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" <[email protected]> wrote: > > ----- Original Message ----- From: "Paul Christensen" <[email protected]> > To: <[email protected]> > 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 - [email protected] > _______________________________________________ It is undesirable to believe a proposition when there is no ground whatsoever for supposing it is true. — Bertrand Russell
