1、Current Status and Developing Tendency for High Frequency Communications Abstract: High frequency (HF) communications play an important role in the field of their communications because of their skywave propagation characteristics. In this paper, two advanced HF radios are selected to introduce the
2、current status for HF communications. After analyzing the demand for future HF communications,the developing tendency for HF communications techniques is also presented. Key words: high frequency (HF) communications； adaptive； high speed modem；anti-jam； network 1 Introduction The shortwave communica
3、tion said that the high frequency (HF) correspondence, the frequency of use scope is 330MHz, mainly uses the sky wave after the ionospheric reflection, does not need to establish relay station then to realize the remote communication. Simultaneously because the ionized layer cannot destroy the chara
4、cteristic, the shortwave communication is one of throughout military command important means that but must obtain a more widespread application, the shortwave communication also waits for in the following several aspects enhancing: 1) Correspondence reliability. Shortwave communication sky wave diss
5、emination because of ionized layer change and multipath propagation influence, but is extremely unstable, signaling multi-diameter phenomenon is serious, retards in a big way, the Doppler shift is big, declines seriously. Simultaneously the shortwave channel is the band width the channel which limit
6、s, the radio-frequency spectrum is been crowded, between the channel does to harass seriously, obtains the reliable correspondence quality has been the shortwave communication pursue goal. 2) Data transfer rate. The tradition shortwave communication rises with difficulty a substantial clause is data
7、 transfer rate is very low (does not surpass 600bit/s). In informationized war the military correspondence transmissions information, has developed from the simple direction order to such as the radar sounding data, the computed result, the high speed image facsimile and so on some requests the data
8、 to pass on the speed high information. 3) Antijamming ability. Because the shortwave communication is under the war condition director the only reliable way, rate shortwave disturbance equipment develops along with the disturbance technologys development as well as some new great merit the successf
9、ully, shortwave communications antijamming way must diversify, the intellectualization, has in different electromagnetic environment survivability. 4) Network. Along with the correspondence more and more to the network development, future shortwave communication should also more consider the network
10、 use and the network management. Uses net to wind the type correspondence, may cause the shortwave communication the information content and the information processing speed enhances greatly, but may also select the best link in the net, increases the information link survivable the nature and saves
11、 the nature obstinately. 2 shortwave communication development present situation Because since the shortwave communication in the military correspondence the interchangeability, the shortwave communication has not started to receive in the 1980s takes seriously. Because many kinds of new technique t
12、he techniques application, like the channel auto-adapted technology, the difference frequency-hopping spread spectrum, the wide band direct sequence spread spectrum technology, the channel coding technology, the channel balanced technology, short wave group the net technology, shortwave communicatio
13、n way existences many questions are solved； And along with the microcomputer, the mobile communication and microelectronic technologys rapid development, person uses the microprocessor, the digital signal processing, enhanced the shortwave communication unceasingly the quality and the data transfer
14、rate, the shortwave communication and the equipment obtains the very big development, many companies has promoted some performance fine equipment and the system one after another, compared with famous included: USs shortwave communication broadcasting station modernization , Australias HF-90H, Swede
15、ns KV90, USs CHESS, American HARRIS Corporations RF-5800 system , Collins companys SELSCAN system and so on. 1) HF-90H Subminiature frequency-hopping shortwave broadcasting station HF-90H promotes by Australian Q-MAC Corporation, the most prominent characteristic was picks to use the intelligent sid
16、eband frequency-hopping spread spectrum.At present the world various broadcasting stations plant provides is the digital voice. The digital voice frequency-hoppings shortcoming is jumps the frequency frequency spectrum insufficient hiding, is distinguished easily, breaks the code and tracks, as show
17、n in Figure 1 . But HF-90H picks the intelligent sideband frequency-hopping pattern which uses is using SSB (Single Sideband Signal) the modulation system biography puts words in somebodys mouth the news number, the instantaneous frequency spectrum looks like the noise very much, in the frequency-ho
18、pping frequency spectrum, because the frequency-hopping code concealment in the voice fluctuation, is unable to determine that the frequency-hopping frequency the establishment, as shown in Figure 2. Fig.1 Instantaneous and accumulated over time spectrum view of HF digital voice ho p per Fig.2 Insta
19、ntaneous and accumulated over time spectrum view of HF SSB voice hopper The shortwave channel is often doping the intense noise and the unwanted signal, for example by the Broadcasting station either Fixed stations strong signal blocking or the clutter crosstalk, in addition fades to fall with the multi-diameter effect creates is unstable, causes the shortwave environment very severe. HF-90H uses the
