GA SMA UNAUTH PENETRATION OF AIRSPACE OAK ARSA.

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YESTERDAY I WAS RETURNING TO OAK AFTER AN UNEVENTFUL DAY. I DEPARTED SJC AND WAS 17 NM SE OF OAK WHEN I TRIED TO REACH BAY ON 135.4 FOR THE ROUTINE ARSA CLRNC. ABOUT 13 MI OUT I GOT MY SQUAWK AND IDENTED. THIS FREQ IS USUALLY VERY BUSY AND ESPECIALLY SO DURING THE CARGO RUSH. ON THE FREQ THEY HAD A TRNEE WITH A SUPVR IN THE BACKGROUND. AS I STARTED TO COME UP ON HWD AT 2500' I BEGAN TO GET CONCERNED SINCE I HADN'T BEEN VERIFIED IN RADAR CONTACT. SINCE THE TRNEE WAS BUSY VECTORING AN LTT AND A COUPLE OF OTHER ACFT; I FIGURED HE HAD ME ON THE SCOPE BUT WANTED TO TAKE CARE OF MORE IMPORTANT THINGS. THIS HAS HAPPENED A NUMBER OF TIMES. SUDDENLY BAY WILL COME IN AND SAY 'FLT ID; RADAR CONTACT; CONTACT OAK TWR 118.3.' I DIDN'T WANT TO INTRUDE INTO THE BUSY FREQ. WHILE PASSING HWD I TRIED TO GET ON BUT BAY WAS TOO BUSY. FOUR MI FROM OAK I GOT A WORD IN AND NOW BAY HAND'T SEEN MY SQUAWK AND I REIDENTED AND WAS TOLD I HAD ENTERED THE ARSA W/O A CLRNC AND WAS GIVEN A NUMBER TO THE FAC. I WAS FOLLOWING A ROUTINE PATTERN THAT BAY HAD ACCEPTED MANY; MANY TIMES. MY SUGGESTION FOR SAFETY IS TO NOT PUT TRNEES ON AT THE MOST CRITICAL TIME OF THE DAY.