Topband: 1/8 wave vertical

[Niko Cimbur]

>From Tom Rauch:

>>If the ground system is very good then there is almost no 
difference at all between top loading, center loading, or 
base loading. The exception would be a poor loading coil 
design, for example a coil that was approaching 
self-resonance at the operating frequency. <<

I am dealing right now with this exact issue.  Lately I  have been using a 55' tall inverted L fed through a UNUN with good results, and was happy with it.   The antenna is located above the Ocean, about 3/4 mile out, on a steel deck, and about 20' above the water (depending in the tide).  So the ground quality is as good as it gets.  I chose the L because of the wide elevation angle coverage. 

 I have to replace the Inverted L because of some environmental issues ( I don't want to go into details here), so I can't have any wires sloping from the vertical any longer. The options I am dealing with are:

1.  Cut away the top wire and bottom load the 55' vertical with a coil
3.  Replace the vertical with a taller one (82' tall), and use a loading coil at the base
3.  Replace the vertical with a taller one (82' tall), put a loading coil at 50' and have a  whip on top
4. Fold back a portion of the antenna at the top whip as a linear loading scheme, kind of a triangle at the top of the antenna
5.  Suggestions?

The easiest option is #1, as it does not require changing the whole antenna and also keeps a lower mechanical profile ( wind ).  I am leaning towards #2, or possibly a bit towards #3.   I  have a feeling  I will not gain much by raising the coil higher from the base, especially considering the drawbacks of the added coil size and mechanical issues, but have this "how much difference" in the back of my head.   I have some large edge wound inductors available  for loading coils, and also a few very big ones made out of tubing.

The antenna will eventually be tuned for 40 and 80 m too. 

I believe the Inverted L is working better for all conditions than the
90' top loaded vertical  I used before, however that is out now.  My feeling was always that the
90' vertical's radiation angle was too low.  The bandwith of the
inverted L is also wider.  I noticed the resonant frequency of the inverted L is
moved by the tide, which is a drawback. (It took me a few times to cut
and re-splice the antenna wire until I noticed a pattern)


Any opinions?

Niko - AC6DD
















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