At 3/12/2005 06:43 PM, you wrote:
>--- Laryn Lohman <[EMAIL PROTECTED]> wrote: > > > > > > --- In [email protected], "Al Wolfe" > > <[EMAIL PROTECTED]> wrote: > > > > > > I've always thought "good quality RG-8X" was > > an oxymoron. > > > > > > < use good quality RG-8X type cable for....> > > > > > > Al, K9SI > > > > Right Al, an oxymoron especially when used in duplex > > service. Any > > braided coax used in duplex service should be silver > > plated braid. > > > > Message 48346 from just a couple of days ago spells > > out some of the > > grief to be found when using RG-8X or any other > > non-silver plated > > cable in duplex service. Good job Bob! > > > > Laryn K8TVZ > >I would mostly agree with this statement, but the >person asking about this is looking for answers that >will work in a specific application. I have used RG-8X >and even RG-58 with excellent results in duplex >systems, especially when the power is relatively low. The 2 systems I reported on run 15 & 22 watts, respectively. Given the level of desense I observed, you would have run less than 2 watts at most, maybe a lot less. >I suppose the thing to do would be to use a DB-420 and >7/8 inch heliax, but this would be impractical for >most mobile/portable repeater setups. I have run into this same problem with my 2 meter portapeater. In fact the first time I observed it was when testing a 3 element yagi that initially had a 10 foot RG-8X jumper on it. I ended up replacing that jumper with RG-142. Regarding the main feed, I tried using 45' of LMR-400 & had good luck with it, but that's probably only because the shield RF currents stayed on the foil shield. If a break ever develops in that foil or the RF "folds over" at a connector, you're doomed for desense. In my case, my guess is that any RF current near the antenna radiated off of the outer shield of the 10' RG-142 section, which is OK because it's silver plated. By the time the RF got to the RG-142/LMR-400 junction, enough of it had radiated away that the outer tin-plated braid of the LMR-400 wasn't an issue. My theory, anyway. If correct, a better solution would be a common-mode choke on the RG-142 to keep RF from getting to the LMR-400's braid. Yet another choice would have been to simply use RG-214 for the entire antenna run, since it's loss at 2 meters is acceptable for lengths < 40 ft. or so. Bob NO6B Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
