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