GULFSTREAM CREW SQUAWKS 7700 WHEN THEY MEANT TO SQUAWK 7600 AFTER SPENDING SOME TIME OFF ARTCC FREQ.

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WHILE CRUISING AT FL430; I APPARENTLY MISCOPIED THE NEXT ATC ASSIGNED FREQ. WHEN NO ONE RESPONDED TO MY XMISSION; I WENT BACK (I THOUGHT) TO THE PREVIOUSLY ASSIGNED FREQ. ACTUALLY; THE PREVIOUSLY ASSIGNED FREQ HAD BEEN LOST. IT WAS LOST DUE TO MY USING THE CTL HEAD FOR THE #1 RADIO IN CONJUNCTION WITH THE REMOTE TUNE (FMS) APPLICATION WITH THE FMS REMOTE TUNE HAVING BEEN PLACED IN PREVIOUS 'DESELECT' BY THE LAST CREW. THE FMS CONFUSION CONTRIBUTED TO THE MISCOM. IT TOOK NEARLY 20 MINS TO RE-ESTABLISH CONTACT WITH ATC. AFTER 15 MINS OF TRYING VARIOUS FREQS OBTAINED FROM VARIOUS SOURCES AND NOT HAVING ANY SUCCESS; I DECIDED THAT FOR SAFETY REASONS I SHOULD SQUAWK 7600 TO ADVISE ATC OF OUR SIT. I MISTAKENLY SQUAWKED 7700. WHEN COM WAS ESTABLISHED WITH ATC; THE CTLR SAID THAT HE WAS RECEIVING OUR 'EMER' SQUAWK. I LOOKED AT THE XPONDER SETTING AND I HAD INDEED TUNED 7700. I INFORMED ATC THAT I HAD MEANT TO TUNE IN 7600. I WAS ASKED IF WE NEEDED ANY ASSISTANCE. I EXPLAINED THAT WE DID NOT AND CONTINUED WITH THE FLT. THE ATC MGR INFORMED ME THE SIT WAS NON DISRUPTIVE. HE CHKED WITH THE CTLRS AND FELT CERTAIN THAT NO RPTS WOULD BE REQUESTED FROM OUR FLC. VERY CAREFUL READING OF THE FMS MANUAL REVEALED THAT WITH THE FMS AUTO TUNE SETUP IN A CERTAIN CONFIGN; IT COULD CAUSE THE 'LAST TUNED' FREQ TO APPEAR TO HAVE BEEN LOST. ALSO; USING BOTH AUTO TUNE AND MANUAL TUNE CAN CAUSE A SIMILAR SIT.