The one problem with using an scope for duplexer tuning most scopes have a 5V-5mv vert range. This is only 60 db, not near enough for duplexer tuning. Using a diode detector reduces this even more due to diode drop. This is getting down to using a Bird watt meter with a number of slugs to tune a duplexer.
You can compensate this with higher power into the duplexer, but one should never tune with much power. To tune a duplexer one needs a meter/sensor that can read down to the 10 uV range. From 1 V this is about 100 db range, what is needed for good duplexer tuning. I guess one could help with a pre-amp on the scope. 73, ron, n9ee/r >From: jistabout <[EMAIL PROTECTED]> >Date: 2008/06/23 Mon AM 04:13:04 EDT >To: Repeater-Builder@yahoogroups.com >Subject: [Repeater-Builder] Re: Duplexer tuning with an Oscilloscope > >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 >> > > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
