Communication basics part 1

Communication Basics
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Prepared 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 language
of 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 ships
were 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 wave
Sine
Square
Triangle
Saw 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=Frequency
C=Speed of light waves
=Lambda (wave length)

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Bandwidth: is the difference between the upper and lower frequencies in a
continuous 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 process
called demodulation. The signal is then
amplified and reproduced into sound
by 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 Waves
Transmitter
Antenna
Radio Waves De-amplifier
De-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 modulation
In 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 by
an 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.
Any Question?

Communication basics part 1

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