At 6/21/2009 14:43, you wrote: >Tony, > >Most UHF mobile notch-only flatpack duplexers will work fine below 50 watts >at a 5 MHz split- but their performance rapidly deteriorates when operated >outside of their stated band limits. For example, a commercial-band mobile >duplexer that was manufactured to operate in the 450-470 MHz band will >likely perform poorly in the 440-450 MHz Amateur band. Although such a >duplexer may SEEM to be working in the Ham 70 cm band, it may have excessive >insertion loss that the owner may not realize. That's because the coupling >loops are set at the factory and not readily adjustable by the owner. > >I once tried to use a commercial-band mobile duplexer on 70 cm in a portable >repeater, and was disappointed in its performance- especially receive >sensitivity. I then ordered a new Celwave duplexer of the same model, but >factory-tuned for my Amateur pair. What a difference! Once the new
Once again, I'm going to go out on a limb & say the above experience is more the exception than the rule. I have several 6-section UHF mobile duplexers here originally tuned in the 460-470 MHz range (so I assume they were made for 450-470 MHz) & they all either MEET specs in the 440-450 MHz range or are only off by a small amount - maybe 1.8 dB loss instead of 1.5 dB. I'd say go for it. If there is excessive insertion loss it can be easily measured with a synthesized TX, isolator, wattmeter & 50 ohm termination. Bob NO6B
