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Cc: Mike Smith <michael.smith20@gmail.com>
From: Paul Nicholson <vlf0403@abelian.org>
Message-ID: <5d959a0f-c16c-e1f4-f04e-738592c7ad40@abelian.org>
Date: Fri, 29 Dec 2017 07:51:35 +0000
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Subject: Re: LF: VLF NA Ebnaut
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Stefan wrote:

 > I'm disappointed.

I can imagine your frustration.

I've examined the software at Forest and all appears to be
working fine, at least as well as my own.  Occasional timing
breaks when the sound card has an overrun or DMA error, but
these are padded over in the signal extraction after vtread,
so no problem there.

 > I remember i asked if the phase of the Alphas, JXN and HWU
 > is reproducable or if it shows the same behaviour.

I remember.  But I'm not sure of the value.  If we see distant
MSK phase changing (which we probably will), is it caused by
the rx or the propagation?   Alpha signals are a bit tricky
to use when there are two transmitters interleaved in the
signal being averaged.

I'll ask Mike if he can set up a near field reference which
we can measure for a few days.

Meanwhile the best reference is W4DEX, a very strong signal at
range 254 km.  Can actually see Dex's EbNaut on a spectrogram!

Compare W4DEX phase at three sites over 3 days:

  W4DEX at Forest
  26/27 +20.3 dB phase -45.0
  27/28 +21.2 dB phase 115.9 shift +160.9
  28/29 +20.4 dB phase -14.0 shift -129.9

  W4DEX at Hawley
  26/27  +5.7 dB phase  115.9
  27/28  +6.0 dB phase  -96.8 shift +147.3
  28/29  +1.3 dB phase -163.5 shift  -66.7

  W4DEX at Todmorden
  26/27 +10.7 dB phase   68.4
  27/28  +9.2 dB phase -140.9 shift +150.7
  28/29  +5.4 dB phase  108.7 shift -110.4

W4DEX signal phase is not repeating night-to-night but we're
seeing roughly the same shifts at Forest and Todmorden,
and also at Hawley when the signal is strong enough for a
good measurement.

Forest rx is looking fine here, so why the phase changes
on VO1NA?

  VO1NA at Forest
  26/27 -1.5 dB phase -121.1
  27/28 -0.1 dB phase    5.1
  28/29 +3.7 dB phase  -33.0

  VO1NA at Todmorden
  26/27 +13.0 dB phase -170.4
  27/28 +12.3 dB phase -169.3
  28/29 +11.4 dB phase -175.0

  VO1NA at Bielefeld
  26/27 +3.0 dB phase  +11.0
  27/28 +2.7 dB phase   -8.1
  28/29 -3.8 dB

Perhaps just the weakness of the signal at Forest?
Eb/N0 -0.1 = S/N 7.5 dB in the 30.6 uHz bandwidth in
which the phase is measured.

--
Paul Nicholson
--