Compromising Emanations of LCD TV Sets

Abstract

This study attempts to characterize the radiated compromising emanations from four typical television sets with liquid-crystal display (LCD), in particular the predictability of format and timing parameters. Three were found to emit clear ultrahigh frequency radio signals visually related to the displayed image, from the display controller or its low-voltage differential signaling link to the LCD panel. Although the input signals to all four products followed the same TV standard, the timing parameters of their emanations differed substantially. Some also frequency-modulate their pixel clock to improve compliance with electromagnetic-interference limits. All digitally rescale the input image to the respective display size. The frame rate at which the display panel is driven is, if at all, only loosely phase locked to the input signal. These observations have implications for eavesdroppers, for the design of test standards to limit compromising emanations from video displays, and for the practicality of detecting the mere presence of an active television receiver by correlating the emanations of the circuitry driving its display panel with a known broadcast TV input signal.