Re: [Repeater-Builder] Help Needed (Guidance and advice) tuning a DB Products Duplexer
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 w6yj_ya...@67hz.net To: Repeater-Builder@yahoogroups.com 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
Re: [Repeater-Builder] Help Needed (Guidance and advice) tuning a DB Products Duplexer
Hello Josh. Look under the caps between the coax connectors. That should be the notch adjustment. They may not go that low,but all you can do is try. Good luck. Butch, KE7FEL/r On Fri, May 28, 2010 at 6:53 PM, Josh josh.kit...@gmail.com 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
RE: [Repeater-Builder] Help Needed (Guidance and advice) tuning a DB Products Duplexer
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. There was a guy at the Hamvention that had several sets of Decibel four-cavity window filters, selling for $50 each, which, to the untrained eye, would look like an older DB4076. As you said, there would be nothing in the hole where the capacitor would be in a regular DB4076. In essecence, what you have are just plain-jane pass cavities. As a second means of confirming that you do, in fact, have a window filter, is there an antenna tee, or are the four cavities cabled together in cascade? If the latter, then you probably have a window filter. And as a third means of confirming, is there is a label on the front? If not, was there any signs of a label having once been there? If not, then that's yet one more indication that it isn't a DB4076. Decibel made two varieties of pass cavities used in window filters in that era. One had adjustable loops (less common), the other had fixed loops. If your loop connectors have a rectangular chrome plate around them with insertion loss calibration marks, you have the less-common adjustable ones. If you just see four philips-head screws and no chromed plate around the connectors, then yours is not adjustable. If you have the adjustable type, you could probably use them as a pass-only duplexer, but with mediocre isolation, even with the insertion loss cranked up higher than you'd like. If you have the non-adjustable ones, they have very tight coupling, so you're not going to get the isolation you'd need for a repeater. Did I buy a piece of junkola? Teach me obie-wan. Not junk, but maybe not what you were expecting... --- Jeff WN3A
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
