Thanks to everyone for their input on this issue. I really appreciate it. I am planning a trip to my site in the next 60 days. I will share my results with the group when I have them.
Regards, Steve K3PHL and KB3LRA 224.180 K3PHL/R Philadelphia, PA PL 127.3 224.820 KB3LRA/R Bridgeton, NJ PL 127.3 http://mywebpages.comcast.net/k3phl --- In [email protected], Paul Kelley <[EMAIL PROTECTED]> wrote: > Steve, > > As others have said it will probably work much better to > separate the lines at the antenna port of the duplexer. > Leave the transmitter and receiver connected as they are > now, but remove the T at the duplexer output and feed the > TX antenna from the TX side of the duplexer and the RX > antenna from the RX side of the duplexer. > > Why? > > All transmitters, no matter how good they are, have some > amount of noise (often referred to as sideband noise) > extending out a few MHz on either side of the carrier. > > A duplexer serves two vital functions insofar as preventing > your repeater from desensing itself. First, it must > attenuate the transmitter fundamental enough to prevent > desense from receiver overload; the notches on the receive > side of the duplexer take care of that. Second, it must > attenuate sideband noise from the transmitter on the > receive frequency (otherwise this noise raises the receiver > noise floor and covers up weaker signals); the notches on > the transmit side of the duplexer handle that. > > With close spacing of the antennas I don't think you will > have enough isolation to drop the sideband noise below your > receiver noise floor without the transmit side of the > duplexer to clean it up before it reaches the antenna. > > Good luck troubleshooting your duplex noise problem! > > The duplexer tuning might be slightly affected by splitting > the lines at the output. If you have the means it would be > worthwhile to check the tuning (at least the notches) after > making this change. > > Paul N1BUG > > > On Sunday 01 May 2005 10:34 pm, k3phl wrote: > > Hello all, > > > > I am considering running split antennas at my 220 MHz > > site in Philadelphia as a test to increase sensitivity > > and troubleshoot a duplex noise issue. The machine is > > currently a modifed Motorola Micor using a TX/RX 4 can > > duplexer, DCI bandpass filter in the RX leg, and a Comet > > Super 22 (220) base antenna. > > > > I am considering running separate Super 22 antennas 12 > > feet apart horizontally. One feedline run will go from > > the transmitter direct to the TX antenna. The other > > feedline run will run from the receiver to RX port of > > duplexer, common port of duplexer to 220 bandpass filter > > and then to the RX antenna. The TX port of the duplexer > > will remain unconnected. > > > > I expect the duplexer to act as a 2 can deep notch, > > eliminating the transmitter from the receiver with the TX > > port open. I assume the TX rejection in the receiver > > line should improve and the resulting RX sensitivity > > should improve since the transmitter has been reduced to > > a strong near field instead of RF on the same line. Is > > this the correct theory of using a duplexer in a split > > antenna site and if so, should the TX port be left > > unconnected or capped with a 50 ohm load? > > > > Thanks in advance, > > > > Steve > > K3PHL 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/
