What I can add from personal experience is that a vertical dipole (center fed
half wave) without radials, on a rocky cliff top is an absolute killer antenna
on the upper HF bands. My vertical dipole works so well that in contests I
often just quit using my yagis because of the hassle of rotating or even
switching them. The omnidirectional vertical is only maybe 3 dB down on very
good directional antennas.
Center fed half waves on 160 are a lot harder to set up, so I have no
experience there. But if I had a used broadcast tower it sure would be fun to
try one.
On Dec 17, 2012, at 7:33 AM, "Carl" <km1h@jeremy.mv.com> wrote:
>
> ----- Original Message ----- From: "Paul Christensen" <w9ac@arrl.net>
> To: <topband@contesting.com>
> Sent: Monday, December 17, 2012 9:07 AM
> Subject: Re: Topband: GAP Vertical Question
>
>
>>> Right, typically a couple hundred ohms. Modeling the base Z of a thick
>>> broadcast tower is very difficult with MoM software. Changes in thickness
>>> can result in large base Z changes.
>>
>> Just to be clear, since the discussion drifted to half-wave radiators, my
>> comment above was specific to the modeling of thick v. thin half-wave
>> radiators, including the 180-195 degree radiators of some well-known 50KW AM
>> stations. The results when modeling the base Z of approx. 1/4-wave
>> radiators is less affected by thickness, probably due to a lower base Z to
>> start with.
>>
>> Paul, W9AC
>
> In the 1920's several BC towers were half waves without radials on hilltops.
> Performance was poor due to the height plus the lack of a decent ground on
> solid rock limiting the ground wave signal to a low value.
> As a side note tapered towers were also in vogue but that presented other
> problems.
>
> It wasnt until the educated scientific studies of the 30's and published
> papers/books that resulted that broadcasters began to standardize.....along
> with some push from the FCC.
>
> Here we are over 70 years later still arguing the subject and embroiled in
> myths and some folks are very protective of their alternate beliefs.
>
> Did the 100mpg carburetor ever exist? Is this planet only 9000 years old (-; ?
>
> Carl
> KM1H
> _______________________________________________
> Topband reflector - topband@contesting.com
>
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