[TowerTalk] Ladder Line Fed Dipole Issue

[Ken]

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.