Abstract: Microprocessor (MPU) controlled voltage controlled oscillator (VCO) linearization circuitry locks the VCO at desired low, center and high frequencies (F.sub.1, F.sub.c and F.sub.h) and measures the magnitudes of the corresponding control voltages (V.sub.1, V.sub.c and V.sub.h). Next, the VCO is swept at a nominal clock frequency to determine the times (T.sub.1, T.sub.2 and T.sub.h) that the control voltages (V.sub.1, V.sub.c and V.sub.h) occur during the sweep cycle. The control voltage of the VCO is then swept at a first and then a second rate during a sweep cycle to assure that the center frequency (F.sub.c) of the VCO occurs at the time (T.sub.c) midpoint of the sweep cycle. As a result, each VCO frequency can be determined by MPU monitoring according to the time that the VCO frequency occurs during the sweep cycle. This circuitry is useful in spectrum analyzers for indirectly determining the otherwise unknown frequency of a received signal.