Elements Of Communication System - Practice Questions & MCQ

Basic elements of a Communication System: 

Information: The idea or message that is to be conveyed is known as information. The message may be individual one or a set of messages.

Signal : A single valued function of time ( that conveys the information ). 

Transmitter : A device which make an incoming message signal suitable for transmission through a channel and subsequent reception.

Transducer: A device that convert one form of energy into another. 

Repeater: It is used to extend the range of signal. Combination of receiver and a transmitter.

Amplifier:  It boosts the power of modulated signal.

Antenna: Signal is radiated in the space with the help of an antenna.

Noise  : An unwanted signal that tend to disturb the transmission and processing of the message signal. Source of noise may be located within the system or out of the system.

Receiver: The device which extract the desired message signal from the received signal at the channel output.

Amplification: It is the process of increasing the amplitude  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.

Attenuation: The loss of strength of a signal while propagating through a medium is known as attenuation.

Modulation:  It is the process carried out at transmitter in which the low frequency message signal is superimposed on a high frequency carrier signal.

Demodulation: The process of retrieval of information from the carrier wave at the receiver. Reverse process of modulation.

Bandwidth of Signals:

The bandwidth of a signal is defined as the difference between the upper and lower frequencies of a signal generated. As seen from the  representation below, Bandwidth (B) of the signal is equal to the difference between the higher or upper-frequency (fH) and the lower frequency (fL). It is measured in terms of Hertz(Hz) i.e. the unit of frequency.

For example, Whenever we tune into a radio we find various stations at varying particular frequencies. The bandwidth of FM radio is 200 KHz from 88.1 MHz to 101.1 MHz for most places. As you tune, the radio you find various stations at various frequencies.

For speech signals, frequency range 300 Hz to 3100 Hz is considered adequate. Therefore speech signal requires a bandwidth of 2800 Hz (3100 Hz – 300 Hz) for commercial telephonic communication. To transmit music,an approximate bandwidth of 20 kHz is required because of the high frequencies produced by the musical instruments. The audible range of frequencies extends from 20 Hz to 20 kHz. Video signals for transmission of pictures require about 4.2 MHz of bandwidth. A TV signal contains both voice and picture and is usually allocated 6 MHz of bandwidth for transmission.

Bandwidth of Transmission Medium

A transmission medium is a material substance (solid, liquid, gas, or plasma) that can propagate energy waves. For example, the transmission medium for sounds is usually air, but solids and liquids may also act as transmission media for sound. The absence of a material medium in vacuum may also constitute a transmission medium for electromagnetic waves such as light and radio waves. While material substance is not required for electromagnetic waves to propagate, such waves are usually affected by the transmission media they pass through, for instance by absorption or by reflection or refraction at the interfaces between media.

Coaxial cable is a widely used wire medium, which offers a bandwidth of approximately 750 MHz. Such cables are normally operated below 18 GHz. Communication through free space using radio waves takes place over a very wide range of frequencies: from a few hundreds of kHz to a few GHz

Spectrum Allocations:

A spectrum is a large bandwidth of frequencies. Cellular or digital methods use this bandwidth for communication. These allocations have arrived with the help of international plans and policies. Often they require an upgrade of existing systems and technologies.

For example:  4G communication is  for cellular device accessible. The upcoming years will see the introduction of the 5G spectrum as well. With such huge bandwidths, easy, reliable and ultra-fast data transmissions are possible regularly.