Skyhawk 172/Cutlass 172
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Conflict Airborne Conflict; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings; Environment - Non Weather Related; Human Factors; Procedure
A C172 was in a published holding pattern at the UBG VOR. A C414 was a departure from UAO airport; approximately 8 miles east of the UBG VOR. Limited departure routes from UAO; most being routed over UBG. Normally; with a good performing airplane; you are able to establish RADAR contact around 2;000 from UAO (the Newberg Sector is both RADAR and non-RADAR; given the location of our single RADAR sensor); but did not see the C414 until approximately 5 miles west of UAO. [I] turned the C414 immediately to avoid the C172. Thought I had cleared the traffic; but TARP thought otherwise. I believe it happened due to our poor RADAR coverage; and poor climb performance of the C414. There are things I could have done also; such as climb the C414 to 3;000. The problem with that however; would be the fact that I would possibly never see C414 on RADAR; because our coverage gets much worse the farther you venture west. Simple answer is: We need another RADAR installation to cover the entire southwest quadrant of our airspace. This airspace contains 80 percent of our student pilot; instrument training airports. There have been several issues over the years with this airspace; and lack of RADAR coverage.
P80 Controller described a loss of separation event between an aircraft holding at UGB VOR and an IFR UAO departure.  The reporter suggested improved RADAR coverage is a must in this area.