"A quarter wavelength 75 ohm coax working into a 50 ohm load, transforms
the 50 ohm load to 112.5 ohms, non-reactive, as it appears at the end of
the coax next to the transmitter, as previously discussed.
Good so far.
"If we place a 50-ohm SWR meter at the near end of the coax, between it
and the rf source (the transmitter), the meter will "see" 112.5 ohms, not
50 ohms nor 75 ohms. It will read 2.25:1 SWR. But the actual SWR on the
coax line remains 1.5:1."
In your example, SWR at any point on a lossless 1/4 wave, 70-ohm line
section is indeed 1.5:1. The Z at the input to the 1/4 section is 112.5+j0.
However, the SWR at any distance from *this point* to the transmitter is not
just "apparently" 2.25:1. It is in fact 2.25:1. The 1/4 wave section not
only transformed the Z, but the Z transformation set up a change in SWR on
any subsequent length of 50-ohm line between the transformer and
transmitter. The SWR at any point on the 50 ohm section [SWR (50)] between
the transmitter and 1/4 wave section is 2.25:1 (although the Z is now
changing along the line) -- and the SWR at any point on the 70-ohm
transformer section [SWR(70)] is 1.5:1.
The moment the characteristic Z changes along a line, the line SWR also
changes. When we hear that "SWR doesn't change along a line," that is true
when the characteristic Z is uniform along the entire length of the line and
the line is loss-less.
Paul, W9AC
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