The Research Of Specialized Receiver On Electromagnetic Leakage

The electromagnetic radiation produced by computer when it works usually contains unscramble contents, people can acquire the original information when it is detected and captured by the relative electromagnetic wave and extracted the taking digital signals, thus results in leaking information. The information leakage caused by electromagnetic radiation is one of the key techniques in computer security.TEMPEST is a technique that based on the information leakage of communication devices, it is a completely new technical subject developed from the EMC area. Studying the computer video information leakage's capture and re-emergence is the key components of TEMPEST, it is very important for assuring the computer information security. The essay introduces the research development of the technique domestic and abroad;it states in detail the theories and characteristics of computer video information electromagnetic leakage and points out that compared with screen information leakage, interface between the display-card and the cable is more valuable in study of computer video information electromagnetic leakage, and analyses the leaking spectrum according to text information also.The essay introduces the systematic structure of superheterodyne , and states the receiver's structure and design target based on that kind of system. It analyses the physical structure and electrical characteristic of varactor and introduces the general theories and typical circuit of electric tune filter. And the author introduces a electronic tune filter's structure and realization based on that theory. Based on broad band and low amplitude of the leaking signal, it brings forward a broad band, high-gain circuit based on uPC1658, and introduces the cascade form which can provide approximately 25db gain for the system. It designs the IF amplifier and demodulation circuit based on TA7680. Because of the need of receiving the high-gain signal, we bring forward a variable high-gain circuit, which can realize the relative large scope variable high-gain for the signal through the adjustment of voltage.Finally, the essay conducts the test of each functional circuit and of the whole systematic adjustment and analyses the test results and points out the next improvement step.