What was found
(CAN) 15 MINUTES INTO CLIMB TO ALTITUDE, PILOTS SAW AND SMELLED SMOKE EMANATING FROM LOWER PORTION OF COPILOT'S WINDSHIELD. AIRCRAFT RETURNED TO BASE OF DEPARTURE, MEANWHILE CIRCUIT BREAKERS FOR WHAT APPEARED TO BE CAUSE OF SMOKE WERE PULLED. WINDSHIELD HEAT BREAKERS WERE PULLED. INVESTIGATION ON GROUND REVEALED STRONG BURNED SMELL EMANATING FROM NR 1 VHF NAV/COMM ONCE REMOVED FROM INSTALLATION RACK. BACK OF NAV/COMM IS LOCATED BELOW COPILOT'S WINDSHIELD AND THIS IS WHY SMOKE WAS COMING FROM LOWER PORTION OF WINDSHIELD. NAV/COMM REPLACED WITH SERVICEABLE UNIT.