[TowerTalk] 80 meter wire vertical

[jimlux]

On 9/13/17 3:00 PM, Jim Brown wrote:
> 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.
>

Very old is an understatement: Cage elements were used by Heinrich and 
Guiglielmo.  I wonder when and how someone figured out that larger 
diameter worked better, and whether it was just a bigger is better idea 
driving it, or whether it is based on measurement/analysis.

Driving a T top load of multiple elements at the turn of the last 
century was fairly common.  There it was basically a capacitive top-hat.
The Titanic used one in 1912, and the Columbia Radio Club used one in 1906.