I really really do appreciate all of the email attempting to rectify my
misunderstanding of proper coax line terminology. However that is a debate
of miniature that I'm sure the original poster is not asking about. The
fact is if you lined up 10 hams and showed them a roll marked RG11 at a
hamfest, I would guess at least 9 of them would expect it to the be foil +
lousy braid stuff of the CATV era.
The fellow was asking about what he could use that was cheap. Commonly
referred to "RG11" - meaning the cheap stuff from the CATV type (whatever
the proper nomenclature is for that) - works fine in ham applications. That
is the point of my comment.
If the guy said "I got plenty of bucks to burn and want it to last in a
direct burial case" I would say to use Buryflex which is marked RG213 and
also works fine. I don't have experience with LMR or hardline here.
From: Jim Brown
Sent: Sunday, August 07, 2016 3:50 PM
Subject: Re: [TowerTalk] Coax Losses on 160 and 75?
On Sat,8/6/2016 10:57 AM, Jeff AC0C wrote:
The one issue that is worth mentioning is making a solid contact with the
rather lousy shield that RG11 has, at least the stuff I have. It's the
essence-of-braid wrapped around some foil.
"RG11" does NOT describe coax. MANY years ago, RG-numbers defined tight
engineering specs. NOW, they are nothing more than generic descriptors
of approximate diameter and impedance. In today's world, "RG11" means 75
ohm coax with an approximate o.d. of 0.4-in. RG8 means 50 ohm coax of
about the same size. RG213 sort of implies 50 ohm cable with a foam
dielectric. That's ALL. It is NOT a spec, it does NOT define loss, nor
impedance, nor Vf. To describe actual coax, we must specify
manufacturer's part numbers and there must be a REAL technical data
sheet for the cable. Only a few cable companies publish REAL tech data
sheets. Belden, Commscope, and Times are are the ones I know of that DO,
and even among those REAL cable companies, some data sheets are FAR
better than others. Try getting data sheets from any of the other
companies that sell coax with their name on it. I tried. None delivered.
You're using a special variety of RG11 designed specifically for CATV
systems. It's greatly cost-reduced to satisfy the needs of those
systems, where most of the signals being transmitted are at UHF and
they're not handling power. There are also RG6 and RG59-size cables
designed for this use.
But the original RG11 coaxes were designed for TRANSMITTING, and for
feeding baseband analog video around facilities. Belden makes several.
They have copper centers and copper braid shields. Their loss at HF is
significantly lower than the CATV coaxes you describe, AND, more
important, they can be soldered to, so you can install Amphenol 83-1SP
connectors on them. Davis RF sells a very nice RG11 that is physically
and electrically similar to Belden's best RG11, 8213. Their BuryFlex is
also very good. But don't expect a data sheet.
I've got some CATV RG6 that's been in my Beverage system and RX antenna
systems for several years. Open up a connection and it ain't pretty --
the Al foil is covered with white powder, the center conductor has
rusted. And this stuff was carefully taped. Run power through these
oxidized connections and you're going to generate RF trash.
73, Jim K9YC
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