On 9/13/2017 2:28 PM, Bill via TowerTalk wrote:
All this talk about 80 meter verticals got me thinking.
For a wire vertical, suppose instead of a single wire, we replaced it
with two wires separated by about three or four inches, connected at
the bottom and top.
Several years ago, I did that with the vertical part of my Tee vertical
for 160M. It's two #10 or #12 THHN conductors, tied together bottom and
top, with separation on the order of 8-10 inches.
Would the bandwidth be increased?
SWR bandwidth approximately doubled in my case.
Would the resonant frequency of the antenna be lowered?
Yes, slightly. Wire insulation also lowers the resonant frequency
slightly. These effects are small, a few percent.
Would there be any advantage to using the two wires?
The increased SWR bandwidth means less re-tuning of the power amp output
and slightly less loss in a long feedline. That's the only advantage.
The effect on field strength is negligible unless it's a very long
feedline, simply because coax loss is pretty low on 80M.
Would there be any change in impedence?
Z at resonance won't change enough to matter (and difficult to measure),
but Z off-resonance will be lower because the resonance has been
broadbanded.
And yes, as KC4YN, adding more conductors will broadband the antenna
even more.
These are VERY old techniques. I recall hearing about them as a new ham
55 years ago.