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Re: [Amps] High SWR

To: amps@contesting.com
Subject: Re: [Amps] High SWR
From: jmltinc@aol.com
Date: Sat, 25 Apr 2009 08:18:05 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Oh, for crying out loud Carl, READ my post.

Where in my post did I mention driven element or tuning?

I was speaking of how the three parameters; SWR, F/B, and gain are 
inter-related in the design of an OPTIMIZED?Yagi. I never spoke tuning. I also 
(purposefully) neglected the matching network (gamma, T, Omega, hairpin, stub, 
etc.) which would present the feedline with a reasonable match.

This information is easily gleaned from:
The Antenna Book, 19th Edition - ARRL
Handbook of Radio Communications, 84th edition - ARRL
Radio Handbook, 23rd Edition - William I. Orr
Or screwing around with your own Yagi.

And for the record, changing the length of a driven element does change the 
other parameters. Take a modeling program, use a sample Yagi, note the gain, 
SWR and F/B. Shorten the driven element and look at the the three figures again.

Changing any combination of length, diameter, or spacing of any of the elements 
will change the characteristics of the antenna due to the mutual coupling of 
the elements. But you knew that already.

See how much better it is when I am ordered not to be brief?

-John, N9RF


-----Original Message-----
From: Carl <km1h@jeremy.mv.com>
To: jmltinc@aol.com
Sent: Fri, 24 Apr 2009 7:31 pm
Subject: Re: [Amps] High SWR


----- Original Message ----- From: <jmltinc@aol.com>?
To: <km1h@jeremy.mv.com>?
Sent: Friday, April 24, 2009 4:58 PM?
Subject: Re: [Amps] High SWR?
?
>I never said that driven element tuning will have any effect on >any?other 
>parameters.?
>?
> Quick enough??
>?
> -John, N9RF?
?
Quick but your above disagrees with what you said earlier?
?
You said:?
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.?
?
In reality VSWR is not a compromise and has nothing to do with the optimization 
process.?
?
Carl?
?
?
>?
>?
> -----Original Message-----?
> From: Carl <km1h@jeremy.mv.com>?
> To: John <jmltinc@aol.com>; amps@contesting.com?
> Sent: Fri, 24 Apr 2009 11:51 am?
> Subject: Re: [Amps] High SWR?
>?
>?
> 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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>?
> ?

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