Research And Design Of Differential Frequency Hopping HF Synthesizer Based On DDS

Differential Frequency Hopping (DFH) is a new type of frequency hopping (FH) communication technique. Its feature is the different method of carrying information with traditional FH technique. DFH transmits information by the correlation between hopping frequency carriers. When DFH is applied to HF communication, HF radio can achieve desirable performance of high hopping rate within a wide HF band, which will improve the data rate and capabilities of anti-jamming and anti multipath fading. This type of FH system will be the one of directions of future HF communication.Direct Digital Synthesis (DDS) is a new generation of frequency synthesis after Direct Synthesis (DS) and PLL frequency synthesis. DDS is a technique for using digital data processing blocks as a means to generate a frequency- and phase- tunable sine wave or other continuous waveform. It's the preferred technique for applications requiring high hopping rate and excellent phase noise performance. In this paper, we make a systemic research on DDS technique. The structure, basic principle and frequency spectrum are discussed in detail. As spur is the key reason limiting DDS's application, we analyze three factors impact spectrum of DDS, and give the solutions to decrease the spur.Hopping rate is the key parameter that determines performance of FH system, so fast FH synthesizer becomes very important. Several design schemes are discussed in this paper, including methods of improving locking speed of PLL and getting higher frequency from DDS. By comparison, a new scheme is put forward.In the last part, the scheme of DFH HF synthesizer is described. DDS chip AD9852 is selected as synthesizer, and TI's DSP chip TMS320C6201 is selected as controller. Interfaces between DSP and DDS, and other key circuit are discussed in detail. By practical circuit experiment, the design realizes high hopping rate, and pure spectrum, completely meets design requirements.