中文摘要：

计算机显示系统辐射发射出含有屏幕信息的电磁波，在远场用接收机可隐秘截获．为了快捷有效地找出截获屏幕信号的最佳频段，提出了一种基于通用设备的方法．首先，在个人计算机关机及开机且显示特制黑白竖条纹图像情况下分别多次测量10MHz～1GHz频段的频谱，通过频谱相减判断出极可能含有屏幕信息的大致频段；然后，在点频及其谐波频点附近查找特制图像信号，若显示全黑图像时此峰值信号消失则可判断其为特制图像信号；最后，综合考虑频点处特制图像信号峰值大小和背景电磁噪声，挑选出最佳截获频段．截获实验结果表明，所选频段可还原出最佳屏幕图像．

英文摘要：

The visual display unit of a personal computer（PC） emits electromagnetic waves that contain the information from the PC display. The information signals can be received and reconstructed secretly in the far field. To choose the best frequency range for receiving the compromising emanations effectively and quickly, a method based on the common equipments is proposed. Firstly, the frequency spectrum of 10 MHz to 1 GHz are measured about 10 times respectively when the PC is displaying special image with white-black vertical strips and power off. The frequency range which may contain the display information can be obtained through frequency subtraction. And then, the special image signal is searched around the dot frequency and harmonics. If the special signal disappears when displaying the total black image, it can be judged to be the real special signal. Finally, the best receiving frequency range can be chosen by comprehensively considering the background electromagnetic noise and the peak value of the special im- age signal in the frequency point. Experiment shows when intercepting the computer display, the optimal image could be restored within the chosen frequency range.