You need to reject the opposite TX on each repeater. Your BP filters were set wrong. You rejected the RX on the TX side - something the duplexer should be doing already. You need to install them in the repeater and reject the other TX. IOW, install a filter in the .16 repeater and notch the .36 TX. A good duplexer should do this as well, but many don't.
Joe M. On Sat 14/02/09 6:34 PM , "wa5luy" wa5...@cablelynx.com sent: > Bare with me this is a bit long. > Our repeater is on 146.76TX / 146.16RX. In the next town the repeater > having the problem is on 147.36TX / 147.96RX. Both repeaters are > Motorola Micors. Our repeater is a 100 watt PA running about 60watts > with a single band pass cavity between TX and a 4 cavity BPBR > duplexer connected to 250 feet of 7/8 hard line and a DB224 antenna. > The distance between repeaters is about 18 miles line of sight with > no obstructions. The other repeater is running a smaller PA driver > with an output of 25 watts. I am not sure of the full power > capability of this driver. This PA then drives a ¼ KW tube type > final set at about 90 watts. This is connected to a 4 cavity BPBR duplexer, > 200 feet of ½ hard line, and a DB224 antenna. > > The problem is when the our repeater 146.76 is in transmit and > someone keys the 147.36 repeater a loop condition is set up locking > on the 147.36 on until the 146.76 drops. Also audio feedback is heard > on the 146.36 repeater. This is typical receiver transmitter intermod. > > Here is what I have done so for. I checked the 146.76 repeater and > there is no signal on it on 147.96 or any other frequency other than > 146.76. I then drove to the 146.36 repeater location and from my car > in front of the repeater building duplicated the problem by > transmitting on 146.76. As we used to say in the phone business, the > trouble is leaving here OK. Next I put a calibrated receiver on the > TX port of their BPBR duplexer and measured about -50DB when the > 146.76 repeater was on. Also I could not squelch out the .76 signal > by holding my hands over the antenna of my handheld radio in the > building. There is lots of.76 signal down there so I suspect > transmitter mixing of the 146.76 with 147.36 in the .36 PA. But > where? I disconnected the ¼ KW PA and hooked the driver up directly > to the duplexer and the mixing signal on 147.96 is worse. I then put > one band pass 147.36, band reject 147. 76 cavity between the PA > driver and the duplexer. To my surprise the mixing signal on 147.96 > is even higher! I also tried a single band pass cavity with about the > same results. Having run out of cavity's I came back home. > > I realize their PA driver most likely needs to be checked. If the > driver PA is ok they will need 30 to 50 DB of isolation between the > 147.36 final and the duplexer which will be at least two cavities. I > was able to duplicate this mixing with a couple of 2 meter radios, a > lossy T connector and a signal generator. I took two high pass > cavities out of a duplexer tuning then to pass 147.36 and reject > 146.76. I ended up with around 70DB of rejection and 2DB in the pass. > I recorded the amount of signal needed to cause the mixing. I then > put the cavities between the signal generator and transmitter. To my > surprise the amount of signal to start mixing was about the same. The > cavities are the type with a T on one port and a compression > capacitor for the reject tuning. > Some questions I have for the group are: > 1. What is the best type of cavity filter to use in this situation > and where should it be placed? > 2. Has anyone else seen that, been there, done that, and what was > your solution? > Any information or ideas will be appreciated. > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > To visit your group on the web, go to: > http://groups.yahoo.com/group/Repeater-Builder/ > Your email settings: > Individual Email | Traditional > > To change settings online go to: > http://groups.yahoo.com/group/Repeater-Builder/join(Yahoo! ID required) > > To change settings via email: > repeater-builder-dig...@yahoogroups.com > repeater-builder-fullfeatu...@yahoogroups.com > To unsubscribe from this group, send an email to: > repeater-builder-unsubscr...@yahoogroups.com > Your use of Yahoo! Groups is subject to: > http://docs.yahoo.com/info/terms/ > > >
