FM broadcast band


The FM broadcast band, used for FM broadcast radio by radio stations, differs between different parts of the world. In Europe and Africa and in Australia, it spans from 87.5 to 108 megahertz - also known as VHF Band II - while in the Americas it ranges from 88 to 108 MHz. The FM broadcast band in Japan uses 76 to 95 MHz. The International Radio and Television Organisation band in Eastern Europe is from 65.8 to 74.0 MHz, although these countries now primarily use the 87.5 to 108 MHz band, as in the case of Russia. Some other countries have already discontinued the OIRT band and have changed to the 87.5 to 108 MHz band.
Frequency modulation radio originated in the United States during the 1930s; the system was developed by the American electrical engineer Edwin Howard Armstrong. However, FM broadcasting did not become widespread, even in North America, until the 1960s.
Frequency-modulated radio waves can be generated at any frequency. All the bands mentioned in this article are in the very high frequency range, which extends from 30 to 300 MHz.

CCIR bandplan

Center frequencies

While all countries use FM channel center frequencies ending in 0.1, 0.3, 0.5, 0.7, and 0.9 MHz, some countries also use center frequencies ending in 0.0, 0.2, 0.4, 0.6, and 0.8 MHz. A few others also use 0.05, 0.15, 0.25, 0.35, 0.45, 0.55, 0.65, 0.75, 0.85, and 0.95 MHz.
An ITU conference in Geneva, Switzerland, on December 7, 1984, resolved to discontinue the use of 50 kHz channel spacings throughout Europe.
The original frequency allocation in North America used by Edwin Armstrong used the frequency band from 42 through 50 MHz, but this allocation was changed to a higher band beginning in 1945. In Canada, the United States, Mexico, the Bahamas, etc., there are 101 FM channels numbered from 200 to 300, though these numbers are rarely used outside the fields of radio engineering and government.
The center frequencies of the FM channels are spaced in increments of 200 kHz. The frequency of 87.9 MHz, while technically part of TV channel 6, is used by just two FM class-D stations in the United States. Portable radio tuners often tune down to 87.5 MHz, so that the same radios can be made and sold worldwide. Automobiles usually have FM radios that can tune down to 87.7 MHz, so that TV channel 6's audio at 87.75 MHz could be received, such as in Birmingham, Alabama, and Denver, Colorado. With the advent of digital television in the United States, this ability will soon be irrelevant when the remaining analog LPTV stations are required by the FCC to shut down or convert to digital by September 2015—but there are still analog television stations in the sparsely-populated regions of northern Canada. There are also analog TV stations on the other continents and on scores of different islands.
In the United States, the twenty-one channels with center frequencies of 87.9–91.9 MHz constitute the reserved band, exclusively for non-commercial educational stations. The other channels may be used by both commercial and non-commercial stations.
Originally, the American Federal Communications Commission devised a bandplan in which FM radio stations would be assigned at intervals of four channels for any one geographic area. Thus, in one area, stations might be at 88.1, 88.9, 89.7, etc., while in an adjacent area, stations might be at 88.3, 89.1, 89.9, 90.7 etc. Certain frequencies were designated for Class A only, which had a limit of three kilowatts of effective radiated power and an antenna height limit for the center of radiation of 300 feet height above average terrain. 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, a station could be Class B or Class C, depending on which zone it was 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 six kilowatts, and the frequency restrictions noted above were removed. As of late 2004, a station can be "squeezed in" anywhere as long as the location and class conform to the rules in the FCC separation table. The rules for second-adjacent-channel spacing do not apply for stations licensed before 1964.

Deviation and bandpass

Normally each channel is 200 kHz wide, and can pass audio and subcarrier frequencies up to 100 kHz. Deviation is typically limited to 150 kHz total in order to prevent adjacent channel interference 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 65.9 to 74 MHz. It was used in the Union of Soviet Socialist Republics and most of the other Warsaw Pact member countries of the International Radio and Television Organisation in Eastern Europe, with the exception of East Germany, which always used the 87.5 to 100 MHz broadcast band—in line with Western Europe.
The lower portion of the VHF band behaves a bit like shortwave radio in that it has a longer reach than the upper portion of the VHF band. It was ideally suited for reaching vast and remote areas that would otherwise lack FM radio reception. In a way, FM suited this band because the capture effect of FM could mitigate interference from skywaves.
Transition to the 87.5 to 108 MHz band started as early as in eighties in some East European countries. Following the collapse of the communist governments, that transition was remarkably accelerated as private stations have been established. This was also prompted by the lack of equipment for the OIRT band and the modernisation of existing transmission networks.
Many countries have completely ceased broadcasting on the OIRT FM band, although 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 this band outside of Russia.
Countries which still use the OIRT band are Russia, Belarus, Moldova, Ukraine, Lithuania and Turkmenistan.
In Czechoslovakia, the decision to use the 87.5 to 108 MHz band instead of 65.9 to 74 MHz band was made in the beginning of the eighties. The frequency plan was created, which was internationally coordinated at Regional Administrative Conference for FM Sound Broadcasting in the VHF band in Geneva, 1984. Allocated frequencies are still valid and are used in the Czech Republic and Slovakia. The first transmitter was put into operation at 102.5 MHz near Prague in November 1984. Three years later, there were eleven transmitters in service across the country, including three in the Prague neighborhood of Žižkov. In 1988, the plan was to set up 270 transmitters in 45 locations eventually. The transition was finished in 1993.
Hungary closed down its remaining broadcast transmitters in 2007, and for thirty days in July of that year, several Hungarian amateur radio operators received a temporary experimental permit to perform propagation and interference experiments in the 70–70.5 MHz band.
In Belarus, only government-run public radio stations are still active on OIRT. All stations on OIRT in Belarus are a mirror of normal FM broadcasts. The main purpose of those stations is compatibility with older equipment.
In 2014, Russia began replacing OIRT-banded transmitter with CCIR-banded FM transmitters. The main reason for the change to CCIR FM is to reach more listeners.
Unlike Western practice, OIRT FM frequencies are based on 30 kHz rather than 50, 100 or 200 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. However, multipath distortion effects are less annoying than on the CCIR band.
Stereo is generally achieved by sending the stereo difference signal, using a process called polar modulation. Polar modulation uses a reduced subcarrier on 31.25 kHz with the audio on both side-bands. This gives the following signal structure: L + R --> 31.25 kHz reduced subcarrier L - R.
The 4-meter band amateur radio allocation used in many European countries is entirely within the OIRT FM band. Operators on this band and the 6-meter 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 meter amateur allocation is only 0.5 MHz or less, and a single broadcast station causes considerable interference to a large part of the band.
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

The FM band in Japan is 76–95 MHz. The 90–108 MHz section was used for analog VHF TV Channels 1, 2 and 3. The narrowness of the Japanese 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 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 radios were formerly marked with "TV Sound" in the 76–88 section. If these radios were sold in the US, 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. The compatibility of "TV sound" with conventional FM radio ended with the U.S. digital TV transition in 2009, with the exception of the limited number of low-power stations on channel 6 that still use analog; these low-power stations will switch to digital in 2021.
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 undesired performance; the converter cannot down-convert in full the regular international FM band to the only 14 MHz-wide Japanese band, and the car's antenna may perform poorly on the higher FM band. Some converters simply down-convert the FM band by 12 MHz, leading to logical frequencies, but leaving off the 102–108 MHz band. Also, RDS is not used in Japan, whereas most modern car radios available in Europe have this system. Also the converter may not allow pass-through of the MW band, which is used for AM broadcasting. A better solution is to replace the radio and antenna with ones designed for the country where the car will be used.
Australia had a similar situation with Australian TV channels 3, 4 and 5 that are between 88 and 108 MHz, and was intending to follow Japan, but in the end opted for the western bandplan, due to CCIR radios that entered the country. There were some radios sold in Australia for 76 to 90 MHz.

Historic U.S. bandplan

Early FM broadcasting in North America originally used the 42–50 MHz band. In 1941, the Yankee Network, which was already using FM for AM station feeds, started operating a station, W39B, in this band from a transmitter atop Mount Washington, New Hampshire, the highest point in the northeast United States. In 1945 the United States FCC decided to move FM broadcasters to the 88–106 MHz band ; this made all the existing FM radios useless, although converters could be purchased. It was even more expensive for broadcasters to rebuild their transmitters to work on the new band. Altogether, the change set FM radio back ten years.
The "devastating" change was successfully lobbied for by RCA, which did not want FM radio to become dominant, although the higher frequencies had fewer interference problems. RCA conducted "an organized campaign of misinformation". This protected RCA's and other networks' investments in AM radio, and avoided competition with television, which RCA wanted to focus on.
In March 2008, the FCC requested public comment on turning the bandwidth currently occupied by analog television channels 5 and 6 over to extending the FM broadcast band when the digital television transition was to be completed in February 2009. This proposed allocation would effectively assign frequencies corresponding to the existing Japanese FM radio service for use as an extension to the existing North American FM broadcast band.

FM radio switch-off

With the invention of DAB+ radio, some countries have planned and started an FM radio switch-off. Norway, in January 2018, was the first country to discontinue FM as a result.