Jon Kåre Hellan wrote:

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.

There are some, like Cebik,

http://www.cebik.com/trans/cmp.html
A Common-Mode Current Picture Show

who believe common mode RF getting into
some electronic metering circuits
produces erroneous SWR readings. Could
that be the reason small changes in
transmission line length sometimes
result in apparent changes in SWR?

Of course, if there are common mode
currents on a coax transmission line,
the impedance of the line seen by the
SWR meter (50 ohms in parallel with the
impedance between the shield's outer
surface and ground) is no longer 50 ohms
and the meter calibration is no longer
correct regardless of whether RF is
getting into the electronics of the
meter. Changing the length of the coax
gives you a new, out-of-calibration
measurement. ;-)

73,

Chuck

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