SA365 DAUPHIN PLT HAS AN NMAC.

Narrative

I WAS ON A MISSION NE OF HOME BASE ZZZ2 AND WAS CANCELLED WHILE IN ZZZ1 CLASS B AIRSPACE. I NOTIFIED TWR OF CANCELLATION OF MISSION AND TOLD THEM I WOULD EXIT CLASS B TO THE S AND RETURN TO ZZZ2 GETTING MY OWN CLRNCS. I SWITCHED TO ZZZ2 TWR AND RECEIVED CLRNC INTO CLASS B AIRSPACE. I WAS MONITORING FREEWAY (ZZZ) UNICOM; BUT NOT ANNOUNCING MY PRESENCE. ON THIS OCCASION THERE WERE 3 ACFT IN THE LCL PATTERN (RWY WAS 18L TFC). I WAS E OF THE ARPT HDG ABOUT 200 DEGS APPROX 7 MI FROM ZZZ2 WHEN WE WERE ASSIGNED ANOTHER MISSION WITH AN APPROX HDG OF 310 DEGS. I CHKED OUT WITH ZZZ2 AND SWITCHED TO TRACON TO LET THEM KNOW I WAS NOW A PRIORITY ACFT. I HAD SWITCHED OFF ZZZ UNICOM IN PREPARATION FOR LNDG AT ZZZ2. WHILE CHKING OUT WITH ZZZ2 AND CHKING IN WITH TRACON; I WAS MAKING A R TURN APPROX 3 DEGS PER SECOND. DURING THIS TURN; I PLACED MY ACFT INTO THE PATTERN AREA OF ZZZ. I STARTED THE TURN AND THE RADIO SWITCHES WITHOUT CLRING MYSELF. I SAW THE C172/182(?) IN MY 11:30 O'CLOCK POS; APPROX 150-200 FT AWAY AT MY ALT. I DID NOT HAVE TO TAKE EVASIVE ACTION BECAUSE I BELIEVE THEY ALREADY HAD. I WENT BTWN THE EVADING ACFT AND ANOTHER ACFT CLBING OUT AFTER TKOF. INITIALLY; I ERRONEOUSLY FIGURED I WAS FAR ENOUGH FROM THE PATTERN TO NOT IMPACT IT. I FAILED TO CONSIDER THAT 3 ACFT WOULD EXPAND THE PATTERN. ADDITIONALLY; I STARTED MY TURN FOR THE NEW MISSION WITHOUT FIRST CLRING MYSELF. IN THE FUTURE I WILL ALWAYS ANNOUNCE MY PRESENCE; EVEN TO AN EMPTY PATTERN; AND I WILL GO BACK TO ONE OF THE BASICS THAT EVERY NEW PLT PRACTICES; CLR YOUR AIRSPACE! BOTH ZZZ2 AND TRACON ADVISED ME OF ACFT IN THE ZZZ PATTERN.