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Old April 7th 05, 11:08 PM
Roy Lewallen
 
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Asimov wrote:

Since a portion of the EM field in open wire line is free to travel
outside the conductor into the environment then we may safely assume
there is an exchange between the environment and the conductor.


If the conductors are perfectly conducting, no part of the field at all
exists within the conductor. With good conductors like copper and at HF
and above, there's very little penetration of the conductor by the
fields, either electric or magnetic. As far as an "exchange" goes, it
sounds like you're trying to describe radiation. If not, what's the
phenomenon you're referring to?

If the
impedance of each is approximately the same then there is less loss in
the interface between the two.


No, that's not true. First of all, a mismatch doesn't cause loss.
Secondly, as I explained in my last posting, the characteristic
impedance of a transmission line isn't the same thing as the
characteristic impedance of free space. If you were to construct a
transmission line with 377 ohms characteristic impedance (numerically
the same as the characteristic impedance of free space), the ratio of
E/H fields between the conductors probably won't be anywhere near 377
ohms, as it is in a plane wave propagating without wires.

It has to do with the reflective
coefficient where the energy is returned.


Well, no. There isn't a bundle of energy trying to escape the line and
bouncing off the air, or bouncing off the air as it travels along the
line, or bouncing off the conductors into the air. So reflection
coefficient isn't applicable here.

You will note 300 ohm open
line has less loss than 100 ohm open line.


Yes, and 600 ohm line has less loss than 377 ohm line. You'll have to
find a way to fit this into your theory if you want to pursue it.

RL The loss in coax is a trade off
to achieve stability.


RL Coax is more stable than open wire line? Does open wire line drift in
RL some way?

It is susceptible to ambient humidity and proximity to conductive
objects (birds, snow, rfi). That is a source of drift in practical
terms.


Thanks for the clarification. Because the differential fields are
completely confined within a coaxial cable, they are indeed more immune
to external influences.

I'm afraid that the conclusions you've reached about loss and
characteristic impedance are based on a poor understanding of
fundamental transmission line operation. The result is some conclusions
that are, and are well known to be, untrue.

If you really feel that you have a viable theory, you should be able to
provide some equations and formulas to quantify the extra loss you're
talking about. The existing theory, formulas and equations, in daily use
for over a hundred years, have been shown countless times to accurately
predict transmission line loss, and they don't include the phenomena
you're describing. So although I think it's highly doubtful that your
formulations will prove more accurate, if you post them they can pretty
easily be tested by actual cable measurement.

Roy Lewallen, W7EL
 
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