11. :
transfer [træns'fɜ:] - ,
amplify ['æmplɪfaɪ] -
transduction [træns'dʌkʃn] -
transducer [trænz'djuːsə ], [trɑːn-] - ; ;
vary ['vɛərɪ] - , ;
convert [kən'vɜːt] - ;
AD converter - - ,
DA converter - - ,
shielding - ( - )
cable ['keɪbl]
coaxial cable [ˌkəu'æksɪəl] -
twisted pair cable - ,
diminish [dɪ'mɪnɪʃ] ,
convey [kən'veɪ]
transition [træn'zɪʃ(ə)n ],[ træn'sɪʒ(ə)n] ,
digitization ['dɪʤɪtaɪzeɪʃ(ə)n] 
, ,
quantization [ˌkwɔntaɪ'zeɪʃ(ə)n] - ( )
bounded
guided -
jacket - ()
optical fiber (=fibre) [faɪbə] - ; ,
induce [ɪn'djuːs] ;
simplex -
half-duplex [hɑːf'djuːpleks] - ,
full duplex - , ,
multiplex [mʌlti pleks]
12. :
As mentioned above, information can be transferred in two forms, analog and digital. An analog format is that in which information is transmitted by modulating a continuous transmission signal, such as amplifying a signal's strength or varying its frequency to add or take away data. For example, telephones take sound vibrations and turn them into electrical vibrations of the same shape before they are transmitted over traditional telephone lines. The process of changing energy from one form into another is called transduction. Some common examples of transducers are a microphone which converts sound into an electrical signal, or an antenna which converts electromagnetic waves into electric current and vice versa.
The main merit of an analog signal is its fine definition. However, its primary disadvantage is that any system has noise i.e., random unwanted variation leading to signal loss and distortion. Electrically, these effects of noise can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair. Other methods of conveying an analog signal are to use modulation or to change the phase of the base signal.
In contrast to analog communications, digital communications are the transfer of discrete messages. These messages may be digital (when originating from a data source, for example, a computer) or may start out as analog, being then converted to digital for modulation, converted back to analog for radio frequency transmission and, finally, converted to digital again. The conversion from the real world analog signal to its discretized digital counterpart is called analog-to-digital (AD) conversion. Analogously, a transition in the opposite direction is shorthanded as DA conversion.
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A digitization process carried out by an AD converter (ADC) is broken into two stages. The first stage is sampling by which a continuous-time signal is reduced to a discrete-time sequence. At the second stage, the ADC converts the continuous range of values to the finite set of discrete values by rounding the input values to the nearest integer numbers. This process known as quantization usually results in deviations from the theoretically perfect reconstruction capabilities, collectively referred to as distortion.
The type of a signal, analog or discrete, used for communications depends on how far the signal has to travel and the medium it will have to pass through. In telecommunications, transmission media are classified into two categories: bounded, or guided media, and wireless, or unguided media. In both cases, communication is in the form of electromagnetic waves.
Bounded media are physical links through which signals are confined to a narrow path and energy waves are guided along a solid medium. Bounded media are made up of an external conductor (usually copper) bounded by jacket material. Three common types of bounded media are twisted pair cables, coaxial cables, and optical fibers. Plain wires can be used, but they are generally unreliable in screening out noise and are rarely considered.
Wireless transmission requires no physical means to define the path a transmitted signal takes. Instead, the waves radiate by inducing a current in a transmitting antenna and then travel through the air or free space. Examples of these media include microwave, radio and satellite transmission.
Any transmission may be simplex, half-duplex, or full-duplex. In simplex transmission, signals are transmitted in only one direction; one station is a transmitter and the other is the receiver. In half-duplex operation, both stations may transmit, but only one at a time. In full duplex operation, both stations may transmit simultaneously. Telecommunications in which multiple transmitters and multiple receivers have been designed to cooperate and to share the same physical channel are called multiplex systems.
13. :
merit ['merɪt]
counterpart ['kauntəpɑ:t] - , , ,
confine ['kɔnfaɪn] (n)
(v) [kən'faɪn]
shorthand ;
deviation [ˌdiːvɪ'eɪʃ(ə)n]
simultaneous [ˌsɪm(ə)l'teɪnɪəs] - ,
14. , :
1. How is information transmitted in an analog format? 2. What is transduction? 3. What transducers do you know? 4. What are the advantages and disadvantages od analog transmission? 5. Are there any ways to reduce noise in analog signal transmission? 6. What is AD conversion used for? 7. What does a digitization process consist of? 8. What are bounded media? 9. How can wireless transmission be described? 10. How are telecommuncations classified depending on the number of transmitters and receivers and the direction of simultaneous transmission?
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15. , :
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; .
16. :
Continuous transmission signal; sound vibrations; fine definition; random unwanted variation; theoretically perfect reconstruction; bounded by jacket material; simplex transmission; full-duplex operation; multiplex systems.
17. :
1. Information can be transferred two forms. 2. Telephones take sound vibrations and turn them electrical vibrations the same shape. 3. Noise in a sommunications system is understood as random unwanted variation leading signal loss and distortion. 4. In contrast analog communications, digital communications are the transfer of discrete messages. 5. A digitization process carried by an AD converter is broken into two stages. 6. In bounded media energy waves are guided a solid medium. 7. In the half-duplex operation, both stations may transmit, but only one... a time.
) : convert; vary; modulate; transfer; transit; define; shield; capable;
B) : discrete; digit; class
C) : currency, presence, frequency, absence
19. :
1) The main merit of an analog signal a) is that any system has noise.
2) The process of changing energy
from one form into another b) is its fine definition.
3) The primary disadvantage of
an analog signal c) is that in which information is
transmitted by modulating a continuous transmission signal.
4) An analog form d) is called AD conversion.
5) The conversion from the
real world analog signal to its
discretized digital counterpart e) is called transduction.
20. :
1. In order for any digital device to successfully interface with an analog signal, that signal must be digitized by means of an analog-to-digital converter or ADC. 2. Any signal, in order to be processed by numerical computing devices, have to be reduced to a sequence of discrete samples, and each sample must be represented using a finite number of bits. 3. Bound transmission occurs when the electromagnetic energy follows a path through a material like a copper cable or fiber optic cable. This is by far the most common type of medium. 4. Unbound media sometimes are referred to as wireless. This type of communication can include radio waves, microwaves, and different forms of light.
21. :
. ( /) . , , - . : ( - () ), - ( - ()- ).
UNIT 4
TEXT 1. Modulation
1. :
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detect [dɪ'tekt] - ,
carrier signal - -,
current ['kʌr(ə)nt ]; ['kɜːr(ə)nt]
alternating current (AC) -
direct current (DC) -
delay [dɪ'leɪ] - ,
pulse code modulation (PCM) - - ,
pulse amplitude modulation (PAM) - - ,
pulse duration modulation (PDM) - - ,
pulse position modulation (PPM) - - ,
sideband - ()
single sideband (SSB) - , ( )
two-way radio -
Phase Shift Keying (PSK) -
Quadrature Amplitude Modulation (QAM) - ( , )
2. :
One way to improve the transmission of a signal is modulation. Modulation is the process of facilitating the transfer of information over a medium. For example, sound transmission in air has limited range for the amount of power your lungs can generate. To extend the range your voice can reach, we need to transmit it through a medium other than air, such as a phone line or radio. The term modulation refers to how information (voice in this case) is encoded so that it can be successfully sent through a medium (wire or radio waves), and can later be detected by a receiver.
There are two main reasons to blend data into a carrier signal. The first reason is to reduce the wavelength for efficient transmission and reception (the optimum antenna size is or of a wavelength). A typical audio frequency of 3000 Hz will have a wavelength of 100 km and would need an effective antenna length of 25 km! By comparison, a typical carrier for FM is 100 MHz, with a wavelength of 3 m, and could use an antenna only 80 cm long. The other reason is to allow simultaneous use of the same channel, called multiplexing. If there were a group of people transmitting signals between 20 Hz and 20 kHz the probability of one signal interfering with another would be very high. With modulation, each unique signal can be assigned a different carrier frequency (like radio stations) and still share the same channel.
The process of modulation means taking either an analog or a digital signal and turning it into an analog signal. The difference between a digital modulation and analog modulation is the nature of the signal that is modulating the carrier. The carrier is always analog - for most of radio and telecommunications today, it is alternating current (AC) in a given range of frequencies.
Common modulation methods include: 1) amplitude modulation (AM), in which the voltage applied to the carrier is varied over time; 2) frequency modulation (FM), in which the frequency of the carrier waveform is varied in small but meaningful amounts; 3) phase modulation (PM), in which the natural flow of the alternating current waveform is delayed temporarily. These are sometimes known as analog, or continuous wave modulation methods, to distinguish them from pulse code modulation (PCM), which is used to encode both digital and analog information in a binary way. The varieties of PCM include pulse amplitude modulation (PAM), pulse duration modulation (PDM), and pulse position modulation (PPM).
Radio and television broadcast stations typically use AM or FM. Most two-way radios use FM, although some employ a mode known as single sideband (SSB).
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More complex forms of modulation are Phase Shift Keying (PSK) and Quadrature Amplitude Modulation (QAM). Optical signals are modulated by applying an electromagnetic current to vary the intensity of a laser beam.
An electromagnetic carrier can be of any frequency depending on the medium and the communications needs. Most media dictate what type of carrier (its frequency, amplitude) can propagate through it and the type of distortions it will suffer while travelling through it.
Anything that is wireless is analog always. Wired signals can be digital or analog. Communications inside a computer are examples of pure digital communications, digital data over digital medium. LAN communications are digital data over analog medium. The AM and FM radios are examples of analog data over analog medium.
In general, when we talk about a digital system, we are usually talking about digital information over an analog medium. However, there are exceptions. PCM, for example, is a form of modulation where there is no carrier, so that makes a pure digital system.
3. :
facilitate [fə'sɪlɪteɪt] - ;
lung [lʌŋ] (n)
temporary ['temp(ə)r(ə)rɪ] -
exception [ɪk'sepʃ(ə)n ], [ek-] -
LAN (local area network) -
4. , :
1. Why is it necessary to use modulation? 2. What does the term modulation refer to? 3. What are two main reasons to blend data into a carrier signal? 4. Is it possible not to use the analog carrier? 5. How is the process that allows simultaneous use of the same channel called? 6. What kind of signals is modulated by applying an electromagnetic current to vary the intensity of a laser beam?
5. , :
; , ; ; ; ; ; .
6. :
Sound transmission, a carrier signal, typical audio frequency, simultaneous use, the probability of one signal interfering, a different carrier frequency, continuous wave modulation methods, wired signals.
7. :
1. Modulation improves the transmission a signal. 2. If we want to extend the range our voice can reach, we transmit it a medium other than air. 3. The first reason to blend data a carrier signal is to reduce the wavelength for efficient transmission and reception. 4. AM, FM and PM are referred as analog, or continuous wave modulation methods to distinguish them PCM. 5. Examples of analog data analog medium are the AM and FM radios.
8. :
