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Most such units transmit in full stereo, though some models designed for beginner hobbyists might not. Aside from the assisted listening receivers, only certain kinds of FM receivers can tune to this band.[33]. Modulation control (limiter) devices are used to prevent this. In the UK odd or even are used. Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around 20 kHz to around 300 GHz.

This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. General Electric sold the station in the 1980s, and today the station is called WRVE.

A handful of radio stations around the country broadcast stereo in this way, under FCC experimental authority. The Amplitude Modulated (AM radio) carrier frequencies are in the frequency range 535-1605 kHz.

In such instances, however, this technique is often surprisingly effective in increasing the station's useful range. Throughout the world, the FM broadcast band falls within the VHF part of the radio spectrum. 23 to 53 kHz (sine quadrature subcarrier) (LF+LR) − (RF+RR) left minus right difference signal. The maximum frequency deviation of the carrier is usually specified and regulated by the licensing authorities in each country. Instead, Radio 1 shared airtime with Radio 2 FM, on Saturday afternoons, Sunday evenings, weekday evenings (10pm to midnight) and Bank Holidays, eventually having its own FM frequency starting in London in October 1987 on 104.8 MHz at Crystal Palace.

Some assistive listening devices are based on FM radio, mostly using the 72.1 to 75.8 MHz band. Today, speech broadcasting (suc…

Some stations in major regional centres simulcast on AM and FM bands.

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Also of note are General Electric stations W2XDA Schenectady and W2XOY New Scotland, New York—two experimental frequency modulation transmitters on 48.5 MHz—which signed on in 1939.

Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave; the older amplitude modulation or AM varies the amplitude of the carrier, with its frequency remaining constant. Because transmitted FM signals use more bandwidth than AM signals, this form of modulation is commonly used with the higher (VHF or UHF) frequencies used by TV, the FM broadcast band, and land mobile radio systems.

The FM tuner then decodes this signal and separates the Left and Right audio channels.

Slight variations in the peak deviation may occur in the presence of other subcarriers or because of local regulations. etc.. FM broadcasting began in the late 1930s, when it was initiated by a handful of early pioneer stations including W1XOJ/WGTR and W1XTG/WSRS, both transmitting from Paxton, Massachusetts (now listed as Worcester, Massachusetts); W1XSL/W1XPW/WDRC-FM, Meriden, Connecticut (now WHCN); W2XMN/KE2XCC/WFMN, Alpine, New Jersey (owned by Edwin Armstrong himself, closed down upon Armstrong's death in 1954); W2XQR/WQXQ/WQXR-FM, New York; W47NV/WSM-FM Nashville, Tennessee (signed off in 1951); W1XER/W39B/WMNE, whose studios were in Boston but whose transmitter was atop the highest mountain in the northeast United States, Mount Washington, New Hampshire (shut down in 1948); W9XAO Milwaukee, Wisconsin (later WTMJ-FM, went off air in 1950, returned in 1959 on another frequency). A mono receiver will use just the L+R signal so the listener will hear both channels through the single loudspeaker. For stereo, pre-emphasis is applied to the left and right channels before multiplexing.

This transfer is accomplished by mixing the original modulated carrier with a sine wave of another frequency. It has advantages that the coverage area provided by the OIRT band is greater than that provided by the more widely used 87.5 - 108 MHz band. At present, the FCC rules do not allow this mode of stereo operation.[18]. It was based on the Telefunken High Com broadband compander system, but was never introduced commercially in FM broadcasting.[22]. Subsequently, it developed steadily until in the 1980s many AM stations transferred to FM due to its superior sound quality and lower operating costs.

As a result of the band being relatively small, and the lower requirement for high fidelity, the channels are only 10 kHz wide. For everything from distribution to test equipment, components and more, our directory covers it. . In most of South Korea, the Americas, the Philippines and the Caribbean, only odd multiples are used. [26], 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.

Regional broadcasters still commonly operate AM stations due to the additional range the broadcasting method offers.

The Crosby system was rejected by the FCC because it was incompatible with existing subsidiary communications authorization (SCA) services which used various subcarrier frequencies including 41 and 67 kHz. FM broadcasting has included subsidiary communications authorization (SCA) services capability since its inception, as it was seen as another service which licensees could use to create additional income.

As transmitter powers increase above a few kilowatts, the operating costs become high and only viable for large stations. Frequency modulation or FM is a form of modulation which conveys information by varying the frequency of a carrier wave; the older amplitude modulation or AM varies the amplitude of the carrier, with its frequency remaining constant. those between channel numbers 200 and 221 are reserved for non-commercial educational broadcasts.

Starting on 1 October 2006, these devices became legal in most countries in the European Union.

As with monaural transmission, it is normal practice to apply pre-emphasis to the left and right channels before encoding and to apply de-emphasis at the receiver after decoding. If 50 Watt ERP is used, it's very likely that 20 miles of range will be achieved. Reducing the high audio frequencies in the receiver also reduces the high-frequency noise. . The knife edge effect can permit reception where there is no direct line of sight between broadcaster and receiver. Therefore, FM is used for most broadcasts of music or general audio (in the audio spectrum). In the United Kingdom the BBC conducted tests during the 1940s,[7] then began FM broadcasting in 1955, with three national networks: the Light Programme, Third Programme and Home Service.

The Japanese VHF FM band is only 14 MHz wide and this limits the number of stations that can be accommodated, and as a result, many stations use AM. Initially the users of SCA services were private analog audio channels which could be used internally or leased, for example Muzak-type services. The narrower bandwidth also helps with selective propagation issues that are more prevalent at these frequencies as well. Just weeks after the court's final decision there was an "FM radio boom" involving small private radio stations across the country. These processes of boosting and then reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively. However, to minimise inter-channel interference, stations operating from the same or geographically close transmitter sites tend to keep to at least a 500 kHz frequency separation even when closer frequency spacing is technically permitted. In the U.S, the FCC publishes curves that aid in calculation of this maximum distance as a function of signal strength at the receiving location. Following this experiment, a long-term test period was proposed that would permit one FM station in each of the top 25 U.S. radio markets to transmit in Quadraplex. The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. 87.9, 88.1 . The guard band around 19 kHz (±4 kHz) must still be maintained, so as not to trigger stereo decoders on receivers. This process produces a beat frequency equal to the difference between the frequencies, and this difference frequency constitutes a third carrier which will be modulated by the original signal.

The GE and Zenith systems, so similar that they were considered theoretically identical, were formally approved by the FCC in April 1961 as the standard stereo FM broadcasting method in the United States and later adopted by most other countries. The test results hopefully would prove to the FCC that the system was compatible with existing two-channel stereo transmission and reception and that it did not interfere with adjacent stations.

Like many other countries in Africa and Asia that drive on the left, New Zealand imports vehicles from Japan.

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Pre-emphasizing these high-frequency sounds would cause excessive deviation of the FM carrier. The Amplitude Modulated carrier frequencies are in the frequency range 535-1605 kHz. German broadcasters were left with only two remaining AM frequencies and were forced to look to FM for expansion.

New Zealand has no indigenous car manufacturers.

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. There were several variations on this system submitted by GE, Zenith, RCA, and Denon for testing and consideration during the National Quadraphonic Radio Committee field trials for the FCC. Today AM is mainly the preserve of talk radio, news, sports, religious programming, ethnic (minority language) broadcasting and some types of minority interest music. Computer modelling is more commonly used for this around the world. This composite signal, along with any other sub-carriers, modulates the FM transmitter.

Most other countries implemented FM broadcasting through 1960s and expanded their use of FM through the 1990s.

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