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From: "hvanesce" <hvanesce@comcast.net>
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Date: Sat, 14 Dec 2013 14:12:28 -0700
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Subject: LF: RE: A short VLF experiment at DK7FC
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Status: O

Stefan,

I will be listening in Arizona.=20

I have a location that is free of cultural noise. Arizona is roughly =
21dB
from London at 9kHz. A bandwidth/FFT-window equal to the length of your =
test
is ~ 30uHz/14-hours, and the SNR advantage of this bandwidth over a 1mHz
bandwidth is ~ 15dB. By this reasoning if your signal is detectable in
London at 1mHz, it could be within 5dB of detectability here.=20

Do you think this is worth trying? One potentially big problem is that I =
am
running on the PC (laptop computer) clock. Does the drift in a PC =
(laptop
computer) clock make detection of a weak signal at 30 uHz impossible? I =
have
checked the stability of my laptop computer clock against some other
references, and notice that if I keep the temperature stable, the clock =
is
stable, but I have not checked this at 30uHz resolution.=20

Whether or not the above idea seems practical, I have another idea: is =
there
an easy way to stream raw data [time-domain data, not FFT (frequency =
domain)
data] to a disk drive? I externally preamplify and digitize the antenna
signal, and normally connect to SpecLab through the computer USB port; I
usually digitize at 96ksps.  14 hours (0200-1400 UTC) at 96ksps is ~ =
2GB,
which would fit easily on any of my disk drives. If I capture the raw =
data
to disk, I can eliminate 20dB of natural noise by post-processing. With =
no
cultural noise, and 20dB less natural noise, I should be able to detect =
your
signal. Clock drift would necessarily not matter in this example; I =
could
inject a weak signal from a stable clock through the antenna, and use =
that
reference clock signal to compensate for the drift of my laptop clock. =20

In any case I will be listening, but if you have thoughts on either of =
the
above methods, I will implement them as soon as possible. If I cannot
implement them in time for tomorrow's test, they will be available for =
your
next test.

73,

Jim AA5BW

=20

-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan =
Sch=E4fer
Sent: Saturday, December 14, 2013 12:50 PM
To: rsgb_lf_group@blacksheep.org
Cc: Paul Nicholson
Subject: LF: A short VLF experiment at DK7FC

Hi all,

Tomorrow the rain probability is just 10% and so i think i can risk to =
run a
short VLF experiment on 8970.00500 Hz. I'm using the fixed antenna at
JN49IK00WD. These days, the QRN is very low for quite a long time!=20
The plan is to run about 500W RF power, or more, depending on the =
voltage
limit of the antenna. And the plan is to start transmitting tonite, =
after
the experiment with VO1NA, i.e. i'll come on air arround 2 UTC, =
hopefully. I
will run the test until the late afternoon. First i'm TXing a stable
frequency until 9 UTC, later some DFCW-600, and then maybe some tests in
OPDS32.
Suggestions welcome.
BUT it all depends on the WX. If it starts to rain then i have to stop.
Will someone give it a try and watch for me?

73, Stefan/DK7FC