Bob, Yes, you are right. Many people have found that the D-Star systems need more isolation than a similar FM system especially the UHF units. There has been much discussion about that. I was only trying to add that the pass/reject type filters do offer far more protection from things outside of your pass filter.
We had an instance with a Broadcast FM radio station on one of the towers killing a 220 MHz machine. One of the first things we did is switched to pass/reject and that knocked out alot of it. Their harmonic was at roughly 211MHz but they were so strong it just made everything deaf. To finish getting rid of the radio station we cut an open stub at a 1/4 wave of the radio station frequency and put a T in the feedline with the stub hanging down. That "dangler" had such high voltage at the end of it, that I sustained a small RF burn when the end of the coax was up against my arm... yes it got covered very quickly after that. On the other hand, what I am actually using on D-Star is a combiner/multicoupler setup. Seperate antenna's with alot of isolation. On the UHF RX though the bandpass of the multicoupler was too narrow, so we used two tuned lines and a T so that one goes to the multicoupler and one goes to a 10 pole DCI filter (I think it's 10 pole) followed by a pre-amp and then pass cans for the indicidual receivers. So, I am with you on this one, as we actually do something very similar. Bob is definately correct that the typical 4 can setup used on the average FM repeater will cause you nothing but headaches, and that includes the ultra nice TX/RX stuff. You either have to go with a 6 can setup using pass/reject or like Bob said, throw an DCI filter between the duplexer and receiver. This is also true of the VHF as well. We fought with this problem for a couple of weeks before we went on the multiplexer with about 40' between the antennas. Bottom line I think for this thread, is repeaters are fussy when it comes to a good feedline and antenna system, and D-Star is even fussier. Dan Thompson d...@waycom.com It will save you alot of headaches. > Daniel > > It is true that The band pass/band reject do offer some protection it > is not as great as many believe. See > http://www.anglelinear.com/repeaters/repeaters.html > > for a description of the limited filtering of most Cavity type > Duplexers. We have duplexers from TX/RX and still needed additional > filtering on 146 and 442. Our 1.2 and one of our 440 duplexers come > from Angle Linear as do out PHMET Preamps. > > We had thought about a triplexer for the 2 1.2 modules but the wait > was too long and we elected to go with 2 antennas (one for each > module) and frequency separation 1285HHz - 12MHz for DV with a > duplexer and 1255MHz for DD as of now we haven't had any problems - > the 2 antennas are about 20' apart, The Duplexer on the DV module is > a 7 section unit with PHME preamp from Angle Linear. > > Bob Cumming > W2BZY > (for K1XC & W4PLB)
