Hi Eric/Merrill, all The split is 4.5 MHz, (154.370/158.985), and we had been having some problems with the old repeater, so I pulled it out of service & started checking the system.
When I got to the duplexers, I noticed that there was excessive loss in them, so I started a re-tune of them. That's how I got here! Hopefully tomorrow the TXRX guy will have found a manual for them. Kind of at a loss trying to figure it out. thanks, Tim --- In [email protected], "Eric Lemmon" <wb6...@...> wrote: > > Tim, > > My TX-RX catalog states that the "28" identifies the unit as "Vari-Notch > Circuit (Pseudo Band Pass)". The "41" identifies the range as 148-174 MHz. > I could not find the "05" in a model number with the other two numbers, but > I suspect that the small size of the modules indicates a spacing of perhaps > 3.0 or 4.5 MHz. What were the tuned frequencies when you received it? Did > it test okay on the original pair? > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of tahrens301 > Sent: Thursday, January 28, 2010 6:21 PM > To: [email protected] > Subject: [Repeater-Builder] Re: VHF Vari-Notch Duplexers - 2" x 2" x 4" ??? > > > > Hi Merrill, > > Yep, that's what the label says. > > Now, gotta figure out why they aren't > living up to specs. > > Tnx > > Tim > > --- In [email protected] > <mailto:Repeater-Builder%40yahoogroups.com> , Merrill <kg4idd@> wrote: > > > > Tx-Rx model 28-41-05 "Vari-Notch" pseudo-pass, notch > > duplexer. > > This is the appx two RU duplexer for wide split repeaters, > > Comprised of five of the two inch square cavities. > > Tx-Rx manual says 2.5 mhz spacing. > > Tag says Tx 1.5 dB insertion for 76 dB isolation, and Rx is 1.1 dB for > > 110dB(Tx is 76dB at Rx and Rx is 110 at Tx) > > Three cavities on Rx, two on Tx. > > > > > > > > On 1/28/2010 8:28 PM, tahrens301 wrote: > > > 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] > <mailto:Repeater-Builder%40yahoogroups.com> , "Rob Lee"<rob@> 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"<tahrens@> > > >> To:<[email protected] > <mailto:Repeater-Builder%40yahoogroups.com> > > > >> 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 > > > > > > > > > > > > > > > > > >
