Hi Joel,
Well, setup is quite simple - For example, if tuning a complete pass/notch type of duplexer, I connect the output of the signal generator to the antenna port of the duplexer. I then connect the scope to whichever side of the duplexer I'm currently tuning, and I also connect a 50-ohm load to the remaining port. Then, I set the frequency of the generator to the pass frequency for the side which I'm tuning, and set the generator output high enough so as to trigger the scope. After the scope is showing a stable display, simply tune the pass adjustments for *maximum* amplitude on the scope, decreasing the generator output as needed. After tuning the pass adjustments, simply retune the signal generator to the notch frequency for the side which you are tuning, and tune the notch adjustments for *minimum* amplitude on the scope, while increasing the generator output as needed. Repeat the above procedure for the other side of the duplexer. All you're doing is using the scope as an output amplitude indicator, just as you would a Spectrum Analyzer (without tracking generator). The neat thing about this is that even VERY small amplitude changes can be easily seen on the scope, so precise tuning is possible, just as with the spectrum analyzer. I've tuned several Motorola T-1500 series UHF pass/notch duplexers this way, both 2 and 4 cavity units, and they work great - no measureable desense. My Oscilloscope uses a Tektronix 7A24 vertical amp plugin, which has a 50-ohm input. But I have also done this with a 7A26 and a 7A16 (both have 1-megohm inputs), and achieved the same results. If I remember correctly, for frequencies around 440-450Mhz, the scope timebase is set at 50ns, and the vertical amp at 1v per division or so. Actually, I usually just set the timebase so as to show several cycles on the display. Any more questions let me know :)..... - Darrell/KA7BTV --- In Repeater-Builder@yahoogroups.com, "v44kai" <[EMAIL PROTECTED]> wrote: > > Hi Darrell, > > I never done it, and will like to try it. Can you send me a sketch of the > setup, with a brief explanation of your procedure for accomplishing this? > Will appreciate it very much Darrell. > > v44kai.....Joel. > > > > ----- Original Message ----- > From: "jistabout" <[EMAIL PROTECTED]> > To: <Repeater-Builder@yahoogroups.com> > Sent: Sunday, June 22, 2008 12:06 AM > Subject: [Repeater-Builder] Duplexer tuning with an Oscilloscope > > > > Hi All, > > > > Just curious if anyone here has used a wide-band oscilloscope (along > > with a signal source, of course) for duplexer and/or filter tuning? > > > > I use an older Tektronix 7904 500mhz scope along with an HP 8640B > > Signal Generator and it works great. I can't really measure filter > > response, but I can see amplitude changes both large and small very > > well, which allows for quite precise tuning. I've tuned a couple of > > pass/notch type duplexers and several notch-only units with this setup > > and they all work nicely. > > > > Anyway, wonder if anyone else does this and general comments on the > > technique. Thanks! > > > > - Darrell/KA7BTV > > > > > > > > > > > > > > ------------------------------------ > > > > > > > > Yahoo! Groups Links > > > > > > > > > -------------------------------------------------------------------- ------------ > > > > No virus found in this incoming message. > Checked by AVG. > Version: 8.0.100 / Virus Database: 270.4.1/1512 - Release Date: 6/21/2008 > 9:27 AM >
