MODE C JUMP OCCURS WHENEVER A DISCRETE BEACON CODE ACFT GETS CLOSE.

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ACR X; AN MLG; WAS DSNDING FROM 14000 FT TO 10000 FT ON A COURSE FROM BANDS INTXN DIRECT TO KAYOH INTXN; ENRTE TO LGB. THIS RTE PASSES APPROX 2 MI N OF HDF ON A 245 DEG BEARING. AS ACR X WAS APCHING 11000 FT; HE ADVISED ATC HE WAS CLBING FOR A TCASII RA. AS I LOOKED AT THE RADAR FOR TFC; I OBSERVED THE MODE C OF A 1200 (VFR) BEACON CODE CHANGE FROM 2700 FT MSL TO 10700 FT MSL IN ONE SWEEP OF THE RADAR. THIS OCCURRED WHEN THE TARGETS WERE ABOUT 2 MI; OR LESS; APART. THE ACFT ON THE 1200 BEACON CODE WAS A USAF MLT Y IN THE PATTERN AT RIV (MARCH AFB). AS SOON AS THE TARGETS PASSED EACH OTHER; THE MLT'S MODE C INDICATED 2500 FT MSL. ACR X STATED HE NEVER SAW ANY TFC. ABOUT 9 MONTHS AGO THIS PHENOMENA WAS A RATHER COMMON EVENT. FREQUENTLY; WHEN WORKING AN IFR ACFT; I WOULD OBSERVE THAT THE MODE C OF A 1200 BEACON CODE ACFT WOULD SUDDENLY JUMP FROM A LOW ALT TO A HIGHER ALT NEARLY APPROXIMATING THE MODE C OF THE IFR ACFT. THIS WOULD ONLY OCCUR WHEN THE 2 ACFT WOULD REACH A POINT WHERE THE TARGETS WERE ABOUT TO MERGE. ONCE THE TARGETS PASSED EACH OTHER; THE MODE C OF THE 1200 BEACON CODE ACFT WOULD RETURN TO NORMAL. IT APPEARS THAT THIS PROB MAY HAVE RETURNED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THE MODE C JUMP OCCURS MAYBE ONCE A DAY; OR POSSIBLY ONCE A WK. IT ONLY HAPPENS WHEN THERE IS ANOTHER ACFT APCHING ON A DISCRETE BEACON CODE. IT IS NOT RESTR TO ONLY MIL ACFT; BUT ALSO INVOLVES OTHER TYPES. NO CONFLICTS HAVE BEEN RPTED; BUT RPTR FEELS THAT ONE MAY IF THE CTLR OR PLT REACT TO THE FALSE TRACK JUMP. FACILITY HAS AN ASR-9 SYS THAT HAS BEEN IN SVC FOR ABOUT 1 MONTH. THE MODE C JUMP PROB HAS BEEN ONGOING FOR ABOUT 1 YR. DOESN'T THINK THAT A UCR HAS BEEN FILED ON THIS; AND NOT SURE IF FACILITY MGR IS AWARE OF IT.