Braid coverage percentage does not in itself define
the leakage of a braided coax. Leakage (or the more
easily measured coupling loss) is a function of nearly
all the cable parameters, including the dielectric,
the lay length, the number of strands in the braid,
etc etc. Although the 'holes' are quite small in terms
of wavelength at HF and even VHF, the leakage is more
related to the mutual inductances of each strand of
braid, and is not directly frequency related. Certain
cables with very low braid coverage have quite low
leakages, and some with quite high braid coverages act
like unplugged sinks. And some with quite high braid
coverages are so poorly designed that they have high
attenuation as well.
The reason why we think that cables are less leaky at
hf is that they are quite difficult to couple into -
it is more a function of the external hf antenna and
external noise than the actual leakage.
73 Roger
VE3ZI/G3RBP
(Formerly Head of Communications Group, British Coal
Mining Research and Development Establishment, and
responsible for design of leaky feeder cables - for
what that's worth!)
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