It’s a common problem: failing ceramic filters, thanks to a design flaw in many transceivers. The FT-857/897 are (in)famous for that, and so are a number of Kenwood models. Recently I repaired and modified four transceivers in short succession. That’s a lot, probably a matter of Murphey’s Law.

The last one on the bench was a Kenwood TS-2000, owned by my neighbor ham Jan PE1LJS. He complained about crackling noises on AM and SSB, even when no antenna was connected. I immediately recognized the problem and offered to fix his rig. In the case of the FT-857/897 only one filter has to replaced, but in case of the Kenwood I didn’t get away with that – I had to replace all three of them in order to get it fixed.

The flaw

When no DC block is located at both the input and output of these ceramic filters, a strange…