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Date: Sat, 16 Jan 2010 14:35:39 +0000
Message-ID: <fc7eccec1001160635l1668d8d6x1f604b06bd7e461b@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
DomainKey-Status: good (testing) 
Subject: LF: WSPR and antenna tweaking
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I noticed the current draw on my 500kHz beacon transmission had dropped this
morning, so dragged a scope into the shed and looked at the relative phase
of voltage and current to the antenna.  The two waveforms appeared to be
about 50 - 60 degrees out so the weather over the last few weeks had shifted
the tuning point of the antenna - or maybe its because everthing is just so
wet now, or the variometer got knocked, or whatever.
Anyway.
A quick tweak of the loading coil and  V and I were coindident again, with a
better current draw. This happened at 1050z

Checking the WSPR database, reports from the two regular local contributors
M0BMU and M0LMH showed a remarkably consistent average increase of 2dB after
the adjustment.   Reports from further afield had too much measurement noise
to see the effect properly, but did show some signs of a similar increase.

Interestingly, the 60 degree phase difference 'ought' to have resulted in a
6dB reduction in antenna current   [COS(60)]  and the DC draw was certainly
around 70% of what it should be - and that includes all the static current
consuming stages of the PA  as well, so I'm just wondering why the signal
did not change pro-rata.

Andy
www.g4jnt.com

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<div>I noticed the current draw on my 500kHz beacon transmission had dropp=
ed this morning, so dragged a scope into the shed and looked at the relati=
ve phase of voltage and current to the antenna.=A0 The two waveforms appea=
red to be about 50 - 60 degrees out so the weather over the last few weeks=
 had shifted the tuning point of the antenna - or maybe its because everth=
ing is just so wet now, or the variometer got knocked, or whatever.</div>

<div>Anyway.</div>
<div>A quick tweak=A0of the loading coil and=A0=A0V and I were coindident=
 again, with a better current draw. This happened at 1050z </div>
<div>=A0</div>
<div>Checking the WSPR database, reports from the two regular local contri=
butors=A0 M0BMU and M0LMH showed a remarkably consistent average increase=
 of 2dB after the adjustment.=A0=A0 Reports from further afield had too mu=
ch measurement noise to see the effect properly,=A0but did show some signs=
 of a similar increase.</div>

<div>=A0</div>
<div>Interestingly, the 60 degree phase difference &#39;ought&#39; to have=
 resulted=A0in a 6dB reduction in antenna current=A0=A0 [COS(60)]=A0 and=
 the DC=A0draw was certainly around 70% of what it should be - and that in=
cludes all the static current consuming=A0stages of the PA =A0as well, so=
 I&#39;m just wondering why the signal did not change pro-rata.</div>

<div><br clear=3D"all">Andy<br><a href=3D"http://www.g4jnt.com">www.g4jnt.=
com</a><br><br></div>

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