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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