Cessna 152
Air Traffic Control Fully Certified
Situational Awareness; Human-Machine Interface
ATC Issue All Types; Aircraft Equipment Problem Less Severe
Air Traffic Control Issued New Clearance
ATC Equipment / Nav Facility / Buildings; Human Factors
While working Harbor RADAR; LGB Tower called and requested diverging headings on 2 'General Aviation' departures; which I approved. While working other traffic; a C152 departed LGB on a left turn heading 160. I identified the aircraft and climbed him to 4;000 FT. The C152 was about 2 NM south of LGB. Shortly there-after; a C182 checked in on frequency at the same time LGB Tower was calling to advise that the C182's transponder wasn't showing a squawk code. After hearing LGB Tower over the speaker; I immediately issued the correct code to the C182; and then answered LGB Tower acknowledging their call. I observed a target near LGB's departure corridor at 400 FT 1 NM west of the airport. I assumed that was the targets I was waiting to 'Tag Up'. At the same time; I issued a heading of 200 degrees to the C152 for climb above arriving traffic to TOA and also to sequence behind other en route traffic he was following. While issuing that heading; I placed a 'bat' on the target I thought to be the C182 and saw the 'bat' pointing northeast bound. Not a heading any departure would be on. Immediately I turned the C152 back to a heading of 160 for divergence. The pilot of the C182 then replied that they got their transponder working; and they tagged up on their code about 2 NM northwest of the C152. Prior to this; there was a short time where there was no indicated primary or secondary return in that area. This is why I turned the C152 in that direction. [We need] better RADAR coverage for low level aircraft in the vicinity of LGB harbor area.
SCT Controller experienced a loss of separation event between two LGB IFR departure aircraft when questionable RADAR tracking failed to properly display the target aircraft; the reporter suggesting improve low level RADAR coverage in the subject area.