I thought the big problem with LMR400 was when used as the feedline up a tower to a repeater antenna. The temperature changes were causing expansion and contraction of the various layers, which rubbed on each other, causing noise.
I would not expect that inside a building, unless of course the building is not at all climate controlled and thus the indoor temps are the same as the outdoor temps and the coax responds the same way. I use RG214 exclusively and have not had a problem with it. I can see how some other double-shielded stuff could be a problem however. Bob M. ====== --- skipp025 <[EMAIL PROTECTED]> wrote: > Hi Jeff, > > > "Jeff DePolo" <[EMAIL PROTECTED]> wrote: > > > Within the last year I/we have had at least 3 > episodes of LMR-400 > > > feed-line causing serious trouble on repeater > systems. At least > > > two of those serious problems have started some > x-value of time > > > after the lmr-400 cable was first installed. > > > But how can this be Skipp, with so many on this > list reporting > > such great results with LMR-type cables on their > repeaters? ;-) > > In this case it was us knowing the expected > performance of the > repeater. I tend to suspect many people actually > don't know how > well their repeater systems should operate, nor > would they notice > less than dramatic gremlins/problems. > > With the LMR-400 in place... the effective rx sens > at the duplexer > output port was over .55uV and desense and grungy > (pop in and out > squelch) operation. > > With the LMR-400 replaced... the effective rx sens > at the duplexer > port was better than .35uV > > I/we would/did notice that type of performance > change because the > primary users are mostly hand held (portable) > radios. Many repeater > owners would be very happy with .55uV effective sens > from a 6100ft > mountain top. In this example the repeater owner > noticed something > was amiss... > > > > My misery with braid+foil cables dates back to the > mid/late 80's > > when 9913 was gaining popularity. > > Nice stuff... but I don't like to use flexible feed > lines that > depend a lot on air-conductor spacing/placement. > Once you've had a > center conductor migration problem... you never > trust that type of > wire again. The last time I found 9913 in a system > it caused a > brand new 1290 repeater power amplifier to fail... > $600 plus damage. > > > I used a 9913 jumper between the Polyphaser and > duplexer when I > > installed a ham repeater. It had just a hint of > desense > > when first installed, which I wrote off as tower > noise, but after > > less than a year, it had worsened to the point of > requiring a full > > investigation which ultimately revealed that 9913 > jumper to be the > > cause. Replaced with something else (RG214 I > think) and the > > desense was totally eliminated. > > At first glance the numbers (spec) on RG-214 are not > great... but > it is a known good performing coax and has never > casued me grief. > > > Around the same time, a ham friend who worked for > one of the cell > > carriers reported that they were pulling ALL 9914 > patch cables > > (similar to 9913, but with a foam dielectric) out > of all of the > > cell sites in the market (which, back then, was > probably only a > > few dozen). I think they were factory cables that > came with > > early Lucent equipment. Anyway, they had so many > problems > > that they were replacing them all with 1/2" > Superflex. > > My general rule of thumb... soft foam center and air > spaced flexible > coax is mostly bad news. > > Firm or hard foam center flexible coax might be > usable... depending > on who, what, where and how. > > > Nowadays, I'll use LMR400DB (DB = direct burial, > i.e. flooded-braid) > > for short runs to non-duplex link yagis or home > station use, but > > that's it. I'm not rich enough to be cheap. > > > > --- Jeff > > I understand Jeff... people have to do what they > have to do... My > post is meant to help people avoid a cold cup of > coffee on a windy > mountain top when one could be elsewhere. > > cheers, > skipp > > ps: You'll notice I didn't say I threw the LMR-400 > jumper away... It > has other applications... > s. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
