HAs anybody used a non ICOM SPEAKERPHONE attached to this transceiver. I have a schematic on the mic input and use shielded connetion, but I get heavy RF-interference when transmitting. The reason I don´t use an original ICOM mic is the need for passive noise reduction. I use it as an emergency transceiver in an airplane. I I could get hold of a schematic on the ICOM HM 234 I suppose I could solve the problem.