AFTER AN FSS BRIEFING A GA ACFT IS QUESTIONED CHALLENGED ABOUT HIS TRANSPONDER CODE ASSIGNMENT BY A MIL TWR CTLR WHILE SQUAWKING 1200 WHEN IN PROX OF CLASS B AIRSPACE NEAR ZZZ; US.

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ON 11/WED/01 I WAS ON A LOCAL SIGHTSEEING FLT. I OBTAINED A THOROUGH WX BRIEFING AND WAS ADVISED OF THE LOCAL NOTAMS FOR THE AIRSPACE IN WHICH I WAS TO FLY AND FILED A VFR FLT PLAN. I OBTAINED MY CLRNC AND WAS GIVEN A TRANSPONDER CODE. I DEP ZZZ1 INTL ARPT AND PROCEEDED ON MY COURSE. ZZZ1 DEP HANDED ME OFF TO ZZZ1 CTR WHO ADVISED ME OF TFC ADVISORIES. I DID NOT OPEN MY VFR FLT PLAN AS I WAS IN CONTACT WITH ZZZ1 CTR. I HAD KEPT THE SAME TRANSPONDER CODE DURING THIS TIME. I INFORMED APCH OF MY INTENTION OF FLYING AROUND THE N SHORE AT WHICH TIME I WAS HANDED OFF TO ZZZ TRACON APCH. I INFORMED THE CTLR THAT I WAS WELL CLR OF HIS AIRSPACE TO THE W AND HE APPROVED MY FREQ CHANGE. AT THAT POINT I WAS STILL TRANSMITTING THE SAME TRANSPONDER CODE I WAS INITIALLY ASSIGNED. I THEN CHANGED THE TRANSPONDER TO 1200 SINCE I WAS CLR OF THE CTLED AIRSPACE. ON RETURNING TO ZZZ1 ARPT; I HAD TO TRANSITION THE ZZZ2 AAF BEFORE ENTERING THE ZZZ1 CLASS B. ZZZ3 TWR QUESTIONED MY 1200 TRANSPONDER CODE. HE THEN INFORMED ME OF THE NEED TO HAVE A PREASSIGNED TRANSPONDER CODE WHEN OPERATING WITHIN 35 MILES OF CLASS B AIRSPACE (EVEN THOUGH I WAS NOT IN THE CLASS B AIRSPACE) AT WHICH TIME I REENTERED MY ORIGINAL ASSIGNED TRANSPONDER CODE. I WAS HANDED OFF TO APCH AND COMPLETED THE FLT TO ZZZ1 ARPT. HOWEVER; I WAS ASKED TO CALL ATC AFTER I GOT ON THE GND. I WAS WELL AWARE OF THE ENHANCED CLASS B AIRSPACE; BUT DID NOT GET THE INFO ABOUT THE PRE-ASSIGNED TRANSPONDER CODE WITHIN THE 35 MI RADIUS OF THE CLASS B AIRSPACE. I AM UNSURE WHERE THE COM BREAKDOWN WAS AS I DO NOT RECALL GETTING THIS INFO DURING MY PREFLT BRIEFING.