Since 12 m and 17 m are narrow bands, it is fairly simple to design very
compact and light weight 2-element beams for general use on those bands.
DE/Dir designs with element spacing in the 0.07-0.08 wl vicinity allow
very compact design. At my site are two possibilities--a 12-17 De/Dir
back-to-back combo using open sleeve coupling for a single feed line, and
a DE/Ref for 17 with an open sleeve coupled DE/Dir for 12 both pointing
the same way. Boom lengths about 10' You can also nest a pair of DE/Ref
with open sleeve coupling effectively. Separate feed designs can be
interlaced effectively as well.
I note this because of the difficulties of trying to modify multiband
designs already optimized for their main tasks--the results are often not
quite what one intended. Letting the main beam do its job and using a
separate 12-17 small beam may yield more happiness and fewer hours of
readjustment in the long run. Even a 12-17 trap rotatable dipole, a 17 m
al. dipole with a 12m wire element suspended beneath to the same feed or
an open-sleeve pair may yield superior results to pressing into service a
beam not designed for those bands, especally if the coax run is long. The
dipole idea is apt to placement on a side arm from the tower since it does
not have to rotate 360 degrees to give full coverage to the horizon and
can be below the main antenna by enough separation to prevent unwanted
interactions and avoid putting one in a stacking-stess-analysis position.
Just some alternatives--and certainly not the only ones--for the thinking
pot. Hope the ideas may 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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