I'll be glad to continue this on an antenna forum if you wish to see the
errors in your statement.
Carl
KM1H
----- Original Message -----
From: <jmltinc@aol.com>
To: <amps@contesting.com>
Sent: Saturday, April 25, 2009 8:18 AM
Subject: Re: [Amps] High SWR
> 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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>>> Amps mailing list??
>>> Amps@contesting.com??
>>> http://lists.contesting.com/mailman/listinfo/amps ??
>>?
>> ?
>
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