ALTERNATOR FAILURE WITH ASSOCIATED LOST COM AND INSTS. ACFT DIVERTED TO MORE SUITABLE ARPT.

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ATC HAD ASKED 15 MINS EARLIER TO RECYCLE XPONDER. HEARD BALTIMORE APCH CALL BUT THEY COULD NOT HEAR OUR REPLY. NOTICED DISCHARGE CONDITION AS XPONDER WAS NOT WORKING I DID NOT USE LOST COM CODE. HAD HANDHELD COM WITH CHARGED BATTERIES; AND AN ADAPTER FOR HEADSET. UNFORTUNATELY; I DID NOT REALIZE I COULD USE THE MIKE WITH THE HEADSET. I; INSTEAD TRIED TO TALK INTO THE HANDHELD WHICH WAS BYPASSED BY THE ADAPTER JACK BEING PLUGGED IN. OUR ORIGINAL DEST WAS HAGERSTOWN; (HGR) I DECIDED TO LAND AT FREDERICK; (FDK) BECAUSE ALTHOUGH I KNEW I HAD 2 1/2 HRS OF FUEL REMAINING; THE GAUGES SAID 'E' AND I WAS NOT ABSOLUTELY SURE THEY WERE ELECTRICALLY DRIVEN. CONSEQUENTLY; WE LANDED SAFELY AT FREDERICK AND CONTACTED BALTIMORE APCH BY PHONE. IN ADDITION I WAS NOT COMFORTABLE ENOUGH WITH THE PROCS ON APCHING A TWR CTLED FIELD WITHOUT COM. MECHS FINDING: ALTERNATOR BELT WORN TO POINT OF NOT ENOUGH CONTACT. REPLACED BELT. ANNUAL DONE IN OCT 94? PERHAPS THE BALTIMORE APCH COULD HAVE DIRECTED US TO CHANGE DIRECTION IF WE COULD STILL HEAR THEM. IE; R 20 DEGS IF LOST COM AND XPONDER AND L 20 DEGS IF IN NEED OF ASSISTANCE.