Mike, Your question is an excellent one! It is true that most duplexers can be tuned to the 90% level using relatively crude methods. It may also be true that repeaters using a duplexer tuned with relatively crude methods may work just fine in non-demanding applications.
In order to squeeze out the last 10% of performance, it takes some more precise methods. A spectrum analyzer with with a tracking generator, whether integral with a service monitor or separate, may gain another 5% of performance. This is the level at which the majority of commercial and public safety systems operate, IMHO. (These percentages are my own WAGs, don't ask me for proof!) That elusive last 5% is achieved with precision obtained only through a network analyzer or a spectrum analyzer equipped with a return-loss bridge. In either case, the equipment is phase-locked to a GPS frequency-disciplined standard, so that basic frequency error is essentially non-existent. When viewed as a transmission loss on a conventional spectrum analyzer or service monitor, the bandpass characteristic of a duplexer is a merely a gentle "hump" in the trace. When viewed as return loss on a network analyzer, or a spectrum analyzer with a return-loss bridge, the exact tuning point is seen as a very sharp dip- an unambiguous tuning point of optimum bandpass. I will readily admit that, until I acquired a network analyzer, I thought I could tune a duplexer within a gnat's eyelash. Not! It was an extremely humbling experience for me to see a significant improvement in the performance of a duplexer that I had previously tuned with my service monitor, once I retuned it on a network analyzer. I think I gained between 0.5 and 1.0 dB in receiver performance, on average. YMMV. 73, Eric Lemmon WB6FLY Michal Smialowski wrote: > I have always tuned duplexers just using a signal generator and a > radio receiver. Peaking the passband and then going for the deepest > notch for the reject. Although this seems to work, the results haven't > been spectacular. I realize that there are many variables to consider. > My question is, does using a spectrum analyzer and a sweep generator ( > I am guessing here) make the process better, and if it does, how so ie > what is the principle behind it?ThanksMike SmialowskiVE7SMLSmithers BC > Canada > > > > > > > --------------------------------------------------------------- > 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 the Yahoo! Terms of > Service. > 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/
