Hi Paul, VLF,
OK, all right, thanks for the helpful report.
So the current transmission could have even better chances with shorter
symbols (80 s) beeing transmitted in the time of ideal SNR.
We will see. At least there should be more coding gain now with 10
characters.
For a long message of 20 characters i would need more ERP if the
transmission should have to fit into this ideal time slot. Impossible
with this small coil. So the symbol length must be longer. That means
the average SNR drops below the necessary limit as we saw now. That
means, if the phase is not a big problem, it must be even more longer :-)
My recent 20 char (which was 18 char actually) message was placed into a
night-day-night time slot. So day-night-day would have been better.
"Day" starts at 4 UTC and holds until 18 UTC these days maybe. So i
could try that again. If that won't work i should try 200s symbols or
the other coding you suggested.
73, Stefan
Am 20.05.2016 07:28, schrieb Paul Nicholson:
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
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