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AM Stereo Broadcasting
Stereophonic AM broadcasting in the USA uses the C-Quam system
of encoding the stereo signal. This system has been the official standard since
1993.
The FCC does not keep a list of which stations operate with AM stereo.
A very brief chronology of the events leading to the adoption of
the AM stereo standard in the USA follows:
1958-62
AM Stereo was first proposed to the Commission in 1958 and 1959
separately by Philco Corporation, Radio Corporation of America,
and Kahn Research Laboratories, Inc. On
September 27, 1961 [21 RR 1616c], the Commission denied these
requests for a rulemaking proceeding on the subject, stating
Contrary to the circumstances which motivated the rule amendments
authorizing and standardizing stereophonic transmissions by FM broadcasting
stations, there is little evidence of public need or industry desire
for similar rule changes with respect to stereophonic transmissions
by standard broadcast stations. Additionally, the
pattern of operation of the nearly 4,000 stations now licensed,
the needs and purposes served and the very nature of the
service itself are such that the beneficial effects of
innovations of this nature are clearly de minimis. . . .
Preliminary consideration . . . indicates that providing a dual
channel transmission system with the requisite separation and
without deleterious effects in an AM system such as standard broadcasting,
presents an appreciably greater problem than in the case of FM.
The FCC denied an appeal of this decision on January 12, 1962.
[21 RR 1616e]
1980's
In 1979-1980, the AM stereo issue arose again. The Commission
originally sought to choose
a single AM stereo system as the standard for the AM broadcast
band. On July 31, 1980 the
Commission issued a Further Notice of Proposed Rulemaking in
Docket 21313 seeking more
information about the five competing systems (Harris, Magnavox,
Motorola, Belar, and Kahn and Hazeltine"). Kahn and Hazeltine
filed appeals with the Commission advocating a
"marketplace approach", in which the various systems would
compete for broadcasters to user their systems.
Subsequently, the Commission agreed to allow the marketplace to
decide which AM stereo
system should be the best, or whether different systems could
coexist (e.g., receivers could
have a multisystem decoding chip to decode the various systems.)
Report and Order, MM Docket 21313, 51 RR 2d 1,
47 FR 13152, released March 18, 1982;
see further 51 RR 2d 1285. As the Commission indicated, this
procedure was a departure
from its traditional procedures, and that the new approach was a
"bold, new step for the Commission to take."
What followed was a series of protracted lawsuits, primarily
between Kahn and Motorola as well as other parties. The other
systems faded out. As neither
broadcasters nor receiver manufacturers wanted to invest in what
could be a losing system, effective implementation of AM stereo
in the USA was delayed.
1992-94
On October 27, 1992 the President of the United States signed the
Telecommunications Authorization Act. A provision of that
act required the FCC to adopt a single stereophonic standard for AM stations
within one year of the signing date.
The Commission initiated a rulemaking
proceeding to accomplish this result. In the Notice of Proposed
Rulemaking in ET Docket 92-298, 8 FCC Rcd 688 (1993), the
Commission noted that of the stations then broadcasting in AM
stereo, 591 used the Motorola
C-Quam system, 37 used the Harris system, and less than 20 used
the Kahn system. The NPRM also indicated that 26 manufacturers
incorporated the Motorola C-Quam
system in at least one model of radio; none used Kahn's system. The NPRM
proposed the adopt
the C-Quam system as the standard, noting that 24 million
receivers had already been sold using
that system. The Commission officially adopted that system in
the Report and
Order in ET Docket 92-298, 8 FCC Rcd 8216, released November 23,
1993 (scanned document). See also the Supplemental Order to ET
Docket 92-298, 9 FCC Rcd 1907 (1994) (PDF).