Hi all,
I was asked by Randy, K0EU about a four-direction switchable
configuration using four Flags mounted back-to-back. This sounded like a
good idea, but having four adjacent vertical wires within a few inches of
each other bothered me enough to model Randy's proposed configuration.
And indeed there is enough coupling to the inactive Flags where the
active Flag suffers a large amount of degradation in its directional
properties and its broadbandedness. Trying different dimensions and
terminations didn't help matters. The Flag, although a very good
directional receiving antenna, does not avail itself to use in a
switchable configuration of two or more Flags erected very closely to
each other.
The Pennant also has this problem if the Pennants are erected with their
vertical sections close together (as one might do with switchable
Pennants which are fed in the centers of their vertical sections).
However, the point-fed Pennant does not have this problem. I have
modeled as many as four point-fed Pennants with their points all within 2
inches of each other with only one Pennant active and the other three
inactive with virtually no difference in performance compared to a single
Pennant by itself.
If you intend to build a switchable system for two, three or four
directions, the only way to do it is with point-to-point Pennants. In
designing a switching system, you must totally isolate each inactive
Pennant from the others by opening BOTH sides of their feedpoints. In a
two-Pennant system, this is easily done using a DPDT relay.
The Pennant and the Flag are quite new, so whenever I discover something
like this, I'll post it. Any of you that use a Pennant or Flag, I'd
appreciate hearing about the results.
73, de Earl, K6SE
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