There have been numerous complaints about RF getting into the Kenwood MC-60 microphone when used with the Kenwood TS-590 HF transceiver. Although a great match, the problem does exist. The fix is simple, which makes one wonder why Kenwood didn't fix it during assembly. Kenwood does not acknowledge the problem and they offer no solution, placing the cure on the user.
What's happening here is that the microphone base is not grounded to the audio input line to the radio. Note in the second picture there's ferrite bead on the microphone cable. This did NOT help the problem. Follow these simple steps and eliminate your RF feedback problem.
From the bottom plate of the microphone stand, remove the two rear rubber feet and the two center positioned screws. The cover will now come off the stand. Unplug the cable connector, freeing the bottom from the stand. Move the bottom plate out of your way.
Purchase a .01 50 WVDC from Radio Shack, P/N 272-1065 Polyester-Film Capacitor, or use your own.
Where the blue cable comes from the microphone and connects to the pins of the microphone plug, solder one side of the capacitor to the plus microphone lead and the other side to the braided ground lead.
Using a solder lug, place the screw hole end over the bottom plate hole and solder it to the ground pin on the plug. You have now bonded your stand ground to microphone ground and the RF is gone.
Don't forget to reassemble your microphone.
I have done this procedure and it works. It is 100% functional and has a professional appearance. It continues to function correctly when using a linear.
A SPECIAL THANKS GOES OUT TO KS6H FOR THE INSTALLATION.