To: rsgb_lf_group@blacksheep.org
References: <4273a2ab-787c-d909-e7d0-d21db21ba18c@n1bug.com>
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From: Paul Nicholson <vlf0403@abelian.org>
Message-ID: <5b388385-8cea-31e1-db86-be153479f53c@abelian.org>
Date: Sun, 22 Oct 2017 20:20:38 +0000
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Subject: Re: VLF: VO1NA
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Recent measurements of carrier from VO1NA on 8270.0075Hz

  Night: 19th/20th 13.9 dB phase   3.0 deg 0.065 fT H-field only
    Day: 20th      10.5 dB phase 101.4 deg 0.034 fT H-field only
  Night: 20th/21st 12.1 dB phase   8.0 deg 0.058 fT H-field only
                   10.8 dB phase   0.0 deg          E-field only
                   14.4 dB E-field and H-field combined
    Day: 21st      12.3 dB phase 104.8 deg 0.038 fT H-field only
                   10.1 dB phase 100.3 deg          E-field only
                   15.2 dB E-field and H-field combined
    Day: 22nd       9.9 dB phase 156.5 deg 0.034 fT H-field only

Apart from today, the day and night phases look repeatable
enough for stacking but more measurements would be nice.

Here's Joe's daytime 21st signal with combined E and H,

  http://abelian.org/vlf/tmp/171022a.gif

This ought to be visible further into Europe.

Some progress now with the new E-field rx.  For some time
I've had a puzzle where the new rx performs on average
0.13 dB worse than the old at the Alpha F1 frequency, when
it should really be half a dB or so better.  I traced the
extra noise to somewhere in front of the front-end.

Now after moving the rx about 20 metres to a new location
and putting in a new grounding system, the noise floor is
about right.

Signals from Joe and Stefan have been very useful: some
comparison S/N dB readings on recent carrier signals:

DK7FC 5170.005 Hz
-----------------
                           Old RX   New RX
  2017-10-21_11:00,+3.5h    13.27    17.07
  2017-10-22_13:00,+3.5h     6.66    15.96

VO1NA 8270.0075
---------------
                           Old RX   New RX
  2017-10-21_11:00,+7h       5.98     8.82

Alpha F1 11904.7619
-------------------
                           Old RX   New RX
  2017-10-21_11:00,+60m     41.48    42.09
  2017-10-21_12:00,+60m     37.84    38.40
  2017-10-21_13:00,+60m     37.88    38.70
  2017-10-21_14:00,+60m     32.13    32.68
  2017-10-21_15:00,+60m     41.09    41.54
  2017-10-22_10:00,+60m     41.15    42.04
  2017-10-22_11:00,+60m     40.38    41.85
  2017-10-22_12:00,+60m     41.75    42.82
  2017-10-22_13:00,+60m     36.80    37.14

The improvement is roughly as expected now.  More improvement
at lower frequencies because the old rx is pretty bad down
there - good enough for whistlers and things but not up to par
for weak amateur radio signals.

I suspect that the extra noise was coming from the grounding
system, either thermal noise or some sort of electrochemical
noise. There's a nice shiny set of 6 ground rods at the new site-

  https://www.screwfix.com/p/earth-rod-3-8-4ft/28044

These are very strong and drive in easily in the soft ground here.

I'm having a lot of trouble with mechanical interference as the
antenna flexes slightly in the wind.  Also some interference
coming in along the DC supply, and one of the DC-DC isolating
converters very occasionally doesn't start up when power
is applied.

I'll get whatever measurements I can over the next day or two
then the rx and antenna is back in for yet another re-build.

--
Paul Nicholson
--