View
231
Download
0
Category
Preview:
Citation preview
8/18/2019 tranmission media.pdf
1/16
Transmission medium
• A transmission medium is any material substance which
can propagate waves or energy.
•Electromagnetic radiation can be transmitted through
media such as optical fiber, twisted pair wires, coaxialcable, dielectric-slab waveguides. They may also pass
through any physical material which is transparent to the
specific wavelength, such as water, air, glass, or concrete.
Electromagnetic waves do not require a transmissionmedium unlike mechanical waves, and so can travel
through vacuum of free space.
8/18/2019 tranmission media.pdf
2/16
•Guided (or bounded)
Waves are guided along a solid medium
such as a transmission line.
• Wireless (or unguided)
Transmissions and receptions are achievedby means of an antenna.
For telecommunications purposes in the United States,
Federal Standard 1037C, transmission media are classified
as one of the following:
8/18/2019 tranmission media.pdf
3/16
Guided or Bounded
Parallel two-wire line
•consists of two wires that are generally spaced from 2 to 6 inches apart
by insulating spacers.
•most often used for power lines, rural telephone lines and telegraph
lines.
•sometimes used as a transmission line between a transmitter and an
antenna or between and antenna and a receiver.
•Has a simple construction.
•High radiation losses and electrical noise pick-up because of lack of
shielding.
8/18/2019 tranmission media.pdf
4/16
Two-wire
Ribbon Type
Line
•also known as “Twin Lead”. •commonly used to connect a televisionreceiving antenna to a home television set.•Same as two-wire open line except uniform
spacing is assured.•the wires are embedded in a low-loss dielectric.(polyethylene).
8/18/2019 tranmission media.pdf
5/16
Twisted Pairs
conductorsInsulating jackets
•Consists of two insulated wires twisted together to form a
flexible line without the use of spacers.
•Not used for transmitting high frequency because of high
dielectric loss.
•types of twisted pair including STP, UTP, and plenum. STP
means shielded twisted pair, UTP means unshielded twisted
pair and plenum wiring is non toxic when burning.
•Twisted pair wiring carries the data in electrons. The reason
behind twisting the pairs is to cancel out interference. These
are the most common cables used in networks and carry the
signal up to 100 meters.
8/18/2019 tranmission media.pdf
6/16
Shielded
Cable Pair
• consists of parallel conductors separated from each other and
surrounded by a solid dielectric. The conductors are containedwithin a braided copper tubing that acts as an electrical shield.
Rubber cover protects the line from moisture and mechanical
damage.
• Advantage- the conductors are balanced to ground; that is,
the capacitance between the wires is uniform throughout thelength of the line.
• The uniform spacing braided copper shield isolates the
conductors from stray magnetic fields.
8/18/2019 tranmission media.pdf
7/16
Coaxial Cable
• Two types: rigid (air) fill coaxial line and flexible (solid) coaxial line.•Used extensively for high frequency application to reduce losses and to
isolate transmission paths.
•it has two conductors, one wire in center and a conductive sheath around it,
that share a "common axis".•example of RG-58 with a BNC connector used in cable television.
• The wiring standards used for network coax are different from those used
for cable TV.
•50 ohm cable, available as RG-8 and RG-11. Used in Thick Ethernet, alsocalled "Ether Hose".
•50 ohm cable, available as RG-58. Used in Thin Ethernet .
•75 ohm cable, available as RG-59. This one is for TV, not networks.
•93 ohm cable, available as RG-62. Used in ARCnet.
8/18/2019 tranmission media.pdf
8/16
Rigid (Air) Fill
Coaxial Line
•
The center conductor is surrounded coaxially by a tubularouter conductor and the insulating material is air. The outer
conductor is physically separated from the center conductor
by a spacer (Pyrex, polystyrene, etc. non conductive material).
•
Advantages- ability to minimize radiation losses, interferenceof from other lines are reduced.
•Disadvantages- expensive to construct, must be kept dry to
prevent leakage between conductors, still excessive to limit
the practical length of the wire.
8/18/2019 tranmission media.pdf
9/16
Solid
Flexible
Coax Cable
•The outer conductor is braided, flexible, and coaxial to the center
conductor. The inner conductor is flexible copper wire that can be
either solid or hallow.
•solid nonconductive polyethylene material that provides both
support and electrical isolation between the inner and outer
conductors.
•Polyethylene plastic is a solid substance that remains flexibleover a wide range of temperatures.
•Coaxial cable is good for transmitting data over long distances
and for reliably supporting higher data rates when using LESS
sophisticated equipment.
8/18/2019 tranmission media.pdf
10/16
Optical Fiber
•can be glass or plastic, and is meant to conduct light instead of
electricity.
•
The conductor is called a waveguide, and is covered withcladding, a material to reflect the signal back into the center of
the conductor.
•two modes: single mode conducts a single signal, while multi-
mode conducts many signals simultaneously.
•harder to install and splice and expensive.
•carries the signal in photons, there is no interference and fiber
can not be tapped into and data stolen.
•Fiber is good for high speed, high capacity transmission
because signal is transmitted quickly.
8/18/2019 tranmission media.pdf
11/16
Wireless or Unguided
Terrestrial Microwave
•Frequency range - 4 to 6 or 21 to 23 GHz
•Cost - moderate to high•Installation - difficult
•Capacity -1 Mbps to 10 Mbps
• Attenuation - relatively high, varies with weather
•
Immunity from EMI - low
•Requires line of sight
•Requires fewer repeaters or amplifiers
•Long haul telecommunication services
• Voice and TV transmission
•Point-to-point links between buildings.
•microwave:
8/18/2019 tranmission media.pdf
12/16
Terrestrial and Satellite Links
8/18/2019 tranmission media.pdf
13/16
Satellite systems•Relay used to link ground stations
•Functions as an amplifier or a repeater
•Can provide point-to-point to multi-point connectivity
• Television distribution
•Long distance telephone transmission
•Private business networks
•Frequency range - 11 to 14 GHz
•Cost - high
•
Installation - very difficult•Capacity -1 Mbps to 10 Mbps
• Attenuation - relatively high, varies with weather
•Immunity from EMI - low
8/18/2019 tranmission media.pdf
14/16
Broadcast Radio
• Omni-directional
• Does not require complex antennas
•
Antennas need not to be precise aligned.• FM radio
• VHF and UHF television
• Data networks
8/18/2019 tranmission media.pdf
15/16
Infra-red
Line of sight is needed
No frequency allocation is needed.
Provides point-to-point connectivity
•Frequency range - 100 GHz to 1000 THz
•Cost - low to moderate
•
Installation - moderate to difficult•Capacity - 1 to 16 Mbps
• Attenuation - varies with weather and light purity
•Immunity from EMI - moderate
Infrared systems come in two types: point-to-point and
broadcast. Point-to-point systems are like the remote
controls we use for televisions.
8/18/2019 tranmission media.pdf
16/16
Broadcast infraredused in single room settings, as these waves willbounce off walls, but not penetrate them.
Factors for Broadcast infrared:
Frequency range - 100 GHz to 1000 THz
Cost - low
Installation - simple
Capacity - up to 1 Mbps Attenuation - high
Immunity from EMI - low
Recommended