An unguided communication medium transmits the information through the air in much the same way as radio stations broadcast their programming. They are also called unbound wireless transmission media because they do not use any physical wire or a closed circuit for data communication.
For eg. microwave, satellite, radio broadcast, infrared,etc.
Microwaves are unguided communication media that use a high frequency band of a radio broadcast transmission to transmit the data through the space (wireless communication). It uses dish shaped antennae for sending and receiving the information. Microwaves are called line-of-sight because the microwave signal cannot bend around the surface of the earth.Hence, transmitter and receiver of a microwave system ,mounted on a very high tower should be in line of sights. This type of communication is not possible for distance communication.When microwaves are used for longer distances, a separate device called repeater is used to amplify the signals because the signals become weaker after traveling certain distances.
Microwave systems have the speed of about 16 Giga bits per second. A microwave system can support about 250,000 voice channels simultaneously. The microwave installation cost is very high as compared to other guided communication media.
These are basically microwave transmission systems in space. A satellite is an amplifier or repeater that receives information from one location on the earth,repeats the data and sends it to one or more receiving location on the earth. Satellite communication media are very cost effective for moving large amount of information specially where there are many receiving locations.
Data transmission costs are independent of distances between two points as long as these two points are within the satellite coverage area. A satellite communication does not need any cables and associated cost for land digging. However the initial cost for setting up the satellite is very high.Satellite communication is the fastest communication medium than others.
Radio Broadcast:Radio Broadcast is an unguided communication medium similar to microwaves and satellite except that the receiving locations need not be in line of sight or have a dish-shaped antennae to receive information transmission.
Infrared is an unguided communication medium that uses a red light (below the of human eye) to transmit information.The common application of is in television and VCR’s with a remote control. In the area of network, infrared is used to connect the local area network in the same room and to connect computer with peripheral device such mouse, keyboard etc.
It is a low cost, low power, wireless radio frequency technology that allows various devices to communicate with each other. One of the advantages of bluetooth over infrared is that close proximity between the communication devices is not required and distance of up to 10 meters or 32 feet are allowed.