Josh, Ed's description for tuning is right on the money. I would try moving the unit just a slight bit to get used to how it tunes before trying to move it over such a wide frequency range. Once you are comfortable with your equipment and how the duplexer tunes, then move it to the new amateur frequency.
Milt N3LTQ ----- Original Message ----- From: "Ed Yoho" <[email protected]> To: <[email protected]> Sent: Saturday, May 29, 2010 12:09 AM Subject: Re: [Repeater-Builder] Help Needed (Guidance and advice) tuning a DB Products Duplexer > Josh wrote: >> 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 >> >> > > Josh, > > The large nut tipped rods in the center of each cavity are the pass > adjustments. Loosen the locking nut at the bottom of each tuning rod and > turn the shafts clockwise to set the pass responses where you want. Be > sure to keep them set high and low as they are labeled. Once the pass is > where you want it, tighten the clamp nuts back down. Then remove the > small round covers between the N connectors on each cavity and use a > small screwdriver or metal tipped tuning tool to _carefully_ put the > notches where they belong. Put the covers back on and enjoy. > > Be sure to put a termination on the side you are not tuning. > > Ed Yoho > W6YJ > > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
