CLOSE PROX GA-SMA GA-SMA. REPORTER ON IFR FLT PLAN WORKING SNA ON V23.

Narrative

I WAS CRUISING ON AN IFR FLT PLAN ON V-23; HDG 120 (NEAR DAMPS INT); ALT 5000; TALKING WITH COAST APCH. ANOTHER PLANE (SINGLE ENGINE; LOW WING) PASSED 10' UNDERNEATH ME. HE CAME FROM MY 7 O'CLOCK POSITION AND LEFT IN MY 1 O'CLOCK POSITION ABOUT 20-30 KNOTS FASTER THAN ME. HE WAS NOT SEEN AS A TRANSPONDER OR PRIMARY TARGET ON THE COAST APCH RADAR (ACCORDING TO CTLR). HE WAS IN LEVEL FLT FOR AS LONG AS I COULD SEE HIM (ABOUT 3 MINUTES) AFTER THE NEAR MISS. MY MAIN PURPOSE IN MAKING THIS REPORT (I ALSO FILED A NEAR MISS REPORT) IS TO POINT OUT THAT RADAR COVERAGE ALONG THE ORANGE COUNTY COAST FROM BALBOA INTERSECTION TO OCN VOR IS NOT VERY GOOD. THE OTHER ACFT IN THIS NEAR MISS WAS LARGE ENOUGH AND 'METAL ENOUGH' TO RETURN A DSCNT RADAR ECHO. YET NONE WAS SEEN. HIS ALT WAS SUCH THAT HE COULD HAVE BEEN A DANGER TO COMMERCIAL TFC DEPARTING SNA OR MIL ARRIVALS TO MCAS EL TORO. MANY TIMES; AT ALTS FROM 3-5000'; COAST APCH HAS BEEN UNABLE TO SEE MY ACFT; EVEN WHEN SQUAWKING AN ASSIGNED TRANSPONDER CODE IN THIS PARTICULAR; HEAVILY TRAVELED AREA. SOMETHING SHOULD BE DONE TO IMPROVE RADAR COVERAGE IN THIS AREA BEFORE A SERIOUS ACCIDENT OCCURS.