[TowerTalk] Shunt fed resonance changing.

[Edward Mccann]

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 at 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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