EXPERIMENTAL ACFT EXPERIENCES NMAC WITH A C172 WHILE TURNING TO FINAL AT A NON-TOWERED ARPT.

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I ENTERED A STANDARD L UPWIND FOR RWY 27 MAKING POS RPTS. A C172 ANNOUNCED HE WAS INBOUND. I ACKNOWLEDGED I HAD HIM IN SIGHT. HE RADIOED THAT HE WOULD COME IN BEHIND ME. I THEN SCANNED THE DOWNWIND FOR OTHER ACFT AND OBSERVED NONE. I ANNOUNCED MY XWIND TURN. DURING THE XWIND; I WAS SCANNING THE DOWNWIND FOR OTHER ACFT. ANNOUNCED AND MADE TURN TO DOWNWIND. WHILE ON DOWNWIND; I DIDN'T OBSERVE ANY ACFT IN FRONT; ON BASE OR FINAL. CONTINUED TO MAKE POS RPTS AND NORMAL DOWN TO BASE; AND BASE TO FINAL TURNS. JUST AFTER COMPLETING MY BASE TO FINAL TURN; I HEARD THE C172 RPT DOWNWIND AND THAT HE HAD BOTH OF US IN SIGHT. I IMMEDIATELY LOOKED TO THE SIDES; THEN DOWN; TO OBSERVE A CESSNA PASSING ME ABOUT 75 FT BELOW. I EXECUTED A GAR. THE CESSNA CONTINUED TO LAND NORMALLY. AFTER LNDG; I SPOKE TO THE C172 PLT. HE SAID PRIOR TO HIS RADIO CALL HE HAD NOT HEARD ANY POS OR INTENTION XMISSIONS FROM THE CESSNA. I BELIEVE THE CESSNA WAS MAKING A STRAIGHT-IN APCH WITH AN INOPERABLE RADIO. FOR MY PART; I SHOULD HAVE BEEN SCANNING BEYOND THE NORMAL BASE AND FINAL PATTERN FOR OTHER ACFT.