SMT ACFT WITH JUMPERS ON BOARD ARE RELEASED OVER JUMP ZONE; BUT IMPROPER COORD WITH ATC RESULTS IN CLOSE PROX OF ARRIVING ACFT TO JUMPERS.

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I WAS CLBING WBOUND OUT OF 13000 FT MSL FOR 14000 FT MSL IN ORDER TO INTERCEPT THE 360 DEG BEARING TO THE DROP ZONE (GPS). I WAS INFORMED OF TFC AT MY 10-11 O'CLOCK POS BY PDX APCH. THE TFC WAS FLYING THE MOXEE 3 ARR INTO PDX. THE MOXEE DIRECTLY OVERLIES THE DROP ZONE. I RPTED THE ACFT IN SIGHT AND WAS ADVISED OF A HORIZON F28 IN TRAIL OF THE LAST TFC BY 6 MI. I DID NOT HAVE THE F28 IN SIGHT AND ADVISED PDX I WAS 2 MINS TO DROP. PDX STATED THAT THE F28 PROBABLY WOULD NOT BE A FACTOR. WITHOUT THE JET IN SIGHT I GOT ESTABLISHED ON JUMP RUN AND LET THE JUMPERS OUT AT THE APPROPRIATE SPOT. I INCORRECTLY ASSUMED THE F28 WAS PAST ME TO THE N. WHILE DSNDING; I SAW THE SHADOW OF THE F28 PASS UNDER ME AND TO MY W; THEN HEARD PDX APCH TELL THE F28 CREW THAT I WAS HOLDING MY JUMPERS; BUT MY JUMPERS WERE GONE AND I INFORMED PDX SO. THE F28 CREW RPTED SEEING JUMPERS PASS 1/2 MI OFF ONE SIDE OF THEIR ACFT. UPON MY OWN QUESTIONING OF THE JUMPERS INVOLVED; I CONCLUDED THEY WERE CLOSER THAN 1/2 MI. 1 JUMPER RPTED BEING ABOUT 2000-3000 FT ABOVE THE F28 WHILE IN FREEFALL. I BELIEVE THE EVENT OCCURRED DUE TO A LACK OF SITUATIONAL AWARENESS ON MINE AND PDX CTLR'S PART. ALSO CONTRIBUTING WAS A LACK OF COM (PDX WAS SWAMPED); AND MY RADIO WAS OCCASIONALLY SCRATCHY. IN THE FUTURE; IF ANY DOUBT EXISTS AS TO AN ACFT'S POS; I WILL ACQUIRE IT VISUALLY OR NOT DROP THE JUMPERS.