I take it by tuning you mean just adjusting the screws, and not adding or changing anything to them?
--- In [email protected], n...@... wrote: > > At 2/10/2009 17:31, you wrote: > >Lou, > > > >I doubt that you can use this band-reject (notch) duplexer at 70 cm without > >factory rework. The coupling loops were designed and positioned > >specifically for the 450-512 MHz band, and they are not externally > >adjustable. The lengths of the jumper cables are unique to the band for > >which the duplexer was originally tuned, and are not appropriate for any > >other band. That duplexer has a specified rejection of 45 dB minimum, which > >may be insufficient for your application. Look at GE LBI-3971 for > >information on this duplexer. > > > >A few years ago, I ordered a Celwave mobile notch duplexer for a 70 cm > >repeater, and I was astounded by its outstanding performance. The > >difference in performance between this duplexer that was ordered from the > >factory for Ham-band use, and one that was (supposedly) retuned from a > >commercial (453-458 MHz) pair, was remarkable. You can probably buy a new > >notch duplexer made for your 70 cm pair for very little more than it would > >cost to rework an existing unit. Moreover, there is much more to changing > >the band coverage than simply turning the tuning screws; it needs to be > >remanufactured for 70 cm. > > > >73, Eric Lemmon WB6FLY > > My experience w.r.t. usable duplexer bandwidth is quite different. I have > a Celwave 6 section VHF HB mobile duplexer that was originally tuned at the > factory for 162/165 MHz. I retuned it down to the 2 meter band for 2.6 MHz > spacing & got IMO very good performance: 85 dB notch on the RX freq & 1.8 > dB loss on the TX freq. > > Every UHF duplexer I own was "made" for 450 MHz & above. Most of them > perform very close to or exceed factory specs after tuning down to 440 MHz > RX/445 MHz TX. > > Now I wouldn't be surprised if every one of my duplexers performed somewhat > better within their respective original bands. But I certainly wouldn't > consider any of them in need of "rework". > > Bob NO6B >
