A B737 CREW INTERCEPTS THE FINAL APCH COURSE WITHOUT CLRNC AT YYZ WHEN THEY INADVERTENTLY LEAVE THE APCH CTL FREQUENCY WITHOUT A CLRNC. CONFUSION OVER THE OP OF THE RADIO CONTROL HEAD IS NOTED AS PART OF THE CAUSE.

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WHILE BEING RADAR VECTORED TO FINAL APCH COURSE (LOC 24) AND NOW TWO MILES FROM INTXN; WE WERE ON 132.8 (YYZ APCH CTL). I; THE PLT NOT FLYING; MISTAKENLY CHANGED THE ACTIVE COM FREQUENCY TO TWR FREQUENCY IN ANTICIPATION OF THE HANDOFF. AS SOON AS I STARTED TO CHANGE THE FREQ I REALIZED WHAT I DID AND QUICKLY TRIED TO FIND THE ORIGINAL APCH CTL FREQUENCY WE WERE JUST USING. AFTER SEVERAL ATTEMPTS I JUST SWITCHED TO TWR; MEANWHILE THE CAPT INTERCEPTED THE FINAL APCH COURSE WITH NO APCH CTL INSTRUCTION TO DO SO. ON INITIAL CALL TO TWR THEY CLRED US FOR THE APCH AND CLRED US TO LAND; ALL WITH NO APPARENT REGARD TO OUR SELF INDUCED (APPROX 45 SEC) LOST COM SIT. THE REASON THIS OCCURRED WAS THAT THERE ARE TWO TYPES OF COM FREQUENCY HEADS USED TO TRANSFER THE 'STANDBY' FREQUENCY TO ACTIVE FREQUENCY STATUS. THE OLDER AND LESS COMMON TYPES (THE ONE WE HAD) USES A TOGGLE SWITCH TO ACTIVATE THE STANDBY FREQUENCY TO ACTIVE FREQUENCY STATUS. IN THE NEWER TYPE; A BUTTON IS PRESSED AND IT TRANSFERS THE STANDBY FREQUENCY WHICH IS ALWAYS IN THE RIGHT WINDOW (OF A TWO WINDOW FREQUENCY HEAD) TO THE ACTIVE FREQUENCY STATUS; WHICH IS ALWAYS IN THE LEFT FREQUENCY WINDOW. THE OLDER TOGGLE SWITCH STYLE COM ALSO HAS A TWO WINDOW FREQ HEAD; BUT EITHER WINDOW CAN BE USED AS THE ACTIVE FREQUENCY OR THE STANDBY FREQUENCY. I PREFER THE NEWER PUSH BUTTON TYPE COM HEAD; IT'S LESS CONFUSING.