On Saturday, September 1, 2012 10:08:23 AM UTC-5, Boomer wrote:
I was shocked to see my antenna change tune radically.

An antenna analysis program like EZNEC would have predicted those results. Since the SWR, Z0, and losses are different going from 450 ohm ladder-line to 600 ohm open-wire line, the 50 ohm SWR and impedance will be different at the shack. There's absolutely nothing to be shocked about - it's just relatively simple physics in action. Here's a transmission line calculator that might help:

http://www.vk1od.net/calc/tl/tllc.php

A free demo (learning) version of EZNEC is available at: www.eznec.com
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73, Cecil, w5dxp.com