Some Background:
I had one of these duplexers in the shop that I 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. The notch depth was considerably reduced and the insertion loss was not consistent with the other cavities. What I found was - the capacitor wasn't bad! The factory didn't mask the top of the cavity correctly and it ended up being painted over some (most?) of the distance of the mating surface where the boxes flange and the top of the cavity contact each other. These surfaces need to be mated properly both mechanically and electrically - or the cavity will not perform correctly.

Before installing the box back onto the cavity, I used Noalox, an electrical contact treatment for aluminum wiring in electrical boxes. Apply it sparangly - don't gob it on.

While not shown in the photos, I did re-write "005" back onto the interior of the box, in pencil, so the next guy knows what's going on.

Below - DB4060 cavity with paint overspray.

Below - DB4060 coupling loop box "005".

Below - DB4060 cavity with overspray removed. Not as easy as it looks...

Below - DB4060 coupling loop box with cleaned mating surface.

The images below are from Jeff WN3A.  They show the resuts of a properly working "B" DB4060 duplexer.

Copyright © March 11, 2025 Kevin K. Custer  W3KKC
All Rights Reserved.

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