8163A/B, 8164A/B, 8166A/B User’s Guide 101Power Measurement 34 Press the [Close] softkey to exit the menu.How to Set the Power UnitPressing the Power Unit softkey allows you to select either W, dB, or dBmas the units in which power is displayed. The Power Unit softkey is visiblewhen you move to the [P] or [Ref ] parameters. Alternatively the PowerUnit can be changed by using the Power Meter menu.What are the Power Units ?Watts (W) are the SI unit for power measurement.You can also measure power in dB or dBm. Values displayed in these unitsare derived from measurement in Watts.By selecting dBm, the following calculation is made:Where,P dBmis the power value displayed in dBm, andP inputis the input signal level in Watts.Power, in units of dBm, is measured relative to 1 mW, it is an absolutepower measurement.By selecting dB, the following calculation is made:Where,P dBis the power value displayed in dB,P inputis the input signal level in Watts, andP refis the chosen reference power value in Watts.Power, in units of dB, is measured relative to a particular reference powervalue. For information on selecting this reference value, see How to Input aReference Level on page 103.P dB 10 P input W( )P ref W( )-------------------------log=
