On Fri, 29 Sep 2006 16:56:07 +1000, Alan Peake
wrote:

Before I go to the trouble of putting up a rhombic, I've been using NEC
to get an idea of the gain, radiation angle etc for various leg lengths.
It all looks very promising on the computer but I'd be interested in
real-world experiences. For example, how well does the real antenna
approach the PC simulation when various factors like wire sag, uneven
ground, presence of trees and shrubbery?

Hi Alan,

Rhombics were the stars of antenna developement in the late 1920s for
RCA. For very long wavelengths, certainly few other practical designs
could achieve the same gains. For shorter wavelengths, other designs
replaced the Rhombic (poor return on real estate in comparison).

If the wire sags such that most of it is on the ground, you suffer.
This is a judgement call otherwise and sag is quite within the ability
to model if judgement demands.

The presences of trees and shrubbery is something all designs suffer.
Unless you are speaking of an antenna in a forest, the Rhombic would
probably do quite well (after all, it is wavelengths long, as are few
trees) until you start getting into short wavelengths.

Rhombics are few and far between these days. Reasons are principally
wavelength based in comparison to available real estate. Few have the
real estate for long wavelengths. If you are working at a short
wavelength, there is a better design to do the same job.

73's
Richard Clark, KB7QHC