I want to build a single Flag antenna that can be switched 180 degrees
and would like to know if anyone knows if this will work, has tried it,
or has any pointers for problems I need to watch out for.
Here’s what I have in mind:
The Flag is 14 feet high by 29 feet wide running, say, North South.
There is a small box in the middle of each vertical section containing a
DPDT relay, a 900-ohm to 50-ohm matching transformer, and a 945-ohm
terminating resistor. Call these the North and South boxes. Both North
and South boxes are fed by coax through bead baluns at the North and
South boxes.
The feed lines from the North and South boxes go to a Center box which
contains a DPDT relay to select which of the North and South feed lines
is connected back to the transceiver receive antenna input.
The relay coils in all three boxes are in parallel and the contacts are
wired so that when no power is applied 1) the Center box selects the
North feed line, 2) the North box connects the output of the matching
transformer to the North vertical section of the Flag, and 3) the South
box connects the terminating resistor to the South vertical section of
the Flag. When power is applied to the relay coils 1) the Center box
selects the South feed line, 2) the North box connects the terminating
resistor to the North vertical section of the Flag, and 3) the South box
connects the output of the matching transformer to the South vertical
section of the Flag.
My biggest concern is the unused piece of coax from the center box to,
say, the South box when using the Flag to receive signals from the
North. It’s open circuited at both ends. Will it effect the operation of
the antenna? If so, are there steps I can take to minimize these
effects? Examples might be careful selection of line length, placement
of the lines relative to the antenna, etc.
And if this works, I’d like to build a duplicate pointing East West. How
far apart would the North South Flag and the East West Flag have to be
to avoid interaction? The ultimate would be to have the two flags cross
each other at their midpoints. Does this have a chance of working?
I don’t suppose I’m the first to dream up this scheme but I can’t find
any references on the web that discuss it. Any help will be appreciated.
Tnx and 73 – Dick, W3OA
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