Robert M. Kimbrell wrote:
I sometimes use a 33 foot vertical with 16 25 foot radials laying on the
ground. I feed this with 450 ohm window line and use it multiband. It is
an excellent performer for me. I want to understand what is happening at
the feedpoint on 20 meters and 40 meters on both conductors of the
feedline.

Assuming the feedpoint impedance on 40m is somewhere
around 35 ohms, the 40m SWR on the 450 ohm line would
be around 13:1. Assuming the feedpoint impedance on
20m is around 1200 ohms, the 20m SWR on the 450 ohm
line would be around 3:1. You probably should make
the ladder-line somewhere around an integer number of
1/2 wavelengths long on 40m and your tuner should be
able to handle the rest. You will have some common
mode current in the system that could cause some
radiation and losses from the ladder-line.
--
73, Cecil http://www.w5dxp.com