> A sidenote to Jim's comment: at least one vendor makes a SHIELDED rotator
> cable. Yes, the usual 8 conductors, with 2 of them over-sized, all
> enclosed with a shield braid and UV-resistant jacket.
The problem with a shield is it simply re-radiates whatever common mode
currents are in the system. Add another shield on top, and it does the same.
They are especially useless if one end is left floating. One example that
wrongly made it in Handbooks is the drop lead for feeding Beverages, adding
a shield does nothing except make the drop wire thicker and electrically
longer.
This is true no matter what you do with the shields at each end, unless each
end has a nearly perfect zero impedance ground. If it did, you could
accomplish exactly the same thing with bypass capacitors and an unshielded
control cable and nearly the same with twinlead in RF!
I can't tell you how many triple and quad shields I pulled out of RFI
problem areas in CATV systems when the real problem causing the common mode
was corrected.
Shields do help for lightning protection (if properly grounded), so they
aren't a total waste.
73 Tom
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