A SOLO C172 STUDENT PLT AT CTAF MCE ENTERED THE VFR PATTERN AS SUGGESTED; BUT WAS DIRECTED TO A NON STANDARD PATTERN CAUSING A B1900 TCAS EVENT.

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I WAS INBOUND TO MERCED ARPT (MCE) TO PRACTICE SOLO TKOFS AND LNDGS. I WAS APCHING FROM THE SE. AFTER LISTENING TO THE ASOS; I DETERMINED THE FAVORED RWY WAS RWY 12. MY PLAN TO ENTER THE TFC PATTERN WAS TO OVERFLY THE ARPT AT 2200 FT MSL (1000 FT ABOVE TPA) THEN FLY TO THE SW AWAY FROM THE ARPT AND MANEUVER TO ENTER THE 45 DEG LEG FOR A R DOWNWIND OF RWY 12. ABOUT 5 MI BEFORE OVERFLYING THE FIELD; I ANNOUNCED MYSELF AS A STUDENT PLT AND ANNOUNCED MY INTENTION TO MANEUVER TO ENTER A R 45 DEG ENTRY FOR RWY 12. DIRECTLY OVER THE RWY AT 2200 FT; I AGAIN ANNOUNCED MYSELF AS A STUDENT PLT; ANNOUNCED THAT I WAS OVER THE RWY AND AGAIN ANNOUNCED MY INTENTION TO MANEUVER TO ENTER A R 45 DEG ENTRY FOR RWY 12. I PROCEEDED TO FLY OUTBOUND AWAY FROM THE ARPT TO GIVE MYSELF ROOM TO DSND TO TPA AND GET TOWARD THE 45 DEG LEG. ABOUT THIS TIME; I HEARD A RADIO CALL FROM A BEECH 1900 AIRLINER ALSO ANNOUNCE INTENTIONS TO ENTER THE PATTERN FOR RWY 12; BUT I DID NOT HAVE IT IN SIGHT. ONCE I WAS ABOUT 3 MI FROM THE ARPT THE BEECH 1900 ASKED ME IF I WAS ON THE DOWNWIND; AND I REPLIED THAT I HAD NOT YET ENTERED THE DOWNWIND. I THEN TURNED L; TOWARD THE 45 DEG LEG FOR R DOWNWIND OF RWY 12. THE CREW OF THE AIRLINER THEN EXPLAINED TO ME THAT I WAS ON THE WRONG DOWNWIND; AND THAT I HAD TO MAKE A 180 DEG TURN TO ENTER R DOWNWIND FOR RWY 12. I SUSPECT THAT THEY MISTOOK MY L TURN TOWARD THE 45 DEG LEG AS A TURN TO ENTER A WIDE L DOWNWIND FOR RWY 30; BUT AT THE TIME I SIMPLY FOLLOWED THEIR INSTRUCTIONS; AND TURNED AROUND TO ENTER A VERY WIDE R DOWNWIND FOR RWY 12. AFTER TURNING AROUND; I SAW THE BEECH 1900 ABOVE ME AT ABOUT MY 10 O'CLOCK POS. I THEN HEARD THE CREW OF THE AIRLINER ANNOUNCE THEIR INTENTIONS TO EXTEND THEIR DOWNWIND TO ALLOW ME TO GO IN FRONT OF THEM. I TURNED BASE; THEN FINAL; AND MADE A TOUCH-AND-GO; ANNOUNCING EACH TURN IN THE TFC PATTERN. APPARENTLY; THE BEECH 1900 HAD TO GO AROUND; BECAUSE AFTER MY TOUCH-AND-GO THE UNICOM INSTRUCTED ME TO EXTEND MY UPWIND AND THAT THEY WOULD CALL MY XWIND TURN. I COMPLIED WITH THEIR INSTRUCTION AND THE CONFLICT APPEARED TO BE RESOLVED. I WAS LATER INFORMED THAT I HAD CAUSED 2 TCAS DEVS OF THE BEECH 1900. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT SOMEONE ON THE GND GAVE HIM THE R 180 DEG TURN INSTRUCTIONS. HE BELIEVES THAT WHOEVER CALLED HIS TURN DID NOT UNDERSTAND HOW HE WAS ATTEMPTING TO ENTER THE TFC PATTERN. THE RPTR DID NOT SEE THE B1900 UNTIL AFTER TURNING ON THE MODIFIED 45 DEG BASE AND HAS NO IDEA HOW CLOSE TOGETHER THEY CAME.