The 28-41-05 is indeed a "Vari-Notch" unit. We have a hundred or so 28-37-06C units in service. The manual for the 28-37-06C covers 17 different models, however, the 28-41-05 is not among those.
Sorry I couldn't help out. Regards, Rob K7TGU ----- Original Message ----- From: "tahrens301" <[email protected]> To: <[email protected]> Sent: Thursday, January 28, 2010 17:28 Subject: [Repeater-Builder] Re: VHF Vari-Notch Duplexers - 2" x 2" x 4" ??? > 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 >> > >> > >> > >> > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
