FLC LEFT ASSIGNED ALT WITHOUT COORDINATING WITH ATC. PLT TALKING ON RADIOS WAS TALKING ON THE WRONG RADIO.

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DURING APCH TO FKL ARPT IN VMC; WE WERE TOLD BY YNG APCH TO EXPECT A VISUAL APCH. YNG WAS WORKING MORE THAN ONE FREQ; BUT WE COULD ONLY HEAR THE CTLR'S XMISSIONS ON OUR FREQ. WE SAW THE ROTATING BEACON AT FKL AT 15 MI OUT. I STARTED TO ACTIVATE THE PLT CTLED LIGHTING WITH #2 COM. AFTER 2 ATTEMPTS I DETERMINED THE PLT CTLED LIGHTING TO BE INOP. AT THE SAME TIME I RPTED TO YNG THAT I HAD THE FIELD IN SIGHT; HOWEVER; I HAD LEFT THE XMIT SWITCH ON #2; SO MY XMISSION WAS ON UNICOM. AT ABOUT THIS TIME WE HEARD AN APCH CLRNC FROM YNG. THE FO (PF) THOUGHT IT WAS FOR US AND BEGAN A DSCNT TO SET UP A PATTERN FOR LNDG. INITIAL ALT WAS 3200 FT MSL; AT 2600 FT MSL I REALIZED MY COM SWITCH WAS ON WRONG XMITTER. I SWITCHED TO YNG; AND CONFIRMED THAT WE HAD ARPT IN SIGHT. HE ASKED IF WE WERE CLRED FOR THE APCH. AT THIS POINT I REALIZED WE HAD BEEN XMITTING ON THE WRONG FREQ. WE WERE THEN CLRED FOR THE APCH AND LANDED AT FKL. BETTER VIGILANCE ON RADIO MGMNT IS A MUST. POSSIBLY WHEN ATC IS WORKING MORE THAN ONE FREQ; WE SHOULD HEAR BOTH SIDES OF THE XMISSIONS OR; WORKING MORE THAN ONE FREQ SHOULD BE ELIMINATED.