RADIO COM PROBLEM RESULTS IN LESS THAN STANDARD SEPARATION BETWEEN 2 ACR. OPERATIONAL ERROR.

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ACR X AND ACR Y ENTERED MY AIRSPACE 10 MI IN TRAIL AT 17000'. BOTH WERE SLOWED TO 250 KTS ALONG WITH 2 MORE RDU ARRS. I TURNED BOTH ACFT TO 190 DEG HDG FOR SPACING ALONG WITH THE THIRD ARR; AND DSNDED THEM TO 16000'. THESE ACFT WERE ON 132.55 (SECTOR 23 FREQ) BECAUSE THE NORMAL SECTOR 24 FREQ (123.85) HAD A STUCK MIC. AFTER TURNING ACR X TO 280 DEGS TO JOIN THE ARR ROUTE; I NOTICED ACR Y WAS NO LONGER ON THE 190 DEG HDG AND TRIED TO PUT HIM BACK ON THE 190 DEG HDG BUT COULD NOT CONTACT HIM. THE FREQ COVERAGE WAS NOT SUFFICIENT ON 132.55. I THEN TRIED TO REACH X BUT HAD LOST HIM AS WELL. I THEN HAD #4 ACFT BROADCAST FOR ACR X TO COME UP ON THE NEXT SECTOR'S (SECTOR 28) FREQ AND WHEN HE DID THEY DSNDED HIM AND RE-ESTABLISHED SEP WITH ACR Y. EACH SECTOR SHOULD HAVE A BACK UP FREQ THAT CAN COVER THE ENTIRE AREA. SUPPLEMENTAL INFO FROM ACN 99436: ACR X AND ACR Y WERE INBND TO RALEIGH ON CONVERGING COURSES BEING WORKED BY SECTOR 24. X WAS ON V66 AND Y ON V615. SECTOR 24 LOST HIS FREQ AND COMBINED WITH SECTOR 23 BECAUSE THERE WERE NO SPARE FREQS. ACR Y WAS DSNDED TO 16000' AND GIVEN A HDG TO GO BEHIND X. ACR X WAS ALREADY AT 16000' TO MAKE ALT AND SPACING REQUIREMENTS FOR THE NEXT SECTOR. X AND Y WERE APCHING THE RADIO LIMITS OF SECTOR 23 AND X ACFT WAS GIVEN A HDG; BUT Y ACKNOWLEDGED THE TURN. RADIO CONTACT WAS LOST BEFORE IT COULD BE CORRECTED. OUR RADIO EQUIP FAILED MUCH TOO OFTEN. IT TOOK ALMOST 5 MINS TO RE-ESTABLISH RADIO CONTACT. THIS TIME WE WERE LUCKY. SUPPLEMENTAL INFO FROM ACN 101166: ADJACENT SECTOR SEQUENCING APPROX 10 ARRS TO RDU. AFTER IN TRAIL SPACING ESTABLISHED THEY ARE HANDED OFF TO OUR SECTOR FOR FINAL DSCNT AND SPD REDUCTION TO APCH CTL. RDU IS A HUB FOR ABC AIRLINES WITH SEVERAL ARR FLOWS AND DEPS DAILY. DURING THESE INTENSE FLOWS AS MANY AS 20 ACFT ON SAME FREQ. ALL WITH ABC CALL SIGNS. ONE ABC ACFT TOOK A CLRNC FOR ANOTHER ABC ACFT; WHICH PUT HIM ON A CONVERGING COURSE AT SAME ALT.