Adoption of FM broadcasting in the United States

Despite FM having been patented in 1933, commercial FM broadcast did not begin until the late 1930s, when it was started by a handful of pioneer raw stations, including W8HK, Buffalo, New York (now WTSS); W1XOJ / WGTR / RLS, Paxton, Massachusetts (now listed as Worcester, Massachusetts); W1XSL / W1XPW / WDRC-FM, Meriden, Connecticut (now WHCN); W2XMN / KE2XCC / WFMN, Alpine, New Jersey (Edwin Property Armstrong us, closed after Armstrong’s death in 1954); W2XQR / WQXQ / WQXR-FM, New York; W47NV Nashville, Tennessee (signed 1951); W1XER / W39B / WMNE, whose studies were in Boston, but whose transmitter was above the highest mountain in the northeastern United States, Mount Washington, New Hampshire (closed 1948); W9XAO Milwaukee, Wisconsin (then WTMJ-FM out of the air in 1950, back in 1959 to another frequency). Also worth noting are the General Electric W2XDA Schenectady stations and W2XOY Nova Scotia, New York-two experimental frequency modulation transmitters of 48.5 MHz, which signed in 1939. Both were merged into a station using the letters call W2XOY 20 November 1940, with the station taking WGFM call letters a few years later, and moving 99.5 MHz when the FM band was transferred to the spectrum shares 88-108 MHz. General Electric sold the station in 1980, and today the station is called WRVE.

On June 1, 1961, at 00:01 (EDT), WGEM-FM became the first FM station in the United States to broadcast in stereo.

The first commercial FM broadcasters were in the United States, but were first used primarily to broadcast their AM sister station simultaneously, transmitting lush orchestral music to stores and offices, transmitting classical music to an audience of Luxury in urban areas, or for educational programming purposes. By the end of 1960, FM had been adopted by “alternative rock” (“AOR-OrientedAlbum Format Rock”) fans, but it was not until 1978 that FM stations exceeded those of AM America North. During the 1980s and 1990s, Top 40 music stations and country music stations later largely abandoned AM to FM. AM today is mainly the prerogative of radio talk, news, sports, religious, ethnic (minority language) broadcasting and certain types of minority music interests. This change turned AM into the “alternative group” that the FM was once. (Some AM stations have started broadcasting simultaneously on, or switching to, FM signals to attract younger listeners and difficulty who receive help in buildings during storms, and near high voltage cables. These stations now focus on their presence on the FM dial.)

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Modulation characteristics

Frequency or frequency modulation is a form of modulation that transmits information by varying the frequency of a carrier wave; The amplitude modulation AM greater or varies the amplitude of the carrier, with its frequency remains constant. With FM the frequency deviation of the assigned carrier frequency at any instant is directly proportional to the amplitude of the input signal and determines the instantaneous frequency of the transmitted signal. As the transmitted FM signals use more bandwidth of AM-band signals, this form of modulation is generally used with the higher (VHF or UHF) frequencies used by television, FM broadcast band systems, and telephony Land mobile.
Armstrong’s first FM transmitter, located in the Empire State Building, New York City, which allows testing of the secrets of its system between 1934 and 1935. licensed as a W2XDG experiment station, is broadcast 41 MHz at a power of 2 KW
A random noise having a triangular spectral distribution of an FM system, with the effect that the noise occurs primarily at the highest frequencies in the audio band. This can be compensated to a limited extent by increasing the high frequencies prior to transmission and further reducing in the receiver. Reducing high audio frequencies in the receiver also reduces high-frequency noise. These amplification methods and thus reduce certain frequencies are known respectively as pre-emphasis and de-emphasis ,.

The amount of pre-emphasis and de-emphasis used is defined by the time constant of a single RC filter circuit. In most countries, a time constant of 50 ms is used. The Americas and South Korea, 75 ms is used. This is worth both mono and stereo transmissions. Pre-emphasis is applied to the left and right channels before multiplexing, stereo.The amount of pre-emphasis that can be applied is limited by the fact that many forms of contemporary music contain higher frequency energy than the musical styles in effect at the birth of FM broadcasting. It can not be pre-emphasized as it would cause excessive deviation of the FM carrier. More modern FM broadcasting systems tend to use the program according to variable pre-emphasis; For example, dbx in the sound system of the BTSC TV, or not at all.

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FM broadcasting

FM broadcasting is a method of radio transmission using frequency modulation (FM) technology. Invented in 1933 by American engineer Edwin Armstrong, it is used worldwide to provide high-fidelity radio broadcast sound. FM broadcasting is capable of better sound quality than AM broadcasts, the head of the competition for radio transmission technology, it is used for most music broadcasts. FM radio stations use VHF frequencies. The term “FM band” describes the frequency band in a country devoted to FM broadcasting.

Worldwide, the FM broadcast band falls into the VHF band. Usually 87.5-108.0 MHz is used, or a part of it, with few exceptions:

The former Soviet republics, and some countries of the former eastern bloc, also used the band 65-74 MHz plus. Frequencies are allocated at 30 kHz intervals. This band, sometimes called band OIRT, is slowly being eliminated in many countries. The countries in the band 87.5 to 108.0 MHz is referred to as the CCIR band.
In Japan, the band 76-95 MHz is used.
The frequency of an FM broadcasting station (more strictly its rated nominal center frequency) is generally an exact multiple of 100 kHz. In most of South Korea, the Americas, the Philippines and the Caribbean, using odd multiples. In some parts of Europe, Greenland and Africa, that even multiple are used. In the United Kingdom, they are used even or odd. In Italy, they are used at a multiple of 50 kHz.

There are other unusual and obsolete FM broadcasting standards in some countries, including 1, 10, 30, 74, 500 and 300 kHz. However, in order to minimize interference between channels, stations that operate by the same or geographically close to the transmitting sites tend to maintain at least one frequency separation of 500 kHz, even when the nearest spacing frequency is technically permissible , With closer tuning reserved for several signal transmitters up to potentially interfering spaced are already more attenuated and therefore have less effect on neighboring frequencies.

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