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Date: Sun, 15 Dec 2013 05:12:50 +0100
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: RE: A short VLF experiment at DK7FC
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Status: O

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 21=
dB
> 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 1mH=
z
> 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=20
need a miracle though. But you/we will get an impression what is=20
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 (lapt=
op
> computer) clock make detection of a weak signal at 30 uHz impossible?
Yes, unfortunately. You need a GPS reference signal. There are some GPS=20
modules on ebay, which provide a 10 kHz reference signal. These in=20
combination with Spectrum lab allow to run a 30 uHz window. On my=20
grabber=20
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber.html you=20
can see the Alpha RSDN-20 line at 11904.7619 Hz which is stable since=20
several days. Your system needs to be stable like that (so that this=20
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 do=
main)
> 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 ~ 2G=
B,
> which would fit easily on any of my disk drives. If I capture the raw d=
ata
> 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 cou=
ld
> inject a weak signal from a stable clock through the antenna, and use t=
hat
> 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: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan Sch=E4f=
er
> 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!
> The plan is to run about 500W RF power, or more, depending on the volta=
ge
> limit of the antenna. And the plan is to start transmitting tonite, aft=
er
> the experiment with VO1NA, i.e. i'll come on air arround 2 UTC, hopeful=
ly. 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 i=
n
> 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
>
>
>   =20