FM broadcast band
Wide band Frequency modulation radio originated in the United States during the 1930s; the system was developed by the American electrical engineer Edwin Howard Armstrong.
An ITU conference in Geneva, Switzerland, on December 7, 1984, resolved to discontinue the use of 50 kHz channel spacings throughout Europe.
Originally, the American Federal Communications Commission (FCC) devised a bandplan in which FM radio stations would be assigned at intervals of four channels (800 kHz separation) for any one geographic area.
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.
In 2017, Brazil laid the groundwork to reclaim channels 5 and 6 (76.1–87.5 MHz) for sound broadcasting use and required new radio receivers to be able to tune into the new extended band (Portuguese: faixa estendida, abbreviated eFM).
[5] In 2023, Chile announced the expansion of the FM band to 76-108 MHz as part of the analog TV shutdown, scheduled for April 2024.
It was ideally suited for reaching vast and remote areas that would otherwise lack FM radio reception.
Many countries have completely ceased broadcasting on the OIRT FM band, although use continues in others, mainly the former republics of the USSR.
Countries which still use the OIRT band are Russia (including Kaliningrad), Belarus,[7] Moldova,[8] Ukraine,[9] and Turkmenistan.
The frequency plan was created, which was internationally coordinated at Regional Administrative Conference for FM Sound Broadcasting in the VHF band in Geneva, 1984.
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.
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.
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.
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.
In the 1930s investigations were begun into establishing radio stations transmitting on "Very High Frequency" (VHF) assignments above 30 MHz.
In October 1937, the Federal Communications Commission (FCC) announced new frequency allocations, which included a band of experimental and educational "Apex" stations, that consisted of 75 channels spanning from 41.02 to 43.98 MHz.
There was significant interest in the new FM band by station owners, however, construction restrictions that went into place during World War II limited the growth of the new service.
One area of concern was the effects of tropospheric and Sporadic E propagation, which at times reflected station signals over great distances, causing mutual interference.
A particularly controversial proposal, spearheaded by the Radio Corporation of America (RCA), which was headed by David Sarnoff, was that the FM band needed to be shifted to higher frequencies in order to avoid this potential problem.
[21] Several low-power television stations colloquially known as "Franken-FMs" operated primarily as radio stations on channel 6, using the 87.7 MHz audio carrier of that channel as a radio station receivable on most FM receivers configured to cover the whole of Band II, from 2009 to 2021; since then, a reduced number have received special temporary authority to carry a special audio carrier on their ATSC 3.0 signals to continue the status quo.
