In my view, if your antenna impedance does not match your feedline
impedance, you do not have a "feedline", but rather a very large
"impedance transformer.
Ken WA8JXM
On 10/27/18 3:23 PM, Paul Christensen wrote:
"I manged to tweak the length of the 300 ohm ladder line to where the SWR
dropped to 1:1 in the middle of the 80 meter band. The SWR decreased on
40 through 10 as well so I can now use my limited range auto-tuner on all
bands. The short 110 foot dipole doesn't seem to be an issue on 80."
What? You mean, your feedline tunes your antenna? Good job.
Just a point of clarification that is often overlooked when discussing
changing line length. The SWR on Tony's 300-ohm balanced feeder did not
change with pruning. This is consistent with countless references that "SWR
does not change with line length" when using lossless, or near lossless
line.
However, pruning the line length did change the combination of resistance
and reactance at the input end of the line, resulting in a near-perfect
50-ohm resistive SWR. The "50-ohm SWR" is often noted as SWR(50). A vector
impedance analyzer would show close to 50+j0 at the feedline input. By
contrast, SWR(300) along the ladder line is likely quite high, but it
matters little with low-loss feeders and provided SWR(300) is not extreme.
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