Re: VLF: EbNaut transmissions on lower frequencies?, pre-tests: 6.47kHz

[Paul Nicholson <vlf0403@abelian.org>]

Summary of recent messages from DK7FC at 6470 Hz.

S/N in 2.5kHz for easy comparison, post blanker.

              Eb/N0   S/N  Phase  Coding  Sym Chars
 5th Oct      -6.9   -73.0  102.2 8K19A  140  15   no decode
 7th Oct       1.1   -68.6   69.4 16K25A  80  15   'DK7FC JN49IK 73'
 12th Oct      0.1   -65.2   77.8 8K19A   40   3   '73S'
 13th Oct     -6.2   -67.0   41.3 16K25A  20  15   no decode

 2nd Nov       1.7   -63.8 -121.1 16K25A  30   7   'SUCCESS'

 3rd Nov      -5.4   -68.5 -120.7 16K25A  30  11   no decode
 5th Nov      -5.0   -68.0 -130.0 16K25A  30  11   no decode
 3rd+5th      -2.3   -65.3 -125.1 16K25A  30  11   'ROCK N ROLL'

 11th Nov      3.9   -62.5 -141.2 8K19A   60   4   'TEST'
 12th Nov      4.9   -59.7 -134.3 8K19A   60   4   'TEST'
 11th + 12th   6.6   -58.1 -137.5 8K19A   60   4   'TEST'
 13th Nov      8.5   -55.6 -138.5 8K19A   60   4   'TEST'
 11th to 13th  8.6   -55.2 -137.8 8K19A   60   4   'TEST'
 14th          3.5   -61.3 -136.8 8K19A   60   4   'TEST'
 11th to 14th  9.9   -54.3 -137.6 8K19A   60   4   'TEST'

> we could try to start an attempt to transfer 50 characters
> on 6.47 kHz
> 10 second symbols 8K19A, taking 07:25:20, each day.

I think it would need 3 or 4 repeats.  If the phase stays this
repeatable it will surely work.

> EbNaut_VLF_list.png

A couple of messages to add: 5th Oct, 13th Oct.

I'm still experimenting with the normalisation.  Sometimes it helps,
other times it doesn't.    Decode performance also depends a little
on the sample rate of the input to the decoder.

6470 is like a completely different band to 8270: different daytime
blanker settings, decoder prefers lower sample rates, normalisation
has more effect.  We are learning how to work this band.

> Congrats to your and our success.

Some of these are the weakest signals so far decoded at VLF, eg 7th
October is 12dB weaker than W4DEX's transatlantic signals. Less than
two electrons charge on the antenna.

I might also add, they probably hold the record for the longest time
taken to decode - over 30 days!

Start tomorrow with 50 chars?

--
Paul Nicholson
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