Re: LF: VO1NA - IZ7SLZ

[Paul Nicholson <vlf0403@abelian.org>]

Markus wrote:

> Despite the fact that no carrier trace was visible in
> Domenico's 0.48 mHz spectrogram ...

> 1:40 UT produced a single good decode of VO1NA in South Italy

Well done, I reckon that to be 5418 km.   I expect that record
will stand for some time.

The signal was -45dB in a 2.5kHz audio bandwidth and had a dB
or two to spare.  I don't think it would have decoded with
one second symbols.

Decodes at DF6NM 2016-03-02/03:

> start  car. sym. offs.
>  UT    dB   dB   mHz
> 23:30 11.9  7.9   0
> 00:00 12.9  10.0 -1.5
> 00:30 16.1  13.6 -1.5
> 01:00 11.6  8.3  -1
> 01:30 16.9 14.2  -0.6
> 02:00 10.7  8.3  -0.6
> 02:30 17.9 14.4  -0.6
> 03:00 14.1 10.8  -0.6
> 03:30  5.7  4.4  -0.8
> 04:00  5.2  5.1  -0.8
> 04:30  3.6  4.0  -0.8

Signals look to be 10dB up compared with recent nights.  We're
seeing the now familiar discrepancy between Eb/N0 calculated
from the carrier S/N and the BER which suggests the phase
isn't very stable and these tests are probably at the limit
of what can be done at MF with message durations of this length.

Markus is probably right with the suggestion that there is a
maximum message duration related to the propagation spreading
and it is likely to be typically just a very few minutes but
I wonder how it varies with distance.

This achievement represents considerable effort and patience
by Markus.   Few of these decodes would have been successful
without spending a lot of time searching for the correct
frequency offset.  For example a 0.6mHz offset is nearly a
whole cycle of phase shift on the 752*2 second messages which
is well beyond the range of the phase search of the decoder.

Today I put up another 150m metres of wire here.  I would
have got more done but for a tendency to sit amongst the trees
taking in the winter scenery in the sunshine.  It is very nice
to be in the woods putting up wire and only hunger and darkness
forced me back indoors.

--
Paul Nicholson
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