"Jimmie D" writes:

"Jon Kåre Hellan" wrote in message
...
Richard Clark writes:

On Tue, 19 Jun 2007 16:45:15 -0400, Chuck

I'm not trying to argue against your main points, but I have a problem
with this:

We ask them to jumper in an extra few feet of transmission line and
check their SWR. They usually are astonished that their antenna needs
tuning again. This is a slam dunk indication of common mode problems.

Unless the SWR on the line is 1:1, changing the length of transmission
line *will* change the impedance seen. Whether there is common mode
current or not.

73
LA4RT Jon

True it will change the impedance seen but not the SWR so unless you are
checking your line with an impedance bridge you should see no change except
that due to cable loss and normally a few feet of feedline does not add any
significant loss. If you do see a change it will be due to currents on thec
coax.

Jimmie

If you only measure SWR, you will see no change. But the text I
commented said "their antenna needs tuning again". You *will* have to
adjust your antenna tuner. Antenna tuner settings don't only care
about the magnitude of SWR, but also about the specific resistive and
reactive impedances.

73
LA4RT Jon