The HP / Agilent 35601A Spectrum Analyzer Interface is a component part of the 3047A Phase Noise Measurement system. The 3047A performs automated phase noise measurements from 5 MHz - 18 GHz. The 35601A contains the mixers, VCO's, IF amplifiers, low pass filters, buffers, and switches necessary for the system to perform either frequency discriminator or quadrature phase detection methods of phase noise measurement.