Research Of Instrument For Detection FSK Signal

With the advantages of antijamming and limited band of spectrum in effect, extensive adaptation, large information, celerity response,and flexibility, Frequency-Shift Auto-Closeddown system has been widely used in Railway communication.However,a portable,real-time detector with high precision for spectrum of Frequency-Shift Keying singnal and experimental studies on developing such a device are presented.The theory of FSK are analyzed,the equations of presenting FSK singal are derived and the spectrum surveyed In consideration of the high SNRof Railway FSK signal ,metnods by orthogonal I,Q two-way processing and re-sampling not enough are put forward to detect signal's two frequencies,amplitudes and low modulating frequency.Two key problems are solved both in theory and in experiment.One is to intercept part of signal with single frequency from FSKsampling sequence.The other is to decide the fold times of spectrum caused by resampling not enough. In addition,the method of extended precision using FFT combining DFT with high precision in local band is derived to balance the conflict between real-time and high precision.According to the emulating algorithm,TMS320C25 DSP is chosen to be the CPU of the detector.Other hardware units such as the 12-Bit A/Dconverter which works by semi-parallel mode with 7 KHz sampling rate,the 64k* 16-Bit EPROM,the 32k* 16-Bit RAM and the display using LCM are designed.Finally , some of emulating and detecting results are provided in this dissertation.