FMPOWER utilizes the FM propagation curves tool to compute the effective radiated power (ERP) necessary to attain facilities comparable to the reference facilities for an FM station class. To utilize this program, only three essential pieces of information are needed: the U.S. state of focus, the station class, and the antenna height above average terrain (HAAT). You can discover the HAAT for a specific FM station by using the FM Query tool. Further details are available after the form.
For instance, FMpower demonstrates that 4.1 kW ERP at a height of 122 meters HAAT is considered equivalent to the reference Class A facilities, which require 6.0 kW ERP at 100 meters HAAT. The parameters for various station classes are explicitly outlined in 47 CFR 73.211 and can be found in a comprehensive table at FM Station Classes and Service Contours.
In cases where the antenna height is relatively lower, FMpower might display an equivalent ERP that exceeds the maximum allowable ERP for the station class. In such situations, a warning message will be generated. In practical terms, this implies that achieving coverage equivalent to the reference facilities for the station class is unattainable with the provided HAAT. This also highlights the significance of antenna height when considering FM and TV facilities’ coverage.
The equivalence among FM facilities is established by comparing the distances to the 60 dBu (1 mV/m) F(50,50) service contour. The only exception to this procedure applies to grandfathered Class A stations governed by rule section 47 CFR 73.213(c). For these grandfathered stations, equivalence is determined by comparing the 34 dBu F(50,10) interfering contour when the HAAT is below the Class A reference HAAT of 100 meters or by comparing the 60 dBu contours if the HAAT is 100 meters or higher.