2. 2
DEDICATION
I dedicate this
effort to my
Parents & Teachers
who Guide
&
Encourage me
during the course
Of
My Studies and
preparation of this
Report.
3. 3
PREFACE
I would like to thank Sir Aslam Shaikh, who give me the opportunity to doing work at Pakistan Broadcast
Corporation (PBC) as an internee, and also I would like to thank Sir Zafar Baloch who guided me during
my whole internships, answered my queries and treat me like a friend and brother.
For four weeks from 8th
April 2015 to 7th May 2015, I did an internship at Pakistan Broadcast
Corporation (PBC)
Really, it was a nice opportunity to have a close comparison of theoretical concept in practical field,
involving the use of Audio Console, Operating Control Room Switcher, Working of Mic, How an
antenna Transmit and Receive Signal Frequency, Why we send the Signals to the Satellite,
This Report may depict deficiencies on my part but still it is an output of a student’ efforts, for which I
beg pardon.
The output of my analysis is summarized in a shape of Internship the contents of the report Shows the
detail of sequence of these.
4. 4
S.No. Topics Page No.
1. Pakistan Broadcast Corporation 5
2. Departments of PBC 6
3. Studio 7
4. Mic 8
5. Types of Mic 9
6. Control Room 13
7. Audio Console 14
8. Analog Transmission 16
9. Antenna 17
10. Transmitter 19
11. Receiver 20
12. STL 21
13. Radiation pattern 21
14. Satellite 23
5. 5
PAKISTAN BROADCAST CORPORATION
Radio is the most effective media tool today even in the era of IT and multimedia communication. In
view of the penetration‚ sweep‚ pervasiveness‚ accessibility‚ cost effectiveness and convenience‚ its
identity can never be lost. It can be tuned anywhere during daily life i.e. while studying‚ driving‚ cooking‚
working in the fields and retiring in the bed. In the present technological revolution and transformation‚
FM broadcast has taken the world by storm. It has taken a lead by virtue of line of sight propagation of
waves and smaller range resulting in good quality and reliable signal.
The broadcasting services is for general reception in all parts of Pakistan through Home and
External Services for the purposes of disseminating information‚ education and entertainment
through programmes which maintain a proper balance in their subject-matter and a high general
standard of quality and morality.
Broadcast such programmes as may promote Islamic ideology‚ national unity and principles of
democracy‚ freedom‚ equality‚ tolerance and social justice as enunciated by Islam.
Broadcast programmes in the External Services to
such countries and in such languages and at such
times as the Federal Government may‚ from time
to time‚ direct.
Bring to public awareness the whole range of
significant activity and to present news or events in
as factual‚ accurate and impartial a manner as
possible.
Carry out instructions of the Federal Government with regard to general pattern or policies in
respect of programmes‚ announcements and news to be put out on the air from time to time.
hold the existing and to construct or acquire additional equipment and apparatus for telephony in
Pakistan for purpose of broadcasting
6. 6
DEPARTMENTS OF PBC
Programming
Engineering
Administration
Accounts
HEADS OF DEPARTMENTS
THE TEAM OF ENGINEERING DEPARTMENT
7. 7
ENGINEERING STRUCTURE
STUDIO
The word studio is derived from the Italian: studio, from Latin: studium, from studere, meaning
to study or zeal
A studio is an artist's or worker's work room, or the catch all
term for an artist and their employees who work within that
studio. This can be for the purpose of
acting architecture, painting, pottery (ceramics), sculpture, woodworking,scrapbooking, photography,
graphic design, filmmaking, animation, industrial design, radio or television production broadcasting or
the making of music. The term is also used for the workroom of dancers,often specified to dance studio.
8. 8
Radio studio
A radio studio is a room in which a radio program or show is produced, either for live broadcast or for
recording for a later broadcast. The room is soundproofed to avoid unwanted noise being mixed into the
broadcast.
Recording studio
A recording studio is a facility for sound recording which generally consists of at least two rooms: the
studio or live room, and the control room, where the sound from the studio is recorded and manipulated.
They are designed so that they have good acoustics and so that there is good isolation between the rooms.
MIC
All microphones convert sound energy into electrical energy, but there are many different ways of doing
the job, using electrostatics, electromagnetism, piezo-electric effects or even the change in resistance of
carbon granules. Fortunately for SOS readers
pondering over which mics to buy, the field of choice
is narrowed considerably when it comes to mics used
in music recording or live performance. The vast
majority of mics used in these applications are either
capacitor (electrostatic) or dynamic (electromagnetic)
models. Both types employ a moving diaphragm to
capture the sound, but make use of a different
electrical principle for converting the mechanical
energy into an electrical signal. The efficiency of this
conversion is very important, because the amounts of acoustic energy produced by voices and musical
instruments are so small.
9. 9
TYPES OF MIC
There are two types of mic
Dynamic mic
Condencer mic
DYNAMIC MIC
Most of you will have used a dynamic mic at sometimes or another, if it looks like a mesh ball on a stick,
then it's almost certainly a dynamic model. In live sound, nearly all the mics used are dynamics, and in
the studio, instruments such as drums, electric guitars, and basses may also be recorded using dynamic
mics. Dynamic microphones have the advantages of being relatively inexpensive and hard-wearing, and
they don't need a power supply or batteries to make them operate.
A lightweight diaphragm, usually made of plastic film, is attached to a very small coil of wire suspended
in the field of a permanent magnet. When a sound causes the
diaphragm to vibrate, the whole assembly works as a miniature
electricity generator, and a minute electric current is produced.
Because the electrical output is so very small, it has to be
amplified using a mic preamp before it is large enough to be
useful.
The weakness of the dynamic mic lies in the fact that the sound
energy has to move both the mic diaphragm and the wire coil
attached to it. The mass of the coil adds to the inertia of the
diaphragm assembly, which in turn restricts the frequency
response of the microphone. In practical terms, the outcome is that dynamic microphones fail to
reproduce very high frequencies accurately. In some applications, this isn't too serious, but if you're
working with an instrument where a lot of tonal detail is contained in the upper harmonics, a dynamic mic
is unlikely to bring out the best in that instrument.
Another side-effect of the finite mass of the diaphragm/coil assembly is that the dynamic microphone is
not particularly efficient a lot of amplification has to be used to make the signal usefully large, and the
more gain you use, the more noise you add to the signal. In the studio where the mic is used very close to
the sound source, this lack of efficiency is not a major problem, but if you're trying to capture a quiet or
very distant sound, then a dynamic mic isn't likely to produce good results.
10. 10
CONDENCER MIC
Condencer mics have been around for several decades, and although modern capacitor mics do
incorporate a few small technical improvements, the sound character has actually changed very little
some of the best sounding models were designed over 20 years ago. Basically, the heart of any capacitor
mic is a pair of conducting plates, one fixed and the other in the form of a moving diaphragm. When the
spacing between the plates changes (as it does when the
diaphragm vibrates) the capacitance varies, and if a fixed
electrical charge is applied to the capacitor, an electrical signal
is produced which faithfully represents the diaphragm
vibration.
To keep the weight down, the diaphragm is often made from
gold-coated plastic film. As a result, the diaphragm assembly
is very light compared to that of a dynamic mic, so the system
is much more efficient, and is capable of capturing harmonics
right up to the range of human hearing and beyond. The size
of the diaphragm also has an effect on the tonal quality of the
mic large diameter models are chosen for vocal work because
of their warm, flattering sound. Small-diaphragm models tend to be chosen where high accuracy is
required.
Even though they are relatively efficient, capacitor microphones still produce such a small electrical
signal that they require a special type of built in preamplifier to bring the signal up to usable levels, and
this is one factor that contributes to the higher cost when compared to dynamic mics. Additionally, all
capacitor mics need a polarizing voltage in order to work. The most common source of polarizing voltage
is the 48V 'phantom' power source, which is why many mixing consoles have a phantom power supply
built in. The term 'phantom power' came about because the polarizing voltage is supplied via the signal
leads of the microphone no additional cabling is needed. Because of the way phantom power is supplied,
all phantom powered microphones must be balanced, and must employ the same wiring configuration.
Budget mixers or cassette multi trackers with unbalanced mic inputs cannot be used with conventional
capacitor microphones unless an external mic preamp (with phantom power) is used.
Broadly speaking, capacitor microphones are more expensive than their dynamic counterparts, but they
are also much more sensitive, and can capture high-frequency detail much more accurately. Furthermore,
the capacitor principle, unlike the dynamic principle, lends itself easily to the production of mics with
switchable pickup patterns
PIEZOELECTRIC MICROPHONE
A crystal microphone or piezo microphone uses the phenomenon of piezoelectricity the ability of some
materials to produce a voltage when subjected to pressure to convert vibrations into an electrical signal.
An example of this is potassium sodium tart rate, which is a piezoelectric crystal that works as a
transducer, both as a microphone and as a slim line loudspeaker component. Crystal microphones were
once commonly supplied with vacuum tube equipment, such as domestic tape recorders. Their high
output impedance matched the high input impedance (typically about 10 mega ohms) of the vacuum tube
11. 11
input stage well. They were difficult to match to early transistor equipment, and were quickly supplanted
by dynamic microphones for a time, and later small electrets condenser devices. The high impedance of
the crystal microphone made it very susceptible to handling noise, both from the microphone itself and
from the connecting cable.
Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical
instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging
environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are
generally piezoelectric devices that contact the strings passing over the saddle. This type of microphone is
different from magnetic coil pickups commonly visible on typical electric guitars, which use magnetic
induction, rather than mechanical coupling, to pick up vibration.
FIBER OPTICS MIC
A fiber optic microphone converts acoustic waves into electrical signals by sensing changes in light
intensity, instead of sensing changes in capacitance or magnetic fields as with conventional microphones.
During operation, light from a laser source travels through an optical fiber to illuminate the surface of a
reflective diaphragm. Sound vibrations of the diaphragm modulate the intensity of light reflecting off the
diaphragm in a specific direction. The modulated light is then transmitted over a second optical fiber to a
photo detector, which transforms the intensity modulated light
into analog or digital audio for transmission or recording. Fiber
optic microphones possess high dynamic and frequency range,
similar to the best high fidelity conventional microphones.
Fiber optic microphones do not react to or influence any
electrical, magnetic, electrostatic or radioactive fields (this is
called EMI/RFI immunity). The fiber optic microphone design is
therefore ideal for use in areas where conventional microphones
are ineffective or dangerous, such as inside industrial turbines or in magnetic resonance imaging (MRI)
equipment environments.
Fiber optic microphones are robust, resistant to environmental changes in heat and moisture, and can be
produced for any directionality or impedance matching. The distance between the microphone's light
source and its photo detector may be up to several kilometers without need for any preamplifier or other
electrical device, making fiber optic microphones suitable for industrial and surveillance acoustic
monitoring.
12. 12
Fiber optic microphones are used in very specific application areas such as for infrasound monitoring
and noise-canceling. They have proven especially useful in medical applications, such as allowing
radiologists, staff and patients within the powerful and noisy magnetic field to converse normally, inside
the MRI suites as well as in remote control rooms. Other uses include industrial equipment monitoring
and sensing, audio calibration and measurement, high-fidelity recording and law enforcement.
ROBIN MIC
Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic field. The
ribbon is electrically connected to the microphone's output, and its vibration within the magnetic field
generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense
that both produce sound by means of magnetic induction. Basic ribbon microphones detect sound in a bi-
directional pattern because the ribbon, which is open to sound both front and back, responds to
the pressure gradient rather than the sound pressure. Though the symmetrical front and rear pickup can be
a nuisance in normal stereo recording, the high side rejection can be used to advantage by positioning a
ribbon microphone horizontally, for example above cymbals, so that the rear lobe picks up only sound
from the cymbals. Stereo recording is gaining in popularity
Some new modern ribbon microphone designs incorporate a preamplifier and, therefore, do require
phantom power, and circuits of modern passive ribbon microphones, i.e., those without the
aforementioned preamplifier, are specifically designed to resist damage to the ribbon and transformer by
phantom power. Also there are new ribbon materials available that are immune to wind blasts and
phantom power.
13. 13
CARBON MIC
A carbon microphone, also known as a carbon button microphone (or sometimes just a button
microphone), uses a capsule or button containing carbon granules pressed between two metal plates like
the Berliner and Edison microphones. A voltage is applied across the metal plates, causing a small current
to flow through the carbon. One of the plates, the diaphragm, vibrates in sympathy with incident sound
waves,applying a varying pressure to the carbon.
The changing pressure deforms the granules, causing the contact area between each pair of adjacent
granules to change, and this causes the electrical resistance of the mass of granules to change. The
changes in resistance cause a corresponding change in the current flowing through the microphone,
producing the electrical signal. Carbon microphones were once commonly used in telephones
CONTROL ROOM
A control room or operations center or operations control center (OCC) is a room serving as a central
space where a large physical facility or physically dispersed service can be monitored and controlled A
control room is a room for production control, and it serves as a
central space where a large physical facility or physically
dispersed service can be monitored and controlled.
Control rooms for vital facilities are typically tightly secured
and inaccessible to the general public. Multiple electronic
displays and control panels are usually present, and there may
also be a large wall-sized display area visible from all locations
within the space. Some control rooms are themselves under
continuous video surveillance and recording, for security and personnel accountability purpose.
14. 14
CONTROL PANEL
A control panel is a flat, often vertical, area where control or monitoring instruments are displayed. They
are found in factories to monitor and control machines or production lines and in places such as nuclear
power plants, ships, aircraft and mainframe computers. Older control panels are most often equipped with
push buttons and analog instruments, whereas today in many cases touchscreens are used for monitoring
and control purposes.
AUDIO CONSOLE
In audio, a mixing console, or audio mixer, also called a mixing desk, is an electronic device for
combining (also called "mixing"), routing, and changing the level, timbre and/or dynamics of audio
signals. A mixer can mix analog or digital signals,
depending on the type of mixer. The modified signals
(voltages or digital samples) are summed to produce the
combined output signals.
Mixing consoles are used in many applications,
including recording studios, public address systems, sound
reinforcement systems, broadcasting, television, and film
post-production. A typical, simple application combines
signals from two microphones (each used by
vocalists singing a duet, perhaps) into an amplifier that
drives one set of speakers simultaneously. In live
performances, the signal from the mixer usually goes directly to an amplifier (unless the mixer has a built
in power amplifier or is connected to powered speakers). Among the highest quality bootleg recordings of
live performances are so called soundboard recordings sourced from the mixer output
A typical analog mixing board has three sections:
Channel inputs
Master controls
Audio level metering
The channel input strips are usually a bank of identical monaural or stereo input channels. The master
control section has sub group faders, master faders, master auxiliary mixing bus level controls and
auxiliary return level controls. In addition it may have solo monitoring controls, a stage talk back
microphone control, muting controls and an output matrix mixer. On smaller mixers the inputs are on the
left of the mixing board and the master controls are on the right. In larger mixers, the master controls are
in the center with inputs on both sides. The audio level meters may be above the input and master sections
or they may be integrated into the input and master sections themselves.
15. 15
PATCH PANEL
A patch panel, patch bay, patch field or jack field is a device or unit featuring a number of jacks, usually
of the same or similar type, for the use of connecting and routing circuits for monitoring, interconnecting,
and testing circuits in a convenient, flexible manner. Patch panels are commonly used in computer
networking, recording studios, and radio and television
In recording studios, television and radio broadcast studios, and concert sound reinforcement systems,
patch bays are widely used to facilitate the connection of
different devices, such as microphones, electric or electronic
instruments, effects (e.g. compression, reverb, etc.), recording
gear, amplifiers, or broadcasting equipment. Patchbays make it
easier to connect different devices in different orders for
different projects, because all of the changes can be made at the
patchbay. Additionally, patchbays make it easier to troubleshoot
problems such as ground loops, even small home studios and
amateur project studios often use patchbays, because it groups
all of the input jacks into one location. This means that devices
mounted in racks or keyboard instruments can be connected
without having to hunt around behind the rack or instrument
with a flashlight for the right jack. Using a patchbay also saves wear and tear on the input jacks of studio
gear and instruments, because all of the connections are made with the patchbay.
Patch panels are being used more prevalently in domestic installations, owing to the popularity of
"Structured Wiring" installs. They are also found in home cinema installations more and more
SWITCHER
Dedicated switching equipment can be an alternative to patch bays in some applications. Switches can
make routing as easy as pushing a button, and can provide other benefits over patch bays, including
routing a signal to any number of destinations simultaneously. However, switching equipment that can
emulate the capabilities of a given patch bay is much more expensive.
For example, an S-Video matrix routing switcher with the same
capability (8×8) as a 16-point S-Video patch panel (8 patch
cables connects 8 inputs and 8 outputs) may cost ten times more,
though it would probably have more capabilities, including audio
follow video and built-in distribution amplifiers.
There are various types of switches for audio and video, from
simple selector switches to sophisticated production switchers.
However, emulating or exceeding the capabilities of audio and/or
video patch bays requires specialized devices like routing
switches and crossbar switches.
Like patch panels, switching equipment for nearly any type of signal is available, including analog and
digital video and audio, as well as RF (cable TV), MIDI, telephone, networking, electrical, and just about
anything else.
16. 16
Switching equipment may be electronic, mechanical, or electro-mechanical. Some switcher hardware can
be controlled via computer and/or other external devices. Some have automated and/or pre-programmed
operational capabilities. There are also software switcher applications used to route signals and control
data within a "pure digital" computer environment.
ANALOG TRANSMISSION
Analog (or analogue) transmission is a transmission method of conveying voice, data, image, signal
or video information using a continuous signal which varies in amplitude, phase, or some other property
in proportion to that of a variable. It could be the transfer of an analog source signal, using an
analog modulation method such as frequency modulation (FM) or amplitude modulation (AM)
FM
In telecommunications and signal processing, frequency modulation (FM) is the encoding
of information in a carrier wave by varying the instantaneous frequency of the wave. (Compare
with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency
remains constant.)
In analog signal applications, the difference between the instantaneous and the base frequency of the
carrier is directly proportional to the instantaneous value of the input signal amplitude.
FM broadcasting is a VHF broadcasting technology, pioneered by Edwin Howard Armstrong, which uses
frequency modulation (FM) to provide high fidelity sound over broadcast radio. The term "FM band"
describes the frequency band in a given country which is dedicated to FM broadcasting. This term is
slightly misleading, as it equates a modulation method with a range of frequencies. Throughout the world,
the FM broadcast band falls within the VHF part of the radio spectrum. Usually 87.5 to 108.0 MHz is
used.
AM
Amplitude modulation (AM) is a modulation technique used in electronic communication, most
commonly for transmitting information via a radio carrier wave. In amplitude modulation,
the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being
transmitted. That waveform may, for instance, correspond to the sounds to be reproduced by a
loudspeaker, or the light intensity of television pixels. This technique contrasts with frequency
modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which
its phase is varied.
AM was the earliest modulation method used to transmit voice by radio. It was developed during the first
two decades of the 20th century beginning with Reginald Fessenden's radiotelephone experiments in 1900
AM broadcasting is the process of radio broadcasting using amplitude modulation (AM). AM was the
first method of impressing sound on a radio signal and is still widely used today. Commercial and public
17. 17
AM broadcasting is authorized in the medium wave band worldwide, and also in parts of the long
wave and shortwave bands
ANTENNA
An antenna (or aerial) is an electrical device which converts electric power into radio waves, and vice
versa. It is usually used with a radio transmitter or radio receiver. In transmission, a radio transmitter
supplies an electric current oscillating at radio frequency (i.e. a high frequency alternating current (AC))
to the antenna's terminals, and the antenna radiates the energy from the current as electromagnetic
waves (radio waves). In reception, an antenna intercepts some of
the power of an electromagnetic wave in order to produce a tiny
voltage at its terminals, that is applied to a receiver to be amplified.
Antennas are essential components of all equipment that
uses radio. They are used in systems such as radio
broadcasting, broadcast television, two way radio, communications
receivers, radar, cell phones, and satellite communications, as well
as other devices such as garage door openers,wireless
microphones, Bluetooth enabled devices, wireless computer
networks, baby monitors, and RFID tags on merchandise.
Typically an antenna consists of an arrangement of metallic conductors (elements), electrically connected
(often through a transmission line) to the receiver or transmitter. An oscillating current of electrons forced
through the antenna by a transmitter will create an oscillating magnetic field around the antenna elements,
while the charge of the electrons also creates an oscillating electric field along the elements. These time-
varying fields radiate away from the antenna into space as a moving transverse electromagnetic field
wave. Conversely, during reception, the oscillating electric and magnetic fields of an incoming radio
wave exert force on the electrons in the antenna elements, causing them to move back and forth, creating
oscillating currents in the antenna.
OMNIDIRECTIONAL ANTENNA
In radio communication, an omnidirectional antenna is a class of antenna which radiates radio
wave power uniformly in all directions in one plane, with the radiated
power decreasing with elevation angle above or below the plane,
dropping to zero on the antenna's axis. This radiation pattern is often
described as "doughnut shaped". Note that this is different from
an isotropic antenna, which radiates equal power in all directions and
has a "spherical" radiation pattern. Omnidirectional antennas oriented
vertically are widely used for nondirectional antennas on the surface of
the Earth because they radiate equally in all horizontal directions,
while the power radiated drops off with elevation angle so little radio
18. 18
energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely
used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM
radios, walkie talkies, wireless computer networks, cordless phones, GPS as well as for base stations that
communicate with mobile radios, such as police and taxi dispatchers and aircraft communications.
Higher-gain omnidirectional antennas can also be built. "Higher gain" in this case means that the antenna
radiates less energy at higher and lower elevation angles and more in the horizontal directions
The radiation pattern of a simple omnidirectional antenna, a vertical half-wave dipole antenna. In this
graph the antenna is at the center of the "donut," or torus. Radial distance from the center represents the
power radiated in that direction. The power radiated is maximum in horizontal directions, dropping to
zero directly above and below the antenna
UNI DIRECTIONAL ANTENNA
A directional antenna or beam antenna is an antenna which radiates or receives greater power in one or
more directions allowing for increased performance and
reduced interference from unwanted sources. Directional
antennas like Yagi-Uda antennas provide increased
performance over dipole antennas when a greater
concentration of radiation in a certain direction is
desired.
All practical antennas are at least somewhat directional,
although usually only the direction in the plane parallel
to the earth is considered, and practical antennas can easily be omnidirectional in one plane.
The most common types are the Yagi-Uda antenna, the log-periodic antenna, and the corner reflector,
which are frequently combined and commercially sold as residential TV antennas. Cellular repeaters often
make use of external directional antennas to give a far greater signal than can be obtained on a
standard cell phone. Satellite Television receivers usually use parabolic antennas.
For long and medium wavelength frequencies, tower arrays are used in most cases as directional antennas
19. 19
TRANSMITTER
A broadcast transmitter refers to an installation used for broadcasting, including radio
transmitter or television transmitter equipment, the antenna, and often the location of the broadcasting
station.
In broadcasting and telecommunication, the part which contains the oscillator, modulator, and
sometimes audio processor, is called the "exciter". Most transmitters use heterodyne principle, so they
also have a frequency conversion units. Confusingly, the high power amplifier which the exciter then
feeds into is often called the "transmitter" by broadcast engineers.
The final output is given as transmitter power output (TPO),
although this is not what most stations are rated by.
Effective radiated power (ERP) is used when calculating station
coverage, even for most non-broadcast stations. It is the TPO,
minus any attenuation or radiated loss in the line to the antenna,
multiplied by the gain (magnification) which the antenna provides
toward the horizon. This antenna gain is important, because
achieving a desired signal strength without it would result in an
enormous electric utility bill for the transmitter, and a prohibitively
expensive transmitter. For most large stations in the VHF- and UHF-range, the transmitter power is no
more than 20% of the ERP.
For VLF, LF, MF and HF the ERP is typically not determined separately. In most cases the transmission
power found in lists of transmitters is the value for the output of the transmitter. This is only correct for
omnidirectional aerials with a length of a quarter wave length or shorter. For other aerial types there are
gain factors, which can reach values until 50 for shortwave directional beams in the direction of
maximum beam intensity.
BLOCK DIAGRAM OF RADIO TRANSMITTER
This is a diagram of a typical Amplitude-Modulated transmitter. The principles of each block and the
principles of Amplitude Modulation are treated in Oscillators and in Signals.
The block diagram is derived from the CW transmitter.
The modulated stage is usually the final amplifier in the transmitter. This is known as high
level modulation. If a following amplifier is used to raise the output power level, it must be a linear
amplifier
20. 20
RECIEVER
In radio communications, a radio receiver is an electronic device that receives radio waves and converts
the information carried by them to a usable form. It is used with an antenna. The antenna intercepts radio
waves (electromagnetic waves) and converts them to tiny alternating currents which are applied to the
receiver, and the receiver extracts the desired information. The
receiver uses electronic filters to separate the desired radio
frequency signal from all the other signals picked up by the
antenna, an electronic amplifier to increase the power of the
signal for further processing, and finally recovers the desired
information through demodulation.
The information produced by the receiver may be in the form of
sound (an audio signal), images (a video signal) or data
(a digital signal). A radio receiver may be a separate piece of
electronic equipment, or an electronic circuit within another
device. Devices that contain radio receivers include television sets, radar equipment, two way radios, cell
phones, wireless computer networks, GPS navigation devices, satellite dishes, radio
telescopes, bluetooth enabled devices, garage door openers, and baby monitors.
In consumer electronics, the terms radio and radio receiver are often used specifically for receivers
designed to reproduce the audio (sound) signals transmitted by radio broadcasting stations historically the
first mass-market commercial radio application.
BLOCK DIAGRAM OF RECIEVER
A simple receiver for the reception of amateur radio SSB and CW signals can be constructed by you at
home. Yes! You could build it yourself!. It uses the direct conversion principle.
This receiver consists of a mixer stage and an audio amplifier.
The mixer converts the incoming signal frequency down to a lower frequency - this time right down to
audio frequencies. It can be considered to be a superhet receiver with a 0 kHz (zero) intermediate
frequency. The derived audio is passed through a simple audio filter to an audio amplifier to drive
headphones or speaker
21. 21
STL
A studio-transmitter link (or STL) sends a radio station's or television station's audio and video from
the broadcast studio to a radio transmitter or television transmitter in another location.
This is often necessary because the best locations for an antenna are on top of a mountain, where a much
shorter tower is required, but where a studio is completely impractical. Even in flat regions, the center of
the station's allowed coverage area may
not be near the studio location or within a
populated area where a transmitter would
be frowned upon by the community, so the
antenna must be placed several miles or
kilo meters away.
Depending on the locations that must be
connected, a station may choose either
a point to point (PTP) link on another
special radio frequency, or a newer all digital wired link via a dedicated T1 or E1 (or larger capacity) line.
Radio links can also be digital, or the older analog type, or a hybrid of the two. Even on older all-
analog systems, multiple audio and data channels can be sent using subcarriers.
Stations that employ an STL usually also have a transmitter-studio link (or TSL) to
return telemetry information. Both the STL and TSL are considered broadcast auxiliary services (BAS).
RADIATION PATTERN
In the field of antenna design the term radiation pattern (or antenna pattern or far field pattern) refers to
the directional (angular) dependence of the strength of the radio waves from the antenna or other source.
Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern may also
be used as a synonym for the near field pattern or Fresnel pattern. This refers to the positional dependence
of the electromagnetic field in the near field, or Fresnel region of the source. The near field pattern is
most commonly defined over a plane placed in front of the source, or over a cylindrical or spherical
surface enclosing it.
The far field pattern of an antenna may be determined experimentally at an antenna range, or
alternatively, the near-field pattern may be found using a near field scanner, and the radiation pattern
deduced from it by computation. The far-field radiation pattern can also be calculated from the antenna
shape by computer programs such as NEC. Other software,like HFSS can also compute the near field.
The far field radiation pattern may be represented graphically as a plot of one of a number of related
variables, including; the field strength at a constant (large) radius (an amplitude pattern or field pattern),
the power per unit solid angle (power pattern) and the directive gain. Very often, only the relative
amplitude is plotted, normalized either to the amplitude on the antenna bore sight, or to the total radiated
power. The plotted quantity may be shown on a linear scale, or in dB. The plot is typically represented as
a three-dimensional graph (as at right), or as separate graphs in the vertical plane and horizontal plane.
This is often known as a polar diagram.
Since electromagnetic radiation is dipole radiation, it is not possible to build an antenna that radiates
equally in all directions, although such a hypothetical isotropic antenna is used as a reference to
22. 22
calculate antenna gain. The simplest antennas, monopole and dipole antennas, consist of one or two
straight metal rods along a common axis.
These axially symmetric antennas have radiation patterns with a similar symmetry,
called omnidirectional patterns; they radiate equal power in all directions perpendicular to the antenna,
with the power varying only with the angle to the axis, dropping off to zero on the antenna's axis. This
illustrates the general principle that if the shape of an antenna is symmetrical, its radiation pattern will
have the same symmetry.
In most antennas, the radiation from the different parts of the antenna interferes at some angles. This
results in zero radiation at certain angles where the radio waves from the different parts arrive out of
phase, and local maxima of radiation at other angles where the radio waves arrive in phase. Therefore the
radiation plot of most antennas shows a pattern of maxima called "lobes" at various angles, separated by
"nulls" at which the radiation goes to zero.
The larger the antenna is compared to a wavelength, the more lobes there will be. In a directive antenna in
which the objective is to direct the radio waves in one particular direction, the lobe in that direction is
larger than the others; this is called the "main lobe". The axis of maximum radiation, passing through the
center of the main lobe, is called the "beam axis" or bore sight axis". In some antennas, such as split-beam
antennas, there may exist more than one major lobe. A minor lobe is any lobe except a major lobe.
The other lobes, representing unwanted radiation in other directions, are called "side lobes". The side lobe
in the opposite direction (180°) from the main lobe is called the "back lobe". Usually it refers to a minor
lobe that occupies the hemisphere in a direction opposite to that of the major (main) lobe.
Minor lobes usually represent radiation in undesired directions, and they should be minimized. Side lobes
are normally the largest of the minor lobes. The level of minor lobes is usually expressed as a ratio of the
power density in the lobe in question to that of the major lobe. This ratio is often termed the side lobe
ratio or side lobe level. Side lobe levels of −20 dB or smaller are usually not desirable in many
applications. Attainment of a side lobe level smaller than −30 dB usually requires very careful design and
construction. In most radar systems, for example, low side lobe ratios are very important to minimize
false target indications through the side lobes.
23. 23
SATELITE
In the context of spaceflight, a satellite is an artificial object which has been intentionally placed
into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural
satellites such as the Moon.
The world's first artificial satellite, the Sputnik, was launched by the Soviet Union in 1957. Since then,
thousands of satellites have been launched into orbit around
the Earth. Some satellites, notably space stations, have been
launched in parts and assembled in orbit. Artificial satellites
originate from more than 40 countries and have used the
satellite launching capabilities of ten nations. A few hundred
satellites are currently operational, whereas thousands of
unused satellites and satellite fragments orbit the Earth as space
debris. A few space probes have been placed into orbit around
other bodies and become artificial satellites to the
Moon, Mercury, Venus, Mars, Jupiter,
Saturn, Vesta, Eros, Ceres,and the Sun.
Satellites are used for a large number of purposes. Common
types include military and civilian Earth observation satellites, communications satellites, navigation
satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also
satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a
number of ways. Well known (overlapping) classes include low Earth orbit, polar orbit, and geostationary
orbit.
About 6,600 satellites have been launched. The latest estimates are that 3,600 remain in orbit. Of those,
about 1,000 are operational, the rest have lived out their useful lives and are part of the space debris.
Approximately 500 operational satellites are in low-Earth orbit, 50 are in medium-Earth orbit (at
20,000 km), the rest are in geostationary orbit (at 36,000 km).
Satellites are propelled by rockets to their orbits. Usually the launch vehicle itself is a rocket lifting off
from a launch pad on land. In a minority of cases satellites are launched at sea (from a submarine or
a mobile maritime platform) or aboard a plane (see air launch to orbit).
Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many
tasks, such as power generation, thermal control, telemetry, attitude control and orbit control
24. 24
USE OF SATELITE IN BROADCAST
Satellite radio is a radio service broadcast from satellites primarily to cars, with the signal broadcast
nationwide, across a much wider geographical area than terrestrial radio stations. It is available by
subscription, mostly commercial free, and offers
subscribers more stations and a wider variety of
programming options than terrestrial radio.
Satellite radio technology was inducted into the Space
Foundation Space Technology Hall of Fame in
2002. Satellite radio uses the 2.3 GHz S band in North
America for nationwide digital audio
broadcasting (DAB). In other parts of the world, satellite
radio uses the 1.4 GHz L band allocated for DAB.
Satellite radio subscribers purchase a receiver and pay a
monthly subscription fee to listen to programming. They
can listen through built-in or portable receivers in
automobiles; in the home and office with a portable or tabletop receiver equipped to connect the receiver
to a stereo system; or on the Internet.
Ground stations transmit signals to the satellites, which are orbiting over 22,000 miles above the surface
of the Earth. The satellites send the signals back down to radio receivers in cars and homes. This signal
contains scrambled broadcasts, along with meta data about each specific broadcast. The signals are
unscrambled by the radio receiver modules, which display the broadcast information. In urban areas,
ground repeaters enable signals to be available even if the satellite signal is blocked. The technology
allows for nationwide broadcasting, so that, for instance US listeners can hear the same stations anywhere
in the country.
