Hi Rob, Sorry, I forgot to put the model number in the original posting!
It's 28-41-05 It has 3 of the blocks in the TX line, and 2 in the RX. It's in a 2 1/4" thick rack panel. I opened one up, and it looks like a helical resonator with a silver slug that goes in and out, and the BNC connectors have a loop that is 90 degrees to the larger coil and has an air variable cap to ground. thanks! Tim --- In [email protected], "Rob Lee" <r...@...> wrote: > > > 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" <tahr...@...> > 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 > > > > > > >
