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FM broadcast band

In most of the world, the FM broadcast band, used for broadcasting FM radio stations, goes from 87.5 to 108.0 MHz. In Japan the FM broadcast band is 76–90 MHz, unlike any other country in the world. The old OIRT band in Eastern Europe was 65.8–74 MHz.

The name "FM band" is misleading, since one can transmit FM on any frequency within the VHF range. All of these bands mentioned are in the VHF band which extends from 30 MHz to 300 MHz. In some countries FM broadcast radio is referred to as "VHF", "UKW" (German "Ultrakurzwelle" — "Ultra Short Wave") or "УКВ" (Russian "Ультра Короткие Волны").


CCIR bandplan

Center frequencies

While most countries use frequencies ending in .1, .3, .5, .7, or .9, some use .0, .2, .4, .6, and .8. Still others use .15, .35, .55, .75, .95, or .05, .25, .45, .65, .85 instead.

An ITU Geneva conference of 1984-12-07 resolved to discontinue the use of 50 kHz offsets throughout Eastern and Western Europe [1].

  • Most nations have used 100 kHz or 200 kHz offsets for FM broadcasting since the 1984 ITU Geneva conference.
  • Some FM digital tuners may not be able to tune in 50 kHz increments; these receivers should not be used by the international traveller.

Some countries, such as Italy which has a heavily-congested FM band, still allow a station on any 50 kHz boundary where it can be squeezed in.

  • The 50 kHz offset helps to prevent co-channel interference, and take advantage of FM's capture effect and receiver selectivity.

ITU Region II Bandplan and Channel Numbering

The original bandplan in North America actually used 42-50 MHz but this was changed in 1945. Currently in Canada and the United States, each channel is numbered from 200 (87.9 MHz) to 300 (107.9 MHz) in increments of 1 (200 kHz). 87.9 MHz, while technically part of TV channel 6 (82.0–88.0 MHz), is used by two class-D stations in the U.S.. Portable radio tuners often tune down to 87.5, so the same equipment can be marketed worldwide. Automobiles are unlikely to go overseas, but usually tune down to 87.7, so that TV channel 6 audio on 87.75 MHz can be received (although at a somewhat lower volume).

In the United States, the center frequencies of 87.9 though to 91.9 are reserved for non-commercial stations only, e.g., religious or educational. The center frequencies 92.1 through to 107.9 may contain either commercial or non-commercial stations. (Neither Canada nor Mexico observe this reservation.)

Originally, the FCC devised a bandplan where stations would be assigned at intervals of 4 channels, or 800 kHz separation, for any one geographic area. Thus, in mid-Missouri, stations might be at 88.1, 88.9, 89.7, etc., while in the St. Louis area, stations might be at 88.3, 89.1, 89.9, 90.7, etc. Certain frequencies were designated for Class A only (see FM broadcasting), which had a limit of 3 kW ERP and an antenna height limit for the center of radiation of 300 feet height above average terrain (HAAT). These frequencies were: 92.1, 92.7, 93.5, 94.3, 95.3, 95.9, 96.7, 97.7, 98.3, 99.3, 100.1, 100.9, 101.7, 102.3, 103.1, 103.9, 104.9, 105.5, 106.3, and 107.1. On other frequencies, stations could be Class B (50 kW, 500 feet) or Class C (100 kW, 2000 feet), depending on which Zone they were in.

In the late 1980s, the FCC switched to a "bandplan" based on a distance separation table using currently operating stations, and subdivided the class table to create extra classes and change antenna height limits to meters. Class A power was doubled to 6 kW, and the frequency restrictions noted above were removed. Basically, as of late 2004, a station can be "squeezed in" anywhere as long as the location and class conforms to the rules in separation table. The rules for second-adjacent-channel spacing do not apply for stations licensed prior to 1964.

The basic formulae determining radio channels for North America as mentioned are as follows:

  • ({\color{Red}\mathrm{MHz}} - 47.9) * 5 = {\color{Blue}\mathrm{channel number}}
  • {{\color{Blue}\mathrm{channel number}} \over 5} + 47.9 = {\color{Red}\mathrm{MHz}}

Deviation and bandpass

Normally, each channel is 200 kHz (0.2 MHz) wide, and can pass audio and subcarrier frequencies up to 100 kHz. Deviation is typically limited to 150 kHz total (±75 kHz) in order to prevent interference to adjacent channels on the band. Stations in the U.S. may go up to 10% over this limit if they use non-stereo subcarriers, increasing total modulation by 0.5% for each 1% used by the subcarriers.

OIRT bandplan

The OIRT FM broadcast band covers 65.8 to 74 MHz. It was used in the Union of Soviet Socialist Republics and most of the other socialist member countries of the International Radio and Television Organisation in Eastern Europe (OIRT), with the exceptions of East Germany and Yugoslavia, which always used the 87.5 to 108 MHz broadcast band in line with Western Europe.

Following the collapse of the communist governments in Eastern Europe, the 87.5 to 108 MHz band began to be adopted and is now in use in all countries. This was prompted by the expansion of broadcasting and the modernisation of existing transmission networks, using new or second-hand transmitters from western countries, together with a general desire for standardisation with the West.

Many countries have completely ceased broadcasting on the OIRT FM band, although declining use continues in others, mainly the former republics of the USSR. The future of broadcasting on the OIRT FM band is limited, due to the lack of new consumer receivers for that band.

Countries which still use the OIRT band include Russia[2], Belarus[3], Moldova[4] and Ukraine[5].

Hungary closed down its remaining broadcast transmitters in 2007, and for the period between 1-30 July 2007, some Hungarian amateur radio operators got a temporary experimental permit to carry out propagation and interference experiments in the band 70-70.5 MHz.

Unlike Western practice, OIRT FM frequencies are based on 10 kHz rather than 50 or 100 kHz multiples. This may have been to reduce co-channel interference caused by Sporadic E propagation and other atmospheric effects, which occur more often at these frequencies.

The 4 meters (70-70.5 MHz) amateur radio allocation used in many European countries is entirely within the OIRT FM band. Operators on this band and the 6 meter (50-54 MHz) band use the presence of broadcast stations as an indication that there is an "opening" into Eastern Europe or Russia. This can be a mixed blessing because the 4 metre amateur allocation is only 0.5 MHz or less, and a single broadcast station causes considerable interference to a large part of the band.

It will be noted that the System D television channels R4 and R5 lie wholly or partly within the 87.5-108 MHz FM audio broadcast band. Countries which still use System D therefore have to consider the re-organisation of TV broadcasting in order to make full use of this band for audio broadcasting.

Japanese bandplan

See also: FM broadcasting in Japan

The FM band in Japan is 76-90 MHz. The 90-108 MHz section is used for TV audio for VHF Channels 1,2 and 3. The narrowness of the Japanese band (14 MHz compared to slightly more than 20 MHz for the CCIR band) limits the number of FM stations that can be accommodated on the dial with the result that many commercial radio stations are forced to use AM.

Many Japanese radios are designed to be capable of receiving both the Japanese FM band and the CCIR FM band, so that the same model can be sold within Japan or exported. The radio may cover 76 to 108 MHz, the frequency coverage may be selectable by the user, or during assembly the radio may be set to operate on one band by means of a specially-placed diode or other internal component.

Conventional analog-tuned (dial & pointer) radios may be marked with "TV Sound" in the 90-108 section. If these radios were sold in the USA, for example, the 76-88 section would be marked TV sound for VHF channels 5 and 6, with the 88-108 section band as normal FM.

Second-hand automobiles imported from Japan contain a radio designed for the Japanese FM band, and importers often fit a "converter" to down-convert the 87.5 to 107.9 MHz band to the frequencies that the radio can accept. In addition to showing an incorrect frequency, there are two other disadvantages that can result in poor reception; the converter "compresses" the frequencies making the stations appear closer together, and the original antenna may perform poorly on the higher FM band. Also, RDS is not used in Japan, whereas most modern car radios available in Europe make use of this system. A better solution is to replace the radio and antenna with ones designed for the country where the car will be used.

Historic US bandplan

Early FM broadcasting in North America originally used the 42–50 MHz band (this range was also used by a class of experimental wideband AM stations known as apex broadcasters). Shortly after WWII the FCC decided to move FM broadcasters to the 88.1–105.9 (later 87.9–107.9) MHz band.

See also

Related topics

  • frequency modulation
  • FM broadcasting
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "FM_broadcast_band". A list of authors is available in Wikipedia.
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