Re: LF: NA VLF

[Paul Nicholson <vlf0403@abelian.org>]

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
--