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Re: [TowerTalk] Elevated vertical

Subject: Re: [TowerTalk] Elevated vertical
Date: Fri, 23 Dec 2011 08:54:43 -0500 (EST)
List-post: <">>
Hi Ken, the statement "low swr does not indicate resonance" is a bit  
narrow. Perhaps "does not unnecessarily indicate resonance" would be more  
If the feedline has a high loss, the swr would be low even with a  highly 
non-resonant load connected
If the feedline loss is low, then minimum swr would coincide with  
resonance. Using your example of 30 ohms, at resonance the resulting 50 ohm 
would be 1.67. Moving off frequency until there is 10 ohms +x results in a 
vswr  of 1.77 (ignoring any change in the 30 ohm value). Moving off frequency 
until  there is 10 ohms -x also results in vswr= 1.77 (also ignoring any 
change to the  30 ohm value).
Minimum vswr then indicates resonance in that system. As you say, resonance 
 does not necessarily provide a low vswr. Resonance does provide minimum 
vswr at  the frequency in use. 
Gerald K5GW
In a message dated 12/22/2011 7:09:30 P.M. Central Standard Time, writes:

A low  SWR does not indicate resonance.   

Resonance does not  necessarily provide a low SWR.

A true quarter wave resonant vertical  over a perfect ground plane has a 
feed impedance of about 30 ohms and  therefore a 1.6:1 SWR "at resonance" 
(assuming 50 ohm coax).   

Seems to me, IIRC, radials for a ground plane should be 5% longer than  the 
radiator (check the Antenna Book to be sure.)


On  Dec 22, 2011, at 5:23 PM, Tom Osborne wrote:

> Hi All
> I just put up an elevated 40 meter vertical.  The feedpoint is  around 15 
> feet or so up and I have 8 radials on it right now.  I  cut the radials 
> same length of the vertical section.  I have  a coil of around 8 turns of 
> coax for a choke.
> It  works good, as the first day I put it up, I worked some Europeans 
> here in Oregon.
> The thing that seems strange is that  at the low end of 40, the SWR is 
> 1.3:1.  As I go up the  band, it goes up to about 1.5:1, then when I get 
> the top of the  band, it goes back down to 1.2:1.
> Is that because some of the radials  are resonating at different parts of 
> band??   73


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