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Date: Fri, 21 Apr 2006 22:59:50 +0200
To: LF-Group <rsgb_lf_group@blacksheep.org>
From: Dick Rollema <dickrollema@casema.nl>
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Subject: LF: Top loading coil at ground level?
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Sorry if you receive this for the second time. But  I got a message from my 
provider that the service was temporary unavailable so don't know whether 
the message was send or not.

To Jim, Peter, LF-group,

I am grateful to Jim and Peter for their interesting comments and 
discussion which I thoroughly enjoyed.

As I mentioned before I first modelled a quarter wave vertical for 
80m  with the top loading coil system under discussion. As capacitive hat I 
used the upper 5m of three guy wires, connected to the top of the 
radiator  under an angle of 30 degrees.
The bottom end of the stub is 1m  above ground level.  At the centre of the 
stub  a  capacitor. By trial and error I found that 1283pF  was needed 
to  bring the system into resonance. At the feedpoint the impedance was 
4925 ohm.  The current minumum occurs at the feed point and the maximum at 
the top of the system. The current responsible for the radiation is the 
vectorial difference of the currents in the two vertical elements. This is 
shown in the following picture that is produced by the Antenna Optimizer 
program.
66d8a9.jpg

The dots indicate the segmentation I selected: 150 segments/half wave.  The 
curved lines indicate the magnitude of the currents. At the bottom end the 
currents in the "stub" are almost equal but in opposite direction. The 
small difference current is flowing in the lower 1m of the radiator between 
feedpoint and bottom end of the stub.

The situation is different of course for the small antennas used at 
LF.  But the principle is the same.

I consider as main advantage of the system that the top coil is at ground 
level and easily accessible. There are no  size and weight restrictions as 
for an elevated coil.  The coil can be made as large and good as you like.

73, Dick, PA0SE  
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<font size=3>Sorry if you receive this for the second time. But&nbsp; I
got a message from my provider that the service was temporary unavailable
so don't know whether the message was send or not. <br><br>
To Jim, Peter, LF-group,<br><br>
I am grateful to Jim and Peter for their interesting comments and
discussion which I thoroughly enjoyed.<br><br>
As I mentioned before I first modelled a quarter wave vertical for
80m&nbsp; with the top loading coil system under discussion. As
capacitive hat I used the upper 5m of three guy wires, connected to the
top of the radiator&nbsp; under an angle of 30 degrees.<br>
The bottom end of the stub is 1m&nbsp; above ground level.&nbsp; At the
centre of the stub&nbsp; a&nbsp; capacitor. By trial and error I found
that 1283pF&nbsp; was needed to&nbsp; bring the system into resonance. At
the feedpoint the impedance was 4925 ohm.&nbsp; The current minumum
occurs at the feed point and the maximum at the top of the system. The
current responsible for the radiation is the vectorial difference of the
currents in the two vertical elements. This is shown in the following
picture that is produced by the Antenna Optimizer program. <br>
<img src="cid:6.1.0.6.2.20060421152209.069d68f0@127.0.0.1.1" width=319 height=316 alt="66d8a9.jpg">&nbsp;
<br>
The dots indicate the segmentation I selected: 150 segments/half
wave.&nbsp; The curved lines indicate the magnitude of the currents. At
the bottom end the currents in the &quot;stub&quot; are almost equal but
in opposite direction. The small difference current is flowing in the
lower 1m of the radiator between feedpoint and bottom end of the
stub.&nbsp;&nbsp;&nbsp; <br><br>
The situation is different of course for the small antennas used at
LF.&nbsp; But the principle is the same.<br><br>
<b>I consider as main advantage of the system that the top coil is at
ground level and easily accessible. There are no&nbsp; size and weight
restrictions as for an elevated coil.&nbsp; The coil can be made as large
and good as you like. <br><br>
</b>73, Dick, PA0SE </font></body>
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