Duplexers and cavities have been tuned for many years without a tracking generator or spectrum analyzer. It is a little easier with a tracking generator or even a spectrum analyzer and a signal generator. But you can do the job with a signal generator that you can keep on frequency and a receiver. It helps to have some kind of signal level meter on the receiver but you can also just tune for quieting by riding the generator level so that the receiver is always noisy. That way you can hear if the level goes up or down.
Using a sweep generator works fine for tuning pass band cavities or even the pass band part of a pass/notch type duplexer but you can't tune the notches with a sweep generator. The reason being is that the detector is not sensitive enough for the low signal levels that you need to work with. A typical diode detector will only work at about -20 to -30 dbm. Even if your sweep generator is able to put out +20 dbm that only lets you look down -40 to -50 db and the duplexer notch is going to be (hopefully) in excess of -70 db. You will never find the peak of the notch. So just a signal generator preferably a synthesized unit so you know what frequency it is on. You could use a tunable generator and a frequency counter but lots of generators tend to shift frequency slightly when you crank up the output level (high enough for the counter to see) and you will be working with the signal attenuated down to -80 to -100 dbm most of the time while tuning the duplexer. You can not afford to have the signal shift around or drift while you are trying to tune things as it doesn't take much of a frequency shift to mess up your tuning. With a good generator tune the pass bands at the proper frequencies first. Then tune the notches at the opposite frequencies. On the transmit cavities you would tune the pass to the transmit frequency and then tune their notches to the receive frequency etc. Then tune the pass tuning at the proper frequency again now that you have everything in the ball park. Then tune the notches again at the proper frequencies. ALWAYS tune the notches last. Do NOT touch the pass tuning again when you are done with the notch tuning. Tuning the pass just slightly will throw the notch way off. Be sure and have a dummy load on the port of the duplexer you are not working with and preferably 6 to 10 db pads on each of the ports that you are working with or you may not have the same tuning when you hook it up to your radio. 73 Gary K4FMX > -----Original Message----- > From: Repeater-Builder@yahoogroups.com [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of w6nct > Sent: Sunday, April 01, 2007 7:39 PM > To: Repeater-Builder@yahoogroups.com > Subject: [Repeater-Builder] Tuning duplexers with sweep generator? > > > I was recently told (by another ham) that I could ONLY tune up my 70cm > duplexer cavities using something called a "tracking generator". > Unfortunately I do not have one; and judging the prices I have seem > for things with that name on the web, I doubt that I can easily budget > to purchase one. > > For some reason, I thought that my father used to tune up resonant > cavities using a sweep generator, oscilloscope, and a frequency > counter; but I don't recall the exact setup he used. > > I inherited his Wavetek (Model #1080, 1GHz) sweep generator, > oscilloscope, and frequency counter. I also have access to an > IFR-1100 service monitor, if I need it (i.e., can be borrowed from a > friend). > > Can I tune up my 70cm duplexer cavities using the equipment I have? > > If so, could someone please indicate the test setup and procedure. > > Thank-you. > > > > > > > Yahoo! Groups Links > > >
