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Date: Mon, 2 Jun 2014 13:09:42 -0700
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Subject: LF: RE: W4DEX trans-Atlantic at 8971 Hz
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Paul and Dex,

Congratulations on another great milestone, and the fine work that went into
making it happen!

Compliments also on agreement between Dex's ERP estimate, LWPC, Paul's
receiver calibration and signal measurements; great work! 

73, Jim AA5BW


-----Original Message-----
From: owner-rsgb_lf_group@blacksheep.org
[mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Paul Nicholson
Sent: Monday, June 2, 2014 12:44 PM
To: rsgb_lf_group@blacksheep.org
Subject: VLF: W4DEX trans-Atlantic at 8971 Hz


At 2014-06-01 10:00 UT W4DEX began a long transmission of GPS locked carrier
at 8971.000 Hz from 35.273N,80.371W.

Between 2014-06-02 00:00 and 06:00 a carrier was measured at that frequency
here in Todmorden 53.703N,2.072W with flux density around  0.05fT.  It was
not very significant so I combined the H-field and E-field receiver outputs
(correcting for their known phase and amplitude response) to produce a
uni-directional antenna response. This brought the signal up to a
significant level.

The signal bearing was roughly west.  W4DEX is bearing 285 deg from here.
The S/N is max on a bearing of 315 degrees which puts the prevailing
south-westerly background nearer to the side of the antenna response.

This gave the signal a respectable 12.5dB S/N in 46uHz bandwidth.

  http://abelian.org/vlf/tmp/w4dex_140602a.gif

This was the strongest peak in a span of over 6500 Fourier bins so is quite
significant.

The carrier was also visible during the daylight path in 23uHz bandwidth
with average strength of around 0.02fT and with similar S/N thanks to the
lower day time noise and reduced bandwidth.

At 2014-06-02 12:00 Dex altered the TX frequency for a blind confirmation
test. Six hours later the carrier (in 46uHz) had vanished and a new signal
appeared at 8971.100 Hz with the same strength.

An email response from Dex confirms 8971.1 as the new frequency.

Range W4DEX to Todmorden UK is 6194 km.

Ratio of day/night flux density agrees well with LWPC predictions for this
path.  LWPC predicts strongest night signal between 00:30 and 04:30 and a
sliding spectrum window agrees with this.

LWPC requires ERP of 150uW to reproduce the observed flux density.  This is
in the center of the ERP range estimated from W4DEX antenna dimensions and
measured antenna current.

--
Paul Nicholson
--