Modulation of 1 MHz clock with low frequency (LF) signals to analyze common-mode radiation from printed circuit boards

A practical methodology for measurements of common mode RF currents modulated with LF noise on cables for prediction of radiated emissions up to 500 MHz for automotive scenario is presented. More specifically, when microcontroller clock frequency operating at 1 MHz rate, is modulated with a low frequency (LF) signal, emanating from a 1.5 kHz pulse train, or a switch mode power supply (200 kHz), in a printed circuit board (PCB) resulting in RF interference is investigated. A measurement methodology in detection, isolation and mitigation of LF signal at high frequency spectral band is outlined.