There is only one frequency of valid resonance: at the frequency where X= j0.
While often minimum SWR occurs at the same frequency, often it does not.
And, sometimes there all false resonances indicated where X =j0 (crossing one
way or the other) at odd-ball frequencies. These are most often tracked to
unwanted Common Mode Currents, or interferences from a roof, a chimney, or
other antenna nearby.
FYI.
Ed McCann
AG6CX
Sent from my iPhone
> On Dec 3, 2018, at 3:30 PM, James Wolf <jbwolf@comcast.net> wrote:
>
> <<How are you determining resonance?? Do you mean minimum SWR? How are you
> measuring it? Are you using the same SWR indicator for low and high power
> levels? Or the rig when running barefoot and the amp when it's in use?
>
> Looking at the SWR at the base of the tower or in the shack. The minimum
> SWR point changes by 50 kHz. Occasionally increasing the power from 100
> watts to 1500 watts will trigger the change. When it changes, it is instant
> - no gradual change.
>
>
>
> <<How are you feeding the tower
>
> Through a series air variable capacitor. The problem appears not to be in
> series cap.
>
>
>
> <<Guy wires that can move can make the tower unsafe
>
> Phillistran guy wires will always move some.
>
>
>
> Jim - KR9U
>
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