25:
200:, with the audio "center" rocking back and forth as if changing the balance knob. This effect is potentially bothersome, especially in a moving vehicle where the received signal changes rapidly, and occupants (particularly the driver) would be more prone to its effects (this was an effect that happened primarily with skywave signals. Groundwave or local coverage usually did not suffer from this issue). This has been alleviated in subsequent revisions. Also, since some stereo information is contained in the
311:(In-band on-channel) "HD" (Hybrid Digital) radio system, so a broadcaster must choose what system they will use. The IBOC system allows transmission of an audio frequency range extending to approximately 15 kHz, 2-ch Stereo on the AM band, but with significant digital artifact and aliasing due to substantial codec inadequacy.
334:
There has been a move to bring back C-QUAM in the last few years, due to the poor sound quality of digital audio encoding at low bit rates. Where AM stereo receivers use a dual IF bandwidth setup, for an extended audio frequency response over mono receivers. Providing for a full, rich stereo sound is
172:
Stage 2 provides the stereo multiplexed (muxed) audio input and replaces the conventional crystal oscillator stage of otherwise AM-Mono transmitters. So as to not create interference with 'envelope detector' receivers, the stage 2 signal takes the multiplexed (muxed) audio signals and phase modulates
180:
extracts the L-R audio from the phase modulated quadrature portion of the signal created in stage 2. The L+R audio can be extracted from either the AM (stage 1) or the PM (stage 2) modulation component. From there, the audio can be readily de-multiplexed (de-muxed) back to 'stereo', a.k.a. Left and
326:
during the day switch to C-QUAM AM Stereo during nighttime operation to reduce sideband digital (hash) interference and to provide long-range stereo reception. A number of HD radio tuners have the limited ability to decode C-Quam stereo transmissions, (typically with lower bandwidth), and as a
318:
still controls IBOC intellectual property through patents, through licensing fees for both the use of the technology, and any modifications to be made, even if the broadcaster in question has purchased the equipment outright and made costly modifications to their transmitter plant in order to
330:
Whereas many stations in the late 2000s changed from C-QUAM to HD Radio, in the 2010s the trend reversed with many HD Radio stations shutting off their digital equipment. However, few of these stations returned to C-QUAM broadcasts.
173:
both, using a divide-by-4 Johnson counter and two balanced modulators operating 90 degrees out of phase with each other. Stage 2 is not amplitude modulated, it is phase modulated, and is made up of both a L+R input and a L-R input.
168:
Stage 1 provides the transmitter with a summed L+R mono audio input. This input is precisely the same as conventional AM-Mono transmission methods and ensures 100% compatibility with conventional 'envelope detector' receivers.
327:
result, reduced audio quality than what could be expected from a specifically designed AMAX/C-QUAM only tuner. C-QUAM AM Stereo transmissions have the same range as AM Monural transmission, a key benefit.
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As of March 2014, there are still a number of AM radio stations in North
America broadcasting in C-QUAM stereo. Among those stations are
418:
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C-QUAM stereo transmitters are available for sale for use in the United States. In Rome, Italy, there is
Broadcastitalia on 1485 kHz.
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The C-QUAM signal is composed of two distinct modulation stages: a conventional AM version and a compatible quadrature PM version.
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simply not possible with digital audio encoding. The down side of analog broadcasting is the amount of unwanted noise.
276:/940: New Orleans, Louisiana. In addition to FCC-Licensed C-QUAM AM broadcast stations, low-powered (<100 mW)
292:
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47:
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127:
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and most other countries. It was invented in 1977 by Norman Parker, Francis
Hilbert, and Yoshio Sakaie, and
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For additional information, see the attached PDF: "Introduction to the
Motorola C-QUAM AM Stereo System".
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can cause problems. Finally, when only part of a sideband is attenuated (as often happens to
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220:, very unpleasant effects result; hence, the C-QUAM system is not often if ever used for
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138:. This extra signal is then stripped down in such a way that it is compatible with the
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157:, this carrier is not necessary for the reconstruction of the original audio sources.
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While C-QUAM is an accepted international standard for AM Radio broadcasting, it is
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244:/630: Chatham, Ontario (covering SW Ontario, Eastern Michigan and Northern Ohio);
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broadcasting, nor by stations which receive a great deal of skywave interference.
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of older receivers, hence the name C-QUAM for
Compatible. A 25
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92:(Compatible QUadrature Amplitude Modulation) is the method of
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Another AM Stereo information and vendor site - meduci.com
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C-QUAM is not perfect, however, in large part because pre-
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355:
Introduction to the
Motorola C-QUAM AM Stereo System
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Very few AM radio stations that broadcast with IBOC
988:
Introduction to the
Motorola C-QUAM AM Stereo System
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1009:Telecommunications-related introductions in 1977
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46:but its sources remain unclear because it lacks
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288:AM Stereo radio stations in the United States
299:Competition from IBOC Hybrid Digital Systems
314:In addition, C-QUAM patents have expired.
419:
405:
176:To recover the 'stereo' audio signals, a
77:Learn how and when to remove this message
996:
16:Method of broadcasting stereo AM radio
797:
400:
18:
13:
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293:AM Stereo radio stations worldwide
272:/850: Ridgefield, Connecticut and
250:North Myrtle Beach, South Carolina
14:
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377:
187:
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345:List of AM stereo radio stations
23:
128:quadrature amplitude modulation
1029:Standards of the United States
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893:Error detection and correction
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268:/1340: Plattsburgh, New York;
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1:
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206:adjacent channel interference
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153:; unlike its counterpart in
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966:Comparison of radio systems
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212:signals reflecting off the
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939:International broadcasting
908:FM extended band in Brazil
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240:/570: Corner Brook, NL;
32:This article includes a
918:Shortwave relay station
817:Audio signal processing
236:/540: Sauk Rapids, MN;
61:more precise citations.
812:Audio data compression
216:), an effect known as
134:the stereo separation
1014:Broadcast engineering
913:Multipath propagation
736:MPEG-1 Audio Layer II
606:Frequency allocations
481:Frequency allocations
96:broadcasting used in
866:Technical (emission)
384:History of AM Stereo
178:synchronous detector
149:is added to trigger
1034:Stereophonic sound
34:list of references
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898:FM broadcast band
805:Technical (audio)
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140:envelope detector
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1024:Radio technology
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960:Radio portal
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934:History of radio
878:AM expanded band
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678:Commercial radio
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218:selective fading
181:Right channels.
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48:inline citations
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38:related reading
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188:Known problems
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126:, C-QUAM uses
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122:developed by
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102:United States
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305:incompatible
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262:Rhode Island
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53:Please help
45:
883:Cable radio
826:Technical (
586:DVB-T2 Lite
442:Terrestrial
283:Also see:
161:Description
59:introducing
998:Categories
765:DirectBand
751:Subcarrier
453:modulation
351:References
214:ionosphere
147:pilot tone
67:March 2012
828:AM stereo
687:Sirius XM
680:providers
599:Satellite
307:with the
228:User base
222:shortwave
202:sidebands
151:receivers
130:(QAM) to
120:circuitry
106:published
94:AM stereo
1019:Motorola
927:Cultural
857:Magnavox
830:formats)
780:SCA/SCMO
775:RDS/RBDS
578:HD Radio
568:DRM/DRM+
563:DAB/DAB+
339:See also
324:HD Radio
316:iBiquity
258:Westerly
155:FM radio
124:Motorola
753:signals
721:AMR-WB+
573:FMeXtra
278:Part 15
274:WYLD-AM
256:/1230:
210:skywave
113:journal
55:improve
847:Harris
842:C-QUAM
731:HE-AAC
708:Codecs
692:Canada
658:DVB-SH
632:S band
627:L band
613:C band
537:L band
428:Analog
248:/900:
136:signal
132:encode
118:Using
108:in an
100:, the
98:Canada
90:C-QUAM
837:Belar
663:S-DMB
653:DAB-S
558:CAM-D
471:COFDM
450:Radio
40:, or
785:DARC
760:AMSS
741:DRA+
622:band
531:high
430:and
309:IBOC
270:WAXB
266:WIRY
254:WBLQ
246:WNMB
242:CFCO
238:CFCB
234:WXYG
194:AMAX
110:IEEE
770:PAD
726:HDC
716:AAC
668:SDR
648:ADR
582:CDR
541:UHF
527:mid
523:low
519:VHF
1000::
529:/
525:/
513:HF
509:SW
503:MF
499:MW
493:LF
489:LW
466:FM
461:AM
264:;
260:,
252:;
204:,
144:Hz
115:.
44:,
36:,
620:u
618:K
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539:(
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491:(
420:e
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406:v
366:1
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65:(
51:.
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