A two port handheld VNA enabling both reflection and transmission measurements to be made over a range of 25 MHz to 3.3 GHz frequency range. The handheld VNA includes a tracking synthesizer (420) which generates an LO signal without a direct connection to a reference oscillator (440), enabling resolution of the LO signal to be independent of a generated RF test signal. Synchronous detectors (501-505, 574, 575) are further included to provide incident, reflected, and transmitted IF signals to an A/D converter (548). To enable operation in the presence of external signals, a feedback dither line is provided from one of the synchronous detector (533) outputs to sweep the frequency of the reference oscillator (440). The handheld VNA also is configured to optionally operate as a frequency monitor to determine the frequency range and power level of incoming signals without upconverting and downconverting to eliminate images as typically done in a spectrum analyzer. The frequency monitoring circuit operates by dividing the frequency range to be monitored into bins. The LO signal is then stepped for each bin until RF signals within the bin frequency range can generate an IF signal. The maximum IF signal power level detected during measurements for the bin is then stored as a power level for signals in each bin.