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Re: [TowerTalk] wire antenna question

To: Blair S Balden <>
Subject: Re: [TowerTalk] wire antenna question
From: Terry Conboy <>
Date: Thu, 13 Nov 2008 09:35:13 -0800
List-post: <">>
At 08:59 AM 2008-11-13, Blair S Balden NP2F wrote:
>Thanks to everyone who responded.  I feel much better about what 
>I've been doing.  Terry, yours made such perfect sense, I thought I 
>should have known it already!  Because the dipole's resonant Z is 
>usually higher than 50 ohms, getting minimum SWR would mean I'd 
>cancelled out all the reactance.  If the resonant Z were less than 
>50 ohms, I could get a lower SWR by introducing a reactive 
>component.  But, I suppose it would be rare to have a dipole with a 
>resonant Z below 50 ohms.


Even if the resonant Z was under 50 ohms, adding reactance of either 
sign will still increase the SWR.

If you have the TLW program from the ARRL Antenna Book, you can put 
in test values to see how this works.
For example, a 40 ohm resistive load with RG-213 shows a 1.25 SWR at 
the load.   With a load of 40 + j 10, the SWR is 1.38.

A low dipole on the low bands can have a resonant Z under 50 
ohms.  EZNEC shows a resonant 160m dipole of #14 bare copper wire at 
1.83 MHz mounted 40 feet above "average" ground has a Z of 39.4 ohms.

73, Terry N6RY 


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