针对近地表频率域电磁探测对发射信号的要求，以直接数字频率合成技术为理论基础，利用单片机与可编程数字逻辑器件FPGA构建硬件控制平台，设计具有通用性的多频信号产生系统，实现单频及多频（双频、三频等）正弦信号的产生。经验证，该方法产生的波形可控性强、谐波失真低、分辨率高，克服了位流法对线圈负载稳定性要求高，伪随机法不能任意设定频率并且THD （总谐波失真）高的缺点。%In this paper, in order to meet the requirements of the transmitting signal in shallow surface FEM do-main, based on the DDS theory, using single-chip microcomputer and programmable logic device as the hardware control platform, the universal multi-frequency signal generating system is realized. A single frequency, multi-fre-quency (dual-band, tri-band) sine signal can be produced in this system. The experiment results show that, wave-forms produced in this way have good quality, pure frequency spectrum and high resolution. Some other methods’ defects can be overcome, such as the high requirement of stream method to the stability of coil load and the pseu-do-random method which cannot arbitrarily set the frequency and the higher THD (total harmonic distortion) . Theoretical simulation and experimental results verify the effectiveness of the method.
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