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
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