ATC Terminology - Primary Target

Having flight following is a real handy service. Most of the time ATC will provide complete details on the traffic such as: traffic, 2 O'clock, 3 miles, 6,500, moving North West. They can do this because there are multiple pieces of information about the "target". Radar can identify that there is something out there and then if there is a transponder with altitude encoding there will be altitude information. Flying in the Bay area we always hear the complete details because we are so close to B and C airspace where transponders are required. However, if you venture beyond the area, it is not uncommon for planes not to have transponders and hence you may get a report of "Traffic" with ALTIUDE UNKNOWN. Often times you may hear ATC call the traffic a primary target, meaning they have identified it only by a radar return but have no transponder information. This does make it more difficult to locate traffic because you have no idea if it is 4000 feet below you or at your same altitude. If needed, you can always request ATC to provide vectors to avoid the traffic.