FLC DSNDED BELOW ASSIGNED CRUISE ALT IN RESPONSE TO A TCASII RA. IN ADDITION; CONTACT WAS LOST WITH CTR UNTIL A CHANGE TO ANOTHER FREQ WAS USED.

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DURING CRUISE AT FL280 UNDER IND CTL 125.7; FREQ BECAME UNUSABLE DUE TO A 'STUCK MIKE.' WE SWITCHED BACK TO LAST FREQ (CLE ON 126.97). AFTER A SHORT TIME THIS CTLR ISSUED AN IMMEDIATE TURN 90 DEG R TO 270 FT. DURING TURN; TCASII ISSUED TA FOLLOWED RAPIDLY BY RA COMMANDING 2000 FPM DSCNT. FOLLOWING RESOLUTION AT 27200 FT RETURNED TO FL280. CTR RETURNED US TO PREVIOUS RTE AND ISSUED USEABLE FREQ. I INITIATED PHONE CONVERSATION AFTER FLT WITH IND WATCH SUPVR. HE DESCRIBED CONFLICT AND RADIO PROB JUST AS WE HAD OBSERVED. HE STATED OTHER ACFT ALSO RESPONDED TO AN RA. HE THANKED US FOR SELF INITIATED FREQ CHANGE. SAID THIS ALLOWED OLD CTLR TO ISSUE TURN WHICH BOUGHT ATC TIME TO SORT OUT RADIO PROB. HE ACKNOWLEDGED TCASII VALUE AS BACKUP. ALERT ACTION BY MY FO TO GET US ON USABLE FREQ PREVENTED POTENTIAL PROB FROM ESCALATING. LESSON LEARNED: IF CTR FREQ IS JAMMED; DO SOMETHING ON YOUR OWN TO RE- ESTABLISH CONTACT; IE; LAST FREQ; 121.5 ETC. SUPPLEMENTAL INFO FROM ACN 289097: I WAS THE PNF ON A DA-900 FLT FROM DETROIT MICH (DTW) TO LOUISVILLE KENTUCKY (SOF).