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Analogue & Digital Signals
Communications Media
Analogue & Digital Signals
Communications Media
TOPICSTOPICS
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Group MembersGroup Members
Aqeel Aqdus 1421-310023
Muhammad Faisal Akram 1421-310252
BSCS(6th)
PRESTON UNIVERSITY ISLAMABAD
IntroductionIntroduction
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What is Signal?
Types of SignalsTypes of Signals
Analogue Signals
(voice)Digital Signals
(computer oriented data)4
Analogue versus Digital Analogue versus Digital
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Analogue Digital
Analogue SignalsAnalogue Signals
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The term "analog" comes from the word
"analogous" meaning something is similar to
something else.
Signal that is continuous in time and can
assume an infinite number of values in a
given range (continuous in time and value)
Analogue SignalsAnalogue Signals
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In the natural world communication signals
are generally analog for example: Hearing with sound waves Sight with light waves
Analog transmissionAnalog transmission
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Characteristics of Analogue SignalsCharacteristics of Analogue Signals
The three main characteristics of analogue
signals are:FrequencyAmplitude Phase
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FrequencyFrequency
Frequency is the rate of change with respectto time.
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If a signal does not change at all, its frequency is zero.If a signal changes instantaneously, its frequency is infinite.
Frequency and period are the inverse of each other.
Two signals with the same amplitude and phase,but different frequencies
Two signals with the same amplitude and phase,but different frequencies
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Amplitude (A)Amplitude (A)
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A maximum value of the signal over time.
This is the strength of the signal.
The decibel (named in honor of Alexander
Graham Bell) is a popular measure of signal
strength. Sound level Type of Sound
40db normal speech
90db lawn mowers
110db shotgun blast
120db jet engine taking off
120db+ rock concerts
Two signals with the same phase and frequency, but different amplitudes
Two signals with the same phase and frequency, but different amplitudes
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PhasePhase
This is the rate at which the signal changes
its relationship to time, expressed as degree.
Analogue signals are sent via
PSTN.Analogue signals cannot be sent via
the ISDN without being first converted to
digital.
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Three sine waves with the same amplitude and frequency.
but different phases
Three sine waves with the same amplitude and frequency.
but different phases
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Digital SignalsDigital Signals
Discrete change between high and lowphysical property (such as voltage or current) over time.
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Digital SignalsDigital Signals
In the manmade world communication signals
are generally digital for example: Sound: telephone, radio, CD Light: television, computer monitor
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Communications Media Communications Media
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IntroductionIntroduction
Communicationo The message (data
and information) is
communicated via the
signal.o The transmission
medium “carries” the
signal.
Mediao Communication
path through which
data and information can be
transmitted.
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Sender Signal Receiver
Transmission medium
Communication MediaCommunication Media
The most commonly used
data communication media include:Coaxial CableTwisted Pair CableFiber Optic CableMicrowaveSatellite
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Coaxial CableCoaxial Cable
Coaxial cable is a two wire conductor with a
large bandwidth than twisted pair cable(TPC).
It is used in television ,radio and Ethernet
LANs.In voice communication systems, each
coaxial cable supports about 60 speech
channels.
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Coaxial CableCoaxial Cable
Advantages
• Cheap to install
• Conforms to standards
• Widely used
• Greater capacity than UTP to carry more conversations
Disadvantages
• Limited in distance
• Limited in number of connections
• Terminations and connectors must be done properly
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Twisted Pair CableTwisted Pair Cable
A type of cable that consists of two
independently insulated wires twisted around
one another. One wire carries the signal while
the other wire is grounded and absorbs signal
interference. It is light weight, easy to install,
inexpensive and support many different types of
network.
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Unshielded Twisted Pair(UTP) CableUnshielded Twisted Pair(UTP) Cable
Type of cable that consists of two unshielded
wires twisted around each other. Due to its low
cost, UTP cabling is used extensively for local
area networks(LANs) and telephone
connections.
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Unshielded Twisted Pair(UTP) CableUnshielded Twisted Pair(UTP) Cable
Advantages
• A high installed base
• Cheap to install
• Easy to terminate
Disadvantages
• Very noisy
• Limited in distance
• Suffers from interference
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Shielded Twisted Pair(STP) CableShielded Twisted Pair(STP) Cable
STP is similar to UTP but with each pair
covered by an additional copper jacket or
foil wrapping. This shielding helps protect the
signals on the cables from external interference.
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Most common twisted-pair cablesMost common twisted-pair cables
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Name Type Bandwidth Applications
Cat3 UTP 16 MHz 10BASE-T and 100BASE-T4 Ethernet
Cat4 UTP 20 MHz 16 Mbit/s Token Ring
Cat5 UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet
Cat5e UTP 100 MHz 100BASE-TX & 1000BASE-T Ethernet
Cat6 UTP 250 MHz 10GBASE-T Ethernet
Fiber Optic CableFiber Optic Cable
Fiber optic cable uses electrical signals to
transmit data. It uses light. In fiber optic cable
light only moves in one direction for two way
communication to take place a second
connection must be made between the two
devices. Fiber optic cable has bandwidth more
than 2 gbps (Gigabytes per Second).
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Fiber Optic CableFiber Optic Cable
Advantages
• High capacity
• Low attenuation
• Can go long distance
Disadvantages
• Costly
• Hard to install
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MicrowaveMicrowave
Microwave transmission is line of sight
transmission. The transmit station must be in
visible contact with the receive station. This sets
a limit on the distance between stations
depending on the local geography. Support at
least 30km distance.
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MicrowaveMicrowave
Advantages
• Medium capacity
• Medium cost
• Can go long distances
Disadvantages
• Noise interference
• Geographical problems due to line of sight requirements
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SatelliteSatellite
In satellite communication, signal transferring between
the sender and receiver is done with the help
of satellite. In this process, the signal which is
basically a beam of modulated microwaves is sent
towards the satellite. Then the satellite amplifies the
signal and sent it back to the receiver’s antenna present
on the earth’s surface. So, all the signal transferring is
happening in space. Thus this type of communication
is known as space communication.
Two satellites which are commonly used in satellite
communication are Active and passive satellites.32
SatelliteSatellite
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Each communications satellite in geo-stationary
orbit around the earth which can support
thousands of speech channels and about 4 TV
channels simultaneously.
SatelliteSatellite
Advantages
• Low cost per user (for PAY TV)
• High capacity
• Very large coverage
Disadvantages
• High install cost in launching a satellite
• Receive dishes and decoders required
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