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[TowerTalk] Fwd: balanced line loss on a mismatched antenna

Subject: [TowerTalk] Fwd: balanced line loss on a mismatched antenna
Date: Wed, 29 Feb 2012 20:53:51 -0500 (EST)
List-post: <">>
Wouldn't a 33 feet wire have a bigger impact? I believe that's the 1/2  
wavelength times 95%. Unless you have some good capacitance at the end, 26  
feet is a little too short.
An insulated, 26 feet guy wire may have enough capacitance to the  tower 
and the ground to be resonant at 10, 15 and/or 20 but that will be  very 
dependant on the distances between the wire, ground and tower.
Hans - N2JFS
Sent: 2/29/2012  12:48:15 P.M. Eastern Standard Time
Subj: Re: [TowerTalk] balanced line  loss on a mismatched antenna

That seemed a bit unlikely to me so I just tried it! I took  a 26ft wire 
and placed it in 3 positions around a 20m Yagi:
4ft behind  the Reflector, 4ft in front of the foremost Director, and 4ft 
off to one  side of the Driven element; in all cases the wire was 
parallel with the  Yagi elements and in the same plane.

The Forward Gain never changed by  more than 0.11dB, the F/Side never 
changed by more than 0.9dB, and the  biggest change in F/B was from 
28.9dB to 24.84dB.
The biggest excursion  in feedpoint impedance was from 22-j14 to 21-j10.

Looking at the very  low current induced into the non-resonant 26ft 
parasitic wire, it's clear  to see why it didn't have much effect on the 

I'd be very  interested to see a model where introducing a 26ft wire has 
a major  impact.

Steve G3TXQ

On 29/02/2012 14:34, Steve London  wrote:
> Just because a nearby antenna is non-resonant does not mean  that it will 
> interact with other antennas.
> Every  ARRL Antenna Book written in the past 30 years has a figure showing
>  "ungrounded guy wire lengths to avoid". It shows 26 feet to be a "magic" 
> for 10, 15 and 20 meters. Now take your favorite modeling  software and 
put this
> "magic" length within a few feet of a 10, 15 or  20 meter yagi. Major 
>  distortion.

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