Design And Analysis Of Frequency Hopped Device With Differential Frequency Hopping Technique

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.