CHAPTER 4
How Electronic Media Work
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LEARNING OBJECTIVES:
After reading this chapter students should be able to understand the following concepts:
Electromagnetism: Describe the characteristics of electromagnetic energy.
Electromagnetic spectrum: Understand the properties and uses of electromagnetic spectrum.
Sound waves: Describe sound waves, and recognize their differences from and similarities to radio
waves.
Radio waves: Delineate the characteristics of radio waves, and understand the relationship between
frequency and wavelength.
Modulation: Understand signals as energy patterns, and understand how sidebands, channels, and
modulation methods differ.
Wave propagation: Describe how waves travel through space and how direct waves, ground waves, and
sky waves differ. Understand how and why coverage contours vary.
Antennas: Understand how reception, transmission, and signal direction are influenced by antennas.
Interference: Differentiate between co-channel and adjacent-channel interference.
AM stations: Comprehend the characteristics of a standard broadcasting, or AM, station, its location in
the spectrum, channel width, power, antenna characteristics, carrier current operation, and classes of
channels and stations.
CHAPTER FOCUS
This chapter concentrates on communication technology and physics of electronic mass media. Questions
from students are valuable guidelines when lecturing on this information. Although we can’t expect
students to understand fully the “mysteries” of electronic media technology, in part because it is difficult
to see and even imagine, they at least need to be aware of key principles and concepts. Take the material
in simple increments, building on them one by one, to remove some of the mystery. To do so, use the
exhibits extensively. They break down the concepts into manageable form.
You will find much here that answers questions students often have. What do VHF and UHF stand for?
Why are they named that? But also, why aren’t FM and AM radio defined by the bandwidth where they
are located, as is the case with television and elsewhere (i.e., UHF radio)? The numbers on the radio dial
or TV tuner lead to a discussion of carrier waves, and the oscillation of the carrier wave to produce a
TERMS, CONCEPTS, AND EXERCISES
Electromagnetism
Terms: electromagnetism, radio waves, frequency, wavelength, spectrum
oCompare electromagnetic spectrum to a piano keyboard. Both represent an orderly progression of
frequencies (from low sounds to higher sounds, from low frequencies to higher frequencies). You
can also talk about the visible spectrum, which comes in the form of a rainbow, where the colors
of light are separated into their unique frequencies, from low to high. Note that above visible light
is ultraviolet radiation. What colors have the highest and lowest frequencies? What is found in the
Radio and Audio Waves
Terms: cycle, Hertz, wavelength, frequency, MF (medium frequency), HF (high frequency), VHF (very
high frequency), kilo-, mega-, giga-, attenuation, non-ionizing radiation, channel, carrier waves,
harmonics, sound waves, tranduction
oReview the numbering system used to measure the cycles per second (Hertz). Note the use of
standard metric multipliers (kilo-, mega-, giga-), which are used to simplify the numbering
system.
oWhat is a carrier wave? What does it mean when we say that to produce a radio wave there must
Information, Formats, and Modulation
Terms: modulation, amplitude patterns, frequency patterns, audio frequency (AF), radio frequency (RF),
signal, amplitude modulation (AM), frequency modulation (FM), static, capture effect, sidebands, single-
sideband (SSB) signal, bandwidth, multiplexing, compression
oWhat happens when a carrier wave is modulated? What happens if you tune an unmodulated
carrier? One way to illustrate modulation is to explain what happens when a TV station goes off
the air. First the station stops modulating its signal, then it stops broadcasting entirely. For a
moment the screen and the sound are void of information. Explain that this is the carrier wave. In
effect, the station is broadcasting “nothing.” When the station turns off its carrier wave, snow fills
the screen and static is heard on the audio. Your television set is tuned to the station’s carrier
frequency on which no signal is being transmitted.
Wave Propagation
Terms: antenna, propagation, omnidirectional antenna, sunspots, shadows, coverage contour, direct
waves, ground waves, soil conductivity, refraction, sky waves, skip zone, ionosphere, directional
propagation, antenna gain, cliff effect
oDiscuss propagation and attenuation. Illustrate these properties by referring to common cases of
energy loss over time and distance.
oWhy is it that most radio and television transmitters do not radiate their signals in omnidirectional
patterns? What is a coverage contour? What is the difference in attenuation characteristics of
higher- and lower-frequency waves?
oExplain differences among ground, sky, and direct waves. See Exhibit 4.d. Note that the lower
Mutual Interference
Terms: co-channel interference, interference zone, selectivity, adjacent channel interference
oDifferentiate between co-channel and adjacent channel interference. How far must TV channels
be spaced to avoid interference problems? Note that television channels 4 and 5 and channels 6
and 7 are not truly adjacent. What lies between channels 4 and 5 and channels 6 and 7? (See
Exhibit 4.a.) Note that FM intervenes between television channels 6 and 7, and a nonbroadcast
AM Stations
Terms: amplitude modulation, clear AM channels, regional AM channels, local AM channels, classes of
AM stations: A, B, C, and D carrier-current stations, Travelers Information Service (TIS), AM stereo,
matrix mode, shortwave AM
oOn what band are AM channels located? What is the channel width of an AM station? How does
this compare to the bandwidth of the telephone? The human ear? FM radio? Why was this
bandwidth chosen?
oIf a station uses a carrier wave of 540, what is the actual band occupied by that station (535–545
KHz)?
oWhy are AM channels classified by the FCC as local, regional, and clear? What regions do they
serve? Why does the FCC further divide AM into four station classes as shown in Exhibit 4.f?
oWhy is the transmitter power of AM radio stations limited to a ceiling of 50 kilowatts? (Allows
FM Stations
Terms: standard or AM broadcasting, frequency modulation, Class A, B, and C FM stations, low-power
(LPFM), LP10, LP100, antenna gain, ERP, dynamic range, FM stereo, subsidiary communications
service (SCS), multiplex, radio broadcast data system (RBDS)
oWhat is the bandwidth of an FM channel? How many FM channels are available? What factors
determine coverage of an FM station?
oWhere is the best location for an FM transmitter in your area?
oWhat advantages does FM have over AM? (Stable coverage pattern, reduced atmospheric
Digital Signal Processing
Terms: analog, digital, sampling, quantized digital encoding, binary codes, bit (binary digit), bit speed,
signal compression, lossless compression, lossy compression
oTo illustrate how sampling is done for digital processing, draw an analog wave form. Then put a
series of dots on the form to show the sample.
oNow discuss how these discrete elements are so close together that they sound continuous.
oThen illustrate the way digital processing prevents loss of quality. Each dot-sample at right is
assigned a digital “on-off” code.
Digital Audio Broadcasting
Terms: digital audio broadcasting (DAB), “in-band, on-channel” (IBOC), IBOC DAB, iBiquity Digital
Corporation, HD radio, radio broadcast data system (RBDS)
oHow can DAB’s adoption affect the current AM and FM system? Here you could talk about DAB
sound quality “improving” the AM band so that the AM signal sounds as clear as the FM signal.
In addition, the cost of converting a radio station to DAB is far less than those for converting a
Digital TV Begins
Terms: high-definition television (HDTV), digital television (DTV), analog, MUSE, Advisory
Committee on Advanced Television Service (ACATS), “Grand Alliance,” Advanced Television Systems
Committee (ATSC), NTSC to digital, new channel allotments, “core spectrum,” DTV Table of
Allotments
oAsk students what benefits DTV offers. Here you need to emphasize consumer costs for purchase
of new sets (and station conversion of equipment to the new standard). How have television set
Digital TV (ATSC) vs. Analog TV (NTSC)
Terms: digital-to-analog convertor, cathode ray tube (CRT), charge-coupled device (CCD), pixel, 525
lines, resolution, interlace, fields, frame, persistence of vision, progressive scanning, compatibility, NTSC
(National Television System Committee), hues, saturation, luminance, TV channel, 6-MHz, DTV, SDTV
oHow does a chip or CCD-equipped camera work? (See Exhibit 4.l. Also, use the picture of old-
fashioned camera tubes to emphasize how smaller tubes made portable cameras, including home
video camcorders, possible.)
oWhat are the scanning standards for American television? Television uses 30 frames per second,
or 60 fields, the odd and even lines of the screen. Two fields, of even lines and odd lines,
DTV Transmission
Terms: MPEG-2 standard, Dolby Digital/AC-3 standard, pilot signal, data segment, segment sync
signal, data frame, data frame sync signal, 8-VSB, ERP, beam tilt
oUse Exhibit 4.p to highlight the components of a digital television system. Point out the
similarities of analog and digital systems.
DTV Reception
Terms: decompression, converter boxes, multicast channels, National Telecommunications and
Information Administration (NTIA), multipath signal interference, ghost images, white spaces, receiving
antenna
oHow will television viewers continue to receive television programs after the digital transition?
Point out that cable and DBS subscribers should not experience signal loss due to the switch to
digital television. Assess NTIA’s program to provide coupons for digital-to-analog converters.
Low-Power TV (LPTV) and Translators
Terms: Low-Power TV (LPTV), Class A LPTV, full-power station, translator
oWho are the audience for LPTV? How wide is the coverage area of an LPTV transmitter? How
Your TV Set
Terms: cathode ray tube (CRT), RGB (Red-Green-Blue) primaries, electron beam, synchronization
signals, liquid crystal display (LCD), backlight, transistor, flicker-free, plasma display panel (PDP), ultra
violet (UV) light, digital light processing (DLP), Texas Instruments, semiconductor chip, organic light-
emitting diodes (OLEDs), liquid crystal on silicon (LCoS), Bravia Internet Video Link, D-Link Media
Lounge
oHow does the cathode ray tube television set work (Exhibit 4.q)?
oEmphasize the ties between yesterday’s vacuum tubes and transistors and today’s chip
technology. If possible, bring an old tube and examples of transistors and chips to class for
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comparison. Visual differences among these devices should bring home the concept of
miniaturization.
oUse Exhibit 4.r to discuss LCD technology. List the proliferation of this technology in the last
PEARSON MYCOMMUNICATIONKIT RESOURCES
Each chapter of the MyCommKit for Head’s Broadcasting in America, 10th Edition includes chapter
learning objectives, practice quizzes, key terms flash card, and select media.
Media available for this chapter:
OUTSIDE AUDIO/VISUAL RESOURCES
Sound and Vision: AM and FM Sound (VHS, 28 min., 1990)
This program constitutes the first part of the Michael Faraday Lecture on Sound and Vision, delivered
before a live audience of British teenagers selected for their interest in either physics or broadcast careers.
Sound and Vision: Television (VHS, 28 min., 1990)
In the second half of the Michael Faraday Lecture on Sound and Vision, young BBC technical staff
members cover the illusion of movement, how images are transmitted, the difference between film and
The Development of Television (VHS, 15 min., 1993)
From the first steps of the pioneers Nipkow, Baird, and Zworykin, this program traces the development of
the medium up to satellite transmission and HDTV. Distributor: Films for the Humanities and Sciences.
Video, Audio, and Multimedia Systems (VHS, 16 min., 1997)
Opening with a brief history of television, this video details such electronic communication basics as
transmitters, receivers, channel frequencies, and satellite transmission. It teaches elements needed to
A Short History of the Recording Industry (VHS, 28 min., 1998)
This video traces the evolution of the record and recording business. Hosted by sound and record archives
curator Bill Shirk, it offers a fun and informative tour of the recording industry, profiling the most
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