[TowerTalk] Non-resonant guy lengths

[John Brosnahan]

>
>Question:
>With an antenna like a 4 square you simply "float" the other three 
>verticals in order to get them out of the picture while you're tuning
>the 4th vertical. These three floating verticals are almost exactly
>resonant with the one you're interested in. Why is it these near
>field resonant structures don't matter in this case but are highly
>unwanted in the case of guy wires?
>
>-- 
>
>73
>Kris N5KM 


Kris, you only need to worry about 1/2 wave resonances.  And the verticals
are 1/4 wave and are only resonate when they are terminated to ground
at the base (or when the length of coax and its termination is equivalent 
to a short) which provides the other half of the half-wave resonance.

To remove the other 1/4 wave verticals from the picture when testing
one of them for resonance you want to disconnect the others from 
their feedlines (as well as ground) since you may not know what their 
feedline lengths (and how it is terminated at the far end) are doing
to the feedpoint.  Maybe it is OK, but maybe it is "grounding"
the other feedpoints making the unwanted verticals resonate by 
transforming the termination (usually just an open circuit) into a short--
which is usually the case when the verticals are current forced with
1/4 wave lines--an open circuit on the far end of the coax gets transformed
to a short at the feedpoint for 1/4 wave feeds.  You can effectively remove
the vertical from the system by shorting the far end of the 1/4 wave
feedline which reflects an open circuit to the feedpoint--but the cleanest
way is just to disconnect the 1/4 vertical from everything at its base.

John  W0UN


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