EXCELLENT Post Wes ! Correct and clearly stated.
Thanks for your contribution to the reflector.
de Tom N4KG
On Fri, 21 Aug 1998 23:39:21 -0500 "Wes Attaway"
<wes@attawayinterests.com> writes:
>
>Let me enter this discussion with a few observations.
>
>First, SWR is an acronym for Standing Wave Ratio. It is a RATIO
>(voltage
>max to voltage min or current max to current min) that exists ALONG
>the
>feedline. It does not have a certain value at one point on the line
>and
>another value at a different point. With a properly operating
>transmission
>line, the SWR is constant along the entire length.
>
>Second, impedance is a value that exists at a given point along the
>line.
>It can be one thing at the input, something else 10 feet further out,
>and
>something else 25 feet down the line. Impedance values repeat
>themselves at
>one-half wavelength intervals. This is why you can vary the length of
>a
>feedline and get different impedances at the line input. But, be aware
>that
>this line-length changing DOES NOT affect the SWR.
>
>Third, there is only ONE thing that determines the SWR along a
>transmission
>line, and that one thing is the load at the end of the line. Don't
>ever let
>someone trick you into thinking differently about this.
>
>What Walt Maxwell is trying to convey is how an antenna tuner matches
>the
>entire antenna system. A tuner does not change the value of the load
>at the
>end of the line, so by definition, it does not change the SWR that
>exists
>along the line. What it does do (if properly adjusted) is perfectly
>re-reflect the reflected waves that exist on the portion of the
>transmission
>line between itself and the antenna. The SWR on the line between the
>TX and
>the tuner is 1:1, but the SWR on the line between the tuner and the
>antenna
>is still the same as it was before the tuner was put into play. You
>can
>have a tuner, or tuners, at any point(s) along a transmission line.
>
>Remember the axiom: the ONLY thing that changes SWR along a
>transmission
>line is the load at the end of the line. Don't get sucked into
>believing
>otherwise.
>
>One last thing: forget about reflections. They don't mean much unless
>you
>have a high loss feedline situation. Even worring about SWR is pretty
>meaningless unless you want to do fast bandswitching with little or no
>tuning hassels. Some operating situations demand attention to SWR,
>but the
>reasons usually have little to do with signal strength. The less you
>worry
>about SWR the more you will enjoy operating. Walt's book, plus many
>other
>texts do a good job of showing just how little effect SWR has on the
>strength of transmitted signals.
>
>Wes - N5WA
>
>
>--
>FAQ on WWW: http://www.contesting.com/towertalkfaq.html
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>
>
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