Unguided Media

The wireless technologies are categorized as unguided media. They are generally used where it is difficult to install cables. Following are different types of unguided media:

1. Radio Technology:

   In this technology, the radio signal (waves with very short wavelength) are used in transmit signals in single or multiple directions. They are good for short range line of sight transmissions so are frequently used for networks in portable computers. This technology saves money where it is difficult and expensive to install cables. This also provides much better mobility in networked devices. However, the disturbance in these networks is high. They are used in radio stations, emergency alarming systems, etc.

2. Infrared technologies:

   They use infrared light for data transmission. LED is used as source to transmit signal and photo diode to receive signals. Signals in this technology are in high frequency range which enables them to give good output. They are used in remote controller of TV, VCD, DVD, etc. However, they have following drawbacks:

   1. Signals cannot penetrate through solid opaque objects such as: walls or objects.
   2. Signals are diluted by light source.
      
      
3. Microwave Technologies

   There are two types of microwave technologies:

   1. Terrestrial microwave systems:

      This technology requires line of sight transmission. It can transmit signals in only one direction at a time which make it necessary to either use two antennae or transceiver for two way communication. It is generally used where installing cables is difficult and expensive such as hilly areas. Frequency range: 4-6 GHz or 21-23 GHz.

   2. Satellite Microwave systems:

      It is similar to other line of sight transmission technologies except that it uses satellite acting as an antennae or repeater. This allows the communication using this technology for communication in any location on earth as long as the signals are not blocked. This technology is very expensive. Frequency range 11-14 GHz. This technology is used GPS, satellite phones, DTH (Direct to Home) televisions systems, international private networks, etc.

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