Communication basics part 1

Communication Basics

1Prepared by: Ahmad Sajjad Safi. CNS Instructor Reference: ISAF & GIZ Training Materials

Introduction to Communication

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The discipline of communication focuses on how people use messages to generate meanings within and across various contexts, cultures, channels, and media.The discipline promotes the effective and ethical practice of human communication.Communication is representation of ongoing message exchange between individuals, or an individual and a group of individuals, with the goal of understanding each other.A communicator encodes (e.g., puts thoughts into words and gestures), then transmits the message via a channel (e.g., speaking, email, text message, radio aids) to the other communicator(s) who then decode the message (e.g., take the words and apply meaning to them).

Introduction to Communication

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History of Communication

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Radio has its roots in the Telegraph.This device was the first widely-used form of long-distance communication.In 1836, Samuel Morse invented a languageof dots and dashes that is still used today.In 1876, Alexander Graham Bell transmitted the human voice over wires for the first time. Soon, his invention moved from the lab to the home and life hasn't been the same since.


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In 1887, Heinrich Hertz demonstrated that electromagnetic waves could be transmitted through the air. As a result, the term "Hertz" is now used to specify cycles per second for the frequency of both sound and radio waves.


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Guglielmo Marconi is commonly credited as inventing radio in 1895 even though there is credible evidence that other inventors were first.Once Marconi patented his invention in England, his next step was to sell it to the marine industry. Soon, the majority of oceangoing shipswere all equipped with his equipment –which made Marconi a very rich man.

Waves

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Waves: In physics, a wave is disturbance or oscillation (of a physical quantity), that travels through matter or space, accompanied by a transfer of energy. Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass transport. They consist, instead, of oscillations or vibrations around almost fixed locations.

Waves

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There are two main types of waves. Mechanical waves propagate through a medium, and the substance of this medium is deformed.For example, sound waves propagate via air molecules colliding with their neighbors.

Waves

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The second main type of wave, electromagnetic waves, do not require a medium. Instead, they consist of periodic oscillations of electrical and magnetic fields generated by charged particles, and can therefore travel through a vacuum. These types of waves vary in wavelength, and include radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

Form of the wave

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The form or shape of the waveSineSquareTriangleSaw tooth

Basic Terms

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Power supply: is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and, as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.

Waves specifications

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Frequency: is the number of occurrences of a repeating event per unit time.For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time.Radio frequency (RF) is a rate of oscillation of a wave per unit of time (per second) and is typically measured in hertz.

F=FrequencyC=Speed of light waves =Lambda (wave length)


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Bandwidth: is the difference between the upper and lower frequencies in acontinuous set of frequencies.


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Wavelength: of a sinusoidal wave is the special period of the wave—the distance over which the wave's shape repeats, generally is measured in meters. Assuming a sinusoidal wave moving at a fixed wave speed, wavelength is inversely proportional to frequency of the wave: waves with higher frequencies have shorter wavelengths, and lower frequencies have longer wavelengths. In the case of electromagnetic radiation—such as light—in free space is the speed of light, about 3×108 m/s.


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Amplitude: of a periodic variable is a measure of its change over a single period (such as time or special period).Peak-to-peak amplitude is the change between peak (highest amplitude value) and trough (lowest amplitude value, which can be negative). With appropriate circuitry, peak-to-peak amplitudes of electric oscillations can be measured by meters or by viewing the waveform on an oscilloscope.


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Frequency Diapason

Radio Waves

Radio Waves Broadcasting Introduction

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In radio transmission, it is necessary to send audio signal (e.g. music, speech etc.) from a broadcasting station over great distances to a receiver. This communication of audio signal does not employ any wire and is sometimes called wireless. The audio signal cannot be sent directly over the air for appreciable distance. Even if the audio signal is converted into electrical signal, the latter cannot be sent very far without employing large amount of power. The energy of a wave is directly proportional to its frequency. At audio frequencies (20 Hz to 20 kHz), the signal power is quite small and radiation is not practicable. The radiation of electrical energy is practicable only at high frequencies e.g. above 20 kHz. The high frequency signals can be sent thousands of miles even with comparatively small power.


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Therefore, if audio signal is to be transmitted properly, some means must be devised which will permit transmission to occur at high frequencies while it simultaneously allows the carrying of audio signal. This is achieved by superimposing electrical audio signal on high frequency carrier.The resultant waves are known as modulated waves or radio waves and the process is called modulation. At the radio receiver, the audio signal is extracted from the modulated wave by the processcalled demodulation. The signal is then amplified and reproduced into soundby the loudspeaker.

Radio Broadcasting, Transmission and Reception

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Radio communication means the radiation of radio waves by the transmitting station, the propagation of these waves through space and their reception by the radio receiver. Down figure shows the general principles of radio broadcasting, transmission and reception. As a matter of convenience, the entire arrangement can be divided into three parts viz. transmitter, transmission of radio waves and radio receiver.

System of Communication

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Sound Waves

Microphone(Transducer)

Electronic Signal

Oscillator (CW)

ModulatorAmplifier

AM/FM

Antenna

Radio WavesTransmitter

Antenna

Radio Waves De-amplifierDe-modulator

AM/FM

Electronic Signal

Loudspeaker(Transducer)

Sound Waves

Receiver


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Transmitter: Transmitter is an extremely important equipment and is housed in the broadcasting station. Its purpose is to produce radio waves for transmission into space. The important components of a transmitter are microphone, audio amplifiers, oscillator and modulator.


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Microphone: A microphone (Transducer) is a device which converts sound waves into electrical waves. When the speaker speaks or a musical instrument is played, the varying air pressure on the microphone generates an audio electrical signal which corresponds in frequency to the original signal. The output of microphone is fed to a multistage audio amplifier for raising the strength of weak signal.


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Amplifier: An electronic amplifier, amplifier, or (informally) amp is an electronic device that increases the power of a signal. The amplifier is often described as the heart or the nervous system of a microphone or loudspeaker. The audio signal from the microphone is quite weak and requires amplification. This job is accomplished by audio amplifiers. The amplified output from the last audio amplifier is fed to the modulator for rendering the process of modulation.


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Oscillation: is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples include a swinging pendulum and alternating current power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but is sometimes used as a synonym of "oscillation".


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Oscillator: The function of oscillator is to produce a high frequency signal, called a carrier wave. Usually, a crystal oscillator is used for the purpose. The power level of the carrier wave is raised to a sufficient level by radio frequency amplifier stages. Most of the broadcasting stations have carrier wave power of several kilowatts. Such high power is necessary for transmitting the signal to the required distances.


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Modulation: A high frequency carrier wave is used to carry the audio signal. The question arises how the audio signal should be ‘‘added’’ to the carrier wave. The solution lies in changing some characteristic of carrier wave in accordance with the signal. Under such conditions, the audio signal will be contained in the resultant wave. This process is called modulation and may be defined as under : The process of changing some characteristic (e.g. amplitude, frequency or phase) of a carrier wave in accordance with the intensity of the signal is known as modulation.Modulation means to “change”. In modulation, some characteristic of carrier wave is changed in accordance with the intensity (i.e. amplitude) of the signal. The resultant wave is called modulated wave or radio wave and contains the audio signal. Therefore, modulation permits the transmission to occur at high frequency while it simultaneously allows the carrying of the audio signal.


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Types of Modulation: As you will recall, modulation is the process of changing amplitude or frequency or phase of a carrier wave in accordance with the intensity of the signal. Accordingly, there are three basic types of modulation, namely ;(i) amplitude modulation (ii) frequency modulation (iii) phase modulationIn India, amplitude modulation is used in radio broadcasting. However, in television transmission, frequency modulation is used for sound signal and amplitude modulation for picture signal. Therefore, our attention in this chapter shall be confined to the first two most important types of modulation.


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Amplitude Modulation: When the amplitude of high frequency carrier wave is changed in accordance with the intensity of the signal, it is called amplitude modulation. In amplitude modulation, only the amplitude of the carrier wave is changed in accordance with the intensity of the signal. However, the frequency of the modulated wave remains the same. The amplitude variations of the carrier wave is at the signal frequency. Amplitude modulation is done byan electronic circuit called modulator.


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Frequency Modulation (FM): When the frequency of carrier wave is changed in accordance with the intensity of the signal, it is called frequency modulation (FM). In frequency modulation, only the frequency of the carrier wave is changed in accordance with the signal. However, the amplitude of the modulated wave remains the same. The frequency variations of carrier wave depend upon the instantaneous amplitude of the signal as shown down. When the signal voltage is zero as at A, C, E and G, the carrier frequency is unchanged. When the signal approaches its positive peaks as at B and F, the carrier frequency is increased to maximum as shown by the closely spaced cycles. However, during the negative peaks of signal as at D, the carrier frequency is reduced to minimum as shown by the widely spaced cycles.


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Operating range. The energy of a wave depends upon its frequency. The greater the frequency of the wave, the greater the energy possessed by it. As the audio signal frequencies are small, therefore, these cannot be transmitted over large distances if radiated directly into space. The only practical solution is to modulate a high frequency carrier wave with audio signal and permit the transmission to occur at this high frequency (i.e. carrier frequency).Wireless communication. One desirable feature of radio transmission is that it should be carried without wires i.e. radiated into space. At audio frequencies, radiation is not practicable because the efficiency of radiation is poor. However, efficient radiation of electrical energy is possible at high frequencies (> 20 kHz). For this reason, modulation is always done in communication systems.


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Advantages : The following are the advantages of FM over AM : It gives noiseless reception. As discussed before, noise is a form of amplitude variations and a FM receiver will reject such signals.(ii) The operating range is quite large.(iii) It gives high-fidelity reception.(iv) The efficiency of transmission is very high.


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The comparison of FM and AM is given in the table below.


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Antenna: Suppose you're the boss of a radio station and you want to transmit your programs to the wider world. How do you go about it? You use microphones to capture the sounds of people's voices and turn them into electrical energy. You take that electricity and, loosely speaking, make it flow along a tall metal antenna (boosting it in power many times so it will travel just as far as you need into the world). An antenna (or aerial) is an electrical device which converts electric currents into radio waves and vice versa. As the electrons (tiny particles inside atoms) in the electric current wiggle back and forth along the antenna, they create invisible electromagnetic radiation in the form of radio waves. These waves travel out at the speed of light, taking your radio program with them. What happens when I turn on my radio in my home a few miles away? The radio waves you sent flow through the metal antenna and cause electrons to wiggle back and forth. That generates an electric current—a signal that the electronic components inside my radio turn back into sound I can hear.


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Types of Antenna: Vertical and Horizontal Polarization antennas.Directional and Non-Directional antennas.The simplest radio antennas are just long straight rods. Many indoor TV antennas take the form of a dipole: a metal rod split into two pieces and folded horizontally. Other designs include circular loops of wire and, of course, parabolic satellite dishes. Three features of antennas are particularly important, namely their,, and.Directionality: they pick up incoming radio waves traveling at right angles to them.Gain: amount by which it boosts the signal.Bandwidth: An antenna's bandwidth is the range of frequencies (or wavelengths, if you prefer) over which it works effectively.


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(i) Practical antenna length. Theory shows that in order to transmit a wave effectively, the length of the transmitting antenna should be approximately equal to the wavelength of the wave.


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Receiver: we tune the desired radio channel and An antenna catch enough of the transmitted electromagnetic waves to provide an electrical signal level sufficient for the receiver to process the signal into useful audio and video. In next slides we will discuss the main parts of and receiver.


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Demodulation: The process of recovering the audio signal from the modulated wave is known as demodulation or detection. At the broadcasting station, modulation is done to transmit the audio signal over larger distances to a receiver. When the modulated wave is picked up by the radio receiver, it is necessary to recover the audio signal from it. This process is accomplished in the radio receiver and is called demodulation.Essentials in Demodulation: In order that a modulated wave is audible, it is necessary to change the nature of modulated wave. This is accomplished by a circuit called detector. A detector circuit performs the following two functions :


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It rectifies the modulated wave i.e. negative half of the modulated wave is eliminated.

It separates the audio signal from the carrier. The rectified modulated wave contains the audio signal and the carrier. It is desired to recover the audio signal. This is achieved by a filter circuit which removes the carrier frequency and allows the audio signal to reach the load i.e.speaker.


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The FM receiver is more complicated and, therefore, more expensive than the normal AM receiver. The FM radio receiver receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts it through demodulation and decoding the signal into a form usable for the consumer, such as sound, pictures, digital data, measurement values, navigational positions, etc. The receiver is tuned to respond preferentially to the desired signals, and reject undesired signals.


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De-amplifier: is an electronic device that decreases the power of a signal. The de-amplifier is often described as the heart or the nervous system of a microphone or loudspeaker. The audio signal from the de-modulator is powerful and requires de-amplification. This job is accomplished by audio de-amplifiers. The de-amplified output from the last audio de-amplifier is fed to the loudspeaker for converting the electrical wave to the sound wave.


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Loudspeaker: When things shake about, or vibrate, they make the sounds we can hear in the world around us. Sound is invisible most of the time, but sometimes you can actually see it! If you thump a kettle-drum with a stick, you can see the tight drum skin moving up and down very quickly for some time afterward—pumping sound waves into the air.


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At the front of a loudspeaker, there is a fabric, plastic, paper, or lightweight metal cone (sometimes called a diaphragm). The outer part of the cone is fastened to the outer part of the loudspeaker's circular metal rim. The inner part is fixed to an iron coil (voice coil, colored orange in the diagram) that sits just in front of a permanent magnet (field magnet, and colored yellow). When electrical signals feed through the speaker cables (red) into the coil. This turns the coil into a temporary magnet or electromagnet. As the electricity flows back and forth in the cables, the electromagnet either attracts or repels the permanent magnet. This moves the coil back and forward, pulling and pushing the loudspeaker cone. Like a drum skin vibrating back and forth, the moving cone pumps sounds out into the air.


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In next chapter you will study about HF, VHF & UHF Communication equipment's.

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Communication basics part 1