Editing FM broadcast band (section)

==OIRT bandplan==<!-- This section is linked from [[OIRT bandplan]] -->
The [[OIRT]] FM broadcast band covers 65.8 to 74&nbsp;MHz. It was used in the [[Soviet Union]] and most of the other [[Warsaw Pact]] member countries of the [[International Radio and Television Organisation]] in [[Eastern Europe]] (OIRT), with the exception of [[East Germany]], which always used the 87.5 to 100 (later 104) MHz broadcast band—in line with Western Europe.

The [[Band I|lower portion of the VHF band]] [[Radio propagation|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 [[skywave]]s.

Transition to the 87.5 to 108&nbsp;MHz band started as early as the 1980s 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]] (including [[Kaliningrad]]), [[Belarus]],<ref>{{cite web|url=http://www.tvr.by/eng/radio/1-kanal/|title=1 канал. Первый национальный канал Белорусского радио|website=www.tvr.by|access-date=19 March 2018}}</ref> [[Moldova]],<ref>[https://web.archive.org/web/19990909135753/http://www.geocities.com/SiliconValley/Code/2523/mdfmlist.html http://www.egocities.com]</ref> [[Ukraine]],<ref>{{cite web|url=http://www.radiofm.narod.ru/fmair.html|title=FM,УКВ-радиостанции в Украине|website=www.radiofm.narod.ru|access-date=19 March 2018}}</ref> and [[Turkmenistan]].<ref>{{cite web|url=http://ukradio.info/OIRT_Tuner/|title=OIRT Tuner|website=ukradio.info|access-date=19 March 2018}}</ref>

In [[Czechoslovakia]], the decision to use the 87.5 to 108&nbsp;MHz band instead of 65.9 to 74&nbsp;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.<ref>[https://www.itu.int/en/history/Pages/RadioConferencesRegional.aspx?conf=4.108 Regional Administrative Conference for FM Sound Broadcasting in the VHF band (Region 1 and certain countries concerned in Region 3) (2nd session) (Geneva, 1984)], Accessed 2019-03-05</ref> Allocated frequencies are still valid and are used in the [[Czech Republic]] and [[Slovakia]]. The first transmitter was put into operation on 102.5&nbsp;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.<ref>[https://www.dx.cz/index.php?&rubrika=9&id=326&PUNipomYAnkadradiovYtdperestrojky.html (Czechoslovak DX Club, in Czech)] Accessed 2019-03-05</ref> The transition was finished in 1993.

In Poland all OIRT broadcast transmitters were closed down at the end of 1999.

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&nbsp;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 (the "western") 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&nbsp;kHz rather than 50, 100 or 200&nbsp;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&nbsp;kHz with the audio on both side-bands. This gives the following signal structure: L + R --> 31.25&nbsp;kHz reduced subcarrier L - R.

The [[4-meter band]] (70–70.5&nbsp;MHz) [[amateur radio]] allocation used in many European countries is entirely within the OIRT FM band. Operators on this band and the [[6-meter band]] (50–54&nbsp;MHz) 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&nbsp;meter amateur allocation is only 0.5&nbsp;MHz or less, and a single broadcast station causes considerable interference to a large part of the band.

The [[Television channel frequencies#Eastern Europe, North Korea|System D]] television channels R4 and R5 lie wholly or partly within the 87.5–108&nbsp;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.