To: rsgb_lf_group@blacksheep.org
References: <579355A36AEE9D4FA555C45D556003AB8FDD9B58@servigilant.vigilant.local>
From: Paul Nicholson <vlf0403@abelian.org>
Message-ID: <bc48ff6e-f7a8-2e18-93d7-146b1f486ce1@abelian.org>
Date: Tue, 9 May 2017 10:26:45 +0000
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Subject: Re: LF: NA VLF
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Status: RO


I can't detect any signal from Joe last night
8th/9th 22:00 to 04:00, not a trace - perhaps
the tx has gone off.

After sweeping for optimum settings, I couldn't get
much improvement.

Daytime reception, S/N = 13.5 dB in 23.148 uHz:

  http://abelian.org/vlf/tmp/170509a.png

Some of the energy is in adjacent bins on this 12
hour integration, the frequency probably drifted
a little, losing a dB or so.

Nighttime, S/N = 14.3 dB in 46.296 uHz:

  http://abelian.org/vlf/tmp/170509b.png

Tried an EbNaut 'decode' of the 6 hour nighttime
signal.  Unmodulated carrier is a valid message which
decodes to a string of '*' characters. Because of the
linearity of the coding, the performance is representative
of any other message with the same settings.

4 chars 16K25A CRC=12 Symbols = 22 seconds, duration 05:52:00
gives

  rank 946 ber 42.2% '****'

  carrier Eb/N0: -0.1 dB
  carrier S/N: 13.53 dB in 47.3 uHz,
              -29.72 dB in 1Hz,
              -63.70 dB in 2.5kHz

The snag is, this 'decode' is only possible because I could
see the signal and measure its frequency.  A real EbNaut
message is invisible and if the frequency is out by more than
about 5uHz it will not decode.

5 chars should just be possible but I could not get it to
decode.
--
Paul Nicholson
--