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Re: [Amps] High SWR

To: "John" <>,<>
Subject: Re: [Amps] High SWR
From: Alek Petkovic <>
Date: Sat, 25 Apr 2009 06:52:20 +0800
List-post: <">>
Don't confuse impedance with resonance,front to back ratio or gain. 
They are all completely separate parameters. Interrelated but 
separate and not appropriate discussion matter on this forum.

Alek, VK6APK

At 12:29 AM 25/04/2009, John wrote:

>Design of a Yagi is a comprimise of SWR, gain, and F/B as they are 
>interdependent. If you optimize for one, the others will change. For 
>low-band beam, F/B is usually most important, but at the expense of 
>gain, SWR or both. If you were to optimize a beam for lowest SWR, 
>you would comprimise gain and/or F/B.
>I don't think it would be a valid statement "that because a Yagi has 
>high SWR it has poor F/B". I think it would be fair to say that if 
>you had LOW SWR, you are lacking in the gain or F/B department.
>-John, N9RF
>   ----- Original Message -----
>   From: Gary Smith
>   To:
>   Sent: Friday, April 24, 2009 11:02 AM
>   Subject: Re: [Amps] High SWR
>   A comment: I have been told that a high swr on a yagi antenna 
> reduces the front to back ratio.  Any truth (facts?) to support this info?
>   73,
>   Gary...wa6fgi
>     ----- Original Message -----
>     From: Gary Schafer
>     To: 'Scott McGrath' ;
>     Sent: Thursday, April 23, 2009 9:26 AM
>     Subject: Re: [Amps] High SWR
>     > -----Original Message-----
>     > From: 
> [] On
>     > Behalf Of Scott McGrath
>     > In reality and especially with a tube amplifier and a Pi 
> output tank the
>     > antenna system can be brought into resonance at a wide range of
>     > impedances and resonance is what we are looking for and it really is
>     > Antenna System Goodness in MOST cases.    As the reflected power is
>     > definitely real but it is best expressed as the reactive power in a
>     > system which effectively is lost.   With ladder line if long 
> enough will
>     > re-radiate some of this 'lost' power.
>     Reflected power is not best expressed as reactive power. It is real power
>     and it is not lost power just because it is reflected. when 
> reflected power
>     sees the matching network in the final amp or antenna tuner it then gets
>     re-reflected back toward the antenna to be ultimately radiated along with
>     the rest of the power. The only "lost power" is that due to the feed line
>     loss on both the forward and reflected power.
>     With ladder line the loss is normally very low and very little 
> forward power
>     is lost and very little reflected power is lost. There can be 
> very high swr
>     (high reflected power) on the line and most all of the 
> reflected power will
>     end up getting back to the antenna to be radiated by the antenna.
>     Ladder line will not re_radiate reflected power any more than it will
>     radiate forward power. If the line is well balanced it will not radiate
>     either forward or reflected power that may be on it.
>     73
>     Gary  K4FMX
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