europe at 8820 Hz
Another plot from Wolf's receiver at Bielefeld,

This covers the full transmission from 22:30 UT in 50.5 uHz
bandwidth. The line at 8820.0000 is 11.7 dB above the
noise in this 1980 bin span.

It is the strongest bin in +/- 0.5Hz (19800 bins).

Of course, I also checked nearby integer frequencies - when using
PPS GPS timing there is the possibility of weak harmonics from
the timing system.

I tried Cumiana with this narrower bandwidth but no improvement.

Paul Nicholson

-----Ursprüngliche Mitteilung-----
Von: Paul Nicholson <[email protected]>
An: rsgb_lf_group <[email protected]>
Cc: wolf_dl4yhf <[email protected]>; Renato Romero <[email protected]>; Michael Smith <[email protected]>
Verschickt: Di, 2 Dez 2014 2:09 pm
Betreff: VLF: W4DEX in Europe at 8820 Hz
Spectrogram of W4DEX at Forest, VA (range 254km)

No sign of any frequency lock problems now. All the energy
is concentrated in one frequency bin so the signal appears a
lot stronger than the previous day.

Unfortunately the rx at Hawley TX stopped sending its VLF
stream yesterday.

W4DEX was quite good strength at Todmorden, getting up to around
0.15 fT which is slightly above LWPC prediction for 150uW ERP.
Actually that's a very good signal - European TXs are often
similar or less strength.

Spectrum plot, average 00:00 to 04:00 UT combining E and H

The above is on the optimum bearing of 310 deg (line of sight
is 285 deg).

Average signal strength 0.12 fT, 13.9 db S/N in 69.4uHz.

E-field S/N is 13.0 dB S/N and combined gives 16.49 dB S/N.

The noise from the south west was fairly high until 02:00 so
it wasn't really a good night for reception. It would probably
not have been successful to try a long BPSK message.

We also see a low significance peak in the spectrum at
Bielefeld Germany (52.146N,8.458E 6918km) in the same period
and bandwidth:

8820.0000 at 10.0dB S/N is the strongest peak in +/-1440
bins but there are noise peaks not much lower. Widening the
range to +/- 0.25 Hz (7200 bins) produces one stronger peak
at another frequency.

I suspect Wolf's receiver is picking up the signal but it is
a dB or so too low to be claimed as a detection. This is an
E-field rx so there is no directivity to exploit.

Cumiana, Italy (44.96N,7.42E 7173km) also shows an insignificant
line at 8820.0000 with 8.8 dB S/N but there are nine stronger
noise peaks in 2880 neighbour bins.

Coherently combining Bielefeld and Cumiana produces a signal
with 11.7 dB S/N

and this is the strongest signal in 23000 adjacent frequency
bins (I didn't look any wider than that +/- 0.8 Hz range
because there are some strong interference lines).

It therefore looks like that Dex is getting into Germany and
Italy but it needs a more significant result - without the
devious trickery that I use to combine receiver outputs.

If there was 50% or so extra antenna current and a good low
background night, the extra 3 dB or so would surely put this in
the bag.

Paul Nicholson

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