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Thursday, May 10, 2012

12th week:unbounded / unguided media


Different between bounded and unbounded media
·        Bounded media are those that use cables for transmitting electricity or light;
·        Unbounded media does not require cabling and includes satellite, microwave and radio transmission.
·        Wireless connections, including 802.11b and 802.11a, are examples of unbounded media.
·        Today, bounded media continue to be more common than unbounded.
Unbounded media / unguided media
-         Translate electromagnetic wave without physical conductor.
-         Signal = broadcasting thru air/water
-         Available for anyone who has a device capable of receiving them
-         2 type of microwave:
1.         Terrestrial Microwave



§  Require line-of-sight transmission and reception equipment
§  The taller the antennas, the longer the sight distance
§  The higher, the stronger
§  So…Usually built on hills / mountains
§  One way direction signal
§  Install system(repeater) with antennas to increase distance
§  2 type of antennas
1.         Parabolic dish
o   Same as it’s name, in a dish shape
o   good at catching a wide range of signal waves
o   directing to a common point(focus)
o   Every wave parallel to the line of sight reflects back to the focus on a common point


2.      Horn
o   looks like a gigantic scoop
o   broadcasts the assembled signals that are deflected outward in a series of narrow parallel beams by the curve head
o   signals are received in a manner are deflected down into the stem
2.      Satellite microwave
§  same principle as terrestrial microwave
§  acting as a super tall antenna and repeater
§  single bounce
§  capability = anywhere on earth
§  high quality communication without huge investment in ground-based infrastructure
§  same speed as earth
§  Geosynchronous satellite = orbit speed is based on distance from the planet
§  Minimum 3 satellites to provide full global transmissions
§  earth à satellite = uplink
§  satellite à earth = downlink

Something you might do not know….
Wireless technology
·        Technology that does not require any wires. (unbounded media)
·        The distances involved may be short such as a few meters as in television remote control
·        Long like thousands or millions of kilometers for radio communications.
Wifi
·        developed to be used for mobile computing devices
·        Transmit data use radio wave
·        IEEE802.11 – standard for implementing wifi
·        IEEE802.11b standard provides a transmit data size up to 11Mbps (Megabyte per second)
·        IEEE802.11a standard provides throughput rates up to 54Mbps



Radio frequency[RF] and cellular phones
·        Cellular phone is one of the wireless devices make use of RF
·        Cell phones work by sending signals to (and receiving them from) nearby cell towers (base stations) using RF waves
·        This is a form of electromagnetic energy that falls between FM radio waves and microwaves
·        RF waves are a form of non-ionizing radiation
·        RF waves are different from stronger (ionizing) types of radiation such as x-rays, gamma rays, and ultraviolet (UV) light, which can break the chemical bonds in DNA.
·        At very high levels, RF waves can heat up body tissues. (This is the basis for how microwave ovens work.)
·        But the levels of energy given off by cell phones are much lower, and are not enough to raise temperatures in the body.
Designation
Frequencies
Free-space Wavelengths
Very Low Frequency
9 kHz - 30 kHz
33 km - 10 km
Low Frequency
30 kHz - 300 kHz
10 km - 1 km
Medium Frequency
300 kHz - 3 MHz
1 km - 100 m
High Frequency
3 MHz - 30 MHz
100 m - 10 m
Very High Frequency
30 MHz - 300 MHz
10 m - 1 m
Ultra High Frequency
300 MHz - 3 GHz
1 m - 100 mm
Super High Frequency
3 GHz - 30 GHz
100 mm - 10 mm
Extremely High Frequency
30 GHz - 300 GHz
10 mm - 1 mm




By Mhui

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