At 7/26/2007 10:54 AM, you wrote: >Skipp said: > >>I don't have time to debate or argue the point... but I will write >>that I don't agree with the above statement. We can go back and >>forth about that later on if you like... > >cruising7388 said: > >Yes, indeed it is a critical length if if is your desire to superimpose >the bandpass curve properly on the >pass curve of the duplexer. It should be an electrical 1/4 wave that >accounts for the velocity propagation >of the cable plus the electrical length of the coupling element in the >Celwave cavity > ><---I suspect Skipp is referring to the same issue BUT....Nate >specifically said he had an extra Celwave BANDPASS cavity. > >Yes I know that if we were dealing with a Bp/Br cavity, coax length >between it and other Bp/Br cavities IS a factor. But I stand by my >comments that all things being equal - coax length absolutely does NOT >matter if the impedances at each end match the coax's characteristic >impedance (ie 50 ohms is maintained). 1/4 wave, odd multiples thereof, >1/2, etc would make absolutely no difference whatsoever is impedance's >matched throughout
50 ohms is ONLY at the pass frequency. The concern here is that the wrong cable length between the pass cavity & duplexer can cause undesired effects at reject frequencies. Specifically, for maximum off-frequency rejection the electrical distance between the pass can & duplexer needs to be a 1/4 or 3/4 wavelength. You can use any other length you wish but then the off-frequency rejection characteristics of the pass cavity may suffer. Bob NO6B
