Fuqua, Bill L wrote:
> Question, how do you place a wire in an hollow conductor with out creating a
> path for RF current on the outside to the inside?
< Answer, you put a shorted stub on each end of the part of the transmission
line where you don't
want the line exposed to the elements (frequently the short in an elbow using
6" or larger line,
think of a "T" being used as a "L" with the other branch being shorted) and
drill a hole through the
outer in the center of short inside the inner (where the inner is silver
soldered to the shorting
flat) and mount a rubber cord gripper, same at the other end at the other stub.
I saw it done once
and I thought is was a silly way to convey the AOL tower light cord (type SJ
cordage) "around a
difficult area" by going through the line.
I would have put it in "water tight flexible" conduit with the conduit
mounted in plastic or
neoprene blocks secured with stainless steel hose bands. The impedance of the
ridged line is
unaffected by anything within the inner conductor and the cordage experiences
none of the high power
UHF signal in the coax until you develop a bad bullet between the stubs.
My reasoning is: if there is any problem with any part of this line 1,000
feet up on the tower
you know the tower crew is gong to pull the AC line out of the RF line and run
it in some kind of
"flexible conduit" mounted in some haphazard manor.
--
Ron KA4INM - I'm proud to be Chuck's pop!
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