C177 PLT HAD CLOSE ENCOUNTER WITH POLICE HELI THAT REQUIRED PLT TO TAKE EVASIVE ACTION. THE HELI THEN MADE REPEATED PASSES ON THE RPTR'S ACFT.

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I WAS PERFORMING AERIAL PHOTOGRAPHY AT 1000 FT AGL ABOUT 2-3 MI W OF DOWNTOWN COLUMBUS; OH. THE ACFT HAS A RYAN 8800 TCAD WHICH INDICATED A TFC CONFLICT AT THE SAME ALT AND 1.5 MI (I HAD IT IN TERMINAL MODE AT THE TIME; +/-500 FT AND 1.5 MI). I WAS NOT TALKING TO COLUMBUS BECAUSE I WAS BELOW THEIR CLASS C AIRSPACE AND THEY WERE BUSY WITH ARRS. THE TARGET CLOSED TO WITHIN 1 MI AT WHICH TIME I DSNDED TO AVOID A CONFLICT IN ALT. I IDENTED THE TARGET AS AN UNKNOWN HELI AND CONTINUED PHOTOGRAPHING MY SITE AT THE LOWER ALT WHICH INVOLVED CIRCLING BACK UP TO 1000 FT AGL. THE SAME PIECE OF TFC REAPPEARED ONCE AGAIN AND MADE SEVERAL PASSES AT ME AT MY ALT AND AT TCAD INDICATED DISTANCES OF 0.3 TO 1 MI. UPON LNDG AND CALLING COLUMBUS FSDO; I WAS TOLD THE TFC WAS A STATE POLICE HELI WHICH HAD FILED A COMPLAINT THAT I WAS FLYING 'LOW AND ERRATIC' OVER A POPULATED AREA. I DSNDED BELOW THE MINIMUM ALT TO AVOID A TFC CONFLICT (A CARDINAL CAN DSND MUCH FASTER THAN IT CAN CLB). I WAS OPERATING AT A SAFE AND LEGAL ALT BEFORE THE CONFLICT AND CLBED BACK UP TO THAT LEGAL ALT AFTER THE THREAT LEFT THE AREA. DID NOT APPRECIATE THE STATE POLICE HELI PLT MAKING SEVERAL CLOSE PASSES TO GET MY TAIL NUMBER. IF THIS SIT PRESENTS ITSELF AGAIN; I WILL ESTABLISH COM WITH THE LCL ATC SO THAT THEY KNOW WHERE I AM AND WHAT I AM DOING.