The Anritsu MS620J is a 100 kHz to 2 GHz Network/Spectrum Analyzer. The MS620J spectrum analyzer is a wide band, very sensitive receiver. It works on the principle of super-heterodyne receiver to convert higher frequencies (normally ranging up to several 10s of GHz) to measurable quantities. The received frequency spectrum is slowly swept through a range of pre-selected frequencies, converting the selected frequency to a measurable DC level (usually logarithmic scale), and displaying the same on the CRT of the Anritsu MS620J. The CRT displays received signal strength (y-axis) against frequency ( x-axis).