Re: LF: VLF NA Ebnaut

[Markus Vester <markusvester@aol.com>]

Hi Paul, Stefan,

my thought was that HWU 18.3 kHz might be near enough to serve as a guide to propagational phase changes on 17.47 kHz, ultimately allowing phase corrections before stacking.

But I'm not sure about the stability of that specific transmitter. Some time around 2007, I used SpecLab's phase-amplitude-monitors (PAM) to observe diurnals on several MSK stations. 1pps lock wasn't available to me at the time, so I used a 10 kHz reference from a Jupiter GPS, which produced useful measurements despite occasional glitches due to soundcard overruns. The NATO transmitters (GBZ, GQD, NAA, NML, NLK, NWC, presumably also NPM, NDT and JXN) seemed to be impeccably on frequency with perfectly repeating phase - I speculate that these signals are actually still being used for submarine VLF navigation.  German DHO was also stable but a few ppb above nominal 23.4 kHz. French HWU was on frequency, but the phase seemed to have some random variations, which might spoil the application for our purpose. But we could fix this by comparing simultaneous observations in Europe and America.

Best 73,
Markus  

  
-----Ursprüngliche Mitteilung-----
Von: Paul Nicholson <vlf0403@abelian.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Cc: Mike Smith <michael.smith20@gmail.com>
Verschickt: Fr, 29. Dez 2017 8:53
Betreff: Re: LF: VLF NA Ebnaut

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
--