Montage Acoustics BT4480

Montage Acoustics HD9001: 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.

AM "radiotelephone" transmission
The entrepreneurs who developed AM "radiotelephone" transmission did not anticipate broadcasting voice and music into people's homes. The term "broadcasting", borrowed from agriculture, was coined for this new activity (by either Frank Conrad or RCA historian George Clark) around 1920. Prior to 1920 there was no concept of "broadcasting", or that radio listeners could be a mass market for entertainment. Promoters saw the practical application for AM as similar to the existing communication technologies of wireless telegraphy, telephone, and telegraph: two-way person-to-person commercial voice service, a wireless version of the telephone. Although there were a number of experimental broadcasts during this period, these were mostly to provide publicity for the inventor's products. True radio broadcasting didn't begin until around 1920, when it sprang up spontaneously among amateur stations. AM remained the dominant method of broadcasting for the next 30 years, a period called the "Golden Age of Radio", until FM broadcasting started to become widespread in the 1950s. AM remains a popular, profitable entertainment medium today and the dominant form of broadcasting in some countries such as Australia and Japan.Montage Acoustics BT4480

Montage Acoustics reviews: AM transmission
The early experiments in AM transmission, conducted by Fessenden, Valdemar Poulsen, Ernst Ruhmer, Quirino Majorana, Charles Herrold, and Lee de Forest, were hampered by the lack of a technology for amplification. The first practical continuous wave AM transmitters were based on versions of the Poulsen arc transmitter invented in 1903, and the huge, expensive Alexanderson alternator, developed 1906-1910. The modifications necessary to transmit AM were clumsy and resulted in very low audio quality. Modulation was usually accomplished by a carbon microphone inserted directly in the antenna wire. The limited power handling ability of the microphone severely limited the power of the first radiotelephones. At the receiving end, the unamplified crystal radio receivers then in use could not drive loudspeakers, only earphones, so only one member of a family could listen at a time.

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FM broadcasting
FM broadcasting is a VHF broadcasting technology, pioneered by Edwin Howard Armstrong, which uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio. The term "FM band" describes the frequency band in a given country which is dedicated to FM broadcasting. This term is slightly misleading, since it equates a modulation method with a range of frequencies. Montage Acoustics Speakers

Montage Acoustics: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.