Gregg, Very well written. Thank you for your effort here. Hopefully your comments will be noted for future reference by others on this list.
73, Neil McKie - WA6KLA Gregg Lengling wrote: > > You should really be using a return loss bridge and a spectrum analyzer and > tracking generator....but yes I know we can't all afford that equipment. > You can fudge by using a signal generator and a receiver, also never never > never tune the duplexers under transmitter power. > > The first thing you need as previously stated is a 3dB pad on the input to > your receiver you are going to use as signal strength indicator. You will > also need a 50 ohm termination for the unused port of the duplexer during > tuning. The pad is similar to those used in cable tv > systems...HOWEVER..those pads are 75ohms and you have a 50 ohm system. > > Step one, Hook your generator to the antenna port and your receiver (with > 3dB pad) to either the transmit or receiver port. Terminate the other port > (ie: if you are tuning the transmit port, terminate the receiver port). > > Before you start on the duplexor..hook your signal generator up to your > receiver with the 3db pad in line and measure the receiver sensitivity of > you receiver (ie: .022uV for 12dB Sinad)....this is your reference. > > In this case we'll say your on the transmit port. The first thing to do is > to tune the pass frequency..this is the plunger on each cavity in the > transmitter side of the duplexer. Generate just enough signal to start > movement of your receiver strength indicator using your transmit frequency. > Now tune all the TX cans one at a time for max throughput...max signal > strength...you will probably have to continually reduce your output from the > generator as you get the unit tuned. Now look at the output level from the > generator....how many dB of insertion loss do you have compared to your > receiver performance with the cavities in line. (Assume anywhere from .6 to > 1.0 dB per cavity loss)...is this the expected value...if yes the pass is > tuned..if not something is wrong. Next you will tune the notches.....with > everything still connected, now set the generator and receiver to your Notch > Frequency (the receiver freq in this case). You can now tune the notches > (usually in the little box on top of the coupling loop with a small access > hole on the side...use an insulated non-metallic tool). Tune these to > attenuate the signal reaching the receiver, one at a time. Now measure the > difference between the generator output and the receiver known sensitivity. > You should have anywhere between 85 and 100 dB of attenuation. In other > words you'll have a huge amount of signal being generated by your signal > generator. > > Now you're done with the transmit side. Now using the same set of > instructions but with the frequencies reversed....do the same to the receive > side. > > When both sides are done...go back and check all your measurements again and > make sure you didn't screw up. > > Yes this will not be perfect using this procedure, but I've found you can be > within a couple of dB of rejection specs, or as they say good enough for > government work until you can beg/borrow/or steal the proper test equipment. > > Good luck. > > Gregg R. Lengling, W9DHI, Retired > Administrator http://www.milwaukeehdtv.org > K2/100 S#3075 KX1 S# 57 > Politics is the art of appearing candid and completely open, while > concealing as much as possible. -States: The Bene Gesserit View > > > -----Original Message----- > From: Mathew Quaife [mailto:[EMAIL PROTECTED] > Sent: Tuesday, April 27, 2004 2:54 PM > To: Repeater-Builder@yahoogroups.com > Subject: Re: [Repeater-Builder] Duplexer Alignment > > The duplexers are a set of TX/RX duplexers, six of them. When you say a 3db > pad, that is something that I am not sure of, is this basically the same > thing as a db pad used in CATV systems? All I know is that the duplexers > were set up as a Varinotch filter system. > > Mathew > > ----- Original Message ----- > From: "Ken Arck" <[EMAIL PROTECTED]> > To: <Repeater-Builder@yahoogroups.com> > Sent: Tuesday, April 27, 2004 2:49 PM > Subject: Re: [Repeater-Builder] Duplexer Alignment > > > At 07:40 PM 4/27/2004 -0000, you wrote: > > >Is there any methods of tuning a set of duplexer without having a > > >Spectrum analyzer. I am in the learning stages again. I have an > > >IFR-500a, so I can generate a signal into them. I know this would > > >work somewhat for the receive, but what does one do for the > > >transmit. > > > > <---Why wouldn't it work for transmit? As a matter of fact, it would work > > just fine by both the receive AND transmit sides of the duplexer. RF is > RF, > > regardless if its -100 Dbm or +10 Dbm, right? > > > > Depending on what kind of duplexer is it (BP/BR or just BR) determines the > > tuning procedure. You might want to check the website to see if yours is > > listed. One thing though - It's a good idea to use a 3 db pad on the > > receiver you're using for tuning, since you have no guarantee it will > > present a 50 ohm load to the duplexer. > > > > Oh, and don't forget to make sure a 50 ohm load is on the duplexer port > > not currently being tuned as well (a 3 db pad would work here as well). > > > > Ken > > -------------------------------------------------------------------------- > ---- > > President and CTO - Arcom Communications > > Makers of state-of-the-art repeater controllers and accessories. > > http://www.ah6le.net/arcom/index.html > > Be sure to see our products at this year's Dayton Hamvention! > > Repeater Builders spaces 707 through 710 > > AH6LE/R - IRLP Node 3000 > > http://www.irlp.net > > > > > > 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! 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