2009-7-27 P,1
Unit 10
Communications Channel
Chapter Three
&Part4 Extensive Reading@ Part 1 Notes to Text
@Part5 Notes to Passage& Part 2 Word Study
@Part3 Practice on Text @Part6 Practice on Passage
2009-7-27 P,2
@ Part 1 Notes to Text
1) It may be defined by a physical wire that connects
communicating devices,or by a radio,laser,or other
radiated energy source that has no obvious physical
presence,连接通讯设备的物理导线、无线电波、激光或其它那些无形的辐射能源，都可说成是信道。
注释,该句是复合句，主语 it指代 a communications channel；谓语是 may be defined; 其状语由两个并列的介词短语构成，分别是 by a physical wire,a radio,laser,和 by other radiated
energy source；定语从句 that connects communicating
devices修饰 a physical wire； that has no obvious physical
presence则修饰 other radiated energy source。
Communications Channel
2009-7-27 P,3
2） Information sent through a communications channel has a
source from which the information originates,and a destination
to which the information is delivered,通过信道发送的信息都有一个信息源和送达的目的地。
注释,该句中的 sent through a communications channel是过去分词短语作定语，修饰主语 information; from which the information
originates和 to which the information is delivered是介词前置的定语从句，分别修饰两个宾语,a source 和 a destination。
2009-7-27 P,4
3） Although information originates from a single source,there
may be more than one destination,depending upon how many
receive stations are linked to the channel and how much energy
the transmitted signal possesses,虽然信息产生于一个信息源，但送达的目的地却可能不止一个，这往往取决于连接信道接收站的数量和已发送信号所拥有的能量高低。
注释,连词 Although引导的是让步状语从句；该句的主句是 there
may be more than one destination；其中短语 more than表示“不止”，“多于”；现在分词短语用作伴随状语，介词 upon的宾语是由
how many 和 how much引导的宾语从句构成的。
4） It really consists of two simplex channels,a forward channel
and a reverse channel,linking the same points,其实全双工通道是由两条单工信道构成的，其中一条是正向通道，一条是反向通道，它们的连接点相同。
注释,主语 It指代,全双工通道”；名词短语 a forward channel and
a reverse channel是宾语 two simplex channels的同位语 ； 现在分词短语 linking the same points是伴随状语。
End
2009-7-27 P,5 End
1,channel n,信道
2,pathway n,路径；通道
10.multibit n,多数据位
11.encapsulation n,压缩 ;包装
3,wire n,导线 12.facilitate v,使容易,使便利
4.laser n,激光 13.duplex adj,双工的
5,radiate v,辐射 14.simultaneously adv,同时地
6,presence n,存在 15.garbled adj,混乱的，引起误解的
7,originate v,起源；发端 16.simplex adj,单工的
8,possess v,拥有 17.half-duplex adj,半双工的
9,encapsulate v,压缩 ； 打包 18.full-duplex adj,全双工的
& Part 2 Word Study
2009-7-27 P,6
Task 1,Listening training
Dictation of some key words
Directions,You will hear some key words twice,most of which are taken from
the Word Study,Then finish the Crossword Puzzle,(See you book p,)
2,Dictation of some key expressions
Directions,You will hear some key expressions twice,most of which are
taken from this text,Then you are asked to complete the missing words.
@Part3 Practice on Text
1) by a ____________wire
2) radiated_______________
3) ___________message units
4) ______________of bytes
5) a radio______________
6) message______________
physical
energy source
multibit
collection
station
exchange
2009-7-27 P,7
Read and Reply
Directions:Students are required to read aloud the whole text after
the teacher,Then give short answers to the following questions:
a) What is the information represented by in a digital
communications channel?
b) What is a collection of bytes grouped into?
Task 2,Read,Write and Translate
In a digital communications channel,the information is
represented by individual data bits,which may be
encapsulated into multibit message units,
A collection of bytes may itself be grouped into a frame
or other higher-level message unit,
A full-duplex channel allows simultaneous message
exchange in both directions,
c) Which allows simultaneous message exchange in both
directions,a half-duplex channel or a full-duplex channel?
2009-7-27 P,8
( )1) Information sent through a communications channel
has only an source from which the information originates,
( )2) A byte,which consists of sixteen bits,is an example of a
message unit that may be conveyed through a digital
communications channel.
( )3) The message source is the transmitter,and the
destination is the receiver,
( )4) Messages may flow in two directions,but never at the
same time,in a half-duplex system,
( )5) It really consists of two simplex channels,a forward
channel and a reverse channel,linking the same points,
Read and Judge
End
F
F
T
T
T
2009-7-27 P,9
Directions:Read the following short passage,Complete it by filling in the missing words.
A,region B,independently C,hexagons D,limiting E,cell
F,local G,coverage H,completely I,range J,transmitters
Mobile communication work by 1)______ transmitter powers,This
restricts the 2)_____ of communication to a small 3)_______,Outside
this region,other 4)______can operated 5)______,Each region is
termed a 6)_______,These cells are often represented in diagrams as
7)_______,In practise the cell shape is determined by 8)_______
propagation characteristics,Together the cells will 9)_______ cover
the area supplied with mobile communication10)________.
Read and Complete
End
D
I A
J B
E
C F
H
G
2009-7-27 P,10
1)五架飞机以五环图案为中心向各方飞开去。（ radiate）
2)将军在危急关头的出现稳定了军心。（ presence）
3)那位商业巨头在许多城市都有房产。 (possess)
4)那个受过惊吓的孩子只能含糊地说出交通事故的经过。
(garbled)
5)这种建筑风格起源于明朝。 (originate)
Read and Translate
Directions:Put the following sentences into English,using the words or phrases given.
End
Five planes radiated from the pattern of the five rings.
The captain’ s presence during the crisis had a calming effect
in the army,
The business giant possesses real estate in many cities,
The frighten child could only give a garbled account of the
traffic accident,
The style of architecture originated from / with the
Ming dynasty,
2009-7-27 P,11
Transmission lines
A transmission line is a pair a conducting wires held apart by an
insulator(绝缘体 )or dielectric (绝缘体 ),They come in a variety of
construction geometries(几何学 ),The simplest and least expensive
form is two-wire (ribbon) cable,Twisted pair cable consists of two
wires sheathed(包裹 ) in an insulator and twisted(绞合 ) together,
Shielded(保护 )pair cable contains two wires surrounded and
separated by a solid dielectric,The dielectric is contained within a
copper braid(网状 ),that shields the conductors from external noise
sources,The entire construction is housed in a flexible,waterproof
cover,
The use of this kind of cable is limited by two factors,attenuation
and cross-talk,There are three principle sources of attenuation,
Resistance (or impedance 电阻 /阻抗 ) losses are simply the loss
resulting from the resistance of the wires,This loss is minimized(减至最小量 ) by the choice of a metal with low resistivity(阻抗 ),Copper is
chosen for this reason,(Gold is even better,and is in fact used on
satellites to reduce losses.) Dielectric losses are caused by the
heating effects
&Part4 Extensive Reading
2009-7-27 P,12
when a varying electric field passes through a dielectric
(insulator),Radiation losses occur because the cable acts
as an antenna,All these losses increase with frequency,
When a transmission line can act as an antenna,it can also
act as a receiver,Lines prone to (倾向于 ) radiation loss are
also susceptable to (易于 )pick-up,or cross-talk,The first two
types described above are particularly prone to this fault,
The shielded pair is designed to reduce this pick-up,
All these lines have strong attenuation at frequencies above
1MHz,They are generally used for low bit-rate
communication,Two-wire ribbon cable is standard for the
connection of individual telephone receivers,Twisted pair(s)
is the normal method of connection for computer terminals
and short high bit-rate connections.
2009-7-27 P,13
Attenuation increases with both frequency and length,It is usually
specified in dB/m at a particular frequency,Because of this fact,it is
not possible to give hard-and-fast rules concerning the bandwidth
availability of transmission lines,A twisted pair can support rates of
several Mb/s over short distances (metres),but over long distances
(kilometres) will be completely unsuitable at these data-rates,
For long distances,or data-rates in excess of several Mb/s,coaxial
cable is used,Coaxial(同轴的 )cable has a central wire,surrounded by
a dielectric,in turn concentrically sheathed in a braided conductor,
The cable is finally surrounded in a water-proof,flexible sheath,
Coaxial cable is familiar to you — it is the cable used to connect
your television ariel,The supreme advantage of this method of
construction is its resistance to radiation losses,The outer
conductor acts to shield out any external fields,whist preventing
any internal fields escaping,
2009-7-27 P,14
Until the advent of optical fibre,coaxial lines were the
standard method of long-distance,high bit-rate
communication,They are expensive (but getting cheaper,
especially as demand rises),and only used where necessary,
Typical attenuation values for coaxial cable are 10dB/Km at
10KHz,50dB/Km at 500MHz,For very long-haul routes,
repeaters and equalisers(均衡器 )are necessary,
For short runs (metres),very high bit-rates are sustainable on
coaxial cable -- up to 1Gb/s,At rates above this,the cables
develop a waveguide action,and dispersion(散射 )becomes a
problem,Although it is possible to design coaxial cable that
has still improved performance,these developments have
been largely superceded(代替 ) by optical fibre.
End
2009-7-27 P,15
@Part5 Notes to Passage
1) Shielded pair cable contains two wires surrounded and
separated by a solid dielectric,The dielectric is contained
within a copper braid,that shields the conductors from
external noise sources,The entire construction is housed in
a flexible,waterproof cover,屏蔽双绞线则是由两根用固体绝缘体封装和隔离的导线构成的。而该固体绝缘体裹着一层铜丝网，
以避免导体受外界噪音源的干扰。而导线的整身装在一个柔软而防水的外套里。
注释,此处用三个句子由内到外来描述 shielded pair cable的结构,
第一个句子是简单句,句中的过去分词短 surrounded and
separated by a solid dielectric是定语,修饰 two wires； 第二个句子是被动句 。 非限定性定语从句 that shields the
conductors from external noise sources修饰 a copper braid；
第三个句子中的 is housed in相当于 be placed / located in。
2009-7-27 P,16 End
2) Lines prone to radiation loss are also susceptable to pick-up,
or cross-talk,易于产生辐射衰减的导线往往容易产生串扰现象。
注释,形容词短语 prone to radiation loss修饰 lines；形容词短语
susceptable to pick-up,or cross-talk则是表语；要注意的是：形容词 prone和 susceptable后面的 to是介词而非不定式符号，所以，
后面只能接名词或动名词。
3） They are expensive (but getting cheaper,especially as
demand rises),and only used where necessary,其价格非常昂贵（虽然随着需求量的上升而越来越便宜），所以只是在必要的地方才会使用。
注释,该句可视为复合句； where necessary是一个省略的地点状语从句,即 where they are necessary。
2009-7-27 P,17
1.Listening Challenge
Spot Dictation
Directions,The following passage will be heard 3 times,During the second time,you
are required to put the missing words or phrases in the numbered blanks according to
what you hear,The third time is for you to check your answers,Now the passage
begins.
An antenna is a transducer designed 1)___________or receive radio waves
which are a class of electromagnetic waves,In other words,antennas
convert radio frequency electrical 2)_________into electromagnetic waves
and vice versa,Antennas are used 3)_______________such as radio and
television broadcasting,point-to-point radio communication,wireless LAN,
radar,and space exploration,Antennas usually work in air or 4)__________,
but can also be operated under water or 5)______________ soil and rock at
certain frequencies for short6)___________,Physically,an 7)________is an
arrangement of conductors that 8)___________a radiating electromagnetic
field in response to an applied alternating voltage and the associated
alternating 9)___________________,or can be placed in an electromagnetic
field so that the field will induce an alternating current in the antenna and a
voltage between its terminals,Some antenna devices (parabola,horn
antenna) 10)__________________________to another type of antenna,
@Part6 Practice on Passage
End
to transmit
currents
in systems
outer space
outer space
distances antenna
generate
electric current
just adapt the free space
2009-7-27 P,18
End of this Unit
Unit 10
Communications Channel
Chapter Three
&Part4 Extensive Reading@ Part 1 Notes to Text
@Part5 Notes to Passage& Part 2 Word Study
@Part3 Practice on Text @Part6 Practice on Passage
2009-7-27 P,2
@ Part 1 Notes to Text
1) It may be defined by a physical wire that connects
communicating devices,or by a radio,laser,or other
radiated energy source that has no obvious physical
presence,连接通讯设备的物理导线、无线电波、激光或其它那些无形的辐射能源，都可说成是信道。
注释,该句是复合句，主语 it指代 a communications channel；谓语是 may be defined; 其状语由两个并列的介词短语构成，分别是 by a physical wire,a radio,laser,和 by other radiated
energy source；定语从句 that connects communicating
devices修饰 a physical wire； that has no obvious physical
presence则修饰 other radiated energy source。
Communications Channel
2009-7-27 P,3
2） Information sent through a communications channel has a
source from which the information originates,and a destination
to which the information is delivered,通过信道发送的信息都有一个信息源和送达的目的地。
注释,该句中的 sent through a communications channel是过去分词短语作定语，修饰主语 information; from which the information
originates和 to which the information is delivered是介词前置的定语从句，分别修饰两个宾语,a source 和 a destination。
2009-7-27 P,4
3） Although information originates from a single source,there
may be more than one destination,depending upon how many
receive stations are linked to the channel and how much energy
the transmitted signal possesses,虽然信息产生于一个信息源，但送达的目的地却可能不止一个，这往往取决于连接信道接收站的数量和已发送信号所拥有的能量高低。
注释,连词 Although引导的是让步状语从句；该句的主句是 there
may be more than one destination；其中短语 more than表示“不止”，“多于”；现在分词短语用作伴随状语，介词 upon的宾语是由
how many 和 how much引导的宾语从句构成的。
4） It really consists of two simplex channels,a forward channel
and a reverse channel,linking the same points,其实全双工通道是由两条单工信道构成的，其中一条是正向通道，一条是反向通道，它们的连接点相同。
注释,主语 It指代,全双工通道”；名词短语 a forward channel and
a reverse channel是宾语 two simplex channels的同位语 ； 现在分词短语 linking the same points是伴随状语。
End
2009-7-27 P,5 End
1,channel n,信道
2,pathway n,路径；通道
10.multibit n,多数据位
11.encapsulation n,压缩 ;包装
3,wire n,导线 12.facilitate v,使容易,使便利
4.laser n,激光 13.duplex adj,双工的
5,radiate v,辐射 14.simultaneously adv,同时地
6,presence n,存在 15.garbled adj,混乱的，引起误解的
7,originate v,起源；发端 16.simplex adj,单工的
8,possess v,拥有 17.half-duplex adj,半双工的
9,encapsulate v,压缩 ； 打包 18.full-duplex adj,全双工的
& Part 2 Word Study
2009-7-27 P,6
Task 1,Listening training
Dictation of some key words
Directions,You will hear some key words twice,most of which are taken from
the Word Study,Then finish the Crossword Puzzle,(See you book p,)
2,Dictation of some key expressions
Directions,You will hear some key expressions twice,most of which are
taken from this text,Then you are asked to complete the missing words.
@Part3 Practice on Text
1) by a ____________wire
2) radiated_______________
3) ___________message units
4) ______________of bytes
5) a radio______________
6) message______________
physical
energy source
multibit
collection
station
exchange
2009-7-27 P,7
Read and Reply
Directions:Students are required to read aloud the whole text after
the teacher,Then give short answers to the following questions:
a) What is the information represented by in a digital
communications channel?
b) What is a collection of bytes grouped into?
Task 2,Read,Write and Translate
In a digital communications channel,the information is
represented by individual data bits,which may be
encapsulated into multibit message units,
A collection of bytes may itself be grouped into a frame
or other higher-level message unit,
A full-duplex channel allows simultaneous message
exchange in both directions,
c) Which allows simultaneous message exchange in both
directions,a half-duplex channel or a full-duplex channel?
2009-7-27 P,8
( )1) Information sent through a communications channel
has only an source from which the information originates,
( )2) A byte,which consists of sixteen bits,is an example of a
message unit that may be conveyed through a digital
communications channel.
( )3) The message source is the transmitter,and the
destination is the receiver,
( )4) Messages may flow in two directions,but never at the
same time,in a half-duplex system,
( )5) It really consists of two simplex channels,a forward
channel and a reverse channel,linking the same points,
Read and Judge
End
F
F
T
T
T
2009-7-27 P,9
Directions:Read the following short passage,Complete it by filling in the missing words.
A,region B,independently C,hexagons D,limiting E,cell
F,local G,coverage H,completely I,range J,transmitters
Mobile communication work by 1)______ transmitter powers,This
restricts the 2)_____ of communication to a small 3)_______,Outside
this region,other 4)______can operated 5)______,Each region is
termed a 6)_______,These cells are often represented in diagrams as
7)_______,In practise the cell shape is determined by 8)_______
propagation characteristics,Together the cells will 9)_______ cover
the area supplied with mobile communication10)________.
Read and Complete
End
D
I A
J B
E
C F
H
G
2009-7-27 P,10
1)五架飞机以五环图案为中心向各方飞开去。（ radiate）
2)将军在危急关头的出现稳定了军心。（ presence）
3)那位商业巨头在许多城市都有房产。 (possess)
4)那个受过惊吓的孩子只能含糊地说出交通事故的经过。
(garbled)
5)这种建筑风格起源于明朝。 (originate)
Read and Translate
Directions:Put the following sentences into English,using the words or phrases given.
End
Five planes radiated from the pattern of the five rings.
The captain’ s presence during the crisis had a calming effect
in the army,
The business giant possesses real estate in many cities,
The frighten child could only give a garbled account of the
traffic accident,
The style of architecture originated from / with the
Ming dynasty,
2009-7-27 P,11
Transmission lines
A transmission line is a pair a conducting wires held apart by an
insulator(绝缘体 )or dielectric (绝缘体 ),They come in a variety of
construction geometries(几何学 ),The simplest and least expensive
form is two-wire (ribbon) cable,Twisted pair cable consists of two
wires sheathed(包裹 ) in an insulator and twisted(绞合 ) together,
Shielded(保护 )pair cable contains two wires surrounded and
separated by a solid dielectric,The dielectric is contained within a
copper braid(网状 ),that shields the conductors from external noise
sources,The entire construction is housed in a flexible,waterproof
cover,
The use of this kind of cable is limited by two factors,attenuation
and cross-talk,There are three principle sources of attenuation,
Resistance (or impedance 电阻 /阻抗 ) losses are simply the loss
resulting from the resistance of the wires,This loss is minimized(减至最小量 ) by the choice of a metal with low resistivity(阻抗 ),Copper is
chosen for this reason,(Gold is even better,and is in fact used on
satellites to reduce losses.) Dielectric losses are caused by the
heating effects
&Part4 Extensive Reading
2009-7-27 P,12
when a varying electric field passes through a dielectric
(insulator),Radiation losses occur because the cable acts
as an antenna,All these losses increase with frequency,
When a transmission line can act as an antenna,it can also
act as a receiver,Lines prone to (倾向于 ) radiation loss are
also susceptable to (易于 )pick-up,or cross-talk,The first two
types described above are particularly prone to this fault,
The shielded pair is designed to reduce this pick-up,
All these lines have strong attenuation at frequencies above
1MHz,They are generally used for low bit-rate
communication,Two-wire ribbon cable is standard for the
connection of individual telephone receivers,Twisted pair(s)
is the normal method of connection for computer terminals
and short high bit-rate connections.
2009-7-27 P,13
Attenuation increases with both frequency and length,It is usually
specified in dB/m at a particular frequency,Because of this fact,it is
not possible to give hard-and-fast rules concerning the bandwidth
availability of transmission lines,A twisted pair can support rates of
several Mb/s over short distances (metres),but over long distances
(kilometres) will be completely unsuitable at these data-rates,
For long distances,or data-rates in excess of several Mb/s,coaxial
cable is used,Coaxial(同轴的 )cable has a central wire,surrounded by
a dielectric,in turn concentrically sheathed in a braided conductor,
The cable is finally surrounded in a water-proof,flexible sheath,
Coaxial cable is familiar to you — it is the cable used to connect
your television ariel,The supreme advantage of this method of
construction is its resistance to radiation losses,The outer
conductor acts to shield out any external fields,whist preventing
any internal fields escaping,
2009-7-27 P,14
Until the advent of optical fibre,coaxial lines were the
standard method of long-distance,high bit-rate
communication,They are expensive (but getting cheaper,
especially as demand rises),and only used where necessary,
Typical attenuation values for coaxial cable are 10dB/Km at
10KHz,50dB/Km at 500MHz,For very long-haul routes,
repeaters and equalisers(均衡器 )are necessary,
For short runs (metres),very high bit-rates are sustainable on
coaxial cable -- up to 1Gb/s,At rates above this,the cables
develop a waveguide action,and dispersion(散射 )becomes a
problem,Although it is possible to design coaxial cable that
has still improved performance,these developments have
been largely superceded(代替 ) by optical fibre.
End
2009-7-27 P,15
@Part5 Notes to Passage
1) Shielded pair cable contains two wires surrounded and
separated by a solid dielectric,The dielectric is contained
within a copper braid,that shields the conductors from
external noise sources,The entire construction is housed in
a flexible,waterproof cover,屏蔽双绞线则是由两根用固体绝缘体封装和隔离的导线构成的。而该固体绝缘体裹着一层铜丝网，
以避免导体受外界噪音源的干扰。而导线的整身装在一个柔软而防水的外套里。
注释,此处用三个句子由内到外来描述 shielded pair cable的结构,
第一个句子是简单句,句中的过去分词短 surrounded and
separated by a solid dielectric是定语,修饰 two wires； 第二个句子是被动句 。 非限定性定语从句 that shields the
conductors from external noise sources修饰 a copper braid；
第三个句子中的 is housed in相当于 be placed / located in。
2009-7-27 P,16 End
2) Lines prone to radiation loss are also susceptable to pick-up,
or cross-talk,易于产生辐射衰减的导线往往容易产生串扰现象。
注释,形容词短语 prone to radiation loss修饰 lines；形容词短语
susceptable to pick-up,or cross-talk则是表语；要注意的是：形容词 prone和 susceptable后面的 to是介词而非不定式符号，所以，
后面只能接名词或动名词。
3） They are expensive (but getting cheaper,especially as
demand rises),and only used where necessary,其价格非常昂贵（虽然随着需求量的上升而越来越便宜），所以只是在必要的地方才会使用。
注释,该句可视为复合句； where necessary是一个省略的地点状语从句,即 where they are necessary。
2009-7-27 P,17
1.Listening Challenge
Spot Dictation
Directions,The following passage will be heard 3 times,During the second time,you
are required to put the missing words or phrases in the numbered blanks according to
what you hear,The third time is for you to check your answers,Now the passage
begins.
An antenna is a transducer designed 1)___________or receive radio waves
which are a class of electromagnetic waves,In other words,antennas
convert radio frequency electrical 2)_________into electromagnetic waves
and vice versa,Antennas are used 3)_______________such as radio and
television broadcasting,point-to-point radio communication,wireless LAN,
radar,and space exploration,Antennas usually work in air or 4)__________,
but can also be operated under water or 5)______________ soil and rock at
certain frequencies for short6)___________,Physically,an 7)________is an
arrangement of conductors that 8)___________a radiating electromagnetic
field in response to an applied alternating voltage and the associated
alternating 9)___________________,or can be placed in an electromagnetic
field so that the field will induce an alternating current in the antenna and a
voltage between its terminals,Some antenna devices (parabola,horn
antenna) 10)__________________________to another type of antenna,
@Part6 Practice on Passage
End
to transmit
currents
in systems
outer space
outer space
distances antenna
generate
electric current
just adapt the free space
2009-7-27 P,18
End of this Unit
