Topband: 1/8 wave vertical

[Michael Tope]

----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>
To: <Topband at 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..................................