> "Jim Cicirello" <[EMAIL PROTECTED]> wrote: > Under what circumstances would you use a circulator on your 2-meter > repeater?
Every one, especially since its my job to make sure there are no problems at the repeater site. > Here is my setting: > A strong RF Site with a 152.480 Paging Transmitter,FM Radio > Station on 103.5. Lots of nearby sidebands and a high noise floor. You can still operate a nearby repeater, but you must take extra precautions. > My ham repeater on 147.210 is getting hit by the Paging and I > suspect the FM Station. What kind of receiver, antenna, feedline and filter/duplexer do you have? > There is a crystal filter on my ham receiver for 152.480, a > good one furnished by the paging company. After going through > the duplexers and crystal filter the sensitivity is on the RX > is naturally down a little. Normally the lattice type receiver filters are setup for the repeater receiver frequency and tend not to be the cure all as hoped by many. As described, your crystal filter doesn't make much sense to some of us. > I also have a VHF Community Repeater that is receiving on 160 > MHz and TX on 153. Although that antenna is lower than the Ham > Antenna it talks better. I know there are a lot of variables, > I have good TX RX Duplexers on both units, a Stationmaster on > the commercial and a G-7 on the Ham which hopefully will become > a stationmaster soon. I just called the paging company > and made them come down as they were splattering a lot of the > high band receivers at the tower. They installed another large > CAN (Filter of some type on top of the cabinet and it looks > like the leads go to the exciter, small RG-58 type cable, > compared to the 1/2" hardline on the output. The paging company should have high Q (most often large diameter) cavities in line after a dual port circulator. Their antenna should be the proper gain and type which when combined with their output power level do exceed the authorized levels stated on their license. One would also hope they have a good quality antenna and feedline, min 1/2 hardline. LMR-400 (and hardline) does have leakage. If they don't have the above inline, you need to work with them to get these things installed. It might be worth your while to try a more modest gain Amateur antenna that has a narrow (amateur ham band) range of operation with an included DC ground. Your feedline of quality. You're looking at some decent cavities using a band-pass, band-reject duplexer, starting off with no receiver preamps. Your transmitter goes into a dual port circulator before the duplexer. It would be prudent to install a "suck out" notch cavity, set to the paging frequency but installed on your repeater receiver. The whole repeater needs to go into a very well shielded cab/box with minimal open (unshielde for rf) holes. RF leakage is a big problem at sites with open frame rack mounted equipment. > There now that I have rambled on I am trying to figure what I can > do to get my ham Mastr II to do as good as the MSF5000. I was > grabbing at straws with the circulator thinking that maybe the FM > Station was coming back down my antenna although I can't measure > it. Any suggestions as everything I do don't make the MASTR II > much better.It is the closest freqquency to the paging. > Thanks 73 JIM KA2AJH There are so many potential combinations of mixing issues possible with the site you describe. Preamps mixing with power amps, bad antennas, over powered nearby transmitter sidebands, noise floor. You've got to start with a well planned square one before you go after the other guys. All things considered, your system properly constructed should play well. You just have to find the wild cards and get them out of the deck. cheers skipp (not skip) skipp025 @yahoo.com www.radiowrench.com Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
