Monday, November 19, 2012


Unguided media transmits electromagnetic waves without using a physical conductor cable or optical fiber. A simple example is the radio waves such as microwaves, mobile wireless, and so forth. Media requires antennas for transmission and reception (transmitter and receiver). There are two types of transmission, Point-to-point (unidirectional) ie where the beam focused on a single target. Broadcast (omnidirectioanl) which is where the signal radiates in all directions and can be received by multiple antennas. Three kinds of frequency areas, among others:
a.       Microwave (microwave) 2-40 GHz
b.      Radio waves 30 Mhz - 1 Ghz
c.       infrared wavelengths
For media are not guided (unguided), the transmission and reception can be achieved by using an antenna. For transmission, antennas emit electromagnetic energy into the medium (usually air) and for the reception, the antenna picks up electromagnetic waves from the surrounding medium. Not guided transmission media (unguided) divided into four parts:
1.      Microwave Terrestrial (Earth's atmosphere)
Type microwave antenna is the most common dish 'dish'. Size is usually about 3 m in diameter. Focus the beam transmitting antenna short to reach the transmission line of sight toward the receiving antenna. Microwave antennas are usually placed at a certain height above the ground to extend the distance between the antenna and were able to penetrate the border. To achieve long distance transmission, it takes a microwave relay towers, and microwave link point to be installed at a certain distance.
Microwave system usability are the main long-haul telecommunications services, as an alternative to coaxial cable or fiber optic. Microwave facility requires fewer amplifiers or repeaters than coaxial cable at the same distance, but still require a line of sight transmission. Microwaves are generally used for the transmission of television or for the transmission of sound.
Users microwave was used to track the short dots between buildings. It can be used for network TV as closed or the data path between the Local Area Network. Short-haul Microwaves can also be used for special applications. For the purposes of the business is the path of microwaves to remote telecom facilities to the same city, through the local telephone company.

2.      Satellite Microwave
Satellite communication is a microwave relay station. Used to connect two or more transmitter / receiver microwave on earth, known as an earth station or ground station. Satellite receives transmissions on one frequency band (uplink), amplifier and repeat signals, and then transmits it to another frequency (downlink). A single orbiting satellite will operate in multiple frequency bands, called transponder channels, or simply transponders.
There are two common configurations for satellite communications are popular are:
a.       Satellites are used to provide point-to-point path between the two antennas of two earth stations
b.      Satellites provide communication between a transmitter and a number of earth station earth station receiver.
In order for satellite communications to function effectively, it is usually necessary to pay attention to the position of stationary orbit above the earth. Instead, each earth station should not be underlined of view all the time. For mrnjadi stationary satellites must have the same rotation period with the Earth's rotation period. Conformity occurs at an altitude of 35,784 km.
Two satellites using the same frequency band, when both are close enough, it will interfere with each other. To avoid this, the new standards require a 4 degrees of space.
Satellite communication is a revolution in communication technology and equally important view of the fiber optic. The most important applications for other satellites are:
a.       Distribution of television broadcast
b.      Transmission distance phone
c.       Private business network
Some characteristics of satellite communication can be described as follows:
·         due to long distances there is a delay spread (propagation delay) of approximately quarter of a second of a transmission from an earth station to be caught by another earth station. Besides emerging issues relating to error control and flow control.
·         microwave is a broadcasting facility, and this is their nature. Many diagnostic station can transmit to the satellite, and the transmissions from the satellite can be received by multiple stations.

3.      Radio Broadcast
The main differences between broadcast radio and microwave is, where are all the way radio (broadcast) while microwave direct (point-to-point). Therefore, the radio does not require a satellite dish antenna, and the antenna does not necessarily lead to the exact source of the broadcast
Radio is a term commonly used to capture the range of frequencies between 3 kHz to 300 GHz. We use the formal term not radio for VHF band and part of the UHF band: 30 MHz to 1 GHz. The range is also used for a number of applications of data networks.
Range of 30 MHz to 1 GHz is the effective range for broadcast communications. Unlike the case for low-frequency electromagnetic waves, the ionosphere is quite transparent to radio waves above 30 MHz. so the transmission is limited to line of sight, and the distance transmitter will not interfere with each other in the sense that there is no reflection of the atmosphere. Unlike higher frequency than zone microwaves, radio waves atenuansi little sensitive when it rains. Because of the long waves, radio waves relatively less experienced atenuansi.
The main source of interference to the radio is a multi-path interference. Reflections of earth, water, and natural or man-made objects can cause multi-path between the antennas. This effect was apparent when the TV receiver displays double images when the plane flew past.
4.      Infra Red
Infrared communication is achieved by using a transmitter / receiver (transceiver) that modulation of coherent light. Transceiver must be in the line of view and through the reflection of the light-colored surfaces such as ceiling. One important difference between the transmission of infrared and microwave radiation is infrared transmissions can not penetrate the wall, so that the problems of security and interference encountered in the microwave is not the case. Furthermore, there are no matters relating to the allocation of frequencies with infrared, because it does not need a license for it. In the mobile phone and PC, infrared media is used to transfer data, but with a standard or protocol that is separate IrDA protocol. Infrared light is light that is not visible. When viewed with a spectroscope the light radiation infrared light will appear on spektruk electromagnetic wavelength over the wavelength of red light.

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