On Fri, 13 May 2005 23:33:40 -0500, Cecil Moore
wrote:

Gary wrote:
I've read for years ( and never asked why ) that when you're operating
into a high SWR that a high impedance feedline ( say 450 Ohm ladder
line VS 52 Ohm coax ) provides much less loss. I think I recall
someone in this group saying that its mostly current losses. Does the
high impedance line have higher voltage points across its length and
therefore less current flow for a give power level ( say 100 watts )
than the 52 Ohm coax ?

The Z0 of a feedline forces the ratio of forward voltage to forward
current to be Z0. It also forces the ratio of reflected voltage to
reflected voltage to be Z0. Let's say we have 100 watts forward and
50 watts reflected on both 450 ohm feedline and 52 ohm coax. The
forward voltage on the 450 ohm feedline is SQRT(100*450). The forward
current on the 450 ohm feedline is SQRT(100/450). The forward voltage
on the 52 ohm coax is SQRT(100*52). The forward current on the 52 ohm
coax is SQRT(100/52). The same pattern holds for reflected signals.
The effect of Z0 on voltage and current is easy to see.

Thanks Cecil ! In your example it appears that the coax is carrying
about 3 times the current of the 450 Ohm ladder line. That explains a
lot.

73 Gary