[BC] RG-8

[Gregory Muir]

A few other things to remember:

The PVC outer covering on normal RG8 cable is hygroscopic, i.e. it absorbs 
moisture.  One can assume what happens when running cable on the ground in 
outdoor conditions while operating under high RF power.  The PVC is not 
stabilized therefore not really rated for extended UV exposure also. 
Plenum-rated cables with FEP Teflon outer coverings are more tame but 
obviously more costly.  Use conduit where possible.

Cables that say "RG8 Type" usually assume that the cable is manufactured to 
resemble the military version of the cable but may not meet the specs (this 
basically applies to any coax with the word "Type" printed on the sheath). 
I say resemble because the impedance, shield coverage and other ratings can 
vary widely beyond the normal range set by standards. I have seen shield 
coverage all the way down to 65% which means lost power along the run not to 
mention impedance problems  and also RFI problems when used in reception 
applications.  It's better to stick with a cable with a MIL rating stamped 
on the sheath when possible because that will guarantee you shield coverage 
within the 90-98% range at all times not to mention a more stabilized 
impedance value.  And I also understand the "midnight Saturday night" 
failure scenario and RS is the only source within a thousand miles.

If you have the inclination to use a more inexpensive grade cable as 
compared to Andrew products, you might try looking at the Times Microwave 
LMR series cables.  They have an overall foil shield (100% coverage) and are 
very robust for most applications at a much cheaper cost.  The only minor 
problems is that it is a significantly stiffer cable as compared to RG8 and 
that it possesses possess a foam internal insulation which is a bit tricky 
to manage at times if you need to solder the center conductor.  RF 
Industries makes crimp-style connectors for this cable (again at reasonable 
prices) but, after attending a RF connector symposium at NIST, I still 
solder the center conductor contact in lieu of crimping whenever possible.

But if you want a super high-grade RG8 braided shielded cable, go with 
RG-214 which has a double silver-plated braid shield and will put you in the 
poor house before your project is completed.

Greg







----- Original Message ----- 
From: <djkelley at frontier.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Sent: Wednesday, April 02, 2008 3:12 PM
Subject: [BC] RG-8


>> Or it's RG-8 (which I've sen many try to use on a 1 KW), and even
>> though it's supposedly a 50 ohm line, most of the time you will see a
>> large variation from 50 Ohms at the other end.
>
> Its remarkable how well a Nautel AMFET-1 performs after replacing a  200' 
> (or so) run of Tandy RG-8 with Andrew half inch.  Been there done  that.
>
> -dan in lansing
>
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