Introduction to Communication System
- The early communication systems were developed by J.C. Bose, G. Marconi, and Alexander Graham Bell, etc.
- The communication industry is one of the oldest, it is since telegraph(1844), telephone(1876) and Radio (1887).
- The current communication technology is Global positioning System (GPS), satellite, mobile and optical communications.
The Elements of An Electronic Communication System
The elements of an electronic communication system are Information, Input transducer, Transmitter, Transmitting antenna, Communication channel, Noise, Receiver, Repeater, Output transducer, Attenuation, Range.
Information (Baseband or Input Signal)
Information or data can be in the form of sound, picture, video, text, etc is given as input to the input transducer.
A transducer is a device that converts the change in a physical quantity such as pressure, temperature, sound to an electrical signal or vice versa.
The transducer converts the information which is in the form of sound, music, pictures or computer data to electrical signals.
The microphone is an example of a transducer that converts sound energy into electrical energy.
It provides the electrical signal from the transducer to the communication channel. It is made of circuits such as an amplifier, oscillator, modulator, and power amplifier.
Used to amplify the weak signal from the transducer.
Oscillators generate high-frequency carrier waves which are generally sine waves for long distances transmission.
Modulator used to superimpose or modulate the baseband signal with the carrier signal to give a modulated signal(FM, AM, etc).
Power Amplifiers are used to raise the power level of the electrical signal in order to reach a great distance.
It throws away the radio signal into space or air in all directions. The radio signal travels with the speed of light i.e 3 x 108 ms-1.
The electrical signal is carried from the transmitter to the receiver using the communication channel with less noise or distortion. There are two types of communication medium, they are wireline communication and wireless communication.
Wireline communication is a point-to-point connection that uses mediums such as wires, cables, and optical fibres. As they are physically connected, Wireline communication cannot be used for long-distance communication. Examples are Telephone, Intercom and Cable TV.
Wireless communication does not need physical connectivity, it uses free space as a communication medium. A wireless communication signal is transmitted by electromagnetic waves using a transmitting antenna.
Consequently, wireless communication is adopted for long-distance transmission. Examples of Wireless communication are mobile, radio, or TV broadcasting, and satellite communication.
It is the unwanted electrical signal that interferes with the transmitted signal. Noise decreases the quality of the transmitted signal.
The noise may be created by man-made automobiles, welding machines, electric motors, etc, or natural such as lightning, radiation from sun and star, and environmental effects. Noise cannot be totally reduced but it can be minimized using different procedures.
Signals are received with the help of receiving antenna and fed to the receiver. The receiver consists of electronic circuits like a demodulator, amplifier, detector, etc. The demodulator obtains the baseband signal from the carrier signal.
Then the baseband signal is identified and amplified using amplifiers. Finally, it is supplied to the output transducer.
Repeaters are used to raise the range or distance of the transmitting signal. It consists of a transmitter and receiver.
The signals are received, amplified, and retransmitted with a carrier signal of a different frequency to the destination. Example: Communication satellite, Wifi Repeater in Home.
Output Transducer converts the electrical signal to its original forms such as sound, music, pictures, or data. Examples of output transducers are loudspeakers, picture tubes, computers, monitors, etc.
The loss of power of a signal while propagating via a medium is known as attenuation.
It is the highest distance between the source and the destination up to which the signal is acquired with enough strength.
“The frequency range over which the baseband signals or the information signals such as voice, music, pictures etc is transmitted is known as bandwidth”. (Tamil Nadu Text Book Corporation #)
Every signal has different frequencies. The type of communication system depends on the nature of the frequency band for a given signal.
Bandwidth gives the difference between the upper and lower frequency limits of the signal. It can also be defined as the portion of the electromagnetic spectrum occupied by the signal.
If v1 and v2 are lower and upper-frequency limits of a signal then the bandwidth BW = v2 – v1.
The bandwidth of Transmission System
“The range of frequencies required to transmit a piece of specified information in a particular channel is called channel bandwidth or the bandwidth of the transmission system”. (Tamil Nadu Text Book Corporation #)
This corresponds to the spectrum that is allotted to be used by the system. For example, AM requires a channel bandwidth of 10kHz to broadcast a 5 kHz signal, whereas a single-sideband system requires only a 5kHz channel bandwidth for the same 5 kHz signal.
This is because, in amplitude modulation, the channel bandwidth is twice the signal frequency. Hence, it is needed to decrease the channel bandwidth to support more channels in the available electromagnetic spectrum.
The antenna is used at both transmitter and receiver end. Antenna height is an important thing.
The height of the antenna should a multiple of ƛ/4. That is h = ƛ/4 where ƛ = c/v, where c is the velocity of light and v is the frequency of the signal to be transmitted.