1. A cable has a solid copper or copper-clad-steel centre conductor surrounded by a non-conductive dielectric insulating material. 2. The dielectric is surrounded by foil and/or copper braid/s which form the outer conductor and also shield against electromagnetic interference (EMI). 3. The outer conductor/shield is encased in a PVC. 4. Twisted pair cable consists of a pair of insulated wires together. 5. Cable twisting helps to reduce noise pickup from outside sources and on multi-pair cables. 6. When cable is twisted at constant twist over the length of the cable, a cable with well defined characteristic impedance is formed. 7. Characteristic of twisted pair is determined by the size and spacing of the conductors and the type of dielectric used between them.
17. :
1. Most modern wire transmission is conducted the metallic-pair circuit. 2. The jacket material serves as a protective covering the environment. 3. A coaxial cable consists two conductors separated by a dielectric material. 4. When many twisted pairs are put together to form a multi-pair cable, individual conductors are twisted pairs with varying twists. 5. Twisted pair cabling consists of two separate, insulated copper wires twisted together specific intervals.
18. :
A) : devise, define, propagate, identify, connect, improve, attenuate, add, configure, resist, radiate
B) : environment, optics, protection, availability, dissipation
C) : reception, reduction, degradation, conversion
19. :
Losses are incorporated into the transmission-line model with the addition of a distributed resistance in series with the inductor and a distributed conductance in parallel with the capacitor. Additional distributed circuit elements can be incorporated into the model in order to describe additional effects. For example, the linear capacitors could be replaced with reverse-biased varactor diodes and the propagation of nonlinear solitons could be studied.
A transmission line transmits energy (electric power, acoustic waves or electromagnetic waves) from one point to another as efficiently as possible with minimum energy loss. Energy can be directed through a regular electric wire but with enormous losses.
20. :
, - , . . . -, , , . -, , . (core), , , . , , , . . .
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UNIT 7
Text 1. Fiber Optics
1. :
be subject (to) ['sʌbʤɪktˌtuː] - (-)
reflection [rɪ'flekʃ(ə)n] -
boundary ['baund(ə)rɪ] -
eliminate [ɪ'lɪmɪneɪt ], [ə-] - ,
cladding ['klædɪŋ] -
layer ['leɪə] -
bundle ['bʌndl] -
multi-mode fiber - -
single-mode fiber -
core [kɔː] - ,
coating -
covering - ;
2. :
Fiber optics (or optical fibre) refers to the medium and the technology associated with the transmission of information as light impulses along a strand of glass or plastic. A fiber-optic strand carries much more information than a conventional copper wire and is far less subject to electromagnetic interference (EMI). Optical fibers of very pure glass are able to carry light over long distances ranging from a few inches or centimeters to more than 100 miles (160 km) with little dimming, owing to it they can be used to illuminate and observe hard-to-reach places.
Fiber optics is based on the optical phenomenon known as total internal reflection. With the simplest form of optical fiber, light entering one end of the fiber strikes the boundary of the fiber and is reflected inward. The light travels through the fiber in a succession of zigzag reflections until it exits from the other end of the fiber. Other forms of optical fibers are designed in such a way that the zigzagging of the light is greatly reduced or virtually eliminated.
The fiber optic strand is constructed in several layers. Most optical fibers made today consist of at least two parts: a core through which the light is transmitted and a protective coating called cladding (either glass or plastic) - that surrounds the core and helps prevent light from leaking from the core. The cladding bends or reflects inward the light rays that strike its inside surface. The core, coating and covering are collectively referred to as a strand. Fiber strand sizes are always referred to in terms of the diameter of the core. Some individual fibers are thinner than human hair and measure less than 0.00015 inch (0.004 mm) in diameter. A detector, such as a photosensitive device or the human eye, receives the light at the other end of the fiber.
Fig. 6. Optical fibers
Fiber strands are typically bundled within a cable. Optical fiber bundles are either coherent or incoherent. In a coherent bundle, the fibers are arranged so that images, as well as illumination, can be transmitted. In incoherent bundles, the fibers are not arranged in any particular way and can transmit only illumination.
There are two basic types of optical fibers: single-mode fibers and multi-mode fibers. Single mode fibers are designed for the transmission of a single ray as a carrier and are used for high-speed signal transmission over long distances. They have much smaller cores than multi-mode fibers, and they accept light only along the axis of the fibers. Tiny lasers send light directly into the fiber. Multi-mode fibers are designed to carry multiple light rays. They have much larger core diameter compared to those of single-mode fibers, and they accept light from a variety of angles. Multi-mode fibers use more types of light sources and cheaper connectors than single-mode fibers. They are mostly used for communication over shorter distances.
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The first studies of fiber optics were made in the late 1800s, but practical development did not begin until the early 1950s. The development of fiber optics was spurred by the introduction of lasers in the early 1960s and by the production of the first optical fibers of very pure glass in 1970. The commercial use of fiber optics, especially in communications systems, developed rapidly in the 1980s.
Today the uses of optical fibers are numerous. Almost all telephone long-distance (cross country) lines are now fiber optic. Fiber-optic cables are also the common medium whenever people talk about the cable TV system or the Internet.
In medicine, optical fibers enable physicians to look and work inside the body through tiny incisions without having to perform surgery. They are used for endoscopes - instruments for viewing the interior of hollow organs in the body. They can also be used for insertion into blood vessels to give a quick, accurate analysis of blood chemistry.
In scientific research and in manufacturing, fiber optic devices carry light to and from hazardous areas, vacuum chambers, and confined spaces within machines. Some instruments use optical-fiber coils as a sensing device; so optical fibers are used to measure temperature, pressure, acceleration, and voltage in industries.
3. :
dimming -
virtually ['vɜːʧuəlɪ ], ['vɜːtjuəlɪ] - ,
leak -
spur [spɜː] -
incision [ɪn'sɪʒ(ə)n] -
surgery ['sɜːʤ(ə)rɪ] -
confined space -
acceleration [əkˌselə'reɪʃ(ə)n] -
4. , :
1. What does the term fiber optics refer to? 2. Why is it possible to use optical fibers to illuminate and observe hard-to-reach places? 3. How does the light travel through the fiber? 4. Where is a protective coating situated? 5. What is the difference between coherent and incoherent bundles? 6. How many types of optical fibers exist and what is the difference between them? 7. How are optical fibers used?
5. , :
; ; ; ; ; ; ; ; ().
6. :
Light impulse; pure glass; zigzag reflections; telephone long-distance (cross country) lines; physician; vacuum chamber.
7. :
