I added a  source follower to the microphone to reduce the impedance to 500 ohms. Mounted on a small PCB within the base of the microphone it draws the necessary DC current via the radio's Mic socket. 

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I also have the dual impedance version with a switched microphone insert. For some Icom radios it needs a 1uF coupling capacitor to prevent DC voltage appearing on the cartridge. It is advisable to add a 1nF capacitor directly across the high impedance tap on the cartridge to prevent RF feedback.