B06 AND PA28 HAVE CLOSE ENCOUNTER. HELI PLT WAS XMITTING INTENTIONS ON WRONG XMITTER.

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I WAS RETURNING FROM AN AERIAL APPLICATION FLT. I APCHED THE ARPT FROM THE SE ON A HDG OF 310 DEGS. I WAS N OF THE RWY EXTENDED CTRLINE AND WAS PLANNING TO LAND ON THE RAMP. APPROX 1/2 MI FROM THE DEP END OF RWY AND AT 600 FT; I OBSERVED A PIPER AT THE SAME ALT AND APPROX 300 FT TO MY L. SINCE WE WERE ABEAM AND IN OPPOSITE HDGS NO EVASIVE ACTIONS WERE TAKEN. I HAD MADE SEVERAL POS CALLS OF MY INTENTIONS TO LAND ON THE RAMP AND HAD HEARD NO RADIO TFC ON THE CTAF. I IMMEDIATELY CHKED MY RADIO PANEL AND THE RADIO WAS SET TO THE CORRECT FREQ. I CONTINUED TO LAND ON THE RAMP AND ON FURTHER CHKING I FOUND MY HEADSET WAS PLUGGED INTO THE COMPANY'S BUSINESS BAND RADIO AND I WAS NOT MONITORING THE CTAF AS I HAD THOUGHT. I HAD FORGOTTEN TO SWITCH THE PLUG TO THE CORRECT RADIO. THE FACT THAT THE PLUG IS ABOVE AND BEHIND THE HEAD DOES NOT LEND IT TO AN EASY VISUAL INSPECTION. PLUS THE LACK OF SIDE TONE WHEN I XMITTED HADN'T RAISED ANY FLAGS; AS THE COMPANY RADIO WHICH I USE WHILE SPRAYING DOESN'T HAVE ANY SIDE TONE. I WAS NOT EXPECTING ANY OTHER TFC AS I HAD WORKED AROUND THE ARPT ON SEVERAL OCCASIONS WITHIN THE PRECEDING 2 MONTHS AND HAD NEVER SEEN ANY OTHER ACFT. I HAD BECOME COMPLACENT WORKING IN A LOW TFC ENVIRONMENT FOR THE PAST 3 MONTHS.