In the proposed spectrum analyzer, open-loop VCO is replaced with PLL synthesizer incorporating digital frequency synthesizer using modulofunction for measuring precise frequencys. Three different frequency bands and channel spacings are realized by single loop synthesizer through the effective design of the system. The newly designed system with square detection has a good linearity of input range from 10mV to 8.5V, as a result the input sensitivity has been improved up to 500uV. The storage function enables us to analyze not only periodic but also nonperiodic wave-form and zoom-in function expands frequency resolution eight times for the dense spectra.