"Dr. Slick" wrote in message
om...
"Mike" wrote in message
...
Hi Kevin,
If you have to cut bits off the coax to get the SWR down, your aerial
isn't
resonant on the frequency being used. The coax is acting like part of
the
aerial.
Get the aerial resonant and it doesn't matter what length of coax you
use as
the SWR will not change.


This would be true assuming the transmission line is truly 50
ohms. It almost never really is.
I've asked this question before, and i got similar answers. The
point about losses in long lines improving the SWR are true of course.
But my point is that even if the antenna is a true 50 + 0j, if the
coax is not a true 50 ohms, and is more like 55 or 45 ohms, then the
length of the
coax WILL matter, in terms of the measured SWR.
Slick

So if I get the set up:
We have a 50 ohm load (antenna) and a non-50 ohm line with a 50 ohm SWR
measuring device.

With this, the "LINE SWR" is still unchanged with line length, but the
impedance seen by the SWR meter will change with coax length. It will vary
around the Zo of the line per the Smith chart. So.... It will show a
varying SWR on this meter. The non-50 ohm like could be considered a
matching transformer, but it won't be matching what we want.

However, with a 55 or 45 ohm line this is all moot - in the noise as far
as being significant to worry about and won't mean anything in practice.


Steve K;9;d;c;i