Airborne SystemsVocabulary
Переведите сочетания на русский язык a) telephone call ___________________________________ ground station____________________________________ digital modulation_________________________________ geostationary satellites_____________________________ public switched telephone network ___________________ b) in-flight terrestrial-based RADIOTELEPHONE satellite-based
Ответьте на вопросы • What are the two types of in-flight radiotelephones? • In what way are calls made in terrestrial-based telephones? • In what way are calls made in satellite-based ones? • In what band does the terrestrial flight telephone system operate? • How far from each other should satellite-based systems be spaced? • Which systems may be employed anywhere in the world? Why?
In addition to the terrestrial cellular telephone systems, there also exist several systems that are used for making telephone calls to the public switched telephone network (PSTN) by passengers on aircraft. These inflight radiotelephones are of two types: terrestrial-based and satellite-based. In terrestrial-based telephones, telephone calls are placed directly from an aircraft to a ground station; in satellite-based ones, telephone calls are relayed via a geostationary satellite to a ground station. In Europe the terrestrial flight telephone system was introduced in 1992 and has been widely used since that date. The system employs digital modulation method and operates in the 1,670 – 1,675 and 1,800 – 1,805 – megahertz bands. In order to cover most of Europe, the ground stations must be spaced every 50 to 70 kilometres. The system based on satellite transmission is available through the use of geostationary – orbit satellites. Satellite – based systems have their specific properties: they are absolutely independent of ground stations. Thus, they may be employed anywhere in the world.
|
