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Re: VLF: 8270.0025 Hz Sunday - VLF MIMO?

To: [email protected]
Subject: Re: VLF: 8270.0025 Hz Sunday - VLF MIMO?
From: Paul Nicholson <[email protected]>
Date: Tue, 7 Feb 2017 22:16:49 +0000
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Markus wrote:

> on air since 9:25 UT: 8270.0025 Hz, 0.35 A, ~ 10 uW.
> ... without interruption until 22:00 UT.

Uwe wrote:

> carrier of 8WX [8270.0000] is on the air agn since 1141UTC.
> carier off ... 2134UTC

Markus wrote:

> Uwe and I could simultaneously send two different EbNaut
> messages on the same frequency, which could then be
> decoded independently.

This is what I expect to happen:

Two different messages, same frequency, same S/N, same coding
and number of chars, simultaneous symbols, will both decode,
so long as their phase is different.  If their received phases
are 90 degrees apart, each will decode with no extra errors.
As the phase difference is reduced, extra symbol errors will
occur.  With zero phase difference, both will still decode
but with about 6dB loss.

If the two transmissions used different coding or message length
or symbol period, they would each decode with the other signal
just adding a little to the background noise.

Certainly no problem if the frequencies are slightly different.
I took 9 hours 12:00 to 21:00 and ran the double carrier into
ebnaut -d.  Each decodes to star messages independently with
constant reference phase at the expected frequency offset.
Best decodes using 8K19A are:

 DJ8WX 21 second symbols, 26 chars, Eb/N0 = 0.2 dB

 DF6NM 34 second symbols, 14 chars, Eb/N0 = 0.9 dB

The above with the loop aligned mid way between the
two bearings.

Paul Nicholson

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