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Date: Wed, 17 Mar 2010 19:43:40 +0000
From: Paul Nicholson <vlf0308@abelian.org>
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Subject: Re: LF: DK7FC's 2nd VLF TX test...
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James Moritz wrote:
 > Paul's 5mHz FFT resolution was longer than optimum for
 > QRSS120 reception.

Yes, the signal was too wide, except during the initial tune-
up when the pure carrier sat nicely inside one frequency bin.

 > DFCW is about 2 -3 times quicker than QRSS,

I should think so. And still easy to read from the spectrogram.
And gain maybe another 25% or more if you switch from Morse to
a more efficient binary prefix coding where you don't need the
inter-character gaps either.

 > see the attachment for about 14 hours duration this
 > morning/afternoon between 8900 - 9100 Hz.

Great diurnal, working nicely there James.  But the interference
is bad.  Looks like a classic case of needing transformer isolation
to disconnect the antenna completely from domestic ground.
Perhaps you can try that easily?   Apart from that, the noise
floor looks great.

Really, more receivers are needed - calibrated receivers that
can return useful measurements.   The average noise floor gives
a kind of standard, if allowance is made for longitude and
there are no thunderstorms or solar/geomagnetic disturbances,
but it is nice to try for an absolute reference.

Mal Hamilton wrote:
 > Frequency and some carrier is NOT PROOF ...
 > I need positive keyed ID to be convinced

Quite agree.  For record purposes it is surely necessary
in amateur radio to transfer some kind of message at least.
So far this has only been done to 16km I think.

However, putting on the physicist's hat, this was a very
satisfactory measurement.  Frequency, timing, and bearing,
in a band devoid of other carriers, provide a sufficiently
unique combination and the result was a good measurement,
good significance.  It was a very rewarding experiment and
has provided the first peg in a propagation model.

This will be a challenging band - it's going to need every
trick in the book to actually transfer messages any long
distance.
--
Paul Nicholson
--