Just how important is a continuos pre-set distance between the wires,
anyway...? And who was it that came up with the necessity of
equally-spaced wire...? And how did they determine the "optimum" distance
the wires...? Would a span of power line cord (a.k.a. "zip cord") do in a
pinch...?
Eddy,
The transmission line mode of the two wires is what brings the far end of
the antenna to the feedpoint. That is what allows the antenna to be
reversed.
If that line is lossy, or if that line is mismatched by just 2.5:1 SWR and
the wrong length, the antenna can easily lose 20 dB of null depth when in
the forward (fires away from feedpoint) direction.
In the reverse direction, where the antenna fires toward the feedpoint
direction, mismatch or loss only affects signal level. SWR or loss does not
affect F/B in the "reverse" directional mode.
You can use any impedance of line you desire if transformers are readjusted
to the correct ratio, and you can even use coaxial cable for the antenna.
The problem comes in when the line has greatly unstable impedance, velocity
factor, and/or loss, and the major problem is mostly in one direction.
I'd avoid exceptionally lossy lines and lines that significantly change
characteristics with weather conditions.
It is easier to make good transformers when impedance ratio of antenna mode
to transmission line mode is close to unity. That's why 400-600 ohm line
spacings are usually best.
73 Tom
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Topband reflector - topband@contesting.com
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