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Date: Sat, 06 Mar 2010 18:26:46 +0000
From: Paul Nicholson <vlf0308@abelian.org>
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Subject: Re: AW: AW: LF: Re: 9kHz noise level
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Stefan wrote (another thread):
 > Is the transmitter on 11,904 transmitting the whole time?

Yes, I think so.  Always seems to be there.  I am using F1 at
11904.761 for frequency lock.

 > [Bernd] cannot really receive the alpha stns.

I would need to know details to help.   As you say, it is not
too difficult to receive.   Here are a couple of spectrum plots,
first with 12Hz resolution averaged for 2 minutes,

  http://abelian.org/vlf/tmp/alpha.100306c.png

You can see F1 11904, F2 12648, F3 14881.

The signal pulses have a repetition period of 3.6 seconds, so at
high resolution we see them break up into separate components.
Here is 11904 at 50mHz resolution,

  http://abelian.org/vlf/tmp/alpha.100306a.png

and at 5mHz,

  http://abelian.org/vlf/tmp/alpha.100306b.png

Note - these graphs show relative amplitude not relative
power.  The noise floor here is natural VLF background, the
system noise floor is 30dB lower.

 > Yesterday i have got a PVC tube with 25cm diameter
 > and 2m long.

Will make a great Tesla coil, maybe h/d is a little long.
Certainly not best for Q factor.  Barrels are great, I have
two big barrel coils for TC at 60kHz, Q was about 170 last
time I measured, but that included some ground resistance.
Will be interesting to see how you get on at 9kHz.  I have
lots of software for modelling solenoid resonance, primary
coupling, etc, but Q is hard to calculate.

I have a further change to make to the spectrum display -
I will rotate the antenna pattern (in software) to null the
prevailing average bearing of the background, this will gain
another dB.   I'm trying a reassigned spectrum display but
I'm not sure it is any help.

Wolf wrote:
 > The question is if the MP3 or Ogg Vorbis compression will
 > leave the weak signals intact;

Nice to meet you on this list Wolf!  We can test that with a
simulated signal.  There is sure to be some loss of S/N ratio.
Could perhaps be minimised by blanking most of the spectrum
to leave all the available bits for the 9kHz band.

This narrow band weak signal work is very interesting and new
to me.  Quite different to the naturally generated signals that
I study.   Talking of which - whistler activity is picking up
again - quite a few in the last two days.  Check out the event
logs at

  http://abelian.org/vlf/detail.php?stream=vlf1

and if there are whistlers about, listen on

  http://abelian.org/vlf/test.html

One day, perhaps, we will have amateur radio beacons which will
be very useful.. and perhaps even whistler mode QSOs!

--
Paul Nicholson
--