----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: <Topband@contesting.com>
Sent: Wednesday, December 26, 2007 6:51 AM
Subject: Re: Topband: 1/8 wave vertical
> The most difficult to deal with loss in a vertical antenna,
> once it is 1/8th wave tall or taller, is in the ground
> system. While it is possible to do something wrong, like
> make the antenna out of a thin resistive conductor or use an
> exceptionally bad loading system design, if even reasonable
> care is taken or with reasonable selection of materials most
> of the loss is in the ground system.
>
> 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. A loading coil
> self-resonant on 4 MHz would not be a good loading coil on
> 160 no matter how the inductor was constructed.
>
> Follow the rules of common sense...use a big hat or
> something with some self-capacitance near the top. Use
> space-wound turns and a good form factor on the coil with
> reasonable size wire. Use a good ground system. The result
> will be almost no difference at all between a 150 foot
> vertical and a 50 foot vertical.
>
> Do things wrong and height can make a great difference.
>
> 73 Tom
>
Tom,
One thing to consider is that many folks who are using short
verticals are doing so because they live on small lots. Because
of this a good ground system isn't always practical. I've paved
or will be paving every square inch of my small lot with radials,
but even when I got the last little patch of ground covered better
than I have now, I'll still have a compromised ground system
compared to someone who can run full length radials with
complete azimuth coverage. Given those limitations (again very
common to city dwellers), I think that there is some worthwhile
advantage in chosing top-loading over base loading.
I would agree that with a good ground system (30 to 60 1/4 wave
radials with fairly uniform angular spacing), the choice of
loading technique won't make that much difference.
73, Mike W4EF..................................
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