§ 73.807 is a core regulation in the Low Power FM radio service. This rule addresses the placement of LPFM stations in respect to other FM broadcast facilities. LPFM stations operating on reserved band FM frequencies (88.1~91.9 MHz) are also required to protect TV facilities on Channel 6 pursuant to § 73.825.
Protection to US FM stations
Main article: Required minimum distance separation to domestic FM facilities.
Other LPFM stations
LPFM stations may only be proposed where they are separated by other LPFM stations on the same channel by at least 24 kilometers (14.9 miles) and on first-adjacent channels by 14 kilometers (8.7 miles). LPFM stations are not required to protect other LPFM stations on second adjacent channels.
Full Service FM stations within the United States
In respect to full-service FM stations operating on the same or the first-adjacent channel of the LPFM, the minimum distance separations required are based on the standard interfering contour of the LPFM station and a distance that is 20 kilometers (12.4 miles) past the standard protected service contour of the full-service station. Each full-service FM service class has specific distances required for separation. This additional 20 kilometer "buffer zone" was adopted in the original LPFM Report and Order in order to assure minimal impacts on LPFM stations in the event that a full-service FM station had to make a modification of their facility.
LPFM stations are also required to protect full-service FM stations on second adjacent channels, however that requirement can be waived if a technical showing is made that the proposed LPFM facility does not cause any actual interference to listeners or potential listeners of the short-spaced second adjacent channel station or stations. In addition, LPFM stations must also protect FM stations on third adjacent channels in cases where the other FM station is carrying a Radio Reading Service. Second and third adjacent channel requirements do not include the 20 kilometer "buffer zone".
In 2011 with the enactment of the Local Community Radio Act of 2010 (LCRA), the use of minimum distance separation methodology and the actual distances that were codified in this rule at the time when the LCRA was enacted must be used. Because of that statutory requirement, the FCC is unable to give any waiver of the distance separation rules in respect to co-channel (same channel) and first-adjacent channel domestic FM facilities.
Class D stations
LPFM stations are required to protect Class D stations operating on the same channel as well as first and second adjacent channels. Second adjacent channel short-spacing can be waived in a manner similar to full-service FM stations.
Super-powered FM broadcast stations
FM stations operating in the reserved band (88.1~91.9 MHz), including class D stations, that are operating with parameters that exceed the maximum allowed for that service class will be protected at the service class that represents the parameters of the actual facility.
Puerto Rico and the U.S. Virgin Islands
Because of the differences in the maximum parameters of FM broadcast stations within Puerto Rico and the U.S. Virgin Islands, the required minimum distance separations from LPFM stations to full-service FM stations are are larger than those in the mainland United States. In Puerto Rico and the Virgin Islands, only classes A, B1 and B are available to full-service FM stations.
For foreign FM stations in the Caribbean region, the FCC does not have any specific bilateral or multilateral agreements with any other nation's administration. Therefore, there are no specific distance separation requirements to other FM facilities outside of the United States territories.
The assignment of frequencies to LPFM stations in Puerto Rico and the U.S. Virgin Islands are also reported to the International Telecommunications Union's Master International Frequency Register. As a result, LPFM stations, especially those in the U.S. Virgin Islands may receive objections and interference complaints from other nations in the Caribbean region. Such objections and complaints would be lodged through the FCC's International Bureau, which will in turn contact the Media Bureau, which may order the LPFM station to cease operations. LPFM stations in the U.S. Virgin Islands should choose a channel that would not cause interference with FM stations in the British Virgin Islands.
FM Translator Stations
In respect to FM stations, LPFM stations are classified into one of three "sub classes". The subclass is based on the translators maximum effective radiated power (ERP) and overall height above average terrain. The sub-class is based on the average distance to the 60 dBu service contour. LPFM stations must protect FM translators on the same channel, first and second adjacent channels using minimum distance separation. Second adjacent channel spacing can be waived using the same method as waivers in respect to full-service FM stations.
While the FM translator service spacing requirements are not specifically mandated by the LCRA, the FCC has customarily not granted any waivers of distance separation on co-channel and first-adjacent channels, even if a finding of no interference is demonstrated. LPFM stations are required to protect FM translators using directional antennas as if they are using a nondirectional antenna.