DEP RADAR CTLR WOULD NOT ALLOW PLT TO LEAVE CTL FREQ WHEN HE EXITED SFO CLASS B.

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VFR FLT FROM OAKLAND ARPT TO SALINAS ARPT. I DEPARTED OAKLAND IN A 116 HP CHAMPION CITABRIA WHICH CRUISES AT LESS THAN 100 KTS AND HAS A SLOW CLB RATE. MY PLANNED RTE WAS A COURSE OF 100-110 DEGS TO CALAVERAS RESERVOIR THEN SSW OVER THE SAN JOSE CLASS C AT 4500 FT THEN DSND TO SALINAS. AT OAKLAND I GAVE ATC MY DEST AND PLANNED ALT AND REQUESTED VFR. I EXPERIENCED DIFFICULTY WITH MY COM -- MUCH STATIC MAKING HEARING DIFFICULT. ATC ALSO COMPLAINED OF POOR XMISSION QUALITY. I WAS INITIALLY VECTORED 090 DEGS AND TOLD TO CONTACT BAY APCH WHICH I DID. BECAUSE OF THE COM DIFFICULTIES AND DESIRE TO MAKE THE FLT VFR; I DETERMINED TO LEAVE ATC AS SOON AS POSSIBLE. AFTER EXITING OAKLAND CLASS C AND SFO CLASS B APPROX 5 NM E OF HAYWARD ARPT; I REQUESTED TO SQUAWK 1200 AND LEAVE THE FREQ. THIS WAS DENIED. OVER THE NEXT 20 OR SO MINS I WAS GIVEN ADDITIONAL VECTORS AND TOLD TO SWITCH FREQS TO ANOTHER BAY APCH SECTOR AT LEAST ONCE; AND MAYBE TWICE. DURING THIS TIME I MADE AT LEAST 3 ADDITIONAL REQUESTS TO SQUAWK 1200 AND LEAVE THE FREQ; AND EACH TIME WAS DENIED. I WAS VECTORED WELL OFF MY PLANNED RTE INCLUDING FLYING OVER THE SOUTHERN END OF SAN JOSE CLASS C; NECESSITATING A CLB TO 7500 FT AND A SUBSEQUENT RAPID DSCNT TO SALINAS. AT NO TIME AFTER THE INITIAL VECTOR WAS I EVER IN ANY CLASS A; C; OR D AIRSPACE. I WAS FINALLY RELEASED FROM ATC WELL S AND W OF THE SAN JOSE CLASS C. I WOULD LIKE TO UNDERSTAND WHY BAY APCH REFUSED AT LEAST 4 REQUESTS TO FLY VFR AND SQUAWK 1200 ON A ROUTING VFR FLT IN CLASS E AIRSPACE.