短波通信概論

1、The introduction of Shortwave Communication systemProfessor Yinjing GuoShandong University of Science and Technology (SDUST)Oct. 2014Who am I?1992.3-1996.8Engineer of PLA1996.81999.8Lecturer of SDUST1999.82004.12Associate professor of SDUST2004.12nowProfessor of SDUSTShortwave radioShortwave radio i

2、s used for long distance communication by means of skywave or skip propagation, in which the radio waves are reflected or refracted back to Earth from the ionosphere, allowing communication around the curve of the Earth. Shortwave radio is used for broadcasting of voice and music, and long-distance

3、communication to ships and aircraft, or to remote areas out of reach of wired communication or other radio services. Additionally, it is used for two-way international communication by amateur radio enthusiasts for hobby, educational and emergency purposes.Propagation characteristicsShortwave radio

4、frequency energy is capable of reaching any location on the Earth as it is influenced by ionospheric reflection back to the earth by the ionosphere, (a phenomenon known as skywave propagation). A typical phenomenon of shortwave propagation is the occurrence of a skip zone (see first figure on that p

5、age) where reception fails. With a fixed working frequency, large changes in ionospheric conditions may create skip zones at night. surface wave propagation: Propagating on the ground, The communication distance is less than 50KmAdvantages Unlike their relative ease in monitoring the Internet, gover

6、nment authorities face technical difficulties monitoring which stations (sites) are being listened to (accessed)Shortwave radios can be used in situations where Internet or satellite communications service is temporarily or long-term unavailable (or unaffordable).Very little infrastructure is requir

7、ed for long-distance two-way communications using shortwave radio. All one needs is a pair of transceivers, an antenna, and a source of energy ，This makes shortwave radio one of the most robust means of communications, which can be disrupted only by interference or bad ionospheric conditions.UsesInternational broadcasting， “Utility” stations（飛機通信）， Clandestine stations（秘密電臺），Numbers Stations ，Amateur radio operators，Time signal and radio clock stationsOver-the-horizon radar.Shortwave relay stationGenerally to target areas that are more than 300 km from the tra