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QAM demodulation requires a coherent receiver. It uses two product detectors whose local reference signals are a quarter cycle apart in phase: one for the in-phase component and one for the quadrature component. The demodulator keeps these product detectors tuned to a continuous or intermittent pilot
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There are several ways of demodulation depending on how parameters of the base-band signal such as amplitude, frequency or phase are transmitted in the carrier signal. For example, for a signal modulated with a linear modulation like AM
810:
which decreases the amplitude of some frequencies relative to others, followed by an AM demodulator. If the filter response changes linearly with frequency, the final analog output will be proportional to the input frequency, as
575:
it to remove one side of the carrier, and then filtering to remove the radio-frequency component, leaving only the modulating audio component. This is equivalent to peak detection with a suitably long time constant. The
539:
radio systems used during the first 3 decades of radio (1884–1914) the transmitter did not communicate audio (sound) but transmitted information in the form of pulses of radio waves that represented text messages in
701:(anything that will pass current in one direction only) or other non-linear component that enhances one half of the received signal over the other and a low-pass filter. The rectifier may be in the form of a single
777:(FM) has numerous advantages over AM such as better fidelity and noise immunity. However, it is much more complex to both modulate and demodulate a carrier wave with FM, and AM predates it by several decades.
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shifts the signal by 90 degrees and multiplies it with the unshifted version. One of the terms that drops out from this operation is the original information signal, which is selected and amplified.
729:
multiplies the incoming signal by the signal of a local oscillator with the same frequency and phase as the carrier of the incoming signal. After filtering, the original audio signal will result.
580:
of the recovered audio frequency varies with the modulating audio signal, so it can drive an earphone or an audio amplifier. Fessendon invented the first AM demodulator in 1904 called the
720:
exploits the simplicity of AM modulation to produce a receiver with very few parts, using the crystal as the rectifier and the limited frequency response of the headphones as the filter.
850:
Receiver structure for QPSK. The matched filters can be replaced with correlators. Each detection device uses a reference threshold value to determine whether a 1 or 0 is detected.
709:. Many natural substances exhibit this rectification behaviour, which is why it was the earliest modulation and demodulation technique used in radio. The filter is usually an
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Another method uses two AM demodulators, one tuned to the high end of the band and the other to the low end, and feed the outputs into a difference amplifier.
544:. Therefore, the receiver merely had to detect the presence or absence of the radio signal, and produce a click sound. The device that did this was called a
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type but the filter function can sometimes be achieved by relying on the limited frequency response of the circuitry following the rectifier. The
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stuck, was used for other types of demodulators and continues to be used to the present day for a demodulator in a radio receiver.
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signal encodes the information into the carrier wave by varying its amplitude in direct sympathy with the
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so there are many types of demodulators. The signal output from a demodulator may represent sound (an
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507:/demodulator, a demodulator is used to extract a serial digital data stream from a
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Process of extracting the original information-bearing signal from a carrier wave
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Many things can act as a demodulator, if they pass the radio waves on
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621:) demodulator. Different kinds of circuits perform these functions.
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is a very simple method of demodulation that does not require a
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causing a fixed rotational offset of the received symbol
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A variant of the Foster–Seeley discriminator called the
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and the error signal is used as the demodulated signal.
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around 1900. An AM radio signal can be demodulated by
495:
These terms are traditionally used in connection with
861:
Quadrature amplitude modulation § Demodulation
780:There are several common types of FM demodulators:
60:. Unsourced material may be challenged and removed.
552:, simple devices that acted as a switch. The term
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906:"Demodulator - Definitions from Dictionary.com"
770:, X, relative to the intended constellation, O.
445:is extracting the original information-bearing
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563:used to transmit sound over radio waves was
1999:Global telecommunications regulation bodies
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679:to be sent. There are two methods used to
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738:carrier is reduced or suppressed entirely
120:Learn how and when to remove this message
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596:which could also rectify an AM signal.
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503:, which is a contraction of the terms
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511:which is used to carry it through a
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650:Received Signal Strength Indication
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1634:Free-space optical communication
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931:, New Scientist, 2 October 1999
531:Demodulation was first used in
45:needs additional citations for
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697:demodulator. It consists of a
654:error detection and correction
13:
1:
965:chapter on All About Circuits
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736:is a form of AM in which the
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2020:Telecommunication portal
1801:Telecommunications equipment
548:. The first detectors were
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1537:Alexander Stepanovich Popov
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804:Foster–Seeley discriminator
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1241:Telecommunications history
908:. dictionary.reference.com
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806:. This is composed of an
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339:Capacity-approaching codes
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1849:Public Switched Telephone
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1661:telecommunication circuit
1622:Fiber-optic communication
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1367:Francis Blake (telephone)
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1162:Optical telecommunication
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795:The signal is fed into a
1760:Orbital angular-momentum
1197:Satellite communications
1036:Communications satellite
825:digital signal processor
624:Many techniques such as
1639:Molecular communication
1462:Gardiner Greene Hubbard
1291:Undersea telegraph line
1026:Cable protection system
617:) demodulator or a PM (
276:Hierarchical modulation
1781:Communication protocol
1567:Charles Sumner Tainter
1382:Walter Houser Brattain
1327:Edwin Howard Armstrong
1135:Information revolution
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829:software-defined radio
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467:software-defined radio
1755:Polarization-division
1487:Narinder Singh Kapany
1452:Erna Schneider Hoover
1372:Jagadish Chandra Bose
1352:Alexander Graham Bell
1083:online video platform
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802:The most common is a
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681:demodulate AM signals
638:frame synchronization
582:electrolytic detector
480:), images (an analog
1597:Vladimir K. Zworykin
1557:Almon Brown Strowger
1527:Charles Grafton Page
1182:Prepaid mobile phone
1110:Electrical telegraph
948:"The ratio detector"
775:Frequency modulation
615:frequency modulation
611:synchronous detector
607:amplitude modulation
586:John Ambrose Fleming
565:amplitude modulation
54:improve this article
1547:Johann Philipp Reis
1306:Wireless revolution
1268:The Telephone Cases
1125:Hydraulic telegraph
786:quadrature detector
537:wireless telegraphy
1745:Frequency-division
1722:Telephone exchange
1592:Charles Wheatstone
1522:Jun-ichi Nishizawa
1497:Innocenzo Manzetti
1432:Reginald Fessenden
1167:Optical telegraphy
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569:Reginald Fessenden
567:(AM), invented by
559:The first type of
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198:Digital modulation
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1796:Store and forward
1791:Data transmission
1705:Network switching
1656:Transmission line
1502:Guglielmo Marconi
1467:Internet pioneers
1332:Mohamed M. Atalla
1301:Whistled language
808:electronic filter
690:envelope detector
646:pulse compression
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1889:Notable networks
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1819:Cellular network
1811:Types of network
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1673:Network topology
1587:Thomas A. Watson
1442:Oliver Heaviside
1427:Philo Farnsworth
1402:Daniel Davis Jr.
1377:Charles Bourseul
1337:John Logie Baird
1046:Data compression
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619:phase modulation
609:), we can use a
594:thermionic diode
463:computer program
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1073:Digital media
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768:constellation
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642:rake receiver
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590:Fleming valve
588:invented the
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521:optical fiber
518:
517:coaxial cable
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71: –
70:
66:
65:Find sources:
59:
55:
49:
48:
43:This article
41:
37:
32:
31:
19:
2071:Demodulation
1732:Multiplexing
1607:Transmission
1572:Nikola Tesla
1562:Henry Sutton
1517:Samuel Morse
1447:Robert Hooke
1412:Amos Dolbear
1347:John Bardeen
1266:
1246:Telautograph
1150:Mobile phone
1105:Edholm's law
1088:social media
1021:Broadcasting
963:Demodulation
943:
933:, retrieved
927:
921:
910:. Retrieved
900:
864:
779:
773:
763:
732:
724:
707:more complex
688:
670:
658:
623:
603:
558:
553:
530:
494:
482:video signal
478:audio signal
454:
451:carrier wave
443:Demodulation
442:
441:
404:Multiplexing
344:Demodulation
343:
116:
107:
97:
90:
83:
76:
64:
52:Please help
47:verification
44:
1932:NPL network
1644:Radio waves
1582:Alfred Vail
1492:Hedy Lamarr
1477:Dawon Kahng
1437:Elisha Gray
1397:Yogen Dalal
1322:Nasir Ahmed
1256:Teleprinter
1120:Heliographs
764:phase error
756:Example of
718:crystal set
661:nonlinearly
455:demodulator
349:Line coding
18:Demodulator
1978:Antarctica
1937:Toasternet
1859:Television
1342:Paul Baran
1274:Television
1258:(teletype)
1251:Telegraphy
1229:transistor
1207:Phryctoria
1177:Photophone
1155:Smartphone
1145:Mass media
935:2017-04-25
912:2008-05-16
892:References
705:or may be
600:Techniques
573:rectifying
561:modulation
542:Morse code
535:. In the
471:modulation
139:modulation
80:newspapers
1962:Americas
1951:Locations
1922:Internet2
1683:Bandwidth
1387:Vint Cerf
1284:streaming
1262:Telephone
1202:Semaphore
1093:streaming
699:rectifier
578:amplitude
505:modulator
110:June 2009
2065:Category
2030:Category
1917:Internet
1907:CYCLADES
1824:Ethernet
1774:Concepts
1698:terminal
1649:wireless
1472:Bob Kahn
1315:Pioneers
1140:Internet
1031:Cable TV
870:See also
866:signal.
823:Using a
811:desired.
788:, which
748:FM radio
742:sideband
714:low-pass
695:coherent
667:AM radio
634:bit slip
554:detector
550:coherers
546:detector
488:data (a
331:See also
136:Passband
2050:Commons
2040:Outline
1993:Oceania
1912:FidoNet
1897:ARPANET
1710:circuit
1279:digital
1008:History
527:History
449:from a
94:scholar
1988:Europe
1958:Africa
1942:Usenet
1902:BITNET
1839:Mobile
1715:packet
1224:MOSFET
1219:device
1016:Beacon
486:binary
475:analog
457:is an
447:signal
257:SC-FDE
96:
89:
82:
75:
67:
1971:South
1966:North
1927:JANET
1864:Telex
1854:Radio
1693:Nodes
1688:Links
1609:media
1187:Radio
1172:Pager
1100:Drums
1066:video
1061:image
1051:audio
790:phase
703:diode
519:, or
501:modem
484:) or
465:in a
354:Modem
101:JSTOR
87:books
1983:Asia
1869:UUCP
1829:ISDN
784:The
758:QPSK
723:The
687:The
461:(or
453:. A
394:OFDM
323:THSS
318:FHSS
313:DSSS
227:MFSK
212:APSK
73:news
1874:WAN
1844:NGN
1834:LAN
1115:Fax
1056:DCT
855:QAM
797:PLL
734:SSB
671:An
592:or
492:).
399:FDM
389:ΔΣM
384:PWM
379:PDM
374:PCM
369:PAM
364:PoM
359:AnM
308:CSS
290:WDM
285:QAM
267:WDM
262:TCM
252:QAM
247:PSK
242:PPM
237:OOK
232:MSK
222:FSK
217:CPM
207:ASK
189:SSB
179:QAM
56:by
2067::
836:PM
744:.
711:RC
683::
673:AM
663:.
652:,
648:,
644:,
640:,
636:,
632:,
628:,
523:.
515:,
184:SM
174:PM
169:FM
164:AM
2001:)
1997:(
992:e
985:t
978:v
915:.
831:.
605:(
431:e
424:t
417:v
123:)
117:(
112:)
108:(
98:·
91:·
84:·
77:·
50:.
20:)
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