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Re: [Amps] High SWR

To: "John" <jmltinc@aol.com>, <amps@contesting.com>
Subject: Re: [Amps] High SWR
From: "Carl" <km1h@jeremy.mv.com>
Date: Fri, 24 Apr 2009 12:51:55 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Please explain how driven element tuning will affect the other 
parameters.

Keep it quick and simple as the moderator gets upset when topics drift 
off amps.

Carl
KM1H




----- Original Message ----- 
From: "John" <jmltinc@aol.com>
To: <amps@contesting.com>
Sent: Friday, April 24, 2009 12:29 PM
Subject: Re: [Amps] High SWR


>
> 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: amps@contesting.com
>  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' ; amps@contesting.com
>    Sent: Thursday, April 23, 2009 9:26 AM
>    Subject: Re: [Amps] High SWR
>
>
>
>
>    > -----Original Message-----
>    > From: amps-bounces@contesting.com 
> [mailto:amps-bounces@contesting.com] 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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