Montage Acoustics HD9001: Modulation

Montage Acoustics HD9001: 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.

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.Montage Acoustics

Montage Acoustics reviews: Clandestine use of FM transmitters
FM transmitters have been used to construct miniature wireless microphones for espionage and surveillance purposes (covert listening devices or so-called "bugs"); the advantage to using the FM broadcast band for such operations is that the receiving equipment would not be considered particularly suspect. Common practice is to tune the bug's transmitter off the ends of the broadcast band, into what in the United States would be TV channel 6 (<87.9 MHz) or aviation navigation frequencies (>107.9 MHz); most FM radios with analog tuners have sufficient overcoverage to pick up these slightly-beyond-outermost frequencies, although many digitally tuned radios do not.

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Market concentration
World War I brought home to nations the strategic importance of long-distance radio; in addition to its military uses in keeping contact with its fleets and overseas forces, a country that didn't have radio could be isolated by an enemy cutting its submarine telegraph cables. In the US, before the war, the radio industry was fragmented by patent monopolies held by competing giant firms, so the best long-range radio technology was owned by two European firms: the British Marconi Co. and the German Telefunken. At its entry into the war in 1917, the US government temporarily took control of the entire US radio industry for the war effort, including the transatlantic wireless stations of these foreign firms. After the war, due to fear of foreign ownership of the US radio industry, there was an abortive effort to create a federal radio monopoly. Montage Acoustics Speakers

Montage Acoustics reviews:Subsidiary communications authorization
In the United States, services (other than stereo, quad and RDS) using subcarriers are sometimes referred to as subsidiary communications authorization (SCA) services. Uses for such subcarriers include book/newspaper reading services for blind listeners, private data transmission services (for example sending stock market information to stockbrokers or stolen credit card number blacklists to stores) subscription commercial-free background music services for shops, paging ("beeper") services and providing a program feed for AM transmitters of AM/FM stations. SCA subcarriers are typically 67 kHz and 92 kHz.