Ok so here's what I've got (I think) http://www.n2ckh.com/FORSALE/REPEATERS/DUPLEXERS/DB4076/DSC02678.JPG
Hamvention special, 4 cavities, appears to be a DB Products 4076 family unit. My bench tools: HP 8924c w/ Spec Analyzer and Tracking Generator. My problem - existing set of cans is tuned for 460~mhz. I need to bring them down to 443/448. It was my understanding that they would have dual adjustments - one for setting the band pass frequency, one for setting the reject frequency. Sounds simple. Except under the 'covers' there is nothing else to adjust... So are they just single frequency pass or notch filters? So thats the first question - The second question is - ok , so if they're just single frequency filters, why can't I spin them 'into the right range' as easily as I thought I'd be able to do.... I've tuned a couple of motorola micor filters on the spec analyzer in the last couple of days, mostly made sense and was smooth as silk... However, after messing with the first can, I'm confused. Moving the adjustment certainly changes the properties of the notching - but it didnt really move the bandpass around... It mostly changed the shape and depth of the notching - not the frequency. What knowledge am I missing - I'm an amateur :) Yes I've seen the 'how to tune db products duplexor' doc - but it talks about dual controls, which apparently I don't have. Did I buy a piece of junkola? Teach me obie-wan. j
