ml wrote:

i was reading some technical spec's on a ladder line feed.

the numbers showed it had sorta hi swr around 5 yet the power loss was
really low for it's run, like about 2watts

this confuses me, i always thought that high swr automatically ment
'loss' so what is the piece i am missing?

even stranger was the same equation as above but run for coax, which had
lower swr but higher power lost, which i then attrib to something like
the resistane of the coax?

boy i am mixed up

The losses at HF are primarily proportional to current. Current is
inversely proportional to the characteristic impedance of the feedline,
i.e. I=V/Z0

So I=V/450 is nine times lower than I=V/50. Even with an "SWR around
5" on the ladder-line and 1:1 on the coax, V/450 is probably lower
than V/50. In fact, for the current to be the same on 450 ohm ladder-
line and 50 ohm coax (for the same power) The RMS voltage on the
ladder-line would need to be nine times the RMS voltage on the
coax. So you see ladder-line can tolerate a relatively high SWR
before its RMS current equals the RMS coax current.
--
73, Cecil http://www.qsl.net/w5dxp


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