The sharing ofpacket radio communications among amateur radio buffs began with packet bulletin board systems PBBSs similar to the BBSs popular with computer hobbyists in the early and mi
Trang 1Fiber Optics Illustrated Dictionary
network transmissions protocols with addresses
as-signed in the ampr.orgdomain
The sharing ofpacket radio communications among
amateur radio buffs began with packet bulletin board
systems (PBBSs) similar to the BBSs popular with
computer hobbyists in the early and mid-1980s The
main differences between the two were that computer
BBSs were primarily interconnected by land-based
telephone lines and modems, whereas packet radio
BBSs were interconnected by wireless radio
fre-quency communications through terminal node
con-trollers (TNCs) with a broadcast distance ofabout 20
miles or so Relays were still necessary for
long-dis-tance packet communications
When the Internet and rCP/IF became well
estab-lished, many computer buffs shut down their BBSs
and migrated to the Internet Packet radio followed
suit, forming the AmprNet to utilize low-cost global
aiIwaves and simultaneous two-way communications
Amateur Radio Emergency ServiceARES A
pub-lic service organization of pub-licen,sed Amateur Radio
Operators of the American Radio Relay League
(ARRL)who voluntarily provide emergency
commu-nications for public service events ARES cooperates
with state and local governments and the American
Red Cross http://www.ares.org!
Amateur Radio International Space Station
ARISS.Anorganization established to research and support the use of amateur radio in space; ARISS evolved out of the Space Shuttle Amateur Radio Ex-periment (SAREX) It serves as an educational out-reach tool and experimental communications testbed
It also provides backup for emergencys~ace com-munications and a medium for "off-duty' commu-nication with friends and family members
A Memorandum of Understanding was signed be-tween ARISS and various national radio organiza-tions in 1996 along with agreements with NASA and the Russian Energia NASA liaises with the public through its Division ofEducation programs and Web site Leadership and consultation are provided by the ARRL and AMSAT ARISS designs, builds, and op-erates amateur radio equipment in cooperation with International Space Station programs It established
ISS Hamas a technical team to support hardware de-velopment, training, and operations while in orbit While the initial communications of SAREX and ARISS were audio only, video is also an important aspect of radio communications and slow scan tele-vision (SSTV) is included in ARISS projections See Space Shuttle Amateur Radio Experiment
http://ariss.gsfc.nasa.gov/
amateur radio operator, ham radio operator A dio broadcasting hobbyist permitted to transmit
ra-AMSAT-OSCAR Satellite Projects - Selected Overview Phase II Satellites - developmental, low-orbit, operational, longer lifespan See OSCAR
Phase III Satellites - operational, high elliptical orbit, longer lifespan
Phase IV Satellites - operational, high geostationary or drifting geostationary orbit, long lifespan
AMSAT-OSCAR 1 12 Dec 1961 Phase-4A 10 lb., beacon, 22-day orbit Initiated by a U.S
west coast group Nonrechargeable batteries Elliptical orbit at 421 kilometers Quarter-wave monopole antenna Morse code telemetry U.S Air Force launched
AMSAT-OSCAR 4 21 Dec 1965 TRWRadio Club construction Elliptical orbit at 34,000
kilometers (intended for circular orbit) No telemetry Sleeve dipole and monopole antennas
AMSAT-OSCAR 8 5 Mar 1978 Phase-2D Circular LEO at 910 kilometers Several
antennas Battery failed June 1983
AMSAT-OSCAR 10 16 Jun 1983 NASAINORAD #14129 Phase-3B Similar to OSCAR I,
with some improvements Coatings provided better temperature control On-board propulsion High-altitude, elliptical, synchronous-transfer Molniya orbit at 35,449 kilometers
AMSAT-OSCAR 13 15 Jun 1988 NASAINORAD #19216 Phase-3C Linear analog
transponder Magnetorquer stabilization Elliptical orbit at 38,000 kilometers, Molniya Carried RUDAK-l, which failed
AMSAT-OSCAR 16 22 Jan 1990 NASAINORAD #20439 PACSAT Sun-synchronous
near-polar LEO at 800 kilometers Store-and-forward file server and AX.25 protocol Digital repeater
Trang 2that permit amateur transmissions require that the
operator be licensed and fulfill certain requirements
In the U.S., also often called ham radio operator.
amateur satellite serviceA radio communication
service using space stations or Earth-orbiting
satel-lites for the purposes of the amateur
radio-communications service See amateur service,
AMSAT, OSCAR See AMSAT-OSCAR Satellite
Projects Chart
amateur seniceRadio communications services for
the purpose ofself-training, intercommunication, and
technical investigations carried out by amateurs, that
is, licensed or otherwise authorized persons interested
in radio technique solely with personal, educational,
or nonpecuniary aims See American Radio Relay
League
amateur televisionAmTV, ATV Black and white or
color image broadcasts through amateur radio
fre-quencies, with or without accompanying sound
broadcast Some amateur enthusiasts prefer to use
ATV to mean fast scan TV over amateur bands, and
SSTV for slow scan image transmission With
ad-vancements in television technology, advanced
tele-visionhas begun to be identified with the ATV
ab-breviation, occasionally causing confusion In the
future it may be advisable to use AmTV to designate
amateur television See slow scan television
amberA very light, transparent or semitransparent,
warm golden substance from fossilization tree resin
from pine trees that have been extinct for millions of
years Amber floats in water and occasionally washes
up on the coasts ofEurope after storms, intermingled
with kelp and other natural debris Sometimes insects
can be found imbedded in the amber, preserved for
centuries Amber can be highly polished and has been
used for jewelry for thousands of years
The chief importance of amber to
telecommunica-tions is its static electrical properties, which can be
observed by rubbing amber with a cloth (or on your
hair) and using it to attract small fragments of tissue
paper In fact, the Greeks observed this property, and
Plato recorded" the wonderful attracting power of
amber " in his Timaeus dialog The Greek word for
amber is elektron
ambientn Environment, atmosphere, mood,
sur-roundings
ambient lightThe light existing in an environment
around and in addition to any deliberately established
lights associated with a system Ambient light may
come from sunlight, reflective surfaces,
phosphores-cent materials, etc and is typically composed of a
variety of wavelengths
Ambient light conditions affect mood and visibility
and may be critically important to optical applications
using precision instruments, those sensitive to light
and those dependent upon specific types or levels of
light for specialized applications (darkroom devices,
microscopes, lasers, telescopes, etc.) The visibility
and size of laser spots, for example, is affected by
the amount and color of ambient light in addition
to the distance traveled before the beam hits a
ambient noise, room noiseThe general acoustic noise level of an environment, usually measured in decibels The ambient noise in terminal rooms with printers or other equipment may be sufficient to cause hearing loss over time Technicians who work long hours with high speed printers should wear ear pro-tection
ambient temperatureThe temperature in the envi-ronment around an object or system Ambient tem-peratures may affect the durability, stability, and per-formance of many types of components, especially conducting materials that conduct not only transmis-sion signals but also ambient temperature For com-ponents that are especially sensitive to temperature extremes or fluctuations, the housings may be designed
to control or mediate ambient temperatures AMDM ATM multiplexer/demultiplexer
America OnlineAOL A large, commercial Internet Services Provider (ISP) that provides access to the Internet, AOL-specific forums, news, email, and other features AOL evolved from Quantum Com-puter Services, conceived by S Case andJ.Kimsey
as a computer BBS providing online information and consumer services through modems In 1989 Quan-tum was renamed to America Online and was launched with realtime chat, email, and special in-terest forums Case became President ofthe company
in 1990 and CEO in 1993 AOL became a publicly traded company in 1996 In 1998, it acquired Compu-serve and ICQ, two well-known network services, as well as MapQuest, in 2000 In 2001, AOL completed
a merger with Time Warner
America's Carriers Telecommunications Associa-tionACTA A U.S.-based trade organization, repre-senting commercial long-distance vendors (nondominant interexchange vendors) Of signifi-cance is the fact that ACTA has lobbied the Federal Communications Commission (FCC) to bar long-dis-tance digital telephony over the Internet The focus ofACTA is providing representation for its members
to various legislative and regulatory bodies, and to further business activities of its members
American Association for Artificial Intelligence AAAI A nonprofit organization founded in 1979 to advance education in and scientific understanding of thought and intelligent behavior and their embodi-ment in machines http://www.aaaLorg/
American Association for the Advancement of ScienceAAAS Descended from the Association of American Geologists and Naturalists, the AAAS was formed with a broader mission in 1848 to promote the development of science and engineering in the United States http://www.aaas.org/
American Association of Physics TeachersAAPT The AAPT supports professional and research phys-ics and physphys-ics education through activities and
pub-lications, including the American Journal
ofPhys-ics, Physics Today, and The Physics Teacher
Phys-ics and engineering (applied physPhys-ics) are at the heart ofthe understanding and development ofall commu-nications systems http://www.aapt.org/
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American Bell Telephone CompanyIn 1875, the
Bell Patent Association was formed by Alexander
Graham Bell with investors willing to finance his
te-legraphy research Two years later, in 1877, The Bell
Telephone Company was formed by Bell, who
in-cluded his associate, Thomas Watson The company
was formally incorporated in Massachusetts in 1878
Theodore N Vail was hired as the general manager
and had a long association with the company and its
successors In 1878, the Bell Telephone Company and
the New England Telephone Company were
consoli-dated into the National Bell Telephone Company
Then, in 1880, American Bell Telephone Company
was incorporated In 1881, American Bell purchased
Western Electric Manufacturing Company and
devel-oped it into Western Electric Company, the equipment
manufacturing arm ofAmerican Bell
American Bell was the parent of the American
Tele-phone and Telegraphy Company (AT&T) AT&T was
established in New York as a subsidiary in 1885 for
handling long-distance calls These two were then
merged into AT&T in 1899 See AT&T; Vail,
Theo-dore N.; Western Electric Company
American Civil Liberties UnionACLU A
promi-nent, nonprofit, nonpartisan, civil liberties
organiza-tion founded in 1920 which now has more than a
quarter million members The ACLU monitors and
protects freedom and takes action against violations
ofcivil liberties wherever they may occur The ACLU
has a strong presence on the Web in light of the fact
that many new freedom-related legislative actions
have been taken as a result of the growth of the
In-ternet The ACLU publishes ACLU Online and the
biweekly Cyber-Liberties Update electronic
maga-zine The ACLU deals with many
telecommunica-tions issues including Web censorship, online privacy,
encryption, and more http://www.aclu.org/
American Communication AssociationACA A
not-for-profit association founded to promote
aca-demic and professional research, theory, criticism,
and debate on human communications ACA
pub-lishes The American Communication Journal, a
pro-fessional, peer-reviewed, online publication
http://www.americancomm.org/
American Engineering Association AEA A
na-tional nonprofit professional association supporting
and promoting American leadership in engineering
http://www.aea.orgl
American Electronics AssociationAeA A
Wash-ington, D.C.-based professional association with
of-fices in the U.S and abroad, founded in 1943 AeA
is dedicated to helping member companies excel in
a global competitive market AeANET is AeA's
means ofcommunicating industry news, surveys, and
public policy issues to its membership
In 200 I, the AeA presented a public policy report to
the 107th U.S Congress asserting the importance of
adapting to a new global Information Age As its
Pub-lic PoPub-licy priorities, the AeA listed expansion of
sci-ence and math education, protection ofprivacy,
sim-plification of Internet taxation, export controls,
res-toration of Presidential fast-track trade negotiating
authority, monitoring of China's conformance with World Trade Organization (WTO) agreements, and broadband deployment through forbearance in regu-lation and the promotion of competition The report further lists statistics for the high-technology indus-try in the Quick Facts Appendix 3 section
http://www.aeanet.org/
American Institute of Electrical Engineers AlEE.
Formed as a result of growing electrical development
in the 1800s and the International Electrical Exhibi-tion in 1884,torepresent the profession and develop standards for the industry Norvin Green, president
of Western Union Telegraph Company, was the first president Alexander Graham Bell and Thomas A Edison were among the first six vice-presidents AIEE was presented The Clark Collection in 190 I
by Schuyler Skaats Wheeler The Clark Collection was one of the world's great libraries of electrical technology Andrew Carnegie further donated $1.5 million for AlEE premises AlEE was merged with the Institute ofRadio Engineers (IRE) in 1963 to form the IEEE See IEEE, Institute of Radio Engineers
American Library AssociationALA A governing body and support group for American librarians The ALA provides member services, workshops, confer-ences, and administrative support The organization has a long history ofservice to the public and its mem-bers The ALA Code of Ethics goes back to a Sug-gested Code of Ethics proposed in 1930
The author acknowledges the generous help received from many librarians in the creation of this dictio-nary http://www.ala.org/
American Mathematical SocietyAMS Alarge pro-fessional society dedicated to promoting mathemati-cal research and education, founded in 1888 Head-quartered in Providence, R.I., the AMS sponsors con-ferences, member services, online resources (e.g., MathSciNet) and a large number of mathematical publications http://www.ams.orgl
American Mobile Satellite CorporationAMSC A commercial provider of seamless mobile communi-cations services across North America under the SkyCell trademark Hughes Communications is the largest shareholder,joined by AT&T Wireless, Singa-pore Telecom, and Mitel Corporation A variety of services are marketed to govemment agencies, emer-gency organizations, and major corporations AMSC
is permitted to provide domestic mobile satellite ser-vices (MSS) in the upper L-band
American Morse Code, Railroad MorseA system
of dots and dashes usedtorepresent characters for distance communications, quite possibly developed
by Alfred Vail, while working with Samuel Morse Due to the fact that American Morse includes some characters with internal spaces, which can be confus-ing to some, it is not often used, International Morse code is preferred See Morse code
American National Standards InstituteANSI A significant U.S private sector, nonprofit, standards-promoting body based in New York ANSI was founded in 1918 by a group of engineering societies and government agencies The ANSI Federation
Trang 4ness of U.S businesses by promoting the
develop-ment and support of consensus standards and
con-formity assessment systems Information on the many
important ANSI standards is available online in the
ANSI searchable database http://www.ansi.org/
American OpticalAO A long-standing American
optical finn known for its eyeglasses, lenses, and
sci-entific instrument components
AO began producing spectacles (eyeglasses) in 1833
after having originally been established as ajewelry
shop.In1838, Charles Spencer began marketing
mi-croscopes, setting up business as Spencer and Sons,
in 1865 In 1869, American Optical Company was
established by G W Wells In 1843, William
Beecher, AO's founder, produced steel eyeglasses on
equipment ofhis own invention Five years later, the
product line was extended to gold frames By 1898,
AO was establishing industry standards for certain
lenses Aresearch laboratory was establishedin1909,
one that was to attract a significant pool oftalent, and
AO was awarded a number of patents in the optics
industry.Inthe early 1920s, the Spencer company
in-troduced optical spectrometers, goniometers, and
re-fractometers.In1935,American Optical acquired the
Spencer Lens Company, which operated as AO's
In-strument Division as of 1945
By the 1920s, the company had expanded from
con-sumer eyeglasses into industrial safety products and
expanded further into military optics in the early
years ofWorld War II
Many renowned scientists in the optical community
have worked at one time or another for American
Optical While AO didn't express much interest in
fiber optics in the 1950s, W Hicks, a recentAO
em-ployee who left to fonn another company, succeeded
in fabricating a fiber filament, through fiber pulling,
that could transmit light as a single-mode waveguide,
in 1959 The potential ofthe single-mode waveguide
was recognized by Elias Snitzer and described by him
in a paper written in 1961
During the 1960s and 1970s, many pioneering
opti-cal mediopti-cal instrument components were produced
by AO In 1999 - 2000, American Optical was
ac-quired by SOLA, an Australian lens company
American Public Power AssociationAPPA A
na-tional American service organization representing
local or publicly owned electric utility companies
http://www.appanet.org/
American Public RadioSee Public Radio
Interna-tional
American Radio MuseumA diverse, well-selected
collection ofover a hundred years history of antique
radio and electrical technologies, including a Tesla
coil, Nipkow disc, Leydenjars, static generators,
pho-nographs, and significant makes and models
ofcrys-tal detectors and historic radios Descended from the
Bellingham Radio Museum, ARM was founded in
the Pacific Northwest by Jonathan Winter
http://www.antique-radio.org/radio.html
American Radio Relay LeagueARRL Founded in
1914 by Hiram Percy Maxim, with assistance from
the ARRL is now a worldwide organization with al-most 200,000 members, headquartered in the United States Tuska was a youthful tinkerer and radio hob-byist when he met Maxim The ARRL name is de-rived from the way in which amateur radio operators, constrained to certain power levels and frequencies, would cooperate by relaying messages from one per-son to another in order to send over greater distances
or difficult terrain
The ARRL cooperates with various radio groups and governing authorities such as the International Tele-communications Union (ITU) and the Federal Com-munications Commission (FCC) Its members have contributed to many of the technological milestones
in communications history, including the pioneering offrequencies that were originally thought to be use-less (and hence were assigned to amateurs) More re-cently, amateur radio enthusiasts have cooperated in satellite communications projects with AMSAT The
ARRL monthly publication QSThas been available
for more than 80 years See AMSAT, International Amateur Radio Union The ARRL's call letters are WIAW http://www.arrl.org/
American Speaking Telepbone Company A his-toric telephone company, based upon the Edison transmitter, established by Western Union in 1877 to compete with the Bell Company With hundreds of thousands ofmiles oftelegraph lines already installed throughout North America that could be adapted for telephone transmissions, Western Union was seen as
a real threat to the Bell empire
American Standard Code for Information Inter-changeASCII An important, alphanumeric 7-bit (128-character) communications standard widely used around the world for the transmission oftextual messages ASCII is a simple system, used on tele-graph systems and computers It doesn't support for-matting attributes such as bold, italic or underline, and
itis primarily useful for English and western Euro-pean languages
ASCII often functions as a lowest common denomi-nator for textual communications since it is supported
by most electronic mail, word processing, text edit-ing, and desktop publishing programs, which may otherwise be incompatible Differing formats are of-ten resolved through ASCII translation and conver-sion See ASCII for a chart showing the characters, control characters, and hex, decimal, and octal val-ues for each See ASCII and see Appendix for a chart, EBCDIC
American Telephone and Telegraph Company AT&T See AT&T for an explanation of the company's origins, history, and technologies American Voice Input/Output SocietyAVIOS A not-for-profit organization dedicated to promoting and supporting speech applications research and tech-nologies Speech applications include voice recog-nition, speech recogrecog-nition, and speech generation, all
of which are now important input and output capa-bilities of computer systems and digital telephony networks http://www.avios.com/
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American Wire Gauge, Brown and Sharpe Wire
Gauge AWG A standardized wire diameter system,
exclusive ofcovering, for nonferrous conductors such
as copper and aluminum With a range from 1 to 40,
lower numbers denote thicker wires, higher ones
thin-ner wires Gethin-nerally, for a specific material, the
cur-rent-carrying capability increases as the diameter of
the wire increases and the AWG number decreases
AWG 1 corresponds to a diameter 00.35 mm with
an amp rating ofca 191, whileAWG 40 corresponds
to 0.799 mm and an amp rating of ca 0.02 With finer
wires manufactured and used for finely detailed
elec-tronics circuits, some charts extend the gauge sizes
down to 0000 (11.68 mm)
Since heavier wires are usually more expensive,
con-sumers tend to purchase the thinnest wire that will
accomplish the task at hand It's important to get wire
that not only is adequate to carry the current desired,
but that is strong enough to bend and stretch,
espe-cially around connectors, panels, punch-down blocks,
etc Ifthe wire breaks at the connection point, it's not
very useful See Birmington Wire Gauge
Ames Research Center ARC Aresearch
organiza-tion dedicated to creating new knowledge and
tech-nologies within NASA's areas of interest ARC was
formed in 1939 by the U.S National Advisory
Com-mittee on Aeronautics (NACA), which became part
of National Aeronautics and Space Administration
(NASA) in 1958
AMHS See Automated Message Handling System
AMI 1 See Alternate Mark Inversion
Amiga Multimedia Personal Computer
The first ofthe Amiga line ofcomputers the Amiga
1000 was released in August 1985 1tfeatured
pre-emptive multitasking, bllilt-in serial and parallel ports,
a Motorola MC68000 CPU with coprocessor chips,
two mOllse/joystick ports, composite or RGB color
graphics up to 640 x 400 pixels (more in overscan
mode), and two-channel (16-voice) stereo sound.
Amiga computer A remarkable personal computer
system for its time, the Amiga was developed by Jay
Miner (hardware), Carl Sassenrath, R.I Mical, et al
in the early 1980s The original Amiga team members
were part of the Hi-Toro company, a small
develop-ment company whose members created the Lorraine, which was bought oul by Commodore Business Ma-chines in the fall of 1984 and became the Amiga The Amiga was well equipped for 1985 with full se-rial, parallel, and joystick ports, full-color graphics, the ability to run multiple screens simultaneously in different resolutions, NTSC video compatibility, built-in 4-channel (16-voice) stereo sound, fast graph-ics display with coprocessing chips, and a Motorola MC68000 CPU chip running at 7.15909 MHz with 32/16-bit internaVexternal addressing
The Amiga had a fully preemptive multitasking op-erating system (working quite well in only 256 kilo-bytes of memory) which came with both a graphical user interface (GUI) and a text command line inter-face, both available for use at the same time It helps
to remember that in 1985 most personal comput-ers lacked peripheral ports and employed single-tasking, monochrome graphics, and command line in-terfaces for prices ranging from $3,000 to $6,000 The Amiga 1000 offered everything built in, including monitor and sound, for under $2,000 The only other computer at the time significantly competitive with the Amiga was the Atari ST (the Apple IIgs never quite made the grade) Other Amiga models, includ-ing the 2000, 3000 and 4000, and updates to theas
were released over the next several years, followed
by a new type of product from Commodore, the CD32
The Amiga is historically significant not only for pro-viding the first viable platform for desktop video, but for its many capabilities that have subsequently been incorporated into other systems (certain patented as-pects ofthe Amiga have been used by prominent com-puter companies in today's mainstream products), showing the prescience and desirability of its design and features Even a decade after its release, most personal computers lacked many ofthe Amiga's early capabilities, despite faster CPUs and other advances
in technology
In 1994 Commodore-Amiga folded due to problems
in executive management and marketing The Amiga product line was acquired by a German company, Escom, AG, (Amiga Technologies) and was later sold
to Gateway, Inc., in 1997 Developers' conferences were reinstituted the same year Gateway subse-quently licensed use ofthe technology and trade iden-tifiers to Amino Development Corporation, later known as the Amiga Corporation Amiga conferences were still being held as of March 2001 See Amiga CD32; Commodore Business Machines; Mindset computer; Miner, Jay
AMIS See Audio Messaging Interchange Specifi-cation
AML I See Actual Measured Loss 2 analog micro-wave link 3 ARC Macro Language Aline-based in-terpreted programming language for the AtcInfo GIS, from ESRI 4 Aurora Macro Language.An object-oriented, event-driven language for the Aurora Edi-tor, a text editor from nText Research
AMLCD active matrix liquid crystal display See active matrix display
Trang 6ing the flow of electric current in alternating or
di-rect current in ampere units.Incommunications
cir-cuits, where current may be very small (below one
ampere), milliammeters and microammeters are used
When ustd as a measuring and diagnostic instrument,
an ammeter is connected in series with a circuit to
measure the current as it passes through If the total
current is above the range of the ammeter, or is such
that it might cause damage to the sensitive
instrumen-tation, part of it may be predirected through a shunt
connected in parallel See ampere, shunt
Historic Ammeter or Ampere Meter
H
Fig 3
~
Historic drawings are often useful for describing
basic mechanics and theforerunners to electronics as
the essential components can be more easily
visual-ized The above diagram shows the basic stlUcture
and components ofa historic ammeter, which is
tech-nologically descendedfrom the galvanometer
[Popu-lar Mechanics, May 1907.J
AMN See Abstract Machine Notation
AMPSee advanced metal powder
ampacityThe current-carrying capability, in
am-peres, of a circuit or cable Typically ampacity is
specified in product descriptions to indicate various
types of cable assemblies, which may collectively
consist of various combinations of wires and
insu-lating materials
AMPASSee Academy of Motion Picture Arts and
Sciences
ampere, amp(symb -A) A unit of measurement of
flow of electric current, named after A Ampere.Itis
a practical meter-kilogram-second unit of~lectric
current equivalent to a flow of one coulomb per
sec-ond, or to the steady current produced by one volt
when applied across a resistance of one ohm
The international ampere was traditionally expressed
as the steady current that will deposit silver at the rate
of0.001118 grams per second when flowing through
a neutral silver nitrate solution
The accepted scientific definition has since been
re-placed by a SI unit of electric current defined as a
constant current that, in two straight parallel infinite
conductors of negligible cross section placed one
meter apart in a vacuum, would produce a force
be-Ampere, Andre-Marie (1775-1836) A French physicist and mathematician who described and de-veloped terminology for the nature of electricity He also sought, in 1820, to formulate a combined theory
of magnetism and electricity following some of the investigations ofH C 0rsted
In 1826, Ampere published an important paper, the
"Memoir on the Mathematical Theory of Electrody-namic Phenomena, Uniquely Deduced from Experi-ence" in which he described electrodynamic forces
in mathematical terms Many later experimenters built on Ampere's ideas, and his discoveries led to the development ofmagnet-moving coil instruments The ampere unit of measure of electric current is named after him See ampere, galvanometer
Andre-Marie Ampere
Andre-Marie Ampere was inspired by the discover-ies of@rsted and worked with Arago to follow them
up Together they further investigated electrical and magneticforces from which Ampere sought to formu-late a unified theory to explain these phenomena.
Ampere's lawIn electromagnetism, the magnetic field associated with an electric current is propor-tional to the current Ampere's law expresses this mathematical relationship and states that for a closed-loop path, the sum of the length elements times the magnetic field in the direction of the length element
is equal to the permeability times the electric current within the loop (Stating the rule in English is easier than calculating the integrals related to complex paths associated with irregular enclosed spaces.) Currents within these bounded spaces are positive or negative Ampere's law has applications in assessing magnetic fields associated with conducting transmission wires and coils Ampere's and Gauss's law together enable mathematical modeling of static magnetic fields Ampere's law does not apply directly to a circuit with
a charging capacitor See Biot-Savart law, Gauss's law, Maxwell's equations
Ampere's ruleBased upon his discoveries in elec-tromagnetism, Andre-Marie Ampere described a
Trang 7Fiber Optics Illustrated Dictionary
Amplitude Modulation
are methods that may significantly reduce output amplitude fading See amplitude
The lOp amplill/de modularion (AM) diagram (A) shows an ul/modulated 'carrier' signal The middle (B) shows the signal modulated so that the amplitude varies through time The bo[(om (C) shows the 'modu-lation envelope' which convE:Ys useJul inJonnatiol/, such as magI/iII/de oJthe modularion.
amplitude modulationAM Avery common means
of adding information to a carrier wave A basic ra-dio wave carries no information By varying or modu-latingthe amplitude in a predetermined way, signals can be created which can be reconstructed as data, sound, or images at the receiving end of the trans-mission This system was adopted in the early tele-graph systems and is familiar in the form of AM ra-dio broadcasts AM rara-dio typically requires about 10 kilohertz of bandwidth and is more subject to noise than frequency modulated (FM) radio Designations
of AM radio frequencies are under the jurisdiction ofthe Federal Communications Commission (FCC), and they have changed from time to time.In 1993, the FCC increased the upper limit of the AM band from 1605 kHz to 1705 kHz Once frequency modu-lation (FM) was developed by Armstrong, it was thought that its superiority would overshadow am-plitude modulation, but AM radio stations are still common decades later
One of the simplest ways to modulate is to create in-tervals of current that are either on or off, as in Morse code telegraph communications and some types of binary computer signaling Most computer modems use amplitude modulation and demodulation to
A
c
B
method for determining the direction in which a
mag-netic needle orients itself when in the vicinity of a
current of electricity See Biot-Savart law, left-hand
rule, right-hand rule
ampere-secondAunit ofelectric charge flowing past
a point in a current-carrying wire per second with a
constant current of one ampere Thus, amperes times
seconds equals coulombs See coulomb
amplificationSee amplify
amplifierAdevice or system that increases the
mag-nitude or intensity of a phenomenon such as sound
This is accomplished in electronics through an
in-crease in power, voltage, or current Amplifying a
sig-nal doesn't necessarily make it louder, bigger,
brighter, etc than the original The effect of
amplifi-cation at the receiving end, or at a transfer point, may
increase the signal that is received above its
charac-teristics at the point it is received, but not
necessar-ily above the original Some systems are intended to
increase the signal above the level of the original, as
in public address systems and blow horns
Amplifi-cation systems seek to minimize the possible
ampli-fication or introduction of noise in the signal, while
increasing the meaningful parts of the signal See
re-generative relay
amplifyTo electrically, mechanically, optically, or
conceptually enlarge; to increase the power or
sig-nal strength of; to make louder; to exaggerate
Am-plification is a crucial process in many
communica-tions technologies that enables signals to be made
effective, audible, or able to travel longer distances
amplitude I.The measure of the magnitude or
ex-tent of some property, movement, or phenomenon
2 The magnitude ofvariation in some changing
quan-tity from an established value such as zero, or from
its extents See amplitude modulation 3.Ina
dia-grammatic representation of a wave, the measure of
the magnitude from the highest point in the
wave-form, to the lowest
amplitude distortionAssuming a fundamental wave
in a steady-state system, an undesirable condition in
which the outgoing waveform differs from the
incom-ing waveform sufficiently to affect the perception or
informational content ofthe signal
amplitude equalizerCorrective electronics, usually
passive, designed to compensate for less than
desir-able amplitudes over a range of frequencies
Equal-izers are used in audio recording and playback
amplitude fadingInan amplitude-modulated carrier
wave, fading is the attenuation of the amplitude
across frequencies, more or less uniformly.In
pas-sive laser communications links, atmospheric
fluc-tuation is one factor contributing to amplitude
fad-ing and quadrature amplitude modulatfad-ing (QAM)
systems may be especially susceptible Barbier et al
have described automatic gain control circuitry to
help reduce fade
Inmultimode, multichannel, optical fiber
interferom-eters, assessment and reduction of amplitude fading
are more complex Kotov et al have suggested that
summing the signal magnitudes over various
chan-nels or selecting a channel with the largest amplitude
Trang 8to analog telephone transmission signals, and back
again at the receiving modem
Various types of amplitude modulation have been
developed, and other nonamplitude modulation
tech-niques exist, such ·as frequency modulation, in which
the frequency ofthe signal, rather than its amplitude,
is varied See absorption modulation, amplitude shift
keying, frequency modulation, modem, modulation,
quadrature phase shift keying
amplitude separationIn television transmissions,
the separation of the incoming signal into a video
component and a synchronization signal component
amplitude shift keying, intensity modulation,
on/off keyingASK A basic type of modulation that
employs a constant-frequency signal, with two
dif-ferent signal levels used to represent binary values
In its simplest form, one state is represented by the
lack of presence of the carrier, and the other by the
presence of the carrier at a constant amplitude, hence
onloffkeying (OOK)
AmprNetSee Amateur Packet Radio Network
AMPSSee Advanced Mobile Phone System
AMRSee anisotropic magneto resistance
AMS1 Account Management System 2 See
Ameri-can Mathematical Society 3 AmeriAmeri-can
Meteorologi-cal Society 4 Attendant Management System 5
automated management system
AMSATThe Radio Amateur Satellite Corporation
Aglobal organization ofamateur radio operators who
share an active interest in building, launching, and
communicating amateur radio technology through
noncommercial satellites AMSAT was founded in
1969 as a result ofthe 1961 Project OSCAR satellite
launchings AMSAT was established as a
not-for-profit educational organization to foster amateur
par-ticipation in space research and communication
Many early launchings have piggybacked as
second-ary payloads on weather satellites More recently,
AMSAT satellites have shared launch vehicles with
other commercial and scientific craft
In the mid-l 990s, AMSAT became associated with
ARISS amateur radio experiments aboard the
Inter-national Space Station Soon after, it became involved
in the internationalPhase 3Dsatellite project, also
called AMSAT-OSCAR 40 (AO-40) This project
supports cameras, sensors, transmitters and
receiv-ers in several radio frequency bands, including S, K,
U, V, L, and X bands It is the fourth of AMSAT's
high-altitude, global communications satellites,
de-signed to replace earlier satellites that failed on launch
or were no longer functional due to limited lifespans
or technical failures As ofApril 2001, efforts were
underway to recover AO-40 In general, the satellite
was in good condition, with some individual glitches
that didn't impinge on overall health However, since
orbit 201, when it lost its solar lock, it was officially
in a state of "hibernation" (unable to sense the Sun)
with the magnetorque system off until solar lock
could be reinstituted
AMSAT now consists of a number of loosely
affili-ated organizations around the world, some bearing
through cooperative rather than formal arrangements
AMSAT sponsors discussion lists and publishes a weekly online report on satellites, covering almost three dozen individual orbiting bodies, including space stations
Many AMSAT enthusiasts are highly skilled techni-cians, and their knowledge and expertise have con-tributed to developing new technologies, in coopera-tion with a number of agencies, including the Eu-ropean Space Agency (ESA) See Amateur Radio In-ternational Space Station See amateur satellite ser-vice and OSCAR for charts of the earlier satellite projects http://www.amsat.org/
AMSCSee American Mobile Satellite Corporation
AMSC-lAcommercial satellite, operating in the L-band frequencies, owned by American Mobile Sat-ellite Corporation AMSC-I provides voice, data, fac-simile, paging, and other mobile communications services, particularly to commercial transport com-panies Communication is through satellite phones
or cellular/satellite hybrid phones
AMSS1 See Aeronautical Mobile Satellite Service
2 Airborne Multi-Spectral Scanner An aircraft-mounted scanning spectrometer for acquiring high-resolution imagery 3 See Asian Mobile Satellite System
AMTORamateurteleprinting over radio
AMTSSee Automated MaritimelMarine Telecom-munications System
analog1 Relating to, similar to, linear, continuous with 2 Circuits or devices in which the output or transmission varies as acontinuous function of the input Here are two examples commonly used to il-lustrate the distinction between analog and digital dis-play and selection systems:
TIme Piece Displays.Most analog watches have con-tinuously sweeping minute and hour hands that move through a 360 degree arc through the ac-tion of internal rotating gears Contrast this to a digital watch which stays on a minute or one-second setting until the next has been reached, and then 'flips over' the display to the next minute in discrete units
Dials and Buttons.Inolder AM radios, the turning
of an analog radio dial will move the station pointer in a continuous path through the various frequencies, and the transitions can be heard as the signals from various stations get stronger and weaker In newer car radios, a push-button digi-tal system is often used (sometimes in conjunc-tion with an analog dial) to store the locaconjunc-tions of preferred radio stations Pushing the buttons 'jumps' to the desired stations without passing through the intervening frequencies
Traditionally, phone conversations were processed as analog transmissions over copper wires Gradually, digital switches and optical backbones were intro-duced, but the link to the customers' premises re-mained analog When computers were first remotely accessed over analog phone lines through modems,
; " ! ,i:\:.r • d
Trang 9Fiber Optics Illustrated Dictionary
it was necessary to convert the digital signals from
the computer to analog signals through modulation
With the growing availability of mobile phones,
ISDN, etc., end-to-end digital transmissions are
pos-sible and conversion from analog to digital is less
often necessary See digital, ISDN, modem
anamorphic Capable of display in varying aspect
ratios in the X and Y axes Traditional television
im-ages are displayed at 4:3 aspect ratios and some
mov-ies are anamorphed (modified as to their aspect
ra-tios) to fit television displays Display systems may
be anamorphic but, more often, the media being
dis-played have been put through an anamorphic process
before being stored and distributed (e.g., DVD
mov-ies) Thus, these images are not so much anamorphic
as they are anamorphed It is entirely possible that
image media may someday be truly anamorphic,
stored in such a way that a computerized display
sys-tem could process the incoming data and display at
the desired aspect ratio in realtime See ananlorphing,
letterboxing
anamorphing Altering the aspect ratio of an image,
optical beam, or other directional entity The tenn is
most often applied in two-dimensional situations
where one dimension or the other is altered, rather
than both.Inimaging systems, this is typically in the
Xand Yaxes.Infabrication processes, parts may be
anamorphed in one or two out of three dimensions
In laser optics, anamorphing prisms are used to
re-duce, enlarge, or correct a beam size or shape Thus,
an elliptical beam from a laser diode, for example,
may be corrected in one dimension by small
anamorphing lenses to create a circular beam
anamux analog multiplexer
ANCAll Number Calling
anchor I.Something that serves to steady or hold,
such as a guy wire or stake.2.In hypertext
program-ming, an element enabling links to related
informa-tion The anchor delimits the two ends of the
hyper-link, designated with a tag as follows:
<A link tag="!ocation">link text</A>
anchor frame 1 In HTML coding, a frame (a
de-fined section of the display) that contains at least one
anchor tag (e.g., <A HREF » pointing to addresses,
data, or images to be associated with that frame The
TARGET tag can be used to specify that an anchor
applies to a specific frame if there is more than one
frame associated with a page 2 In advanced
televi-sion (ATV) technologies, a video frame used for
pre-diction, most commonly an I-frame or P-frame
B-frames are not used as anchor B-frames See ATSC
Digi-tal Television Standard
Anchorage Accord An ATM Forum document
com-prising Foundation Specifications needed to assemble
an ATM network infrastructure This important suite
established criteria for maintaining interoperability
ofATM products and services There were five dozen
specifications listed in the Anchorage Accord,
includ-ing intercarrier specifications, LAN emulations,
in-terface requirements, physical layer specifications,
traffic management specifications, and testing suites
The approval of the Accord was announced by the
ATMForum Technical Committee in April 1996 The step was an important one in forging working rela-tions among theorists, specificarela-tions developers, and commercial implementers and was instrumental in furthering the acceptance and adoption ofATM as a networking technology The Committee assured de-velopers that specifications would be downwardly revised if interoperability problems were found in actual implementation In August 1997, six additional specifications were announced, mainly to facilitate Internet connections and the transmission of converg-ing multimedia data over ATM (e.g., voice or video overATM)
The Accord documents can be downloaded free of charge from the ATM Forum specifications archive
on the Web See asynchronous transfer mode http://www.atmforum.com!
ancillary charges Charges for optional or value-added services
ANDSee Automatic Network Dialing
Anderson bridge Adevice, usually employing a gal-vanometer, that measures reactance in order to de-termine capacitance or inductance by balancing against a frequency standard
Andreessen, Mark Andreessen developed the first version of Mosaic, the precursor to the Netscape Navigator browser, in early 1993 while at the Na-tional Center for Supercomputing Applications He was working with the Software Development Group developing for Unix In 1994, he joined forces with Mark Bina, some of his colleagues at the University
of Illinois, and developers from Silicon Graphics to fonn Mosaic Communications They essentially re-wrote the code, as the new Mosaic company didn't have the rights to market the version developed at the University The company also had to change its name,
so as not to infringe on the University rights to "Mo-saic" as a tradename The new company was called Netscape Communications and is now well-known for creating the Web browser known as Netscape Navigator
Andrew File System AFS A distributed file system named for Andrew Carnegie and Andrew Mellon AFS grew out of a collaboration between Carnegie-Mellon University and International Business Ma-chines (IBM)
anechoic I Not echoing or reflecting sound 2 An environment without noise, or without significant noise Sound recording rooms are designed to echo
as little as possible, with thick, porous materials re-sembling foam egg crates absorbing the sound so it
is prevented from reflecting back to the recording equipment Speakerphones work better in anechoic environments See acoustics
angle Within the context of the central point in a cir-cular reference, the displacement between two lines
or surfaces originating or passing through the same reference point relative to one another, usually ex-pressed in degrees or radians If the two lines or sur-faces are equivalent, the angle is considered to be zero The number usedtoexpress the magnitude of the angle increases as the angle increases through a
Trang 10equivalent, thus a 360 arc in degrees or 21t arc in
ra-dians.
Basic Angle Designations
3600 or 2u radians
Angles are commonly designated with semicircles
or squares (90°) are expressed in degrees or radians,
based upon 360 degrees in a circle or 21C radians.
The concept of angle is intrinsic to almost every
as-pect ofoptics Because light is said to travel in straight
lines unless it is reflected or refracted in measurable,
predictable ways in its interaction with common
op-tical components, the geometry ofangles enables the
calculation of distances which, in turn, makes it
poossible to model, design, fabricate, and use
thou-sands of optical components
angle of acceptanceSee acceptance angle
angleof arrival The angle between the Earth's
sur-face and the center of a radiant beam from the
antenna to which it is radiating
angleof beam The predominant range ofdirection
of radiant energy from a directional
transmit-ting antenna
angle of deflectionSee angle of divergence
angle of divergenceIn a cathode-ray tube (CRT),
for example, the spread or divergence of an
electron beam from an imaginary center
posi-tion for that beam as it travels from the cathode
to the coating on the inside surface of the front
ofthe tube Awell-focused beam should spread
as little as possible Higher amplitudes tend to
result in higher divergence Aperfectly straight
beam has an angle of divergence that equals
zero See spreading loss
angle of incidenceThe angle at which a radiant
beam (or line) encounters an obstacle or
theo-retical reference, calculated in relation to the
perpendicular (normal) from the surface of the
obstacle See incidence angle for a fuller
expla-nation and diagrams
angle of radiationThe angle between the Earth's
surface and the center of a radiant beam from
the antenna from which it is radiating
See normal, Brewster's angle, Snell's law
angle brackets< >Symbols very commonly used
in programming code as delimiters or arithmetic
op-erators These are best known as greater than(» and
less than«)symbols.InHTML, the angle brackets
delimit markup tags, e.g.,<p>signifies a paragraph
opening
Angles - Degrees/Radians/Triangle
This diagram illustrates how angles are derived relative to the center ofan imaginary circle and a be-ginning reference point Shown clockwisefrom the top are eqUivalent measurements on two common geomet-ric scales,degreesandradians
The Greek letter theta(6)is often used to designate
an angle and the Greek letters alpha (a) and beta (/3) often refer to specific angles that are compared or mathematically summed (e.g., the combined angles ofa triangle add up to180~which is a useful refer-encefor calculations, especially when combined with Pythagorean concepts for right triangles (a triangle with a 90° angle]).
Angle of Incidence Example
This simplified diagram of an electromagnetic in-cident wave encountering a dielectric with different refractive properties illustrates the angle ofincidence (a) and the angle ofrefraction (f3) as well asnormal
which is established, by definition, as 90°perpendicu-lar (at right angles) to the plane upon which the inci-dent wave makes contact with the intervening dielec-tric.