PA28 PLT TOOK EVASIVE ACTION FROM ANOTHER PA28 IN VRB CLASS D AIRSPACE WHILE ON BASE LEG TURNING TO FINAL.

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I WAS INBOUND TO VRB ON A VFR FLT PLAN FROM ORL. ABOUT 15 MI FROM VRB; I CONTACTED ST PETERSBURG FSS TO CANCEL MY FLT PLAN; ADVISING I HAD VRB IN SIGHT. ABOUT 10 MI N OF VRB; I CONTACTED THE VRB TWR AND ADVISED I WAS INBOUND FOR A FULL-STOP AND HAD THE ATIS INFO. THEY ADVISED ME TO ENTER AND RPT A 2 MI L BASE FOR RWY 11R. AS I APCHED THE FINAL APCH COURSE FOR RWY 11L AT 1000 FT MSL; THE TWR CALLED AND ADVISED ME TO CHANGE RWYS TO RWY 11L. TWR ADVISED MY TFC TO FOLLOW WAS ON A 3/4 MI FINAL AND I WAS #2 TO LAND. I RESPONDED THAT I HAD THE TFC IN SIGHT AND WAS CLRED TO LAND ON RWY 11L AND BEGAN MY TURN TO FINAL. ABOUT 1 - 1 1/2 MI FROM THE THRESHOLD OF RWY 11L AT ABOUT 700-800 FT MSL; ANOTHER PIPER PA28-161 (IT WAS A COMPANY PLANE) CAME UNDERNEATH ME ABOUT 75-100 FT BELOW FROM MY 7-8 O'CLOCK POS. BOTH HE AND I WERE DSNDING AND HE CONTINUED HIS DSCNT AND LNDG TO RWY 11L. I MADE AN IMMEDIATE R TURN; BANKING 45-50 DEGS; APPLIED FULL PWR; AND BEGAN A GAR TO AVOID THIS ACFT. THE OTHER ACFT MADE NO EVASIVE ACTION AND ACTED AS IF HE/SHE NEVER SAW MY ACFT. I CLBED ON THE RWY HDG TO 1200-1300 FT MSL AND AFTER 1 MIN; I WAS ABLE TO CONTACT THE TWR TO ADVISE I WAS GOING AROUND AND OVERFLYING THE RWY (RWY 11L) AT 1300 FT MSL DUE TO THE ACFT TURNING FINAL IN FRONT OF ME. TWR ADVISED ME TO CONTACT THE TWR ON THEIR OTHER FREQ. APPARENTLY; THE TWR WAS IN THE PROCESS OF SPLITTING FREQS DUE TO HIGH TFC VOLUME AT THE TIME. BOTH THE FIRST CTLR ON 126.30 AND THE SECOND CTLR ON 133.15 SEEMED UNAWARE OF THE INCIDENT THAT OCCURRED. THE SECOND CTLR ADVISED ME I WAS CLR TO RE-ENTER A L DOWNWIND FOR RWY 11L AND THAT I WAS CLRED TO LAND. I PROCEEDED TO LAND SAFELY; WITHOUT INCIDENT. I AM NOT SURE IF THE OTHER ACFT WAS ON FREQ 126.30 OR 133.15. I DO NOT KNOW IF THIS WAS PLT OR CTLR ERROR. I ALSO DO NOT KNOW THE INSTRUCTIONS GIVEN TO THE OTHER ACFT. HE MAY HAVE BEEN CONFUSED ABOUT WHICH TFC HE WAS FOLLOWING TO THE RWY. I THINK IT IS TERRIBLE THAT THE CTLRS WERE UNAWARE OF THE INCIDENT. SPLITTING FREQS DURING THAT TIME OF HIGH TFC VOLUME WAS UNACCEPTABLE. THERE IS A POSSIBILITY THAT THE 2 CTLRS DID NOT COORDINATE TFC WELL BTWN THE 2 FREQS.