This Javascript calculator uses the FM or TV propagation curves to find the distance to a service or interfering contour, or the corresponding field strength at a given contour distance.  More after the form.


This function uses the FCC's CURVES program to make calculations of the F(50,50) FM and NTSC (analog) TV service curves, the F(50,10) interfering signal curves, and the F(50,90) digital TV service curves.  Printable copies of these propagation curves are available at FM and TV Propagation Curves Graphs.

Antenna Height Above Average Terrain (HAAT) values for a particular FM or TV station can be obtained from the FM Query or the TV Query, or use the HAAT Calculator.  The class of an FM station may be retrieved from the FM Query.

FM Broadcast Radio

F(50,50) protected service contours for FM stations are defined as follows:

  • 54 dBu contour for commercial Class B stations
  • 57 dBu contour for commercial Class B1 stations
  • 60 dBu (1 mV/m) contour for commercial Class A, C3, C2, C1, and C stations
  • 60 dBu for all classes of noncommercial educational stations in the reserved band (88.1 to 91.9 MHz)

For LPFM (low power FM) stations, the 60 dBu service contour is not protected from interference caused by changes made to regular FM stations:

  • 60 dBu service contour for LPFM stations

For radio stations, the service contour generally does not define the outer limit of listenable signal.  In the absence of interference, FM stations can often be heard in locations well beyond the protected service contour.  That extended service is not protected from interference caused by other stations.

City coverage for commercial FM stations is defined by the F(50,50) 70 dBu contour, per Section 73.315.  For noncommercial educational stations (except LPFM), coverage over the community of license is defined by the 60 dBu contour (see Section 73.515).

For the appropriate FM interfering contour, please consult Section 73.509 for noncommercial educational stations (88.1 MHz to 91.9 MHz) or Section 73.215 for commercial FM stations (92.1 MHz to 107.9 MHz).

If you already know the FM station class and the HAAT, use FMpower to compute the effective radiated power (ERP) needed to achieve coverage equivalent to the reference (maximum) facilities for the station class.

Digital Television (DTV)

For DTV TV stations, service is defined to exist where the received signal strength exceeds the limit shown in the following table, using the F(50,90) propagation curves.  These field strength values are defined in Section 73.622 and Section 73.625).   Note that the channel corresponds to the channel the station is transmitting on, which may not correspond to the "virtual channel"  number that a viewer sees.

Channels DTV Noise-Limited Service Minimum Field Strength over Community of License
Transmit Channels 2 through 6 28 dBu 35 dBu
Transmit Channels 7 through 13 36 dBu 43 dBu
Transmit Channels 14 through 36 41 dBu 48 dBu

Note: Using ERP and HAAT to define the F(50,90) contour may not give identical results to the more complex methods of noise-limited coverage prediction used for DTV allocations work.

NTSC (analog) Television  (retained for reference)

For NTSC (analog) TV stations, the service contours were as follows (from Section 73.683 and 73.685 before the October 2023 rule revisions):

Channels Grade B
Service Contour
Grade A
Service Contour
City Grade
Service Contour
Transmit Channels 2 through 6 47 dBu 68 dBu 74 dBu
Transmit Channels 7 through 13 56 dBu 71 dBu 77 dBu

Transmit Channels 14 through 69       

64 dBu 74 dBu 80 dBu
Frequencies corresponding to TV channels are available from Section 73.603.

Information about AM and FM broadcast radio stations is available at the Audio Division on the FCC's website, and at Broadcast Radio Links

Information about TV stations is available at the Video Division.

FCC > Media Bureau > Audio Division and Video Division.