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.
