Basic Elements of a Communication System
Every communication system has three essential elements-transmitter, medium/channel and receiver. The block diagram shown in Fig. depicts the general form of a communication system.
In a communication system, the transmitter is located at one place, the receiver is located at some other place (far or near) separate from the transmitter and the channel is the physical medium that connects them.
The purpose of the transmitter is to convert the message signal produced by the source of information into a form suitable for transmission through the channel.
The receiver has the task of operating on the received signal. It reconstructs a recognizable form of the original message signal for delivering it to the user of information.
There are two basic modes of communication:
`text(Point-to-point)` and `text(Broadcast)`.
In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver. Telephony is an example of such a mode of communication.
In the broadcast mode, there are a large number of receivers corresponding to a single transmitter. Radio and television are examples of broadcast mode of communication.
`text(BASIC TERMINOLOGY USED IN ELECTRONIC COMMUNICATION SYSTEMS)`
(i) `text(Transducer :)` Any device that converts one form of energy into another can be termed as a transducer. In electronic communication systems, we usually come across devices that have either their inputs or outputs in the electrical form. An electrical transducer may be defined as a device that converts some physical variable (pressure, displacement, force, temperature, etc) into corresponding variations in the electrical signal at its output.
(ii) `text(Signal :)` Information converted in electrical form and suitable for transmission is called a signal. Signals can be either analog or digital. Analog signals are continuous variations of voltage or current. They are essentially single-valued functions of time. Sine wave is a fundamental analog signal. All other analog signals can be fully understood in terms of their sine wave components. Sound and picture signals in TV are analog in nature. Digital signals are those which can take only discrete stepwise values. Binary system that is extensively used in digital electronics employs just two levels of a signal. �0� corresponds to a low level and �1� corresponds to a high level of voltage/ current.
(iii) `text(Noise :)` Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in a communication system. The source generating the noise may be located inside or outside the system.
(iv) `text(Transmitter :)` A transmitter processes the incoming message signal so as to make it suitable for transmission through a channel and subsequent reception.
(v) `text(Receiver :)` A receiver extracts the desired message signals from the received signals at the channel output.
(vi) `text(Attenuation :)` The loss of strength of a signal while propagating through a medium is known as attenuation.
(vii) `text(Amplification :)` It is the process of increasing the amplitude (and consequently the strength) of a signal using an electronic circuit called the amplifier. Amplification is necessary to compensate for the attenuation of the signal in communication systems. The energy needed for additional signal strength is obtained from a DC power source. Amplification is done at a place between the source and the destination wherever signal strength becomes weaker than the required strength.
(viii) `text(Range :)` It is the largest distance between a source and a destination up to which the signal is received with sufficient strength.
(ix) `text(Bandwidth :)` Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.
(x) `text(Modulation :)` The original low frequency message/information signal cannot be transmitted to long distances because of various reasons. Therefore, at the transmitter, information contained in the low frequency message signal is superimposed on a high frequency wave, which acts as a carrier of the information. This process is known as modulation.
(xi) `text(Demodulation :)` The process of retrieval of information from the carrier wave at the receiver is termed demodulation. This is the reverse process of modulation.
(xii) `text(Repeater :)` A repeater is a combination of a receiver and a transmitter. A repeater, picks up the signal from the transmitter, amplifies and re-transmits it to the receiver sometimes with a change in carrier frequency. Repeaters are used to extend the range of a communication system. A communication satellite is essentially a repeater station in space.
In a communication system, the transmitter is located at one place, the receiver is located at some other place (far or near) separate from the transmitter and the channel is the physical medium that connects them.
The purpose of the transmitter is to convert the message signal produced by the source of information into a form suitable for transmission through the channel.
The receiver has the task of operating on the received signal. It reconstructs a recognizable form of the original message signal for delivering it to the user of information.
There are two basic modes of communication:
`text(Point-to-point)` and `text(Broadcast)`.
In point-to-point communication mode, communication takes place over a link between a single transmitter and a receiver. Telephony is an example of such a mode of communication.
In the broadcast mode, there are a large number of receivers corresponding to a single transmitter. Radio and television are examples of broadcast mode of communication.
`text(BASIC TERMINOLOGY USED IN ELECTRONIC COMMUNICATION SYSTEMS)`
(i) `text(Transducer :)` Any device that converts one form of energy into another can be termed as a transducer. In electronic communication systems, we usually come across devices that have either their inputs or outputs in the electrical form. An electrical transducer may be defined as a device that converts some physical variable (pressure, displacement, force, temperature, etc) into corresponding variations in the electrical signal at its output.
(ii) `text(Signal :)` Information converted in electrical form and suitable for transmission is called a signal. Signals can be either analog or digital. Analog signals are continuous variations of voltage or current. They are essentially single-valued functions of time. Sine wave is a fundamental analog signal. All other analog signals can be fully understood in terms of their sine wave components. Sound and picture signals in TV are analog in nature. Digital signals are those which can take only discrete stepwise values. Binary system that is extensively used in digital electronics employs just two levels of a signal. �0� corresponds to a low level and �1� corresponds to a high level of voltage/ current.
(iii) `text(Noise :)` Noise refers to the unwanted signals that tend to disturb the transmission and processing of message signals in a communication system. The source generating the noise may be located inside or outside the system.
(iv) `text(Transmitter :)` A transmitter processes the incoming message signal so as to make it suitable for transmission through a channel and subsequent reception.
(v) `text(Receiver :)` A receiver extracts the desired message signals from the received signals at the channel output.
(vi) `text(Attenuation :)` The loss of strength of a signal while propagating through a medium is known as attenuation.
(vii) `text(Amplification :)` It is the process of increasing the amplitude (and consequently the strength) of a signal using an electronic circuit called the amplifier. Amplification is necessary to compensate for the attenuation of the signal in communication systems. The energy needed for additional signal strength is obtained from a DC power source. Amplification is done at a place between the source and the destination wherever signal strength becomes weaker than the required strength.
(viii) `text(Range :)` It is the largest distance between a source and a destination up to which the signal is received with sufficient strength.
(ix) `text(Bandwidth :)` Bandwidth refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.
(x) `text(Modulation :)` The original low frequency message/information signal cannot be transmitted to long distances because of various reasons. Therefore, at the transmitter, information contained in the low frequency message signal is superimposed on a high frequency wave, which acts as a carrier of the information. This process is known as modulation.
(xi) `text(Demodulation :)` The process of retrieval of information from the carrier wave at the receiver is termed demodulation. This is the reverse process of modulation.
(xii) `text(Repeater :)` A repeater is a combination of a receiver and a transmitter. A repeater, picks up the signal from the transmitter, amplifies and re-transmits it to the receiver sometimes with a change in carrier frequency. Repeaters are used to extend the range of a communication system. A communication satellite is essentially a repeater station in space.