Can we wind our way back to addressing the original query which asked if there is a critical length for the interconnect between a BP BR duplexer and added pure pass cavities? I can't speak for all bottle manufacturers, but I own 8 Wacom BP BR duplexer + pass cavity arrays some of which go back to the early eighties. Lloyd Alcorn was kind enough and patient enough to give me a pretty good nuts and bolts education on cavity characteristics. He said in no uncertain terms that there were optimum cable lengths for both the interconnects between the duplexer cavities and also an optimum length for any pure pass cavities added to the chain. For the added pure pass cavity, the optimum interconnect length would ensure that the pure pass curve would superimpose over the duplexer curve. When I did some experimenting with the pure pass cable length, it validated his point. If I significantly lengthened or shortened this cable, the tracking generator would indicate that the pass curve was no longer superimposed on the duplexer curve. It would either lead or lag the duplexer curve producing two results: 1) the composite curve began to show some distortion and 2) the total attenuation at the desired frequency was higher than when the optimum cable length (supplied by Lloyd) was used. So my take is that there are critical cable lengths involved for adding a pure pass cavity to a BP BR duplexer, but I would be interested to hear from anyone aboard who has the necessary hardware kicking around to repeat that experiment and either replicate or refute the results I got. As I said, my sole cavity experience has been with Wacoms, but I find it difficult to believe that this parameter is OEM specific. K7IJ
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