LGT TOOK TRAFFIC CALL AS ALT ASSIGNMENT AND BUSTED ALT. ARTCC CTLR CORRECTED.

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I; AS RADAR CTLR; ACCEPTED A HDOF FROM RDU APCH ON LGT CLBING TO 12000'. UPON INITIAL CONTACT; I RECLRED THE ACFT TO 13000' ONLY BECAUSE I HAD A SLOWER ACFT AT 14000'. I CALLED TFC; SHORTLY THE LGT PLT RPTED ABOUT TO LEVEL 13000'. I CALLED TFC; TOLD THE PLT TO EXPECT HIGHER WHEN HE WAS IN FRONT. WHEN I SAW THE MODE C OF THE LGT INDICATE 13500' I QUESTIONED THE PLT TO SEE IF PERHAPS IT WERE AN ERRONEOUS READOUT. THE PLT SAID HE THOUGHT HE HAD BEEN CLRED TO 14000'. I THINK THE SITUATION WAS CAUSED BY THE PLT'S INATTN TO THE XMISSIONS AND ALSO BY POOR FREQS. THE PLT SAID SOMETHING WHICH WAS UNINTELLIGIBLE AT THE TIME; BUT COULD BE MADE OUT ON THE TAPE. IF THE FREQS IN ACTUAL USE WERE AS CLEAR AS THE TAPES PLAYED LATER; PROBS LIKE THIS WOULD BE VERY MINIMAL INDEED. SUPPLEMENTAL INFO FROM ACN 94538: RPTED IN AT 13000'. LATER REQUESTED HIGHER ALT. WE WERE ADVISED THAT THERE WAS TFC BUT UNDERSTOOD WE WERE CLRED TO 14000'. I RPTED LEAVING 13000 FOR 14000'. LATER CENTER ASKED OUR ALT. I RPTED 13700 FOR 14000'. SHE ADVISED WE WERE CLRED ONLY TO 13000'. DSNDED TO 13000'. I THINK THIS INCIDENT WAS CAUSED BY POOR QUALITY RADIOS USED BY AIRLINES AND ARTCC. I ALSO THINK THAT THE SCHEDULE I WAS FLYING CONTRIBUTED TO THE MISUNDERSTANDING. THIS WAS MY FOURTH DAY OF FLYING GETTING UP AT XB00 TO XC30 IN MIDDLE OF THE NIGHT. SUPPLEMENTAL INFO FROM ACN 94282: THE CTLR (ZDC) CALLED AND ASKED OUR ALT. THE CAPT (NOT FLYING) SAID PASSING 13700' FOR 14000'. THE CTLR RESPONDED WE WERE CLRED TO ONLY 13000'. AT THAT POINT THE COPLT (FLYING) STARTED TO DSND TO 13000'. AT THAT POINT THE CAPT SAID TO THE CTLR HE HAD REPEATED BACK THAT WE WERE CLRED 14000'; THE CAPT THEN SAID THAT HE HAD SAID TO THE CTLR (OVER THE RADIO) AND AS WE WERE GOING THROUGH 13000'; 'OUT OF 13 FOR 14.' I ALSO HEARD THE CAPT SAY THIS. AT THIS POINT I ONLY REMEMBER THE CTLR TELLING CLRED TO 13000'; BUT AS THE CAPT CALLED OUT OF 13000' FOR 14000 I LOOKED UP TO SEE WHAT WAS SET IN THE ALT ALERT WINDOW; WHICH SOMEONE (I THINK THE CAPT) HAD SET 14000'. JUST AS I WAS ABOUT TO QUESTION THE CLRNC; THE CTLR ASKED WHAT ALT WE WERE OUT OF. I SHOULD HAVE CHKED TO SEE WHAT ALT THE CAPT HAD SET IN THE WINDOW; ESPECIALLY WHEN THE CTLR HAD SAID WE COULD NOT HAVE HIGHER DUE TO TFC. EVEN THEN WE WERE OUT OF 10000' I SHOULD HAVE PAID MORE ATTN TO WHAT THE PLTS WERE DOING INSTEAD OF MY ENGRING DUTIES. SUPPLEMENTAL INFO FROM ACN 94440: WE WERE TALKING TO A FEMALE CTLR WE ASKED FOR HIGHER. WE WERE AT 13000'. I HEARD HER SAY SOMETHING ABOUT 14000'. THE CAPT RESPONDED TO HER WE WERE LEAVING 13000 FOR 14000'. AT 13700' SHE ADVISED US WE WERE ONLY CLRED TO 13000' AND THAT THE 14000' GIVEN WAS FOR HIGHER TFC. WE IMMEDIATELY DSNDED TO 13000'. A CONTRIBUTING FACTOR MOST CERTAINLY IS THE XF20 LCL E COAST DEP REQUIRING US TO GET UP AT XC15 HOME TOWN TIME (SLEEP DEPRIVATION IS CUMULATIVE). ALSO; THROUGH DISCUSSIONS WITH OTHER PLTS IN THE PAST RE: THE RECEPTION OF THE FEMALE VOICE; CONCENSUS SEEMS TO BE THAT THERE IS A GREATER INCREASE IN DIFFICULTY IN UNDERSTANDING (PROBABLY DUE TO THE PITCH AND NOT TERMINOLOGY). ALSO THE RECEPTION QUALITY OF THE GND STATION EQUIP IN VARIOUS AREAS OF THE COUNTRY IS POOR.