Learjet 40
Air Traffic Control Fully Certified
Other / Unknown
ATC Issue All Types
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings
I was working Local Control at the time of the event. We had just changed the flow to a north configuration (Runway 36; Runway 35; and Runway 32). There were a few departures; both VFR and IFR as well as one Cessna VFR in the pattern. A LR40 called for departure with an eventual flight plan to the southeast. I cleared the LR40 for take off Runway 35 with a restriction to fly runway heading. This was due to other traffic; a VFR on a fan heading of 030. After clearing the LR40; I continued with other duties. As the LR40 was tagging up; I got a Conflict Alert. I looked at the TDW to see what was going on and the LR40 was in Conflict Alert with another transponder north of the airport. It took me a couple seconds to recognize what was happening and it took me aback because I could not figure out who the other aircraft could be. As it turned out; there was a duplicate beacon north of the field. The LR40 was in conflict with the dupe beacon. The LR40's data tag should have been associated with the aircraft which was about 1 mile north of Runway 35. Instead; the actual beacon of the LR40 had no data tag. The dupe beacon which was approximately 3 miles north of Runway 36 had the LR40 data tag. It took about 15 seconds for the LR40 data tag to establish on the real beacon and then a few seconds more before the dupe beacon went away. This was a terrible distraction at this moment. Recommendation; to have an ASR system free of anomalies like dupe beacons; this as not been a big problem with our ASR-11 system at LNK so it was weird to see it today.
LNK Controller voiced concern regarding a false 'Conflict Alert' apparently caused by a 'split target' and/or 'ghost/duplicate' target anomaly.