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
