Lesson: It is not necessary to measure every frequency, in order to do phase calibration. OVSA Procedure: • Determine reference phase calibration, say once per month (or whenever an active element is changed) • Determine daily phase calibration on 6 frequencies, once every 2 hours, to determine slopes and offsets. • Lobe ambiguities are eliminated (can tell whether 170o or –190o), so calibrations can be done less often.