Adding 50 feet of lossless line will not change the VSWR. It will rotate the
impedance (seen at the TX end) around the Smith Chart.
If the tuner can handle the 'new' impedance as well as the 'old' impedance
the antenna system will perform the same either way.
When analyzing center fed dipoles (with NEC) using 450 ohm line I see some
wild impedances that don't look good for the typical tuner balun. Sometime I'll
have to analyze the baluns in detail to see how they respond the very high and
very low impedance loads.
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