RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Not really. I had not seen this in any of my older catalogs, and I wondered if in fact the unit was made by Decibel Products. Like many RF products, ferrite isolators in particular, the frequency range stated in a manufacturer's catalog refers to the capability to construct- which is not the same as the field-tunable range of a specific product. I was curious if the window filter (AKA preselector) could be useful in the 70 cm Amateur band without modifying the coupling loops or jumper cables. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jeff DePolo Sent: Monday, May 31, 2010 6:09 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Yes, they did sell window filter as a separate catalog item, but if they were sold as such they would have had a factory sticker on it. The ones I have don't have a sticker, which is why I said they were probably part of a package that would likely have had an SP part number rather than a DB. These cavities are very tightly coupled, typically about 0.3 dB or so insertion loss per cavity. Strung together, the total insertion loss is about 1.5 dB. Because of the coupling, each cavity individually doesn't have a very high Q, so if you were to take one of these units and split it to try to make a duplexer out of it, you'd probably only get about 40 dB or so of isolation at 5 MHz offset. Even if you did want to try it, you'd have to change cable lengths to get the pass response of each cavity to add on-frequency rather than creating a wide window filter passband as they were originally cabled. They do tune fine down to 440 as-is (i.e. as a window filter). --- Jeff -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Eric Lemmon Sent: Monday, May 31, 2010 12:52 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Not really. I had not seen this in any of my older catalogs, and I wondered if in fact the unit was made by Decibel Products. Like many RF products, ferrite isolators in particular, the frequency range stated in a manufacturer's catalog refers to the capability to construct- which is not the same as the field-tunable range of a specific product. I was curious if the window filter (AKA preselector) could be useful in the 70 cm Amateur band without modifying the coupling loops or jumper cables. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Monday, May 31, 2010 6:09 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Kuby, You might start with Electronic and Radio Engineering by Frederick Emmons Terman, 4th Ed. 1955 in the Circuit Elements and Circuit Theory section. And try Radio Engineering Handbook by Keith Henny, 5th Ed. 1959 in Chapter 6, Wave Guides and Resonators by Harald Schutz. Also Principals of Radar 3rd Ed. 1952 by J. Francis Reintjes and Godfrey T. Coate in ch.9, Resonant Lines and Cavities. And Microwave Transmission Design Data by Theodore Moreno, 1948, ch. 13 Cavity Resonators. Then when you finish with these publications you will have all the answers to all your questions and then some. WA9ZZU --- On Mon, 5/31/10, Kuby n6...@yahoo.com wrote: From: Kuby n6...@yahoo.com Subject: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer To: Repeater-Builder@yahoogroups.com Date: Monday, May 31, 2010, 1:22 PM Anyone have white papers or info on how to modify/design cavities? What would it take to move a window 465 can to 445/435 tunable? What is the design parameters for the N connector straps? What is the design of existing tunable cans (L/C components)? --- In Repeater-Builder@yahoogroups.com, Eric Lemmon wb6...@... wrote: Not really. I had not seen this in any of my older catalogs, and I wondered if in fact the unit was made by Decibel Products. Like many RF products, ferrite isolators in particular, the frequency range stated in a manufacturer's catalog refers to the capability to construct- which is not the same as the field-tunable range of a specific product. I was curious if the window filter (AKA preselector) could be useful in the 70 cm Amateur band without modifying the coupling loops or jumper cables. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jeff DePolo Sent: Monday, May 31, 2010 6:09 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
You forgot the most important text: Microwave Spectroscopy by Townes Shalow. 73, Dick, W1KSZ -Original Message- From: allan crites wa9...@arrl.net Sent: May 31, 2010 8:38 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Kuby, You might start with Electronic and Radio Engineering by Frederick Emmons Terman, 4th Ed. 1955 in the Circuit Elements and Circuit Theory section. And try Radio Engineering Handbook by Keith Henny, 5th Ed. 1959 in Chapter 6, Wave Guides and Resonators by Harald Schutz. Also Principals of Radar 3rd Ed. 1952 by J. Francis Reintjes and Godfrey T. Coate in ch.9, Resonant Lines and Cavities. And Microwave Transmission Design Data by Theodore Moreno, 1948, ch. 13 Cavity Resonators. Then when you finish with these publications you will have all the answers to all your questions and then some. WA9ZZU --- On Mon, 5/31/10, Kuby n6...@yahoo.com wrote: From: Kuby n6...@yahoo.com Subject: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer To: Repeater-Builder@yahoogroups.com Date: Monday, May 31, 2010, 1:22 PM Anyone have white papers or info on how to modify/design cavities? What would it take to move a window 465 can to 445/435 tunable? What is the design parameters for the N connector straps? What is the design of existing tunable cans (L/C components)? --- In Repeater-Builder@yahoogroups.com, Eric Lemmon wb6...@... wrote: Not really. I had not seen this in any of my older catalogs, and I wondered if in fact the unit was made by Decibel Products. Like many RF products, ferrite isolators in particular, the frequency range stated in a manufacturer's catalog refers to the capability to construct- which is not the same as the field-tunable range of a specific product. I was curious if the window filter (AKA preselector) could be useful in the 70 cm Amateur band without modifying the coupling loops or jumper cables. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jeff DePolo Sent: Monday, May 31, 2010 6:09 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
I didn't want to overwhelm the gentleman. wa9zzu --- On Mon, 5/31/10, Richard W. Solomon w1...@earthlink.net wrote: From: Richard W. Solomon w1...@earthlink.net Subject: Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer To: Repeater-Builder@yahoogroups.com Date: Monday, May 31, 2010, 8:09 PM You forgot the most important text: Microwave Spectroscopy by Townes Shalow. 73, Dick, W1KSZ -Original Message- From: allan crites wa9...@arrl.net Sent: May 31, 2010 8:38 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Kuby, You might start with Electronic and Radio Engineering by Frederick Emmons Terman, 4th Ed. 1955 in the Circuit Elements and Circuit Theory section. And try Radio Engineering Handbook by Keith Henny, 5th Ed. 1959 in Chapter 6, Wave Guides and Resonators by Harald Schutz. Also Principals of Radar 3rd Ed. 1952 by J. Francis Reintjes and Godfrey T. Coate in ch.9, Resonant Lines and Cavities. And Microwave Transmission Design Data by Theodore Moreno, 1948, ch. 13 Cavity Resonators. Then when you finish with these publications you will have all the answers to all your questions and then some. WA9ZZU --- On Mon, 5/31/10, Kuby n6...@yahoo.com wrote: From: Kuby n6...@yahoo.com Subject: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer To: Repeater-Builder@yahoogroups.com Date: Monday, May 31, 2010, 1:22 PM Anyone have white papers or info on how to modify/design cavities? What would it take to move a window 465 can to 445/435 tunable? What is the design parameters for the N connector straps? What is the design of existing tunable cans (L/C components)? --- In Repeater-Builder@yahoogroups.com, Eric Lemmon wb6...@... wrote: Not really. I had not seen this in any of my older catalogs, and I wondered if in fact the unit was made by Decibel Products. Like many RF products, ferrite isolators in particular, the frequency range stated in a manufacturer's catalog refers to the capability to construct- which is not the same as the field-tunable range of a specific product. I was curious if the window filter (AKA preselector) could be useful in the 70 cm Amateur band without modifying the coupling loops or jumper cables. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jeff DePolo Sent: Monday, May 31, 2010 6:09 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Mine don't have labels on them. Usually they were sold as part of an SP package that included the window filters, multicoupler, etc. I haven't tuned or swept this particular set, but from experience, the cavity resonance will tune over a wide swath, probably the full 406-512 MHz, but the loop lengths may not be optimal over such a wide span (depending on how the cavities are being used), and likewise, the cable lengths will vary. You have something in particular in mind you want me to test? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com ] On Behalf Of Eric Lemmon Sent: Sunday, May 30, 2010 12:29 PM To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder
RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Sorry to hear you got the proverbial shaft. But all's not lost. If you need a duplexer, I'll trade you a Motorola T1504 (pass/reject) duplexer in good shape that I had on my table at Dayton that didn't sell. I was asking $125 for it. I'll trade you straight across if you pick up shipping in both directions, and I'll even tune it on the VNA and send you the plots. I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Josh Sent: Saturday, May 29, 2010 9:27 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer Certainly not what I was expecting... Yeah, I bought one from 'that guy'. It's more than an untrained eye - he straight lied to me... said 'under these caps are where you'll tune the capacitors' - I should have popped one off and looked down the hole. Maybe he was clued in, maybe he wasnt - either way, that's what I bought. Dangit :P So if all I have are pass cavities what 'are' they good for ? Guess I've got to find another dupelxer. j --- In Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com , Jeff DePolo j...@... 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. 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] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
Jeff, Can you positively identify the window filters by part number? Also, what is the useful frequency range of the units you purchased? 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Jeff DePolo Sent: Sunday, May 30, 2010 8:39 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer snip I bought two sets of those window filters from the same guy, but I knew what they were, caveat emptor is the golden rule at Dayton or any other hamfest. Actually I think I gave him $75 for the pair, and I took the two cleanest/newest ones he had (the newer dark-tan ones). --- Jeff WN3A snip
Re: [Repeater-Builder] Re: Help Needed (Guidance and advice) tuning a DB Products Duplexer
All is not lost Josh - I'm running Motorola T1507 which are 4-can pass-only cavities on my Micor. Actually pass-only are better for commercial sites since they will help keep out a lot of intermod on either side of how they are tuned. Pass-notch on the other hand will pass the tuned frequency, but do a poor job of everything else rejection (other than the notch of course). On 05/29/2010 08:27 PM, Josh wrote: Certainly not what I was expecting... Yeah, I bought one from 'that guy'. It's more than an untrained eye - he straight lied to me... said 'under these caps are where you'll tune the capacitors' - I should have popped one off and looked down the hole. Maybe he was clued in, maybe he wasnt - either way, that's what I bought. Dangit :P So if all I have are pass cavities what 'are' they good for ? Guess I've got to find another dupelxer. j --- In Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com, Jeff DePolo j...@... 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. 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
