Narrative:

I was working aircraft #1 through my sector. I observed a 'V' (aircraft #2) which indicated a VFR act within 1 mi of aircraft #1, but saw no primary or secondary return associated with the target. Targets often appear and disappear at my facility. On the second sweep after first noticing the possibility of aircraft #2's existence, aircraft #1 asked if I was talking to the mooney at his altitude that 'got kind of close.' as he was speaking, the 'V' showed an indicated altitude of 8000 ft. The mooney came out of nowhere. I had my upper radar altitude filter limit set at 11500 ft. I tracked the mooney's (aircraft #2's) course for 20 mi and he stayed level at 8000 ft. I suppose the mooney could have been on my scope all along and I just didn't notice him. His course might have gone over the radar cone of silence, but he didn't materialize until 10 mi from the radar, which is pretty far from the main bang not to be seen at 8000 ft. We have a history of lousy radar (primary, secondary and ARTS) at rockford. Airways facilities was working on a bad beacon channel today. We've discontinued surveillance approachs to 2 runways here because of inadequate primary. Our radar was under article 65 for almost a yr. We have a book to track radar problems which we controllers fill out daily. I'm used to waiting for a few sweeps to confirm a target's existence before issuing traffic, due to the unreliability of the radar. If we had better radar the pilot could be looking for traffic.

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Original NASA ASRS Text

Title: RFD CTLR CONCERNED WITH POOR RADAR RETURNS WHEN C310 COMPLAINS ABOUT AN MO20 PASSING WITHIN CLOSE PROX WITHOUT A TA.

Narrative: I WAS WORKING ACFT #1 THROUGH MY SECTOR. I OBSERVED A 'V' (ACFT #2) WHICH INDICATED A VFR ACT WITHIN 1 MI OF ACFT #1, BUT SAW NO PRIMARY OR SECONDARY RETURN ASSOCIATED WITH THE TARGET. TARGETS OFTEN APPEAR AND DISAPPEAR AT MY FACILITY. ON THE SECOND SWEEP AFTER FIRST NOTICING THE POSSIBILITY OF ACFT #2'S EXISTENCE, ACFT #1 ASKED IF I WAS TALKING TO THE MOONEY AT HIS ALT THAT 'GOT KIND OF CLOSE.' AS HE WAS SPEAKING, THE 'V' SHOWED AN INDICATED ALT OF 8000 FT. THE MOONEY CAME OUT OF NOWHERE. I HAD MY UPPER RADAR ALT FILTER LIMIT SET AT 11500 FT. I TRACKED THE MOONEY'S (ACFT #2'S) COURSE FOR 20 MI AND HE STAYED LEVEL AT 8000 FT. I SUPPOSE THE MOONEY COULD HAVE BEEN ON MY SCOPE ALL ALONG AND I JUST DIDN'T NOTICE HIM. HIS COURSE MIGHT HAVE GONE OVER THE RADAR CONE OF SILENCE, BUT HE DIDN'T MATERIALIZE UNTIL 10 MI FROM THE RADAR, WHICH IS PRETTY FAR FROM THE MAIN BANG NOT TO BE SEEN AT 8000 FT. WE HAVE A HISTORY OF LOUSY RADAR (PRIMARY, SECONDARY AND ARTS) AT ROCKFORD. AIRWAYS FACILITIES WAS WORKING ON A BAD BEACON CHANNEL TODAY. WE'VE DISCONTINUED SURVEILLANCE APCHS TO 2 RWYS HERE BECAUSE OF INADEQUATE PRIMARY. OUR RADAR WAS UNDER ARTICLE 65 FOR ALMOST A YR. WE HAVE A BOOK TO TRACK RADAR PROBS WHICH WE CTLRS FILL OUT DAILY. I'M USED TO WAITING FOR A FEW SWEEPS TO CONFIRM A TARGET'S EXISTENCE BEFORE ISSUING TFC, DUE TO THE UNRELIABILITY OF THE RADAR. IF WE HAD BETTER RADAR THE PLT COULD BE LOOKING FOR TFC.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.