C172 PLT GAVE POS RPT TO TWR INBOUND FOR LNDG; TWR IDENTED A RADAR TARGET AND QUERIED RPTR IF IT WAS HIM TO WHICH HE AFFIRMED. ACTUALLY IT WAS ANOTHER ACFT GOING TO A NEIGHBORING ARPT AND TWR AGAIN QUESTIONED RPTR WHO THEN REALIZED THE TARGET WAS A DIFFERENT ACFT AS TWR GAVE RPTR TFC ALERT ON THAT TFC.

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WE WERE INBOUND VFR TO SQL AND RPTED TO THE SQL TWR 2 MI SE STANFORD UNIVERSITY AT 2500 FT MSL. THIS IS APPROX 8 MI SE OF SQL. SQL TWR REPLIED 'RADAR CONTACT OVERHEAD SLAC (STANFORD LINEAR ACCELERATOR CTR)' WHICH AT THAT POINT WAS ABOUT 3 MI AWAY. THAT SEEMED CLOSE ENOUGH TO ME; SO I REPLIED; 'ROGER.' SHORTLY THEREAFTER; TWR ASKED IF I WAS 'IDENTING 1200.' SINCE I WAS FLYING VFR AND SQUAWKING 1200; I REPLIED 'AFFIRMATIVE.' SHORTLY AFTER THAT; THE TWR ASKED ME TO CONFIRM I WAS OVER SLAC. AT THIS POINT I FIGURED SOMETHING WAS UP AND SAID; 'NEGATIVE' AND REPEATED I WAS SE OF STANFORD. TWR THEN GAVE ME A 12 O'CLOCK; 1/2 MI; SAME ALT TA; AND WE CROSSED RIGHT BEHIND A CESSNA BOUND FOR PAO. STANDARD PROC FOR PAO IS TO RPT OVER SLAC AND IDENT. PAO IS APPROX 5 MI E OF SLAC. I WAS CUTTING DIRECTLY ACROSS THIS PATH. I SHOULD HAVE RPTED 'NEGATIVE IDENT' WHEN ASKED. IT DID NOT OCCUR TO ME THAT THE TWR WAS TRYING TO DISTINGUISH ME FROM ANOTHER TARGET. I SHOULD HAVE QUERIED THE TWR WHEN THEY GAVE AN INCORRECT POS ON INITIAL RADAR CONTACT. TWRS IN CLOSE PROX MIGHT CONSIDER ASSIGNING DIFFERENT XPONDER CODES TO INBOUND VFR TFC; EG; 1201 FOR PAO AND 1202 FOR SQL.