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Re: VLF: 8270

To: [email protected]
Subject: Re: VLF: 8270
From: Paul Nicholson <[email protected]an.org>
Date: Sat, 07 Feb 2015 09:50:06 +0000
In-reply-to: <[email protected]>
References: <[email protected]>
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Uwe wrote:

> did you record your VLF spectrum the last days ?

Yes it is always recording.  I am looking for your message on
all of the days you list.

But, so far with no success.

It is very strange because the signal seems quite strong.
Sometimes you sent some carrier before and after the messages.
The carrier has good signal strength and should decode easily
with Eb/N0 of +2dB or more.

I confirmed this by running some of your carrier into the
decoder.  With this coding scheme, a steady carrier is a valid
message (with any symbol period or coding) and the carrier
decodes fine, even with much shorter symbol periods.

(The code is linear, so the all-zero-bits message is
representative of any message).

I don't know what is wrong.  Only one transmission shows a hint
of reference phase (after squaring) and on that one, the symbol
timing looks fine (unless it is out by 10 seconds or some other
multiple of the symbol period).  But it still doesn't decode.

Does everything look ok at your end Uwe?   Are you using
wsend2v2.exe and is the relay operating reliably?

I took some phase measurements from the bits of carrier and it
looks fairly steady.  Although the before and after carriers
on 2015-02-03 have quite different phase.

Yesterday you sent a long carrier.  In 10 minute steps the
phase was

 2015-02-06_12:30 -106.2
 2015-02-06_12:40 -117.5
 2015-02-06_12:50  -83.7
 2015-02-06_13:00 -142.0
 2015-02-06_13:10  -94.7
 2015-02-06_13:20  -92.0
 2015-02-06_13:30  -95.3
 2015-02-06_13:40 -126.7
 2015-02-06_13:50 -116.1
 2015-02-06_14:00 -112.1
 2015-02-06_14:10  -90.5
 2015-02-06_14:20 -136.8
 2015-02-06_14:30  -89.6
 2015-02-06_14:40  -74.5
 2015-02-06_14:50  -89.2
 2015-02-06_15:00 -101.8
 2015-02-06_15:10 -104.5

It is jumping about a bit but is not too bad.  I sent 9440
seconds of this carrier into the decoder and it decoded easily
with Eb/N0 at +1.5dB estimated from the symbol error rate.

I continue to investigate - this should decode very easily,
signal strength is well above the limit for this mode.

--
Paul Nicholson
--

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