[amsat-bb] Re: Feed Line Loss @ Freq vs. Price

[Nate Duehr]

> Side comment to Nate:  What is your problem with LMR cables?

LMR is essentially a braid-over-foil design, which if it moves physically
(has to be tied down properly), all those little "contact points" between
the "bumpy" braid and the "flat" foil are all little passive-intermod
connections waiting to make noise, in a duplexed system, anyway.

LOTS of people have reported major noise issues with it, in specific
environments... a few of the more sensitive commercial tower sites have
banned its use... citing it as an intermod/mixing problem in high-RF
environments.  Not many, but a few.

So it's not really "my" problem, but an overall lack of understanding of
its limitations when it got "popular" in the last few years.

> I have a commercial 75w VHF repeater using about 60-feet of LMR-600
> in service for over ten years with absolutely no problems.  This site
> has about 7 other repeater users, BTW.

You're lucky.

This thread has some of the recent conversation about it on
Repeater-Builder... feel free to come over there and ask questions...
basically the consensus over there right now is... "If you're getting away
with it, great... if you want to do it right, run hard-line."

http://www.mail-archive.com/repeater-builder@yahoogroups.com/msg35670.html

Hunt around the thread for more info.  There was a really nice article
written by Andrew (taken with a grain of salt, since they have a dog in
this fight), that described the typical "desense" type noise levels
introduced in a system by using LMR.  It was significant numbers at longer
cable runs, hardline is much "quieter".  Unfortunately, I can't find the
article right now.

Personally I have no "problem" with LMR, it's just a trade-off like
anything else.  The entire VHF and up rover setup for the Jeep is done
with LMR400 for the weak-signal stuff, using crimp N-connectors... but I
won't put it on repeaters anymore.

Saw a chunk of it creating mixing problems one time... only takes once for
me to decide messing around with sub-standard cabling at the site "isn't
worth it"... when hardline is no more expensive (other than connectors)
and lasts over 10 years, even in harsh environments...

As someone pointed out, pre-made 1/2" hardline is actually CHEAPER than
some variants of LMR these days... LMR got "popular" and the price went
up.

-- 
Nate Duehr, WY0X