Don and All,
I agree that many of the RG-59 and RG-6 coax available will work just
fine. In two cases I found RG-59 CATV-type coax purchased at a big box
store that showed real signs of heat-stress after a few months of
operation at 100+ watts.
My observation is that quality and suitability of typical RG-59
CATV-type coax varies widely. Some, certainly not *all*, may not be
suitable for amateur transmission service. And I'm quite sure that when
the stuff sold in poly bags and off the racks in the mass-merchandisers
was manufactured, the materials selected was *not* based on its ability
to handle 100 watts or more of rf.
Doug -- K0DXV
I
Don Wilhelm wrote:
Doug,
I beg to differ. There are physical properties that give rise to the
characteristic impedance which are related to the dielectric
properties and the relative conductor diameters for the center
conductor and the braid. These same properties will create a
particular RF voltage handling characteristic for the coax in question
(or any coax for that matter).
The real difference in coax quality is the shielding percentage of the
outer braid. That has nothing to do with the RF voltage handling, but
it certainly has a lot to do with the leakage from the coax. In the
extreme, a coaxial cable could have similar leakage characteristics as
open wire line, but again that is not related to the RF voltage
handling characteristics.
So look for a coax that has 90% or greater braid coverage. There is
the 'quad shield' RG6 that is quite good in shielding characteristics,
but I do not know if it is available in white jacket material.
As it has been mentioned, the white jacket is not as UV protective as
the black, so for use indoors, it really does not matter, but outside,
use the cable jacket that is rated for UV protection.
73,
Don W3FPR
Doug Person wrote:
There are many types of cable designated RG-6 and RG-59. Many are
not designed to handle rf voltages typical of ham transmissions. My
suggestion is to be *careful* what you select. Good quality RG-59,
the type broadly used by hams many years ago, is hard to find right
now. We're not talking about what the cable companies are using -
we're talking about what you can buy at Wal-Mart or Home Depot.
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