Thanks, Steve,

Good post. You do need to read a little mo by mentioning Doppler
shifts, I was illustrating that a linear system can generate new
frequencies without violating the law of superposition. No
relativistic effects needed he a two-tone train whistle will not
distort in the superposition sense under Doppler shift, but it can
generate new (or different) frequencies. My point was that generation
of new frequencies is not necessarily a valid test for nonlinearity.


My position on antennas is the same as yours. Earlier posts were
confusing as the term 'linearity' was being applied to antennas in two
ways. One in the electrical superposition sense (by me) and the other
in current distribution along the antenna element. Electrically,
antennas are very linear (I believe) even when their current
distribution along the element length is not.

I stopped posting when I realized we were discussing two different
things.

73,
Glenn AC7ZN



Steve N. wrote:
wrote in message
oups.com...
... By the way, generating new frequencies is not necessarily a violation
of superposition (though it usually is). Consider a system undergoing
a constant Doppler shift.

73,
Glenn AC7ZN


Glenn,
boy! I can't read all these posts, so I was trying to see where you were
going and asking by just skimming, primarily your posts.

The above caught my eye. Doppler is not "generating new frequencies" as a
non linearity does. A non-linear system will produce harmonics with one
exitation frequency and produce the common mixing / IM with multiple
exitation (superimposed) frequencies. I think trying to mix relativistic
effects in with the stationary world is an unnecessary complication of a
linearity discussion.
If I have time I'll try to follow the thread to see what you're really
after...but. If it takes mega watts to see some non linearity in an
antenna, who cares? and more importantly how will you know whree it is
occuring since things like the junction of two connectorc can produce enough
IM to mask other, smaller sources. If you tried an experiment looking
for IM / Mixing you might try to use a receiver becaue a receiver could be a
very sensitive detector...but you'd have to have a pretty good receiver.
Something like a kW LO and mixer to have a really good intercept.
I'm not sure of the point here... Do antennas cause IM?
Sounds like a deadend arena to me.

73, Steve, K9DCI