Note was made of a short boom 12/17 beam. Recently, Force 12 built a
special of this sort for someone going into the wilds down under--and the
response following the trip was quite positive. do not know if Tom
Schiller plans to add the beam to the catalog, but anyone interest might
inquire. As I recall, it was a pair of DE/Refl using open sleeve
coupling.
Somewhere in my files also, I have a design for a 17m DE/Refl/12m DE/Dir
design with the same feed. My recollection says this can be set up for
direct feed (choke balun always recommended). I'll see if I can dig it
up. Memory says that the 12 m elements actually helped the 17 m gain a
bit, and the 17 m helped the 12 m F-B--forward stagger is what the
principle is sometimes called. If I can find the model file, I'll post
the design.
Incidental note on modeling open sleeve coupling: both NEC-2 and -4 have
difficulties accurately modeling two wires at different frequencies in
very close proximity. Open sleeve coupling tends to place wires at the
brink of this phenomenon. Fairly noncomplex designs that do not require
too many segments can be confirmed on MININEC (which does not have this
problem). However, be prepared to move the elements just a bit from the
modeled positions. You know you are within the boundaries of the
phenomenon if you see the gain of the fed dipole rise in the presence of
the second element close by. Details on the phenomenon in NEC-4 are in a
recent QEX. You can "slow down" the difficulty by being sure that the
segments inthe two elements are well aligned.
-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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