[TowerTalk] perfect braid...

[Roger Parsons]

Just to say that I agree with this evening's posts and
conclusions from Tom W8JI and Jerry K4SAV on this
subject.

Just a couple of points:

The external field from even a perfectly shielded coax
cable is related to the curvature and finite thickness
of the outer conductor.

The leakage from a cable is not solely related to the
percentage braid coverage. It is also affected by the
velocity factor, the lay length, the impedance and the
grouping, size and configuration of the braiding
wires. It cannot be calculated with any degree of
precision without knowledge of all the parameters.

Leakage from any coaxial cable will establish a Gaubau
(single wire mode) wave on the outside of the cable
after several wavelengths. If there is a second
parallel cable there will be transfer to the coaxial
mode on the second cable. However, it is most unlikely
that it could be measured as even with purpose
designed leaky feeders closely adjacent it would be at
least 100dB down on the primary cable coaxial mode.
With any half decent normal coaxial cable it could
easily be 200dB down. If the cables are lying on the
ground, or in a cable tray, the single wire mode would
have very high attenuation and the coupling would be
utterly miniscule.

73 Roger
VE3ZI





	
	
		
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