Expert: Marc Ebelini - 10/29/2009

Question
Does a typical aircraft radio supply voltage to the headset microphone?  I have an electret mic that needs a DC voltage to operate, and I'm wondering if the radio supplies that voltage on the ring connection of the microphone jack.  Thanks.

Answer
Originally the old aircraft radios used carbon mic's that used the voltage to excite the carbon pile. Because of the poor quality of the carbon mic's amplified mic's came in being. Back in the old days we would have to tap the mic's to loosen the carbon particles for better performance. Then electret mic's became popular. In the early days poorly shielded amplifiers were prone to RF feedback. Not being completely up to date on all the new equipment I will add that in some of the new equipment the mic tip is not used for keying the transmitter. The current used by the electret mic is used to key the transmitter. Why? If the electret mic circuit is open then transmitter will not send out an unmodulated carrier. Hope this satisfies your question. As they say in China. No voltage, no worky. Thanks for one of the best questions I have received in a long time. Understanding the basic workings of your aircraft's equipment makes for a good pilot.