Point of curiosity.... In the amateur radio world I noticed repeaters with negative offsets -5 mhz.... in 70cm band do you need a different duplexer, factory set for negative offset? I can't imagine that your standard cavity and notch duplexers would be able to be tuned in reverse.... for example instead of 440/445 a negative 445/440 offset.... can't find any info on this, or even experiment (do not have skills or equipment for tuning) Anyone have some knowledge in this area? thanks 301