greg z wrote:
I'm putting up a fullwave loop for 160m, fed with 450 ohm window line,
what are the feedline lenghts to avoid?

Just on 160m or on other HF bands? A fullwave loop has a
feedpoint impedance around 100 ohms plus or minus height
effects. That's an SWR of 4.5:1 on the window line giving
impedances between 100 ohms and 2000 ohms with reactance
magnitudes in the same ballpark. If your tuner will handle
those ranges, any feedline length will be OK. It's a lot
easier to avoid certain feedline lengths on 10m than on
160m. :-)
--
73, Cecil, W5DXP