COMMUNICATION AND COMMUNICATION SYSTEMS ....
Elements Of Communication Systems
The definitions of the terms used in the communication system are discussed below.
Information
Message or information is the entity that is to be transmitted. It can be in the form of audio, video, temperature, picture, pressure, etc.
Signal
The single-valued function of time that carries the information. The information is converted into an electrical form for transmission.
Transducer
A device or an arrangement that converts one form of energy to the other. An electrical transducer converts physical variables such as pressure, force, temperature into corresponding electrical signal variations. Example: Microphone – converts audio signals into electrical signals. Photodetector – converts light signals into electrical signals.
Amplifier
The electronic circuit or device that increases the amplitude or the strength of the transmitted signal is called an amplifier. When the signal strength becomes less than the required value, amplification can be done anywhere in between transmitter and receiver. A DC power source will provide for the amplification.
Modulator
As the original message signal cannot be transmitted over a large distance because of their low frequency and amplitude, they are superimposed with high frequency and amplitude wave called carrier wave. This phenomenon of superimposing of message signal with a carrier wave is called modulation. And the resultant wave is a modulated wave which is to be transmitted.
Again there are different types of Modulation.
i. Amplitude Modulation (AM)
The process of changing the amplitude of the signal wave by impressing or superimposing it on a high-frequency carrier wave, keeping its frequency constant is called amplitude modulation.
ii. Frequency Modulation (FM)
Frequency modulation is a technique in which the frequency of the message signal is varied by modulating with a carrier wave. It is better than deficient than amplitude modulation because it eliminates noise from various sources.
iii. Phase Modulation (PM)
The phase of the carrier wave changes the phase of the signal wave. The phase shift after modulation is dependent on the frequency of the carrier wave as well. Phase modulated waves are immune to noise to a greater extent.
Transmitter
It is the arrangement that processes the message signal into a suitable form for transmission and subsequently reception.
Antenna
An Antenna is a structure or a device that is radiate and receive electromagnetic waves. So, they are used in both transmitters and receivers. An antenna is basically a metallic object, often a collection of wires. The electromagnetic waves are polarised according to the position of the antenna.
Channel
A channel refers to a physical medium such as wire, cables, space through which the signal is passed from transmitter to the receiver. There are many channel impairments that affect the channel performance to a pronounced level. Noise, Attenuation and distortion to mention the major impairments.
Noise
Noise is one of the channel imperfection or impairment in the received signal at the destination. There are external and internal sources that cause noise. External sources include interference, i.e. interference from nearby transmitted signals (cross talk), interference generated by natural source such as lightning, solar or cosmic radiation, from automobile generated radiation, etc. The external noise can be minimised and eliminated by appropriate design of the channel, shielding of cables. Also by digital transmission external noise can be much minimised.
Internal sources include noise due to random motion and collision of electrons in the conductors, thermal noise due to diffusion and recombination of charge carriers in other electronic devices. Internal noise can be minimised by cooling and using digital technology for transmission.
⎫ A different cable design.
⎫ Proper design of the channel.
⎫ Use digital transmission
⎫ Using BPF or LPF at the receiver side.
Attenuation
Attenuation is a problem caused by the medium. When the signal is propagating for a longer distance through a medium, depending on the length of the medium the initial power decreases. The loss in initial power is directly proportional to the length of the medium. Using amplifiers, the signal power is strengthened or amplified so as to reduce attenuation. Also, digital signals are comparatively less prone to attenuation than analogue signals.
Distortion
It is also another type of channel problem. When the signal is distorted, the distorted signal may have frequency and bandwidth different from the transmitted signal. The variation in the signal frequency can be linear or non-linear.
Receiver
An arrangement that extracts the message or information from the transmitted signal at the output end of the channel and reproduces it in a suitable form as the original message signal is a receiver.
Demodulator
It is the inverse phenomenon of modulation. The process of separation of message signal from the carrier wave takes place in the demodulator. The information is retrieved from the modulated wave.
Repeaters
Repeaters are placed at different locations in between the transmitter and receiver. A repeater receives the transmitted signal, amplifies it and send it to the next repeater without distorting the original signal.
Block Diagram of Communication Systems
The block diagram given below represents the flow of the signal from the source to the destination. The role of every device and arrangement discussed above is better understood.
conductor.Communication is simply the act of transferring information from one place, person or group to another.
Every communication involves (at least) one sender, a message and a recipient. This may sound simple, but communication is actually a very complex subject.
The transmission of the message from sender to recipient can be affected by a huge range of things. These include our emotions, the cultural situation, the medium used to communicate, and even our location. The complexity is why good communication skills are considered so desirable by employers around the world: accurate, effective and unambiguous communication is actually extremely hard.
With the development of human culture,revolutionary changes occured in the field of communication. In earlier days our communication systems were limited to ‘telephone’ and ‘telegraph’ only .
TYPES OF COMMUNICATION
1- Line Communication
2- Wireless Communication
LINE COMMUNICATION -;
In line communication there is a physical connection between source and destination. The wired connections between two points are known as transmission lines.Line commutation is a Class-F SCR commutation technique in which, a thyristor is turned off due to natural current zero and voltage reversal after every half cycle.
Eg.. TELEGRAPHY
the science or practice of using or constructing communication systems for the transmission or reproduction of information.
Telephony -;
Telephony is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties.
Telex -;
Telex is an international system used especially in the past for sending written messages. Messages are convert into signals which are transmitted, either by electricity or by radio signals, and then printed out by a machine in another place.
Fax - ;
Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer or other output device. The original document is scanned with a fax machine (or a telecopier), which processes the contents (text or images) as a single fixed graphic image, converting it into a bitmap, and then transmitting it through the telephone system in the form of audio-frequency tones. The receiving fax machine interprets the tones and reconstructs the image, printing a paper copy.
Early systems used direct conversions of image darkness to audio tone in a continuous or analog manner. Since the 1980s, most machines modulate the transmitted audio frequencies using a digital representation of the page which is compressed to quickly transmit areas which are all-white or all-black.
Internet -;
The Internet is the global system of interconnected computer network that uses the Internet protocol suite(TCP/IP) to communicate between networks and devices. It is a network of networks that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies. The Internet carries a vast range of information resources and services, such as the inter-linked hypertext documents and application of the World,Wide,Web (WWW), electronic male, telephony, and file sharing .
WIRELESS COMMUNICATION -
Wireless communication is the electromagnetic transfer of information between two or more points that are not connected by an electrical conductor The most common wireless technologies use radio wave . With radio waves, intended distances can be short, such as a few meters for bluetooth or as far as millions of kilometers for deep-space radio commmunication. It encompasses various types of fixed, mobile, and portable applications, including two-ways radio , cellular telephone, personal digital assistant (PDAs), and wireless networking. Other examples of applications of radio wireless technology include GPS units, garage door opener , wireless computer, keyboard and headsets, headphones, radio recievers, satellite televission, broadcast television and cordless telephones. Somewhat less common methods of achieving wireless communications include the use of other electromagnetic wireless technologies, such as light, magnetic, or electric fields or the use of sound.
Radio broadcast -;
is transmission of audio (sometimes with related metadata) by radio waves intended to reach a wide audience. Stations can be affiliated to radio networks broadcasting a common radio format, either in broadcast syndication or simulcast or both. Signals can be either analogs audio or digital audio . Television broadcasting also uses radio frequencies, but includes video signals.
TV broadcast -;
regulations is among the most popular consumer applications operated in Ku-bands, generally in the 10.7–12.75 GHz frequency range. The first section of the satellite-TV reception chain consists of the low noise block (LNB) installed in the focus of the outdoor antenna dish. The LNB is in charge of converting the microwave signal down to intermediate frequency in the 950–2150 MHz frequency range.
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