1. All transmitted signals are to some extent by the environment through which they propagate. 2. Reduction in power is called . 3. is any undesired change in the amplitude or phase of any component of an information signal that causes a change in the overall waveform of the signal. 4. The of channel attenuation as the signal frequency is varied is known as the attenuation spectrum. 5. and distortion are commonly introduced by all transmission media. 6. Since all practical conductor materials are characterized by some electrical resistance, part of the electric current is always lost by to heat.
9. :
1. All transmitted signals are degraded by the environment which they propagate. 2. The principal cause power loss is dissipation. 3. A radiating antenna converts a time-varying electric current an electromagnetic wave or field. 4. Signal degradation generally falls three types: noise, distortion, and attenuation. 5. Propagation of the wave is always accompanied a flow of electric current through the conductor. 6. Optical wavelengths are naturally suited high-rate broadband telecommunication. 7. Both noise and distortion are commonly introduced all transmission media, and they both result in errors in reception.
Text 2. Wire Media Types
10. :
Bundled -
hard-drawn -
tensile corrosion ['ten(t)saɪl] [kə'rəuʒ(ə)n] - -
insulate ['ɪnsjəleɪt] -
crosstalk -
foil -
jacket -
shield [ʃiː ld] - ,
shielded twisted pair (STP) - ( )
unshielded twisted pair (UTP) -
impedance [ɪm'piːd(ə)n(t)s] - ,
twist [twɪst] -
axis ['æksɪs] -
strand [strænd] ,
solid conductor -
stranded conductor - ;
skin-effect - -,
dissipation factor -
braid -
flame retardant [rɪˈtɑːd(ə)nt] -
attenuation constant -
11. :
Most modern wire transmission is conducted through the metallic-pair circuit, in which a bundled pair of conductors is used to provide a forward current path and a return current path. The most common conductor is hard-drawn copper wire, which has the benefits of low electrical resistance, high tensile strength, and high resistance to corrosion. The basic types of wire media found in telecommunications are twisted pair cables and coaxial cables.
Twisted pair cabling was initially used as the main connector in telephone communication. It consists of two separate, insulated copper wires twisted together at specific intervals to help block crosstalk interference.
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The most commonly used form of twisted pair is unshielded twisted pair (UTP). It is just two insulated wires twisted together. Data communication cables and normal telephone cables are of this type. Shielded twisted pair (STP) differs from UTP in that it has a foil jacket that helps prevent crosstalk and noise from outside source. In data communications there is a cable type called FTP (foil shielded pairs) which consists of four twisted pair inside one common shield (made of aluminium foil).
The impedance of a cable is actually a function of the spacing of the conductors, so separating the conductors significantly changes the cable impedance at that point.
When many twisted pairs are put together to form a multi-pair cable, individual conductors are twisted into pairs with varying twists to minimize crosstalk. Specified color combinations are used to provide pair identification.
The coaxial cable is a flexible transmission line and typically is used to connect two electronic instruments together.
A coaxial cable consists of two conductors separated by a dielectric material. The center conductor and the outer conductor, or shield, are configured in such a way that they form concentric cylinders with a common axis (hence co-axial).
The center conductor may be made of various materials and constructions. Most common constructions are solid or stranded conductors. Solid conductors are used in permanent, infrequently handled or low flex applications and stranded conductors used in flexible cable applications. Common materials include copper, tinned or silver plated copper, copper clad steel and copper clad aluminum. Plated copper is used to aid in solderability of connectors or to minimize corrosion effects. Because of a phenomenon known as skin-effect, copper clad materials may be used in higher frequency applications.
Insulation, or dielectric materials, are used to provide separation between the conductors. It is desirable that the material has stable electrical characteristics (dielectric constant and dissipation factor) across a broad frequency range. The most common materials used are polyethylene (PE), polypropylene (PP), fluorinated ethylene propylene (FEP) and polytetrafluoroethylene (PTFE).
The outer conductor is typically made from a number of smaller aluminum or copper conductors combined together. These conductors are woven together to form a braid around the dielectric core. For higher frequency applications, a second braid or aluminum foil tapes are often added to improve attenuation and shield effectiveness.
The jacket material serves as a protective covering from the environment and may also serve to add in the overall flame retardant properties of the cable. Typical materials include polyvinyl chloride (PVC), PE, FEP and polyvinylidene fluoride (PVDF).
An optical cable is one of the easiest ways to connect your devices together to transfer a digital sound signal. Also known as SPDIF or Toslink, an optical cable consists of a fibre optic that transfers light rather than an electrical signal as a digital coaxial cable would. There are many different types of cable available, and which one you choose really depends on what you will be using the cable for.
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12. :
spacing ['speɪsɪŋ] - ,
flexible ['fleksəbl]
outer ['autə] ,
handle ['hændl] - -
tin[tɪn]
weave (woven; woven) - ,
plated -
clad steel - ( - , .)
solderability [səuldərə'bɪlɪtɪ] - ,
polyethylene [pɔlɪ'eθɪliːn] - (PE)
polypropylene [pɔlɪ'prəupɪliːn] - (PP)
polytetrafluoroethylene [pɒlɪtɛtrəflʊərəʊ'ɛθɪliːn] - ,
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1. What kind of cabling was initially used as the main connector in telephone communication? 2. How is the form of twisted pair with just two insulated wires twisted together called? 3. What is the difference between STP and UTP? 4. What is the way to minimize crosstalk? 5. Is it possible to identify pairs in a multi-pair cable? 6. Where are solid and stranded conductors used?
14. , :
, ; ; ; ( ); ; ; ; ( ):
15. :
Data communication cables, multi-pair cable; minimize crosstalk; dielectric material; concentric cylinder; solid conductor; stranded conductor; aluminum foil tape; flame retardant properties; digital sound signal.
16. :
