This application note describes in detail the steps required to make a noise figure measurement on a spectrum analyzer using the "Y Factor" technique. Background equations are presented for each step of the calculation. In addition, guidelines are provided to ensure a repeatable measurement. Measurement uncertainty is then reviewed, including contributions due to the noise source, analyzer, and the DUT itself. Finally, a software utility is presented that automates the noise figure calculation using four measurements from a spectrum analyzer. The utility checks the measurement guidelines and highlights potential problem areas. It then calculates the noise figure for the DUT along with the measurement uncertainty.