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DB4060 Tuning Advice

 

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I have zero experience tuning duplexers but I have been following the
repeater builder list for several years, trying to learn and because it
is so interesting.?
Recently, our club received a? VHF DB Products 4060 four can duplexer from what was reportedly a working repeater (SK, I think).? I seem to have foolishly volunteered to check it out and retune it to a new VHF pair.? I have a nano VNA, a sig gen and SA to work with as well as lots of dummy loads, attenuators, HTs etc.? But zero experience so I am begging for advice.

My initial plan was to check and tune the cavities for good SWR at the TX and RX frequencies (2 cans each)? Then to examine the insertion loss of each cavity individually.? But I have no idea what to expect.? What should be the expected insertion loss of a single cavity?? What should be the expected loss be at the rejection dip tuned by the series cap in the loop?? So far I am seeing only about -30dB at the dip.?
I have already discovered a bad cap in one of the cans.? There may be other problems.? So far, I cannot even be sure whether these are the "B" models for the ham band but am assuming so since the SK's repeater was VHF.? The whole diplexer was thickly painted so that I cannot see any ID numbers on the loop boxes either inside or outside.? Any and all advice will be gratefully accepted.? 73, Jerry W6OJE

 

Hi Gerald,
?
There is tuning advice on repeater-builder.com for this model. ? And many others here to help?
?
One thing I do want to say is that if the club is planning on taking this and using it on a Yaesu Fusion (or Bridgecom), there won't be enough isolation.?? I will leave it to others as to how much you actually need (I believe about -100db).?? The reason for this is that the Yaesu is basically two radios in a box, and doesn't have the isolation to start with as a GE MASTR II, Micor or a lot of other "ancient" radios with front ends and low TX noise.?? If that's not what you are trying to do, you can ignore this, but this question comes up about twice a year on here.
?
Andy
WJ9J
 

I retuned my DB4060 by first tuning the bandpass on all four cavities to the correct frequency and then going back and tuning the notches for minimum signal pass through on the notch frequency..
I hit dead on specs that way without a problem. It's on 100 w Quantar.... Didn't use a VNA or anything like that


On Mon, Mar 10, 2025, 9:29 PM wj9jrg via <wj9jrg=[email protected]> wrote:
Hi Gerald,
?
There is tuning advice on for this model. ? And many others here to help?
?
One thing I do want to say is that if the club is planning on taking this and using it on a Yaesu Fusion (or Bridgecom), there won't be enough isolation.?? I will leave it to others as to how much you actually need (I believe about -100db).?? The reason for this is that the Yaesu is basically two radios in a box, and doesn't have the isolation to start with as a GE MASTR II, Micor or a lot of other "ancient" radios with front ends and low TX noise.?? If that's not what you are trying to do, you can ignore this, but this question comes up about twice a year on here.
?
Andy
WJ9J
 

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Jerry,

I'm willing to help you quantify what you have and get your duplexer tuned correctly.? I can do that here - or in private emails.? Your choice.

To answer your immediate questions - the insertion loss you should be experiencing per cavity is 0.5dB or slightly less and the resulting notch depth should be 37 dB.? Then - when fully cabled, the total insertion loss per leg should be less than 1.5dB per leg (1.0dB typical) and around -83 / -85 dB notch depths.? The reason the notch depth is greater than the simple sum of the two cavities is there's an additional 5.5dB (or so) of additional notch depth per cavity interconnect cable.? I don't have a copy of my VNA graphs for this duplexer - but Jeff uploaded a set of graphs in post #197414 (of this group) for one he rebuilt and converted from "C" to "B" some years ago.

If you're only having problems with one cavity, the issue you are experiencing with reduced notch depth may be caused by corrosion or something between the flange on the connector / loop box and the top of the cavity.? I had one of these in the shop that I also thought had a bad adjustable capacitor because I couldn't get the notch to tune correctly with the same number of turns as the other cavity.? I found the factory didn't mask the top of the cavity correctly and it ended up being painted over some of the distance of the mating surface where the boxes flange and the top of the cavity contact each other.? I have photos of what I did to correct the problem and after the surfaces were burnished, the cavity worked as it should - the capacitor was not bad.? I decided to do all four cavities and the duplexer easily made specification after the work.

These duplexers are known for poor silver plating, where the plating "sheds" off.? To fix this requires a lot of work to disassemble and re-plate with silver.?

I'll get the photos together and put on a web page - and post them here...? In the mean time - go to the page on RB and look at all of the information concerning the DB4060 and DB4062 duplexer and read it.? The spec sheet and the info on can be viewed to see which coupling loop assemblies you need for the 2M ham band.? There is also information in the archives of this group by Jeff WN3A that will help you.

Kevin W3KKC


On 3/10/2025 9:45 PM, Gerald Lucha via groups.io wrote:


I have zero experience tuning duplexers but I have been following the
repeater builder list for several years, trying to learn and because it
is so interesting.?
Recently, our club received a? VHF DB Products 4060 four can duplexer from what was reportedly a working repeater (SK, I think).? I seem to have foolishly volunteered to check it out and retune it to a new VHF pair.? I have a nano VNA, a sig gen and SA to work with as well as lots of dummy loads, attenuators, HTs etc.? But zero experience so I am begging for advice.

My initial plan was to check and tune the cavities for good SWR at the TX and RX frequencies (2 cans each)? Then to examine the insertion loss of each cavity individually.? But I have no idea what to expect.? What should be the expected insertion loss of a single cavity?? What should be the expected loss be at the rejection dip tuned by the series cap in the loop?? So far I am seeing only about -30dB at the dip.?
I have already discovered a bad cap in one of the cans.? There may be other problems.? So far, I cannot even be sure whether these are the "B" models for the ham band but am assuming so since the SK's repeater was VHF.? The whole diplexer was thickly painted so that I cannot see any ID numbers on the loop boxes either inside or outside.? Any and all advice will be gratefully accepted.? 73, Jerry W6OJE
 

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The replacement piston trimmer cap is a Johanson 5602 1-30 pF 250V. I’ve seen a number of DB4060/4062 cavity sets with a blown trimmer cap. FWIW not an easy cap to source.?

If you look at the specs of the DB4060 4 cavity duplexer, each leg of two series cavities offers 80 dB isolation with 1.5 dB insertion loss. ?If you measure one side of the duplexer that is what you would expect to see.

Ralph W4XE

On Mar 10, 2025, at 8:46?PM, Gerald Lucha via groups.io <gvlucha@...> wrote:

?









I have zero experience tuning duplexers but I have been following the
repeater builder list for several years, trying to learn and because it
is so interesting.?
Recently, our club received a? VHF DB Products 4060 four can duplexer from what was reportedly a working repeater (SK, I think).? I seem to have foolishly volunteered to check it out and retune it to a new VHF pair.? I have a nano VNA, a sig gen and SA to work with as well as lots of dummy loads, attenuators, HTs etc.? But zero experience so I am begging for advice.

My initial plan was to check and tune the cavities for good SWR at the TX and RX frequencies (2 cans each)? Then to examine the insertion loss of each cavity individually.? But I have no idea what to expect.? What should be the expected insertion loss of a single cavity?? What should be the expected loss be at the rejection dip tuned by the series cap in the loop?? So far I am seeing only about -30dB at the dip.?
I have already discovered a bad cap in one of the cans.? There may be other problems.? So far, I cannot even be sure whether these are the "B" models for the ham band but am assuming so since the SK's repeater was VHF.? The whole diplexer was thickly painted so that I cannot see any ID numbers on the loop boxes either inside or outside.? Any and all advice will be gratefully accepted.? 73, Jerry W6OJE

 

I think the isolation is measured from tx to rx port or the other direction with the antenna port terminated. Insertion loss would be one leg to the antenna port.?
 

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On 3/11/2025 8:55 AM, Kevin Custer wrote:
I'll get the photos together and put on a web page - and post a link here...


As promised....



Kevin W3KKC

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