ARTCC RADAR CTLR CLBING AN ACR DH8 ENRTE TO CYN; ACR RECEIVED AND REACTED TO A TCASII RA AND WAS IN CLOSE PROX TO A C210 THAT WAS VFR. PHL APCH WAS IN CONTACT WITH THE C210; BUT RPTR ALLEGES THAT THE C210 DID NOT PAINT ON HIS SCOPE DUE TO A NEW RADAR SITE THAT COVERS THAT AREA.

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WORKING ACR X; DHC8; DEPARTED PHL ROUTED VIA V312 CYN BOUNO3 HPN; CHKS IN OUT OF 6400 FT CLBING TO 9000 FT. NEW RADAR SITE RECENTLY COMMISSIONED QIE (GIBBSBORO) LOCATED 6 NM N OF V312 AT ALBEK. RADAR DATA ON ACR X WAS UNRELIABLE DURING HDOF FROM PHL APCH; BUT SEEMED NORMAL AFTER HDOF ACCEPTED. UNKNOWN TO THE CTLR WORKFORCE; RADAR DATA ON UNTRACKED (INTRUDER) TARGETS VERY UNRELIABLE. AS ACR X APCHED ALBEK I CLBED HIM TO 11000 FT. HE ADVISED THAT HE HAD A TFC ALERT. THERE WAS NO OTHER TARGETS NEAR HIM. HE THEN ADVISED THAT HE HAD A TCASII RA AND WAS DSNDING. 30 SECONDS LATER HE ADVISED CLR OF TFC AND RESUMING CLB. HE SAW THE TFC AT THE LAST MOMENT. PHL APCH YELLED OVER THE HDOF LINE THAT THEY WERE WORKING THE C210; SMA Y; AND THAT HE HAD THE DHC8 IN SIGHT; BUT ALL THE TCASII ACTIONS HAD ALREADY OCCURRED. THE POOR PERFORMANCE AND LOCATION OF THIS NEW RADAR SITE IS CAUSING A SAFETY HAZARD. THIS SITE REPLACES QDP (TREVOSE; PA). I DON'T KNOW WHY THEY ARE DECOMMISSIONING QDP. AFTER ACR X RPTED CLR OF TFC; THE C210 APPEARED ON MY SCOPE; SBOUND AT 8500 FT.