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Re: [TenTec] OT SWR VS Power Loss

To: "Wayne Whitman" <wwhitman@fastmail.fm>, "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] OT SWR VS Power Loss
From: "Alfred Lorona" <w6wqc@dslextreme.com>
Reply-to: Alfred Lorona <w6wqc@dslextreme.com>, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 6 Jul 2008 18:19:14 -0700
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
Wayne wrote"

> How can a tuner at the tx end change the impedance mismatch between the
> feedline and the antenna into a match?
> Did you mean to say " a mismatch between the end of the feedline and the
> antenna"?

Perhaps I should have said that it establishes a  'conjugate match' to avoid 
confusion.. In a system such as rig/tuner/line/antenna a conjugate match 
established at any point in that system results in a conjugate match at 
every other point in the system. A tranmission line acts like a transformer. 
If you attach an impedance at one end, a certain impedance will appear at 
the other end. It's magnitude depends on the line length, characteristic 
impedance of the line, frequency, and the impedance attached at one end. 
Thus, by changing the impedance at one end, you can effectively change the 
impedance at the far end. Conjugate matching is required for maximum power 
transfer and that is what a tuner does. It's adjusts the far end impedance 
so that maximum power gets transferred from the line to the antenna 
regardless of the impedances of either.

So, regardless of the impedance values of the line and antenna, the use of a 
tuner at either end establishes the required conjugate matching condition 
for maximum power transfer and thus maximum radiation. If your rig pumps 100 
watts, 100 watts gets radiated less the amount of power lost in the line due 
to its inherent loss and loss due to a finite swr. Putting the tuner at the 
antenna eliminates line loss due to a finite swr. It's  the ideal place to 
put it but, as Jerry pointed out, it has certain undesireable disadvantages, 
namely, its hard to get at it.

Putting the tuner at the rig end results in line loss due to a finite swr 
but there is no loss due to an impedance mismatch at the line/antenna 
junction! If the loss due to swr is unacceptable, the only thing you can do 
is use a shorter or a lower loss line.

73, AL

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