Communication channel act as interface between transmitter and receiver. It is also called as transmission medium. Communication channel can be divided into wired medium and wireless medium. Wired medium is further divided into twisted pair cable, Co-axial cable and Optic Fiber Cable (OFC). Wireless medium is divided into Radio waves, Microwaves and infrared waves.
TWISTED PAIR CABLE:
Twisted pair cable comprises of two separate insulated copper wires which are twisted together. These copper wires are 1mm in diameter.
REASON FOR TWISTING:
The transmitting signal is affected by noise, crosstalk and electromagnetic interference. To reduce these effects wires are twisted. The two primary reasons behind twisting is to reduce incoming and outgoing noise. Every circuit is made up of two wires, positive and negative. The positive wire contains positive current and negative wire contains negative current as a result they will be cancelled out. Hence the noise disappears. Whenever an electric current flows through the circuit it will induce magnetic field. The reverse is also true. This will cause a signal to jump from one circuit to another circuit called crosstalk. Hence placing these wires close to each other will reduce incoming and outgoing noise in the circuit
Twisted pair cables are used in telephone lines, LANs and DSL lines.
TYPES OF TWISTED PAIR CABLES:
STP (Shielded Twisted Pair) consists of twisted wires with metallic shield and is used to prevent electromagnetic interference from in and out of the circuit. This metallic shield provides extra protection. UTP (Unshielded Twisted Pair) consists of twisted wires without metallic shield.
CO – AXIAL CABLE:
It is made up of four layers namely centre conductor, insulator or dielectric, conducting shield and outer jacket. The centre conductor is made up of copper wires and it carries the high frequency signal. This wire is surrounded by dielectric made up of plastic. This dielectric is surrounded by conducting shield made up of copper, aluminium or other metal. This stops electromagnetic interference. The entire cable is insulated by outer jacket. The signal is carried by both centre core and metallic shield. The insulator prevents both from interfering with each other. So, the signal is carried over long distance with less signal loss.
It is used for cable televisions, cell phone signal boosters and telephone lines. Connectors are used at each end of the cable.
FIBER OPTIC CABLE:
It is made up of thin strands of glass or plastic called optical fiber which is thinner than human hair. Three main parts of fiber optic cable is core‚ cladding and coating. The middle part of the cable is core which carries light signal. The core is surrounded by cladding. The cladding is used to keep the signal inside the core. The coating protects cladding and core. Coating is done based on the environment. It absorbs shocks, nicks and moisture. Fiber optic techniques requires LED or laser at transmitting side , because it converts electrical signal into light pulse and photoelectric cells on receiver side, because it turn back the light pulse into electrical signal. This light signal bounces inside the fiber optic cable. If the light hits glass (when it is placed less than 42 degree) it reflects back again into the glass. This is total internal reflection. Hence it is used to keep the signal inside the cable.
It can be used for long distance communication.
Wireless communication is a method of transmitting information from one place to another through space without using cables or any other physical medium. So antennas are used. Antenna is a device which converts electrical information into electromagnetic waves and vice versa. These waves propagate through space. Hence antennas are used in both transmitter and receiver. The installation process of wireless communication is less expensive‚ low cost and it is very easy to use.