> ... if cavities are properly tuned to 50 ohms, the length of > 50 ohm coax between them doesn't make one bit of difference.
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... > IMHO, the additional cavity is a waste of time and effort until > you identify the source of the interference (and made sure your > duplexer is first properly tuned) I would agree the band-pass cavity is probably a popcorn fart until you really figure out what is going on. I've recently spent a bit of time tracking down a number of similar mix problems and I will say that none of them were from the same source/reason. The lastest similar gremlin I sourced was a real beast, which was cured simply by putting the covers completely back on the various rf boxes. And much to my surprise the mix problem did not decrease in value until the 3rd from the last (out of 27) box cover screws was inserted back in place. Depending on how often the problem comes back I would first check for possible mixing, receiver blocking, receiver & preamp 3rd order problems. You've said the mix numbers were already figured with some type of computer program... but that's not a 100% tell all. Taking a first shot in the dark with cavities... I'd probably try to insert a notch or suck out cavity on the other repeater/base station tx frequency... in your/my repeater/receiver antenna line/ path. Relative to the grand scheme of things... tis probably better to suck than to bandpass (in this case). You'd probably get more bang for your buck... (result for your effort). cheers, s.
