On Tue, 23 Aug 2005 22:47:28 +0200, "Meindert Sprang"
wrote:

"Bob" wrote in message
.. .
On Tue, 23 Aug 2005 11:33:18 -0400, Gary Schafer
wrote:
The amount of shielding of coax cable is of little importance in most
typical radio installations.

disagree. with the increasing amount of electronics on boats nowadays,
more shielding is better.

Theorethically yes. In practice, it doesn't matter that much. A shield works
because it creates loops of current, opposite of that in the inner conductor
which keeps the field in.

during transmission. in receiving it acts as a ground.

A practical mesh size on for instance parabolic
antenna's is 1/10 of the wavelength. This will yield a good field
reflection. So on VHF, where the wavelength is about 6 ft, a mesh size of 7
inches would already shield. On many older FM radiostations, "coax" was was
made by an inner conductor surrounded by a "screen" of many (say 20) outer
conductors supported by metal rings.

except many electronics systems operate at freqs far above VHF.


again, disagree. many people report GPS, electronic compass, and
computer problems when they key up their radios. of course some of
this is overload from the antenna, etc. but more shielding on the
cable reduces inteference to and from the radio.

This kind if interference is more likely caused by improper termination
(standing waves), which causes currents to flow on the outside of the
shield. Nothing to do with bad shielding.

several components are responsible for reducing interference.
shielding is one of them. again, it's a matter of selection. why use
58 when superior cables are available?

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