PVT PLT OF A C172 ENTERED CLASS C AIRSPACE WITHOUT FIRST CONTACTING APCH CTL. THEN; AFTER RECEIVING CLRNC; DSNDED FROM ASSIGNED ALT DUE TO NOT HEARING THE CLRNC CLRLY ON A NEWLY INSTALLED LOANER RADIO.

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I WAS ON THE RETURN LEG OF A 2.3 HR FLT TO AN AVIONICS SHOP; WHERE BOTH RADIOS HAD BEEN CHKED BECAUSE OF NUMEROUS PLT SQUAWKS. ONE OF THE RADIOS WAS REPLACED BY A LOANER FROM THE SHOP. THE ACFT DID NOT HAVE DME OR AREA-NAV EQUIP. I WAS TRACKING THE MSN VOR INBOUND AND USING PILOTAGE. I PICKED UP MSN ATIS AS SOON AS POSSIBLE (ABOUT 40 NM OUT) AND STARTED TO LOOK FOR ONE DISTINCTIVE LANDMARK WHICH I WANTED TO RPT OVER ON MY INITIAL CALL-UP TO MSN APCH. UNABLE TO LOCATE THAT LANDMARK; I REALIZED A SIMILAR-LOOKING LANDMARK (TOWN AND LAKE) IN ABOUT A 20 NM DISTANCE. THERE WAS HOWEVER AN EASILY IDENTIFIABLE (BIG) ARPT NEXT TO THAT TOWN WHICH SHOULD NOT HAVE BEEN NEXT TO MY LANDMARK. EVEN THOUGH I HAD THE MSN ARPT IN SIGHT FROM 20 NM (WHICH IS THE ARPT I TRAINED AT) I FAILED TO REALIZE THAT I MUST HAVE PASSED MY LANDMARK AND WAS ALREADY STARING AT MY DEST. AT ABOUT 10 NM DID I FINALLY DISCOVER THAT MSN WAS AHEAD AND ENTERED A 360 DEG TO CALL UP APCH WITHOUT GETTING CLOSER. AFTER RADAR CONTACT; THE CTLR STATED I WAS 9 MI FROM THE FIELD AND SHOULD NOT EVER CALL UP THAT LATE AGAIN. ATC WAS HARD TO READ ON THE LOANER RADIO WHICH WAS IN USE. THE CTLR GAVE ME A CLRNC CONTAINING A HEADING; RWY TO EXPECT AND ALT TO MAINTAIN ON MY DSCNT. DUE TO THE BAD RADIO I DID NOT UNDERSTAND THE ALT RESTR AND READ BACK THE HEADING ONLY. EVEN THOUGH I KNEW THE CTLR MUST HAVE SAID SOMETHING ELSE; I DID NOT VERIFY; MOSTLY BECAUSE IT COULD HAVE BEEN SOMETHING ABOUT MY FAILURE TO CALL AGAIN AND I FELT ALREADY EMBARRASSED AND DID NOT WANT TO GET INTO MORE EXCHANGES WITH THE CTLR. WHEN I WAS DSNDING THROUGH 2600 FT THE CTLR ASKED TO 'CONFIRM LEVEL AT 3000 FT.' I DENIED; LEVELED OFF. THE CTLR EXPLAINED THE ALT RESTR WAS FOR TFC SEPARATION. IT IS UNKNOWN TO ME IF OTHER ACFT WERE CLOSE. IT IS STILL UNCLR TO ME WHY I DID NOT RECOGNIZE THE VERY FAMILIAR MSN ARPT EARLIER. FACTORS FOR THE MISPERCEPTION WERE THAT I WAS TIRED DURING THE ENTIRE FLT AND HAD NOT HAD ENOUGH SLEEP THE NIGHT BEFORE. SHORTLY BEFORE APCHING MSN; I WAS CRUISING AT 10500 FT MSL WITHOUT OXYGEN WHICH NOTABLY ENHANCED THE TIREDNESS. MAINTAINING VMC OVER A BROKEN LAYER KEPT ME FROM USING PILOTAGE DURING PARTS OF THE LEG. A FIRST-TIME PAX IN THE COPLT SEAT WAS A DISTR; TOO. I WRONGLY DID NOT PERCEIVE MYSELF BEING 'LOST' WHEN I WAS AND DID NOT MAKE USE OF THE DUAL VOR RECEIVERS TO DETERMINE MY POS.