© 2008 The McGraw-Hill Companies 1Broadcast Wave Propagation and Television Modified by Sunantha Sodsee

© 2008 The McGraw-Hill Companies

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BroadcastBroadcast

Wave Propagation and Television

Modified by Sunantha Sodsee


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Radio-Wave PropagationRadio-Wave Propagation

Radio-Wave Propagation Through Space The three basic paths that a radio signal can take

through space are: Ground wave Sky wave Space wave


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Radio-Wave Propagation Through Space: Ground Waves

Ground or surface waves leave an antenna and remain close to the earth.

Ground waves actually follow the curvature of the earth and can travel at distances beyond the horizon.


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Ground waves must have vertical polarization to be propagated from an antenna.

Ground-wave propagation is strongest at the low- and medium-frequency ranges.

AM broadcast signals are propagated primarily by ground waves during the day and by sky waves at night.


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Ground or surface wave radiation from an antenna.


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Radio-Wave Propagation Through Space: Sky Waves

Sky-wave signals are radiated by the antenna into the upper atmosphere, where they are bent back to earth.

When a radio signal goes into the ionosphere, the different levels of ionization cause the radio waves to be gradually bent.


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The smaller the angle with respect to the earth, the more likely it is that the waves will be refracted and sent back to earth.

The higher the frequency, the smaller the radiation angle required for refraction to occur.


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Sky wave propagation.


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Radio-Wave Propagation Through Space: Space Waves

A direct wave, or space wave, travels in a straight line directly from the transmitting antenna to the receiving antenna.

Direct-wave radio signaling is often referred to as line-of-sight communication.


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Direct or space waves are not refracted, nor do they follow the curvature of the earth.

Line-of-sight communication is characteristic of most radio signals with a frequency above 30 MHz, particularly VHF, UHF, and microwave signals.


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Line-of-sight communication by direct or space waves.


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Radio-Wave Propagation Through Space: Space Waves

Repeater stations extend the communication distance at VHF, UHF, and microwave frequencies.

A repeater is a combination of a receiver and a transmitter operating on separate frequencies.


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The receiver picks up a signal from a remote transmitter, amplifies it, and retransmits it (on another frequency) to a remote receiver.

Repeaters are widely used to increase the communication range for mobile and handheld radio units.


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In a trunked repeater system, multiple repeaters are under the control of a computer system that can transfer a user from an assigned but busy repeater to another, available repeater, thus spreading the communication load.

Communication satellites act as fixed repeater stations.

The receiver-transmitter combination within the satellite is known as a transponder.


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TV Signal (Analog)TV Signal (Analog)

The TV signal consists of the sound and the picture.

The sound is stereo and the picture carries color information as well as the synchronizing signals that keep the receiver in step with the transmitter.


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TV signals are assigned to frequencies in the VHF and UHF range.

Although TV is still transmitted by radio waves, most viewers get their TV signals via a cable.

cable TV that carries the “over-the-air” TV channels as well as premium and specialized channels of programming.


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Scanning is a technique that divides a rectangular scene into individual lines.

The standard TV scene dimensions have an aspect ratio of 4:3; that is, the scene width is 4 units for every 3 units of height.

To create a picture, the scene is subdivided into many fine horizontal lines called scan lines.


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Generating the Video Signal: Principles of Scanning The camera takes the light intensity and color details in

a scene and converts them into an electrical signal.

the scene to be transmitted is collected and focused by a lens upon a light-sensitive imaging device.

The scene is divided into smaller segments that can be transmitted serially over a period of time.

This subdivision process is known as scanning.


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Each line represents a very narrow portion of light variations in the scene.

The greater the number of scan lines, the higher the resolution and the greater the detail that can be observed.

The electrical signals derived from each scan line are referred to as the video signal.


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Simplified explanation of scanning.


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The bandwidth of a video system determines the resolution.

The greater the bandwidth, the greater the amount of definition and detail.

The light in any scene can also be divided into its three basic color components by passing the light through red, green, and blue filters. The result is the generation of three simultaneous

signals (R, G, and B) during the scanning process by the light-sensitive imaging devices.


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How the camera generates the color signals.


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Satellite TVSatellite TV

One of the most common methods of TV signal distribution is via communication satellite.

The TV signal to be distributed is used to frequency-modulate a microwave carrier, and then is transmitted to the satellite.

Satellites are widely used by the TV networks, the premium channel companies, and the cable TV industry for distributing their signals nationally.


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Satellite TV distribution.


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With direct broadcast satellite (DBS) TV, the system is designed for consumer reception directly from the satellite.

The new DBS systems feature digitally encoded video and audio signals, which make transmission and reception more reliable and provide outstanding picture and sound quality.

The DBS satellite uses the band Ku band with a frequency range of 11 to 14 GHz.


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The advantage of using the Ku band is that the receiving antennas may be smaller for a given amount of gain. The biggest problem is the increased attenuation of the

downlink signal caused by rain. because the wavelength of Ku band signals is near

that of water vapor. Therefore, the water vapor absorbs the signal.

The digital signal is transmitted from the satellite to the receiver using circular polarization.


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DBS Receivers The receiver subsystem begins with the horn antenna,

which picks up the Ku band signal and translates the entire 500-MHz band down to the 950- to 1450-MHz range.

The RF signal from the antenna is sent by coaxial cable to the receiver.

The received signal is passed through another mixer with a variable-frequency local oscillator to provide channel selection.


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Digital TelevisionDigital Television

• Objectives of Digital-TV Multiplication of programs which can be sent over a

transmission line Audio transmissions Flexible choice of Quality Encryption can be used for Pay-Services Data Transfer Method


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• What is Digital Video Broadcasting (DVB) ? Most used Standard for Digital Television Standards

DVB-S for Satellite Transmissions DVB-C for Cable Transmissions DVB-T for Terrestrial Transmissions

DVB-T2


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• Why Digital ? Digital Technology‘s displace Analog Analog Receiving is rarely "Perfect" Interferences

Mountains Buildings Forrest’s other Emitters

Few Programs DVB-T

Information divided on many Frequencies Along-sent Error Corrections Common Frequency Broadcasting


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Analog TV Standard definition (SD) 480p – Picture is 704 x 480

pixels, sent at 60 complete frame/sec Screen: 4:3 Audio: Stereo 2 channels

Digital TV Full High Definition (Full HD) 1080p – Picture is 1920

x 1080 pixels, sent at 60 frame/sec Screen: 16:9 Audio: Surround 5.1 channels


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• What I have to expect ? You can use very small Antennas You can watch TV in your Car Enough Signal Power nearly perfect Picture Less Signal Power a black Screen Regardless…

not necessarily a better Picture Some Stations use old Encoders Rarely a Dolby-Digital Soundtrack


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DVB-S Analog


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Digital TV (DTV), also known as high-definition TV (HDTV) The goal of HDTV is to greatly improve the picture and

sound quality. The HDTV system is an extremely complex collection

of digital, communication, and computer techniques.

In HDTV both the video and the audio signals must be digitized by A/D converters and transmitted serially to the receiver.


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HDTV Transmission Concepts: HDTV Transmitter In an HDTV transmitter, the video from the camera

consists of the R, G, and B signals that are converted to the luminance and chrominance signals. These are digitized by A/D converters.

The resulting signals are serialized and sent to a data compressor.

MPEG-2 is the data compression method used in HDTV.

The signal is next sent to a data randomizer.


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HDTV Transmission Concepts: HDTV Transmitter

The modulated signal is up-converted by a mixer to the final transmission frequency, which is one of the standard TV channels in the VHF or UHF range.

A linear power amplifier is used to boost the signal level prior to transmission by the antenna.


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HDTV transmitter.


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HDTV Transmission Concepts: HDTV Receiver What does a DTV receiver do?

Receives digital TV broadcasts from a cable, satellite or terrestrial network

Decodes them Outputs them to a television or other display device This display device is usually a television


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HDTV Transmission Concepts: HDTV Receiver

The signals are demultiplexed into the video and audio bit streams.

The video signal is converted back to the digital signals that will drive the D/A converters that, in turn, drive the red, green, and blue electron guns in the CRT.

DVB-H is a special form of TV now being developed for use on cell phones and other small-screen devices.


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Types of digital TV receiver Set-top box (STB)

The most common type Varies in functionality and features from very basic to very

advanced May be integrated with other types of device

E.g. a DVD player or PVR system

Integrated Digital TV (IDTV)

Receiver is built into a TV set Can receive digital or analog broadcasts with no extra hardware

PC with digital tuner card

Similar to analog TV tuners, except it decodes digital TV signals


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TV ReceiverTV Receiver

Plasma: A plasma screen is made up of many tiny cells filled with a special gas.

When the gas is excited by an electric signal, the gas ionizes and becomes a plasma that glows brightly in shades of red, blue, and green.

The cells are organized to form triads that are mixed and blended by your eye to form the picture.


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TV ReceiverTV Receiver

LCD. Liquid-crystal displays use special chemicals, sandwiched between pieces of glass, that are designed to be electrically activated so that they block light or pass light.

When a bright white light is placed behind the screen, the red, blue, and green sections of the screen pass the desired amount of light.


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Radio BroadcastRadio Broadcast

AM - Amplitude Modulation where the amplitude of a carrier wave is varied in accordance with so

me characteristic of the modulating signal

FM - Frequency Modulation A method of impressing data onto an alternating-current (AC) wave b

y varying the instantaneous frequency of the wave.

HD Radio HD Radio technology transmits digital audio and data alongside exist

ing AM and FM analog signals. According to Ibiquity, the developer of this technology makes "...your AM sound like FM and FM sounds like CDs.“

www.about.com


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Radio BroadcastRadio Broadcast

HD Radio is a digital radio broadcast service that offers higher quality audio, clear, static-free reception, more programming choices and text-based information, such as artist, title, weather information and multicasting, which is the ability to receive multiple programs on the same radio frequency (example 97.1-1, 97.1-2,97.1-3, etc.) HD Radio requires a special tuner to receive the broadcast.

Internet Radio It feels like radio and sounds like radio but it's not really radio by

definition. Internet Radio - also referred to as "streaming" provides the illusion of

radio by separating audio into small packets of digital information, sending it to another location (your computer) and reassembling the packets into one continuous stream of audio.

www.about.com


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Satellite RadioSatellite Radio


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Radio AudiencesRadio Audiences


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BroadbandBroadband

Modified by Sunantha Sodsee


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Dialup Internet AccessDialup Internet Access

Problem - Speed World Wide Wait Telephone lines Using Technology designed for voice not computers Analog Modems are at the limit of their capability

Technology Solution - Broadband


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Broadband

Broadband refers to a range of technologies that enable always-on, high-speed access to the Internet and

other electronic services.


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Broadband over Power LineBroadband over Power Line

BPL (Broadband over Power Line) technology makes possible high-speed Internet access over ordinary residential electrical lines.

Computer network information can be transmitted over the lines using signaling frequencies higher than the electrical signals.

Taking advantage of otherwise unused transmission capability of the wires, computer data can be sent back and forth across the BPL network with no disruption to power output in the home.

Unfortunately, some limitations of BPL have greatly affected its popularity. BPL tends to generate much radio interference over the utility lines it runs. This interference negatively affects amateur radio operators and has generated m

uch government regulatory attention around the world.

www.about.com


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DSL

DSL is a high-speed Internet service like cable Internet. DSL provides high-speed networking over ordinary phone lines using

broadband modem technology.

DSL technology allows Internet and telephone service to work over the same phone line without requiring customers to disconnect either their voice or Internet connections.

DSL technology theoretically supports data rates of 8.448 Mbps, although typical rates are 1.544 Mbps or lower.

DSL Internet services are used primarily in homes and small businesses.

DSL Internet service only works over a limited physical distance and remains unavailable in many areas where the local telephone infrastructure does not support DSL technology. www.about.com


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HDSL

HDSL service provides equal bandwidth for both downloads and uploads, offering data rates up to 2,048 Kbps. Note that HDSL requires multiple phone lines to

accomplish this. HDSL features "always on" combined voice and data

services. HDSL enjoyed some popularity in years past, but the

technology has effectively been replaced by alternatives like SDSL that only require one phone line and offer similar performance and reach.

www.about.com


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SDSL

SDSL is a form of Digital Subscriber Line (DSL) service that provides equal bandwidth for both uploads and downloads. SDSL was one of the earliest forms of DSL to not require multiple t

elephone lines.

SDSL possesses all of the common characteristics of DSL, including an "always on" combination of voice and data services, availability limited by physical distance, and high speed access compared to analog modems.

SDSL supports data rates up to 3,088 Kbps.

www.about.com


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ADSL

ADSL is a type of DSLInternet service commonly used in homes. The 'A' in ADSL refers to its asymmetry:

ADSL connections provide comparatively more bandwidth for downloads than for uploads.

ADSL is designed to support the typical home user who frequently downloads large amounts of data from Web sites and P2P networks but upload relatively less often.

ADSL works by allocating a majority of the available phone line frequencies for communication of downstream traffic.

ADSL is technically capable of up to 6 Mbps (roughly 6000 Kbps), but ADSL customers in practice obtain 2 Mbps or lower for downloads and up to 512 Kbps for uploads. www.about.com


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RADSL

RADSL is an implementation of ADSL that automatically adjusts the connection speed to adjust for the quality of the telephone line. This feature allows RADSL service to function over longer

distances than does ordinary ADSL, an important feature in suburban neighborhoods.

In RADSL, the broadband modem is configured at startup to test the phone line and adjust the data rate. RADSL typically operates at a lower date rate than regular ADSL. RADSL provides relatively more bandwidth for downloads and less

for uploads.

www.about.com


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VDSL

VDSL was developed to support exceptionally high-bandwidth applications such as High-Definition Television (HDTV). VDSL is not as widely deployed as other forms of DSL service. VDSL can achieve data rates up to approximately 51,840 Kbps, making it the

fastest available form of DSL. VDSL relies on fiber optic cabling. VDSL is designed to work more as a business service that uses ATM

internetworking rather than as a consumer service that utilizes IP.

The performance of VDSL depends significantly on the physical distance traversed by wires: Shorter distances mean faster networking. The technology was originally named VADSL ('A' for asymmetric), but VDSL

has now been improved and can operate in either symmetric and asymmetric modes. www.about.com


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Home Networking TechnologyHome Networking Technology


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Additional ReferencesAdditional References

Steve Morris, “An introduction to DTV receiver technology”,2005, [http://www.interactivetvweb.org]

Rik Van de Walle, “An Introduction to Digital Television”, Universiteit Gent, [multimedialab.elis.ugent.be]

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© 2008 The McGraw-Hill Companies 1Broadcast Wave Propagation and Television Modified by Sunantha Sodsee