Verifying RF amplifier characteristics at EMC lab

Abstract

This paper deals with the measurement of AM percent modulation of the radio-frequency fields used in RF immunity test (conducted and radiated) International standards set a requirement on the amplitude modulation depth of the RF voltages to be injected in CDN (or antennas) and prescribe a tolerance around the nominal value to be verified using a scope. Such small tolerance (5%) is difficult to measure with an oscilloscope and (moreover) other discrepancies of the modulated signal are not visible on the oscilloscope. Using a spectrum analyzer the modulation depth and the harmonic contents as well other types of distortion can be seen at a glance with higher accuracy.