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Montage Acoustics BT4480: Broadcasting in Europe
In Europe, broadcasting took a different course. Radio transmission had always been more tightly controlled by government in this region, partly because countries were smaller and closer together; for example, in the UK receiving equipment as well as transmitters had to be licensed. There was a feeling in countries like the UK and France that the radio spectrum was a national resource which should not be surrendered to private interests, motivated by profit, who would pander solely to the desire for entertainment. Radio should serve higher purposes of public information and education. In addition, totalitarian countries for political reasons kept mass communications media under government control. So in much of Europe, broadcasting developed as a government-owned or government-supervised monopoly. It was largely funded not by on-air commercial advertising as in the US, but by taxes on sales of radios, and user fees in the form of an annual "receiver license" that anyone owning a radio had to buy.
United States
In the US, the nationwide telephone carrier AT&T was the first to create a network and take the radical step of commercial advertising. It developed a broadcasting model based on its telephony business: "toll" broadcasting. Its flagship station, WEAF in New York, in August 1922 was first to air commercial advertising, selling half-hour and hour blocks of airtime to commercial "sponsors" that developed entertainment shows containing commercial messages. It had a monopoly on quality telephone lines, and by 1924 had linked 12 stations in Eastern cities into a "chain". RCA and Westinghouse attempted to organize their own network around their flagship WJZ, but were hampered by AT&T's refusal to lease them lines. In 1925 court decisions stripped AT&T of its monopoly over broadcasting, and it decided to get out of radio. AT&T sold WEAF to RCA, which formed the nucleus of the new NBC network. In 1927, to reduce the "chaos" on the airwaves, the government came down on the side of the advertising model, establishing two classes of broadcast licenses: the "A" or "general public interest" stations which sold time impartially to anyone, received favorable frequency assignments and flourished, and the "B" or nonprofit "propaganda" stations, mainly special-interest, political or religious stations which represented a point of view, were phased out.Montage Acoustics reviews
Montage Acoustics HD9001: AM radio technology
AM radio technology is simpler than frequency modulated (FM) radio, Digital Audio Broadcasting (DAB), satellite radio or HD (digital) radio. An AM receiver detects amplitude variations in the radio waves at a particular frequency. It then amplifies changes in the signal voltage to drive a loudspeaker or earphones. The earliest crystal radio receivers used a crystal diode detector with no amplification, and required no power source other than the radio signal itself.
In North American broadcasting practice, transmitter power input to the antenna for commercial AM stations ranges from about 250 to 50,000 watts. Experimental licenses were issued for up to 500,000 watts radiated power, for stations intended for wide-area communication during disasters. One such superstation was Cincinnati station WLW, which used such power on occasion before World War II. WLW's superpower transmitter still exists at the station's suburban transmitter site, but it was decommissioned in the early 1940s and no current commercial broadcaster in the U.S. or Canada is authorized for such power levels. Some other countries do authorize higher power operation (for example the Mexican station XERF formerly operated at 250,000 watts). Antenna design must consider the coverage desired and stations may be required, based on the terms of their license, to directionalize their transmitted signal to avoid interfering with other stations operating on the same frequency.
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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 acoustic HDQ 4101 A
Montage Acoustics Speakers: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.
