3 Transmission Media Part 2
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Transcript of 3 Transmission Media Part 2
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ASET
Transmission
Media
Part 2
Module 1
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ASETUnguided Media
Unguided media, or wireless communication, transport
electromagnetic waves without using a physical conductor.
Instead the signals are broadcast though air and are available
to anyone who has a device capable of receiving them.
The section of the electromagnetic spectrum defined as radio
communication is divided into eight ranges, called bands,
each regulated by government authorities.
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ASETWireless transmission waves
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ASET
Electromagnetic spectrum for wirelesscommunication
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ASETPropagation of Radio Waves
Radio technology considers the earth as surrounded by twolayers of atmosphere: the troposphere and theionosphere.
The troposphere is the portion of the atmosphere
extending outward approximately 30 miles from the earth'ssurface.
The troposphere contains what we generally think of asair. Clouds, wind, temperature variations, and weather in
general occur in the troposphere. The ionosphere is the layer of the atmosphere above the
troposphere but below space.
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ASET
Propagation methods
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ASET
Ground propagation. In ground propagation, radio wavestravel through the lowest portion of the atmosphere, huggingthe earth. These low-frequency signals emanate in alldirections from the transmitting antenna and follow thecurvature of the planet. The distance depends on the power
in the signal. In Sky propagation, higher-frequency radio waves radiate
upward into the ionosphere where they are reflected back toearth. This type of transmission allows for greaterdistances with lower power output.
In Line-of-Sight Propagation, very high frequency signalsare transmitted in straight lines directly from antenna toantenna.
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ASETBands
Band Range Propagation Application
VLF 330 KHz Ground Long-range radio navigation
LF 30300 KHz GroundRadio beacons and
navigational locators
MF 300 KHz3 MHz Sky AM radio
HF 330 MHz SkyCitizens band (CB),
ship/aircraft communication
VHF 30300 MHzSky and
line-of-sight
VHF TV,
FM radio
UHF 300 MHz
3 GHz Line-of-sight UHF TV, cellular phones,paging, satellite
SHF 330 GHzLine-of-
sightSatellite communication
EHF 30300 GHzLine-of-
sightLong-range radio navigation
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ASET
transmission and reception are achieved by meansof an antenna
directional
transmitting antenna puts out focused beam transmitter and receiver must be aligned
omnidirectional
signal spreads out in all directions
can be received by many antennas
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ASETOmni directional Antennas
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ASET
Unidirectional antennas
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ASETRadio
radio is omnidirectional and microwave is directional
Radio is a general term often used to encompass
frequencies in the range 3 kHz to 300 GHz.
Mobile telephony occupies several frequency bandsjust under 1 GHz.
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ASETInfrared
Uses transmitters/receivers (transceivers) thatmodulate noncoherent infrared light.
Transceivers must be within line of sight of each
other (directly or via reflection ). Unlike microwaves, infrared does not penetrate walls.