Text Recovery from EM Leakage of Computers

A text receiving and recovery system was designed for EM information leakage from computers.After EM leakage is intercepted by a broad band antenna,band-pass filtered and amplified,the vertical and horizontal synchronization signals are captured by a phase locked loop circuit.The synchronization signals are sampled and processed by an analog-digital converter to get digital video signals.Then,the noises of video signals are filtered using an average filter.At last,the text in the digital video is recovered using a matched filter.An experimental result shows that text can be recovered from EM leakage 12 m away for a Pentium 486 computer with a CRT display,and the signal to noise ratios of the vertical and horizontal synchronization signals are increased by 18.7 dB with the average filter.