An inexpensive portable RF (radio frequency) microcontroller-based digital spectrum analyzer is automatically calibrated for passband amplitude tilt/variations. Resulting software-obtained calibration parameters are used during operation to reduce or eliminate passband amplitude errors. The spectrum analyzer also includes a PLL frequency synthesizer arrangement, but the PLL controls a VCO only during calibration to derive calibration values for controlling a digital-to-analog converter. During normal operation, the VCO is driven in an open loop configuration under software control using such calibration values--achieving nearly the accuracy of closed loop operation while avoiding the penalty of long PLL lock time. These amplitude and frequency calibration techniques and arrangements permit the spectrum analyzer to have relatively inexpensive components and circuit arrangements and nevertheless achieve high accuracy over a wide band.