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Date: Sat, 20 Mar 2010 10:50:15 +0000
From: Paul Nicholson <vlf0308@abelian.org>
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Subject: Re: LF: Cooperative ionosphere effects
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Some daily plots of the background noise amplitude at 8.97kHz,
each point averaged across 12Hz for 120 seconds, and rescaled
to 1Hz bandwidth:

  http://abelian.org/vlf/live/100305.9kHz.png
  http://abelian.org/vlf/live/100306.9kHz.png
  http://abelian.org/vlf/live/100307.9kHz.png
  http://abelian.org/vlf/live/100308.9kHz.png
  http://abelian.org/vlf/live/100309.9kHz.png
  http://abelian.org/vlf/live/100310.9kHz.png
  http://abelian.org/vlf/live/100311.9kHz.png
  http://abelian.org/vlf/live/100312.9kHz.png
  http://abelian.org/vlf/live/100313.9kHz.png
  http://abelian.org/vlf/live/100314.9kHz.png
  http://abelian.org/vlf/live/100315.9kHz.png
  http://abelian.org/vlf/live/100316.9kHz.png
  http://abelian.org/vlf/live/100317.9kHz.png
  http://abelian.org/vlf/live/100318.9kHz.png
  http://abelian.org/vlf/live/100319.9kHz.png

Some days are quieter than others, compare for example the
12th with the 17th - a 6dB difference during the day.

The average bearing of the noise is as important as the
amplitude.   If it is broadside to the wanted signal we gain
typically another 6dB, sometimes even more.

Therefore, we can expect 12dB or more difference between a
day with favourable conditions and a poor day.  Conditions
for the test Monday 15th were not ideal, noise was not at
its lowest and the bearing was unfavourable at the time.

Alexander wrote:
 > You  mentioned  'cooperative D-layer' before.

Sorry, this is just my use of language.  I just mean that
the D-layer and the noise is working in our favour - it is
cooperating with us.  I don't refer to a physical effect.

I wrote:
 >> My 'dream' would not be dx records, but to find a
 >> cooperative role

Alex:
 > What does it mean?

Here I mean that amateurs might be able to find a way to
cooperate with researchers to do something useful.

For example, detection and measurements of whistler ducts...

If a thunderstorm is present beneath or near the entrance
to a duct, some of the sferic energy will travel through
the duct and be dispersed into whistlers at the other end.
They often reflect back from the far end back to the source
to produce a 2-hop whistler, or sometimes multi-hop as the
sferic energy bounces back and forth.

Researchers have to rely on a thunderstorm being present,
otherwise the duct is not detected.  The 'causative' sferic has
to be identified for each whistler and its location determined
from lightning triangulation systems.  The size (width) of
the entrance can be estimated from the statistics of these random
sferics, and much information about the magnetosphere can be
determined from analysis of the whistler signals themselves.

If a beacon transmitter was present beneath the duct entrance,
beaming upwards, some signal will pass through and echo back
by reflecting from the upper surface of the ionosphere at
the far end.  The transit time is half a second or so as the
whistler mode signal passes far out into the magnetosphere.
It can be amplified - laser fashion, by interaction with plasma.

If an echo is detected, a duct is present and measurements can
be made without relying on the luck of having a thunderstorm
nearby.   Perhaps this could be done at low ERP - I haven't done
the calculations, but one might imagine a system comprising a
beacon tx with slow triangular FM and a rx or coherent network
of rxs scanning for a weak delayed echo - the same triangular
modulation but delayed perhaps up to half a second or so.
Software would have to de-chirp the triangle for all range
of delays, with continuous moving average over 10 or 20 mins
to dig the echo out of the noise.  If that could be made to
work, researchers would be falling over themselves to get at
your data!

Well that is just an 'off the top of the head' suggestion
to illustrate the kind of cooperation I mean.   It is very
advanced but I don't think any part of it is beyond amateur
capability.  It requires many different skills to come together
in a joint effort.  If it actually worked, the value to research
could be immense.

Isn't this kind of thing so much more meaningful than just
exchanging callsigns and signal reports (rewarding though that
is to those involved)?  Perhaps the VLF band should be treated
by amateurs as a place to do experiments, rather than just
another band on which to score dx points.

--
Paul Nicholson
--