Montage Acoustics HD9001: Quadraphonic FMIn 1969 Louis Dorren invented the Quadraplex system of single station, discrete, compatible four-channel FM broadcasting. There are two additional subcarriers in the Quadraplex system, supplementing the single one used in standard stereo FM. The baseband layout is as follows:
50 Hz to 15 kHz Main Channel (sum of all 4 channels) (LF+LR+RF+RR) signal, for mono FM listening compatibility.
23 to 53 kHz (cosine quadrature subcarrier) (LF+LR) - (RF+RR) Left minus Right difference signal. This signal's modulation in algebraic sum and difference with the Main channel was used for 2 channel stereo listener compatibility.
23 to 53 kHz (sine quadrature 38 kHz subcarrier) (LF+RF) - (LR+RR) Front minus Back difference signal. This signal's modulation in algebraic sum and difference with the Main channel and all the other subcarriers is used for the Quadraphonic listener.
61 to 91 kHz (cosine quadrature 76 kHz subcarrier) (LF+RR) - (LR+RF) Diagonal difference signal. This signal's modulation in algebraic sum and difference with the main channel and all the other subcarriers is also used for the Quadraphonic listener.
95 kHz SCA subcarrier, phase-locked to 19 kHz pilot, for reading services for the blind, background music, etc.
Home radio 1920's
In the 1920s the home radio evolved from a forbidding technological device which was esthetically unattractive and difficult to operate, to a consumer item, a piece of furniture, housed in an attractive wooden cabinet, with simple controls designed for anyone to operate, which occupied a place of honor in the living room. Prior to the introduction of the high-fidelity, long-playing record in the late 1940s, AM radio offered the highest sound quality available in a home audio device. Luxury models offered large speakers, "electric eye" tuning (a special type of vacuum tube, which provided a visual aid in tuning), mechanical push-button "memory" of favorite stations, sometimes with booklets of adhesive labels for the buttons with station call letters, and -- an inexpensive but impressive feature -- shortwave bands that allowed access to distant, often foreign, stations. Accessory, then factory-installed radios became available for cars.Montage Acoustics BT4480
Montage Acoustics: FM radio microphones
The FM broadcast band can also be used by some inexpensive wireless microphones, but professional-grade wireless microphones generally use bands in the UHF region so they can run on dedicated equipment without broadcast interference. Such inexpensive wireless microphones are generally sold as toys for karaoke or similar purposes, allowing the user to use an FM radio as an output rather than a dedicated amplifier and speaker.
Montage Acoustics reviews
The first commercial FM broadcasting stations
The first commercial FM broadcasting stations were in the United States, but initially they were primarily used to simulcast their AM sister stations, to broadcast lush orchestral music for stores and offices, to broadcast classical music to an upmarket listenership in urban areas, or for educational programming. By the late 1960s FM had been adopted by fans of "Alternative Rock" music ("A.O.R.—'Album Oriented Rock' Format"), but it wasn't until 1978 that listenership to FM stations exceeded that of AM stations in North America. During the 1980s and 1990s, Top 40 music stations and later even country music stations largely abandoned AM for FM. Today AM is mainly the preserve of talk radio, news, sports, religious programming, ethnic (minority language) broadcasting and some types of minority interest music. This shift has transformed AM into the "alternative band" that FM once was. (Some AM stations have begun to simulcast on, or switch to, FM signals to attract younger listeners and aid reception problems in buildings, during thunderstorms, and near high tension wires. Some of these stations now emphasize their presence on the FM dial.) Montage Acoustics
Montage Acoustics HD9001:Shortwave broadcasting
The discovery in the 1920s of the "skip" or "skywave" propagation mechanism, in which high frequency radio waves are reflected back to Earth beyond the horizon by the ionosphere, made the shortwave frequencies above 1 MHz, previously considered useless, a useful band for long distance broadcasting.
Montage Acoustics: AM stereo
In the late 1970s, in an unsuccessful effort to stem the exodus of the music audience to FM, the US AM radio industry developed technology for broadcasting in stereo. Stereo is the standard in the music recording industry, and FM broadcasting had adopted a stereo standard early, in 1961. The technology was challenging because of the narrow 20 kHz bandwidth of the AM channel, and the need for backward compatibility with non-stereo AM receivers. In 1975 the US Federal Communications Commission requested proposals for AM stereo standards, and four competing standards were submitted: Harris Corporation's V-CPM (Variable angle Compatible Phase Multiplex), Magnavox's PMX, Motorola's C-QUAM (Compatible Quadrature Amplitude Modulation), and Kahn-Hazeltine independent sideband system. All except the Kahn-Hazeltine system used variations on the same idea: the mono (Left + Right) signal was transmitted in the amplitude modulation as before, while the stereo (Left - Right) information was transmitted by phase modulation.
Modulation
Frequency modulation is a form of modulation which conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.Montage Acoustics reviews
Montage Acoustics Speakers: The AM radio industry
The AM radio industry suffered a serious loss of audience and advertising revenue during this time, and the value of an AM broadcast license was eventually to decline substantially. The industry coped with this by developing new "narrowcasting" strategies. Network broadcasting gave way to format broadcasting; instead of broadcasting the same programs all over the country, AM stations specialized in different "formats" which appealed to different audience segments: regional and local news, sports, "talk" programs, programs targeted at minorities. "Talk radio", which avoided the need for the broadcaster to pay music royalties, appeared during this period as a consequence of the less expensive "air time", and the need to develop alternative programming, at reasonable cost, to replace the lost network programming. Rather than live music, stations played cheaper recorded music, and developed the "Top 40" format, which capitalized on (and created) the popularity of new rhythm and blues and rock music.
Montage Acoustics HD9001
Digital services
Digital services are now also available. A 57 kHz subcarrier (phase locked to the third harmonic of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System signal, providing extra features such as Alternative Frequency (AF) and Network (NN). This narrowband signal runs at only 1187.5 bits per second, thus is only suitable for text. A few proprietary systems are used for private communications. A variant of RDS is the North American RBDS or "smart radio" system. In Germany the analog ARI system was used prior to RDS for broadcasting traffic announcements to motorists (without disturbing other listeners). Plans to use ARI for other European countries led to the development of RDS as a more powerful system. RDS is designed to be capable of being used alongside ARI despite using identical subcarrier frequencies. Montage Acoustics BT4480
Montage Acoustics BT4480:Distance covered by stereo FM transmission
The range of mono FM transmission is related to the transmitter's RF power, the antenna gain, and antenna height. The U.S. FCC publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location.
For stereo FM, the range is significantly reduced. This is due to the need to lower the modulation index of the main (sum) signal to accommodate the presence of the 38 kHz DSB-SC (double side-band suppressed-carrier) subcarrier and 19 kHz pilot tone. Many stations use extreme audio compression to keep the sound above the background noise for "distant" listeners, at the expense of degrading the sound quality.
In the late 1970s, in an unsuccessful effort to stem the exodus of the music audience to FM, the US AM radio industry developed technology for broadcasting in stereo. Stereo is the standard in the music recording industry, and FM broadcasting had adopted a stereo standard early, in 1961. The technology was challenging because of the narrow 20 kHz bandwidth of the AM channel, and the need for backward compatibility with non-stereo AM receivers. In 1975 the US Federal Communications Commission requested proposals for AM stereo standards, and four competing standards were submitted: Harris Corporation's V-CPM (Variable angle Compatible Phase Multiplex), Magnavox's PMX, Motorola's C-QUAM (Compatible Quadrature Amplitude Modulation), and Kahn-Hazeltine independent sideband system. All except the Kahn-Hazeltine system used variations on the same idea: the mono (Left + Right) signal was transmitted in the amplitude modulation as before, while the stereo (Left - Right) information was transmitted by phase modulation.
Modulation
Frequency modulation is a form of modulation which conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.Montage Acoustics reviews
Montage Acoustics Speakers: The AM radio industry
The AM radio industry suffered a serious loss of audience and advertising revenue during this time, and the value of an AM broadcast license was eventually to decline substantially. The industry coped with this by developing new "narrowcasting" strategies. Network broadcasting gave way to format broadcasting; instead of broadcasting the same programs all over the country, AM stations specialized in different "formats" which appealed to different audience segments: regional and local news, sports, "talk" programs, programs targeted at minorities. "Talk radio", which avoided the need for the broadcaster to pay music royalties, appeared during this period as a consequence of the less expensive "air time", and the need to develop alternative programming, at reasonable cost, to replace the lost network programming. Rather than live music, stations played cheaper recorded music, and developed the "Top 40" format, which capitalized on (and created) the popularity of new rhythm and blues and rock music.
Montage Acoustics HD9001
Digital services
Digital services are now also available. A 57 kHz subcarrier (phase locked to the third harmonic of the stereo pilot tone) is used to carry a low-bandwidth digital Radio Data System signal, providing extra features such as Alternative Frequency (AF) and Network (NN). This narrowband signal runs at only 1187.5 bits per second, thus is only suitable for text. A few proprietary systems are used for private communications. A variant of RDS is the North American RBDS or "smart radio" system. In Germany the analog ARI system was used prior to RDS for broadcasting traffic announcements to motorists (without disturbing other listeners). Plans to use ARI for other European countries led to the development of RDS as a more powerful system. RDS is designed to be capable of being used alongside ARI despite using identical subcarrier frequencies. Montage Acoustics BT4480
Montage Acoustics BT4480:Distance covered by stereo FM transmission
The range of mono FM transmission is related to the transmitter's RF power, the antenna gain, and antenna height. The U.S. FCC publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location.
For stereo FM, the range is significantly reduced. This is due to the need to lower the modulation index of the main (sum) signal to accommodate the presence of the 38 kHz DSB-SC (double side-band suppressed-carrier) subcarrier and 19 kHz pilot tone. Many stations use extreme audio compression to keep the sound above the background noise for "distant" listeners, at the expense of degrading the sound quality.