With the development of the technology, life is filled with increasing information equipment. When they work, a great deal of information will be radiated. For the leaked information, an interception system is built with USRP (Universal Software Radio Peripheral), and the line synchronization signal was extracted with a method called cepstrum. Compared with the method of autocorrelation, the new method is more conducive to find the interval between the neighboring peaks. And the system has more obvious advantages compared to the traditional system composed of AD (Analog-Digital) and DSP (Digital Signal Process) devices. It is small in size, inexpensive, reconfigurable, and it is convenient to operate. The results of experiments indicate that 16 fonts can be reconstructed clearly. It fully reflects its superior performance.