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Re: [TowerTalk] wire antenna question

Subject: Re: [TowerTalk] wire antenna question
From: Steve Hunt <>
Date: Fri, 14 Nov 2008 09:53:55 +0000
List-post: <">>
Be aware that there are some "extreme" cases where minimum VSWR and 
Resonance do not occur at **exactly** the same frequency.

For example, if I take a 34ft folded dipole, and am silly enough to feed 
it through a 50 Ohm line, I get:

Minimum VSWR: 5.72 @ 13.62 MHz where Z=283.8-j23.66
Resonance: Z=288.2+j0 @ 13.7 MHz where VSWR=5.76

It just depends how fast the resistive component is changing relative to 
the reactive component as you move away from resonance. Using the 
previous 40+j0 example, if away from resonance the impedance had become 
45-j4 the SWR would have fallen from 1.2 to 1.1, not risen. This rapid 
shift of the resistive component tends not to happen on simple antennas 
like dipoles, but can occur in more complex arrays.

Steve G3TXQ


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