[thompsonbr87]

This is in-line between the Com connector on my KX-155 and the antenna. No markings on it. What is it?

 

[Mel]

It's a "notch" filter. I reduces interference with GPS.

 

[maniago]

https://www.aircraftspruce.com/cata...MIvt3o0a374gIVi0sNCh1r-QXfEAQYAiABEgKRIvD_BwE

Not cheap......but if you need it, you need it.