Hi Paul, VLF,
OK, the QRN is very low!
Let us start a series of experiments. I would like to continue working
on the idea to build an overylay of a few transmissions to rise the SNR
and to lead to a decode by that way. Also i would like to use the 8K19A
mode again just that i am able to decode the message on my own PCs (via
the remote stream from the tree) so i can test if it works. You know
the text files generated by SpecLab contain numbers like "8269.6142
-1.3112E-08 -7.4201E-08 -1.2608E-08 -5.5143E-08 2.7815E-08" and so on.
If i could add them simply by adding the numbers/values i could build
the same overlay, coherently? This is what i want to experiment with.
Also for you, i chose a message with less characters, so you can get a
decode and see the phase pattern. Then you can see how much SNR
improvement you will get when adding the data of two transmissions with
known SNR and you will see (if the start time and length is kept
constant) how the phase varies each day.
So:
f = 6470.00000 Hz
Start time: 11.11.2016 08:00:00 UTC (Daily repetition)
Symbol length: 60 s
Characters: 4
CRC 16
Coding 8K19A
Duration: 7h, 44m, 0s
Antenna current: ~ 280 mA
I hope that will lead to some better understanding of the propagation
on that 46km band and for getting an idea if that coherent adding of
daily transmissions makes sense, and where the limit of the SNR
improvement tends to.
Suggestions welcome.
73, Stefan
Am 06.11.2016 21:50, schrieb Paul Nicholson:
Stefan wrote:
> f = 6470.00000 Hz
> Start time: 03.11.2016 06:00:00 UTC
> Symbol length: 30 s
> Characters: 11
> CRC 16
> Coding 16K25A
and
> A second transmission is running now [5th Nov]
> Same message, symbol length, phase orientation
> and start time...
No decode of either message.
I added the two days coherently and that also failed to
decode. I tested the processing with simulated signals
and that gave the expected 3dB gain.
Looked at the cross correlation of the two days but can
see nothing. The simulated signals at about Eb/N0 0.0dB
are visible on a cross correlation.
This will only work if the received phase doesn't change
much from one day to another. We may need some luck, some
stable weather and ionosphere.
To keep the office warm, the computer is trying some
range of phase shifts between the two days.
--
Paul Nicholson
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