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Message-Id: <5.1.0.14.0.20060419162451.02431a98@u0019445.kuleuven.be>
Date: Wed, 19 Apr 2006 16:29:49 +0200
To: rsgb_lf_group@blacksheep.org
From: Rik Strobbe <rik.strobbe@fys.kuleuven.be>
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Subject: Re: LF: Top load coil at ground level?
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Hi Dick,

I guess you are right with
"The stub functions as a transmission line to transfer the inductive 
reactance of the coil to the top of the radiator."

But I am afraid that for any reasonable antenna height (< 50..100m) the 
stub is that short (in wavelengths) that it will hardly transfer any reactance.
What is the result when you model both quarter wave 80m antennas (+/- 20 m 
height) for 2200m ?

73, Rik ON7YD - OR7T

At 14:54 19/04/2006 +0200, you wrote:
>To All from PA0SE,
>
>By chance I came across an interesting article in the Dutch weekly (!) 
>magazine Radio Expres of 11 January 1934. It referred to an article in the 
>Proceedings of the IRE of December 1933 by Nickle, Dome and Brown on a 
>procedure to increase of the feed point impedance of a vertical antenna by 
>means of top loading. A normal way is to use a series resonant circuit as 
>in fig.1, consisting of a capacitive hat and a coil. The coil is in a 
>awkward position for tuning. The alternative by Nickle, Dome and Brown is 
>to use a short circuited stub slightly shorter than an quarter wave that 
>at its top end produces the proper inductive reactance for series 
>resonance with the capacitive hat. Indicated in fig. 2a. The system is 
>tuned by moving the short circuit at the bottom up or down. The left leg 
>of the stub is doubling as the radiator. An easier way of tuning is to 
>make the stub too short and lengthening it with a coil(b) or a stub that 
>is too long and shortening it by a capacitor (c). I modelled a quarter 
>wave vertical for 80 m according to (c) using Antenna Optimizer by Brian 
>Beezley, K6STI. When in resonance the feed point impedance was raised from 
>36 ohm without top load to 4925 ohm! The radiation diagram was identical 
>to the one for the unloaded vertical within a few tenths of a dB.
>
>It occurred to me that the system could perhaps also be used for a 136kHz 
>vertical. Using system (b) in fig.2 the loading coil between top of the 
>radiator and topload could be at ground level. The stub functions as a 
>transmission line to transfer the inductive reactance of the coil to the 
>top of the radiator. Of course a second coil could be inserted between 
>bottom of the stub and ground for matching and feeding of the antenna.
>
>What do you think?
>
>73, Dick, PA0SE
>
>
>
>
>


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<html>
Hi Dick,<br><br>
I guess you are right with <br>
&quot;<font face=3D"Courier New, Courier">The stub functions as a
transmission line to transfer the inductive reactance of the coil to the
top of the radiator.</font>&quot;<br><br>
But I am afraid that for any reasonable antenna height (&lt; 50..100m)
the stub is that short (in wavelengths) that it will hardly transfer any
reactance.<br>
What is the result when you model both quarter wave 80m antennas (+/- 20
m height) for 2200m ?<br><br>
73, Rik ON7YD - OR7T<br><br>
At 14:54 19/04/2006 +0200, you wrote:<br>
<blockquote type=3Dcite class=3Dcite cite>To All from PA0SE,<br><br>
<font face=3D"Courier New, Courier">By chance I came across an interesting
article in the Dutch weekly (!) magazine <i>Radio Expres </i>of 11
January 1934. It referred to an article in the <i>Proceedings of the
IRE</i> of December 1933 by Nickle, Dome and Brown on a procedure to
increase of the feed point impedance of a vertical antenna by means of
top loading. A normal way is to use a series resonant circuit as in
fig.1, consisting of a capacitive hat and a coil. The coil is in a
awkward position for tuning. The alternative by Nickle, Dome and Brown is
to use a short circuited stub slightly shorter than an quarter wave that
at its top end produces the proper inductive reactance for series
resonance with the capacitive hat. Indicated in fig. 2a. The system is
tuned by moving the short circuit at the bottom up or down. The left leg
of the stub is doubling as the radiator. An easier way of tuning is to
make the stub too short and lengthening it with a coil(b) or a stub that
is too long and shortening it by a capacitor (c). I modelled a quarter
wave vertical for 80 m according to (c) using Antenna Optimizer by Brian
Beezley, K6STI. When in resonance the feed point impedance was raised
from 36 ohm without top load to 4925 ohm! The radiation diagram was
identical to the one for the unloaded vertical within a few tenths of a
dB.<br><br>
It occurred to me that the system could perhaps also be used for a 136kHz
vertical. Using system (b) in fig.2 the loading coil between top of the
radiator and topload could be at ground level. The stub functions as a
transmission line to transfer the inductive reactance of the coil to the
top of the radiator. Of course a second coil could be inserted between
bottom of the stub and ground for matching and feeding of the
antenna.<br><br>
What do you think?<br><br>
73, Dick, PA0SE <br><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>
</font><br><br>
<br>
</blockquote><BR>
<BR>
<FONT FACE=3D"Arial" SIZE=3D2>Disclaimer: <A HREF="http://www.kuleuven.be/cwis/email_disclaimer.htm">http://www.kuleuven.be/cwis/email_disclaimer.htm</A> for more information.</FONT>
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