At 8/30/2008 10:22, you wrote: >This question is best posed on the Repeater-Builder list >([email protected]), but I know the answer: A mobile (notch) >duplexer will not work at a 600 kHz split. Even a 3 or 4 MHz split results >in unacceptable performance. > >I have built a portable repeater for 2m, using the special TASMA "portable >repeater pair" of 147.585 MHz input and 144.930 MHz output- a split of 2.655 >MHz-
Glad to hear someone besides me is making good use of that pair. > but I had to use a Celwave 5085-1 duplexer to make it work. The 5085 >duplexer is about twice the size of a mobile notch duplexer, and it is >intended for splits as narrow as 3 MHz. With careful tuning on a network >analyzer and using a 1-to-10 watt Motorola 1225 full-duplex transceiver, it >performs very well. I'm surprised you had to go to something a bit bigger than the standard 6-section mobile duplexer to make it work. I have a total of 3 VHF mobile duplexers & 2 of them are quite a bit smaller than the 5085-1, but they still perform adequately: ~2.1 dB loss & 65 to 70 dB notches. I actually put a VHF UHS preamp on one system to try to squeeze a little more S/N out of it & it actually worked in that it didn't introduce any desense or IMD. Unfortunately the site noise is so high in LA that I don't think it actually made a significant improvement in S/N. Bob NO6B
