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.