Part 73, Subpart G, Section 73.811 is a core regulation that defines the maximum and minimum effective radiated power (ERP) of LPFM stations.
Maximum power of LPFM stations
Main article: Height above average terrain
LPFM stations at a height above average terrain (HAAT) of 30 meters (98.4 feet) or less has a maximum ERP of 100 watts (0.1 kilowatts).
At HAAT levels above 30 meters, the maximum ERP is adjusted to a level where the 60 dBu service contour of the LPFM station does not exceed 5.6 kilometers (3.5 miles).
LPFM stations operating in the Mexico Strip Zone, a distance within 125 kilometers (77.7 miles) of the Mexican border are limited to 50 watts ERP in the direction of Mexico at HAAT levels of 42 meters (137.8 feet) or less.
Minimum power of LPFM stations
Normally, the minimum power of an LPFM station is half of the ERP as the maximum.
At HAAT levels of 30 meters or less, the minimum ERP of an LPFM station is 50 watts.
At HAAT levels above 30 meters, the minimum ERP is adjusted to a level where the 60 dBu service contour of the LPFM station does not exceed 4.7 kilometers (2.9 miles).
Regulatory history
This rule was first created in the 2000 LPFM Report and Order to establish two LPFM service classes LP-100 (the current LPFM service) at LP-10 (10 watts at 30 meters HAAT). In 2012, the rule was amended in the Sixth Report and Order to reflect the elimination of the LP-10 class of service.
Federal Register citation
78 FR 2105, Jan. 9, 2013
Text of regulation 47 CFR §73.811
§ 73.811 LPFM power and antenna height requirements.
(a) Maximum facilities. LPFM stations will be authorized to operate with maximum facilities of 100 watts ERP at 30 meters HAAT. An LPFM station with a HAAT that exceeds 30 meters will not be permitted to operate with an ERP greater than that which would result in a 60 dBu contour of 5.6 kilometers. In no event will an ERP less than one watt be authorized. No facility will be authorized in excess of one watt ERP at 450 meters HAAT.
(b) Minimum facilities. LPFM stations may not operate with facilities less than 50 watts ERP at 30 meters HAAT or the equivalent necessary to produce a 60 dBu contour that extends at least 4.7 kilometers.