GA PLT MISSES OM CALL TO TWR AND INCURS AN NMAC WITH ANOTHER GA ON 1 MI FINAL.

Narrative

HAD RECEIVED RADAR VECTOR FROM SHV APCH TO INTERCEPT LOC FOR LOC RWY 14 INTO DTN (SHREVEPORT DOWNTOWN). AT INTERCEPT; APCH DIRECTED TO CALL TWR; NO MENTION MADE OF CANCELLATION OF RADAR SVCS AND SQUAWK NOT CHANGED. TWR CLRED TO LAND AND INSTRUCTED ME TO CALL THE OM. I WAS STILL IN IFR CONDITIONS AT TIME OF CALL. CONTINUED APCH; BUT FAILED TO CALL THE OM. AT 1.8 DME; I LOOKED FOR THE RWY AND SAW C172 APPROX 100 FT OFF L WING. MADE IMMEDIATE R 360 DEGS. THE C172 HAD AN INSTRUCTOR ONBOARD; AND I HAD MONITORED XMISSIONS THAT MADE ME BELIEVE IT WAS NOT AT ARPT; BUT WAS SETTING UP FOR AN APCH. ON GND; I CALLED TWR TO DISCUSS AND ACKNOWLEDGED FAILURE TO CALL OM; AND LEARNED THAT THEY DO NOT HAVE RADAR AT THEIR TWR. DTN SITS UNDER THE SHV-BAD CLASS C; AND I NEVER RECEIVED ANY INDICATION THAT RADAR SEPARATION WAS BEING DISCONTINUED. CORRECTIVE ACTION: MORE ATTN TO COM PROCS TO CALL OM (FOR ME). FOR OTHER ACFT: CFI OUGHT TO BE LOOKING OUTSIDE OF COCKPIT (THEY NEVER SAW ME). TWR: NEEDS RADAR. APCH: WHEN HANDLING TFC IN IMC NEEDS TO CLARIFY/EMPHASIZE CANCELLATION OF RADAR SVCS.