Hi Jim,
Am 14.12.2013 22:12, schrieb hvanesce:
Stefan,
I will be listening in Arizona.
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.
Do you think this is worth trying?
It is always worth trying, just for the fascination :-) I think we would
need a miracle though. But you/we will get an impression what is
possible. It least the QRN is very low these days!
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?
Yes, unfortunately. You need a GPS reference signal. There are some GPS
modules on ebay, which provide a 10 kHz reference signal. These in
combination with Spectrum lab allow to run a 30 uHz window. On my
grabber
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html you
can see the Alpha RSDN-20 line at 11904.7619 Hz which is stable since
several days. Your system needs to be stable like that (so that this
stable signal can be displayed like that).
More answers later. I have to sleep now. It is 5:12 AM here...
73, Stefan
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.
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.
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
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Stefan Schäfer
Sent: Saturday, December 14, 2013 12:50 PM
To: [email protected]
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!
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
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