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: [email protected] 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: <[email protected]> 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 > > > > > Yahoo! Groups Links 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! Groups is subject to: http://docs.yahoo.com/info/terms/
