Rick,
Your modeling parallels mine. Narrow primary beamwidth for a fixed
antenna with many side lobes. The advantages appear to be two. a. Many
fewer types of moving parts to wear out, and hence usually simpler
techniques ("brute force?) of repair when things go wrong. b. Wide
operating bandwidth, with useable gain over at least 1 2:1 frequency
range. However, when the angles are calculatedto minimize side
lobes--which also means maximum additive power from the wires in the
diamond--for one frequency, they are not optimally angled for such
addition at the others frequencies of use, which ordinarily means more
side lobe strength.
Short of finding a rotatable island in the salt water ocean on which to
plant the rhombic, I suspect that Yagi stacks will continue to be the
dominant gain array for most installations. However, for areas of the
world where the parts are unobtainable, excessively expensive, or weather
constrained, the rhombic may have a place--since it can often be built
with surplus poles and wire and the labor of installation is the sweat
equity that replaces Yagi installation $ equity. For example, if one has
access to the poles, wire, and land, one can set up a switchable array of
Vee-beams (a cousin to the rhombic) either bi-directional or
uni-directional to cover the horizon. That is a rare situation in urban
and suburban US, but not in some parts of the world.
When rhombics were antennas to dream about, Yagi design was not what it is
today, so the differences really stood out. Today's Yagis are far
superior in both mechanical and electrical design than those of the late
1950s: lighter, sounder, and better performers. I recommend the
following exercise for those with modeling software: obtain some designs
from handbooks in the late 1950s and model them. Then, as a convenient
source of models, try the K6STI collection that comes with the ARRL
Antenna Book (or any other current designs). Note how often gain results
in almost no F-B ratio and how often F-B ratio results in excessive gain
claims for the older antennas. Rhombics are pretty much where they always
have been, but Yagi technology has come a very long way in 40 years. In
the note at my site on 6 long-boom 20 meter Yagis, the performance
obtained by any one of them would not have been possible back then--and
could not have been clearly recognized if obtained by accident. Today,
such performance is routine.
On the other hand, the rate of tower/pole climbing will likely always be
greater for Yagis than for rhombics.
Thought a wee bit of perspective might be useful.
-73-
LB, W4RNL
L. B. Cebik, W4RNL /\ /\ * / / / (Off)(423) 974-7215
1434 High Mesa Drive / \/ \/\ ----/\--- (Hm) (423) 938-6335
Knoxville, Tennessee /\ \ \ \ / / || / (FAX)(423) 974-3509
37938-4443 USA / \ \ \ \ || cebik@utk.edu
URL: http://web.utk.edu/~cebik/radio.html
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