At 6/29/2008 21:24, you wrote: > > [EMAIL PROTECTED] wrote: > > I'm going to disagree here. Gary said he's only moving > > 12.5 kHz, & I've never seen any coaxial resonator in common > > use (that means VHFLB cavities being used @ UHF don't count) > > that has enough Q that 12.5 kHz is going to make a > > significant difference. > >You've never taken a real close-in detailed look at the >notch of a high quality UHF cavity..? A misaligned notch >point 12.5 KHz off can be many dB of useful protection is >misplaced.
Maybe a dB or two at most. I claim that once you take that duplexer off the spectrum analyzer/tracking gen. & install it in your system, the actual isolation may very well change more than that due to notch pulling from the non-50 ohm TX, RX and/or antenna. So all your efforts of squeezing every last fraction of a dB out of the duplexer notches are for naught. > > I say don't bother having the duplexer retuned unless you > > think it would need retuning without any frequency change. > > Bob NO6B > >It's OK to disagree and its also OK to be detail orientated >when you're trying to get the maximum possible performance. If the above is true, then if your system isolation margin is only a couple of dB (IOW a 2 dB degradation in your duplexer's reject notches results in desense), you're using the wrong equipment to begin with. For "maximum performance", there should be enough margin in the duplexer isolation so that minor shifts in the reject notches don't degrade the system sensitivity. Bob NO6B
