To: rsgb_lf_group@blacksheep.org
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From: Paul Nicholson <vlf0403@abelian.org>
Message-ID: <573EA094.3040205@abelian.org>
Date: Fri, 20 May 2016 05:28:52 +0000
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Subject: Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests:
 6.47kHz
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Status: O


Measurement of reconstructed carrier from the 31.5 hour message,
In approximately 8 hour blocks (34.7uHz):

  From       To         Signal    S/N      Phase  Noise
  16th 21:00 17th 05:00 0.077 fT  11.0 dB  112.7  0.022  fT
  17th 05:00 17th 13:00 0.063 fT  17.4 dB   75.2  0.0085 fT
  17th 13:00 17th 21:00 0.041 fT   9.2 dB   83.5  0.0143 fT
  17th 21:00 18th 04:30 0.05  fT   3.8 dB  125.0  0.032  fT

Day/night phase shift up to 50 degrees which is about what was
expected, although this is a long average so it could be varying
more on shorter timescales to make the signal apparently weaker.

The 18th from 00:00 onwards was noisy.

Overall, would have needed to average about 14dB in this
bandwidth (34.7 uHz) to have a reasonable chance (~50%)
of decode.

Daytime is doing better than nighttime. In 17.36 uHz we have

  17th 04:00 to 20:00 0.057 fT  18.2 dB

  (eg 11 chars, 72 seconds, Eb/N0 = +0.23 dB)

Or, in 34.7 uHz

  17th 05:00 to 13:00 0.063 fT  17.4 dB

  (eg 9 chars, 40 seconds, Eb/N0 = +0.2 dB)

Conclusion is that it's not the phase that's blocking these
long messages, it's the poor nighttime S/N.

--
Paul Nicholson
--