DC9 FLC ON A STAR ARR FORGOT THE FREQ AFTER ARTCC CTLR GAVE THEM A COM FREQ XFER CAUSING THEM TO BE OUT 2-WAY COM FOR SEVERAL MINS.

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WHILE LEVEL AT FL180 ON SHAFF 4 ARR INBOUND TO NEWARK; WE WERE GIVEN A FREQ CHANGE. I READ BACK FREQ AND CHANGED. THERE WAS NO RESPONSE ON NEW FREQ. I COULD NOT READ THE OLD FREQ I HAD WRITTEN. WE CONTACTED A KNOWN FREQ FROM OUR CHART AND ATC GAVE US THE CORRECT FREQ. WE HAD GONE TO 134.2 INSTEAD OF CORRECT FREQ OF 134.3. WE WERE ON COURSE AND AT LAST ASSIGNED ALT. WE WERE OUT OF ATC CONTACT FOR ABOUT 3 MINS. ATC CTLR GAVE US A VECTOR THROUGH THE INBOUND COURSE FOR SPACING; AND ASKED WHAT HAD HAPPENED AND I ADVISED HIM OF THE FREQ CHANGE CONFUSION. THERE WAS NEVER ANY KNOWN CONFLICT OR TCASII ADVISORY. THE CTLR NEVER SAID ANY MORE OTHER THAN HE INITIALLY THOUGHT WE HAD LEFT FREQ BY TAKING ANOTHER FLT'S FREQ CHANGE BY MISTAKE; WHICH I EXPLAINED WAS NOT THE CASE; BUT INSTEAD INCURRED AN INCORRECT FREQ CHANGEOVER PROB. IT WOULD BE HELPFUL IF ENRTE CHARTS HAD AT LEAST ONE DEFAULT FREQ FOR EACH SECTOR PRINTED ON THE MAP THAT YOU COULD REFER TO. LACK OF DUAL HEAD COM RADIOS WAS ALSO A CONTRIBUTING FACTOR.