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From: Paul Nicholson <vlf0403@abelian.org>
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Date: Tue, 9 May 2017 19:15:38 +0000
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Subject: Re: LF: NA VLF
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Jim wrote:

 > I noticed that you used phase with Watson-Watt,

I use the formula which is given in your png attachment, where
Vy is the N/S complex amplitude and Vx is the E/W.  And atan2
implements the arctan.

It produces an azimuth modulo 180 degrees and the ambiguity
is resolved by looking at the relative phase of E and H.

The azimuth from this formula corresponds to the major axis
of the ellipse that you would see if you connected the E/W and
N/S loop signals to the X and Y signals of a scope: a Watson-
Watt DF display.

The apparent azimuth from this method often differs from the
true azimuth of the incident signal - polarisation error.

With signals of low elevation the polarisation error tends to
zero.  It also tends to zero with elliptical polarised incident
signals where the major axis is vertical. The error will be bad
if the polarisation axis is significantly tilted away from the
vertical.

There are a couple of other methods of measuring azimuth
which have less or even no polarisation error. For example the
Poynting vector method, and the Tsuruda and Hayashi NPE method.
I've never successfully used either of these because they need
very accurate phase calibration of the 3-channel receiver.

Joe wrote:

 > That's a relief, Paul.

I can see the daytime signal too now.  Both night and day sigs
are half the amplitude compared with yesterday.  Noise was
a bit higher overnight too.    Frequency looks good, 93 uHz
above 8270.007.   Can't see the overnight signal at Forest.

I'm glad you began transmission on Sunday instead of Monday!
Let's see what the next 24 hours does if you can stay on-air.

--
Paul Nicholson
--