On 8/7/2016 1:04 AM, Jeff AC0C wrote:
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.
I would be ham number 10.
https://www.pasternack.com/flexible-0.405-rg11-75-ohm-coax-cable-pvc-jacket-rg11a-u-p.aspx
No foil and it looks like good braid coverage, although coverage
is not in the specs.
CATV system coaxes have not used RGxx based numbering systems
for at least 30 years. Most of the stuff I've seen is from
Commscope. For example, for drops:
http://www.commscope.com/catalog/broadband/product.aspx?id=15
Notice that it's called "Series 11" to avoid any direct
association with the old military RG (Radio Guide) nomenclature.
Here's a typical "series 11" drop (two cables with the yellow tags).
http://802.11junk.com/jeffl/pics/Comcast/slides/Comcast-cabling.html
The others are "series 6" coax.
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.
I'll second that. Most of my rooftop antenna farm coax cables are
various flavors of 75 ohms. The selection of coax and a running
experiment with waterproofing coax connectors using Teflon tape, were
inspired by various long forgotten arguments over their effectiveness.
I think I started the testing in the 1980's. The only problems so
far are that F-connectors work just fine, but a few compression type
75 ohm BNC connectors have fallen apart.
The cable designation problem is even worse when discussing RG-6 type
cables. The only thing they all have in common is that they will
all accept at least one type of F-connector. Dimensions, dielectric,
shielding, jacket material, and cladding will all vary. What's
important at 160 and 75 meters are copper losses. Dielectric losses
begin to have an effect above 1GHz. So, if you're shopping for cheap
CATV coax cable, think about how much copper you're getting.
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.
If you're going to invest in trenching between the tower(s) and the
shack, perhaps running PVC conduit might be more cost effective than
direct burial cable. You can use cheaper coax cable, that will help
offset the cost of the PVC. Extra credit if you add expansion joints,
pressurize the conduit, provide the means to collect and extract
any accumulated water, and leave room for additional cables.
50 ohms vs 75 ohms.
http://www.microwaves101.com/encyclopedias/why-fifty-ohms
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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