, , , - .
Poltava was written by Pushkin in 1828.
to be (Participle II), . III .
, to be, - Participle II.
Indefinite Passive
Present I am (am not) asked. Am I asked?
He, She, It is (isnt) asked. Is he asked?
You, We, They are (arent) asked. Are you asked?
Past I, He, She, It was (wasnt) asked. Was he asked?
You, We, They were (werent) asked. Were you asked?
Future I, We shall (shant) be asked. Shall we be asked?
You, He, She, It will (wont) be asked. Will you be asked?
Exercise. , - . .
1. His friend often invites him to international conferences.
2. We shall build a new house next year.
3. Bell invented the telephone in 1876.
Communication Satellite
, .
Artificial, via, serve, tower, launch, fuel, adjust, cause, power, frequency, mutual, division, assign
Words to be leant
artificial satellite
to facilitate
via
relay tower
low-noise
launch ,
capacity
rotation rate
solar cell
to supply ,
adjust
to offset ,
to cause , ,
reference point
to complete ,
to reduce
power output
range
mutual interference
multiplexed
frequency band ,
Text
A communication satellite is an artificial satellite placed into orbit around Earth to facilitate communication on Earth. Most long-distance radio communication across land is sent via microwave relay towers. The towers, 30 to 60 m (100 to 200 ft) high, are typically spaced 30 to 50 km (20 to 30 mi) apart, and 100 of them are needed to cross the United States. In effect, a satellite serves as a tall microwave link or a cable, it can interconnect any number of stations that are included within the antenna beams of the satellite rather than simply the two ends of the microwave link. The concept of using a satellite repeater was first proposed by Arthur C. Clarke in the October 1945 issue of Wireless World. The development of powerful rockets in the mid-1950s and the simultaneous development of sensitive low-noise receiving equipment made communication satellites a realistic consideration.
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The period from 1958 to 1963 was one of experimentation with both active satellites, those electronic instrumentation, and passive satellites, those which simply reflected signals. On Dec. 18, the U.S. Army places Score in a low altitude orbit. It had only one voice cannel and could retransmit messages directly or store them for later playback. On Aug. 1960, NASA launched ECHO, a passive aluminized plastic balloon, 30 m (100 ft) in diameter, into an orbit 1 600 km (1000 mi) above the Earth. In 1962 experiments were conducted on TELSTAR and RELAY, medium-altitude active satellites with the capacity of the television channel or several hundred voice channels. In 1963, SYNCOM 2 became the first
synchronous satellite with a period matching the Earths rotation rate. These satellites proved the concepts and were the later commercial satellite design.
Communication satellites are platform that house radio receivers and their antennas receive signals from the Earth stations, and amplify and pass the signals to a transmitter and antenna, with sufficient power to the amplifiers (about 500 watts in Intelsat IV); fuel to periodically adjust the satellites position to offset forces caused by the Sun and Moon; and altitude control equipment to keep the satellites antenna pointed properly at the Earth, using either the Sun, the edge of the Earth, or radio beacon on Earth as a reference point. Telemetry encoders and transmitters measure voltages, currents, temperatures, and other parameters describing the condition of the satellite and transmit this information to Earth. Finally, a structure must house all this equipment. For example, an Intelsat V weighs more than 1 950 kg (4 300 lb).
The major Earth stations that communicate with these satellites typically comprise an antenna about 30 m (100 ft) in diameter, a receiver that is cooled to 14 K in order to reduce its noise, and a radio transmitter with a power output in the range of several hundred to several thousand watts to send signals to the satellite. Smaller Earth stations are also used, but on a more restrictive basis because of their greater demands on satellite capacity.
International and domestic satellites use frequency bands that already heavily used by terrestrial radio relay stations: 5 925 to 6 425 megahertz or MHz (1 hertz = 1 cycle per second) from Earth station to satellite; and 3 700 to 4 200 MHz from satellite to Earth station. Mutual interference is avoided by appropriate location of the Earth stations; for example, they are not located within major telecommunications centers. Some satellite systems operate on the basis of frequency division each Earth stations is assigned, a different radio frequency on which are multiplexed, or packaged, all of the voice channels carried by that station. Alternatively, speech signals can be converted to digital pulses, and such pulses from the various stations are interleaved in time and amplified in the satellite through a common receiver/transmitter. In order to meet the needs of increased communications traffic, projected at more than 1000 000 circuits in the 1990s, speech will be converted to digital bits, a method already used to a great extent in communications networks.
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Additional capacity is obtained by using the same frequency band several times over multiple narrow beams from the satellite, and by extending the
frequency band to the 11 and 14 GHz region and eventually to other bands. Private business satellites for a wide variety of services are becoming common, and the availability of higher-powered satellites permits smaller antennas for Earth stations, with modest traffic demands. (The range of 12.2 to 12.7 GHz, for example, is already reserved for direct broadcasting to individual users). Satellites are coming into routine use for communications to ships and planes. The trend will be toward higher capacity at lower cost for each circuit. In some areas of the world, satellites can broadcast directly to individual homes.
I. , .
1. A communication satellite is(where, how, what)
2. Most long- distance radio communication is sent(when, why, how)
3. A satellite serves as(whose, who, what, how)
4. Arthur C. Clarke proposed(why, which, when, what)
5. The U.S. Army places Score in(what, when, where)
6. NASA launched ECHO on(why, how, when, where)
7. Communication satellites amplify and pass signals to(what, where, why, how)
8. Telemetry encoders and transmitters measure(who, how, what)
9. Mutual interference is avoided(why, who, how, where)
10. Additional capacity is obtained(why, when, where, how)
II. , ,
III. , ,
Unit 11.
Grammar Revision
