The duplexer that you have may not be a "Vari-Notch" unit. Your description sounds like a "30 series" unit (Model number will start with a 30 e.g. 30-36-01A)
The 30 series VHF duplexers are specially designed to work with repeaters that exhibit problems when connected to high selectivity duplexers. This design uses three standard notch type filters on the transmitter side which provide excellent noise filtering while maintaining a relatively low VSWR over a wide frequency range. This helps minimize transmitter sensitivity to cable length between the duplexer and the transmitter and also reduces the potential for transmitter spurs. The receiver portion of the duplexer incorporates three pseudo bandpass filters to give isolation to the transmit carrier and reduce interference and intermodulation caused by other nearby transmitters. Because different types of cavity filters are used for the transmit and receive sides of the duplexer, it is important that the correct model be used. Model numbers are different for units designed for either the transmitter higher or lower than the receiver frequency. I have tuning instructions if this sounds like the unit. Rob K7TGU ----- Original Message ----- From: "tahrens301" <[email protected]> To: <[email protected]> Sent: Thursday, January 28, 2010 15:37 Subject: [Repeater-Builder] VHF Vari-Notch Duplexers - 2" x 2" x 4" ??? > Well, I thought this thing was tuned up, > but obviously something is wrong. > > These are a set of the 2x2x4" cavities... > have a plunger in the front, and a variable > cap adjustment on the back. Also, a pair of > BNC connectors on the capacitor side. > > The plate says Duplexer Vari-Notch, > 147-174 > > It also implies that the TX has a 1.5dB > insertion loss, but darned if I can get > only about 4.5. > > I've talked to the guys at TX/RX, and they > are looking for a book on them, but nothing > yet. > > Anybody have any tuning instructions/info on > them? > > The plunger is marked 'pass low', and the cap > is reject high. Pretty much self explanatory, > and they tune ok, but the insertion loss is > higher than it appears it should be. > > Thanks, > > Tim > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
