[TowerTalk] 80 meter wire vertical

[Jim Brown]

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.

Exactly the same thing happens with a tower, either as a radiating 
element or as a passive reflector. Somewhere I've seen an equation for 
the equivalent diameter of a triangular tower. As I recall, it's roughly 
0.7x the width of one of the triangular sides.

73, Jim K9YC