[TowerTalk] how does one accomplish a 'stud' for elements?

[ve4xt at mymts.net]

I'm wondering if Optibeam's design uses 1/4-wl 15 meter stubs mounted such that the open end of the stub is at a distance from the boom that is not a resonance point on 15.

Butternut's HF6 et al. multiband verticals use such a stub to create a 1/4-wl vertical on 15, by placing the open end of the stub at the 15-m 1/4-wl location on the vertical.  The stub decouples the rest of the antenna above the open end of the stub on 15. Butternut uses the stub to create resonance, but who says you couldn't use such a stub to create nonresonance?

A 1/4 wl on 15 is just more than 11 feet, if you placed such a stub on a 40-m element so the open end is, say, five feet out from the boom, wouldn't 15-m RF then face a high impedance on that element? Butternut faces the open end of the stub towards the feedpoint, so I'm assuming you would face the open ends of stubs towards the boom.

To take the idea even one step further, is it possible to use these stubs not only to detune the 40-m elements on 15, but also to act as additional parastic elements on 15?

Modelling might present you with the ideal stub lengths and locations.  

73, kelly, ve4xt 


Sent from my iPad

> On Jan 2, 2016, at 8:04 AM, StellarCAT <rxdesign at ssvecnet.com> wrote:
> 
> Specifically adding something to a 4 element 40 to eliminate 15 meter interaction? I believe Optibeam does this – not sure how they do it. Is this just using the element with a parallel line tuned through a cap for max current on 15? If so any suggestions on how long to make it and where specifically to put it on each element 1/2? 
> 
> Or is there a way to use a relay, open normally, closed when on 15 that would add some impedance to the antenna causing it to be detuned at 15? 
> 
> Alternatively I can rotate the antenna 90 degrees but boy it would be so much better not to have to do that to avoid interaction on 15. 
> 
> thanks in advance,
> 
> Gary 
> K9RX
> 
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