【作者】 孔曦；

【导师】 沈保锁；

【作者基本信息】 天津大学 ， 通信与信息系统， 2006， 硕士

【摘要】 跳频通信技术具有良好的保密性能、抗干扰性能和多址组网性能,不但在军事通信中得到了广泛应用,而且在民用方面也越来越显示出它的优势。差分跳频技术是一种新型的跳频通信技术,它的信息携带方式不同于传统跳频技术,它是用跳变的载波之间的相关性来传送信息的。与传统跳频技术相比具有跳速高、传输带宽宽、硬件构成简单等特点,并在抗干扰、抗衰落能力上显示出了突出优势。频率合成器是跳频系统的心脏,它的各项性能指标对跳频通信系统的性能具有决定性的影响。本论文阐述了跳频技术以及差分跳频技术的基本理论,讨论了跳频通信系统中采用的三种频率合成技术:直接频率合成技术(DS, Direct Frequency Synthesis)锁相环频率合成技术(PLL,Phase-locked Loop Synthesis)直接数字频率合成技术(DDS, Direct Digital Frequency Synthesis )重点论述了DDS的工作原理,基本结构和输出频谱,并论述了以DDS和PLL相结合的组合式频率合成器。最后,本论文提出了单片机控制的,基于DDS的短波差分跳频频率合成器的设计方案。方案中采用ADI公司的新型DDS芯片AD9854作为频率合成器,单片机选用和MCS-51兼容的AT89C51,时钟采用15MHz的有源晶振。完成了输出幅度均衡的单片机控制流程设计,对椭圆函数低通滤波器的幅频特性进行了计算机仿真,并对整个方案中的各环节进行了分析。希望本论文能在今后频率合成器的设计实践中,为大家开拓新的思路提供一些参考。更多还原

【Abstract】 Frequency Hopping Communication Technique (FHCT), with features of high security, strong anti-jamming and optimal multiple access, not only has been used in military communications, but also shows more and more advantages in public day-life use. Differential Frequency Hopping Technique (DFHT) is a new type of FHCT, its method of carrying information is different with that of the traditional Frequency Hopping Technique. DFHT can achieve more desirable performance, including higher hopping rate, spectral re-use, multi-path fading mitigation, and stronger interference resistance. Furthermore Differential Frequency Hopping (DFH) system needs less hardware and can be implemented easily.Frequency Synthesizer is the heart of the FH system. Its performance has the critical influence on the over-all capability of FH system. In this paper the theory of FH and DFH have been described systematically. I also introduce three patterns of frequency synthesize techniques: Direct Frequency Synthesis (DS); Phase Lock Loop Frequency Synthesis (PLL); Direct Digital Frequency Synthesis (DDS). The character of each pattern has been analyzed in details. I take emphasis on the principle and frequency spectrum of DDS. I also want to discuss with you about a combined frequency synthesizer scheme composed of DDS and PLL.In the last part, I put forward the scheme of monolithic chip microcomputer controlled, DDS based short wave DHF frequency synthesizer. In my scheme, the following components are recommended: new-style DDS chip from ADI company, AD9854 as frequency synthesizer; monolithic chip microcomputer AT89C51, compatible with MCS-51 products; 15MHz precise and stable crystal oscillator. I make the flow-chat by monolithic chip microcomputer, the output amplitude equalization can be achieved. As the result of go though this process, I also simulate the LPF feature of amplitude-frequency by computer, and make analysis each step in the over-all scheme.I hope my paper could bring you some new ideas or new ways of practice in DDS applying.更多还原