Chris,

Try a 1:1 balun instead of the 4:1. You are matching the impedance seen at the shack end of the feedline, and that can vary from very low to very high. The impedance you have to match is NOT the characteristic impedance of the feedline. The 600 ohm line simply acts as an impedance transformer. The only time you will see a 600 ohm impedance at the shack end of that feedline is when the far end is terminated by 600 ohms, and I suggest that is not true of the feedpoint impedance at the antenna.


73,
Don W3FPR

On 2/13/2018 8:55 AM, Chris Hallinan wrote:
I have a very similar setup.  K3 -> KPA500 -> MFJ 994BRT 600W autotuner
mounted remote -> Balun Designs 4:1 -> 600 Ohm open wire line to 80 m
doublet.

It works fantastic on 80-20, but will not tune better than about 2:1 on
17.  I cannot use the KPA500 on 17 because the SWR is too high.  Nothing
I've tried works.  I'm wondering if it is simply the tuning
range/resolution of the MFJ-994BRT?  I like the idea of remote mounting, as
I have only a couple feet of coax between the tuner and the balun, thus
minimizing SWR-related feedline loss.
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