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FM Service Contour Data Points

In response to many requests for radio service area data, the Audio Division of the Media Bureau, Federal Communications Commission (FCC), releases predicted service contour data points on a regular basis.  Generally, updated files are posted to the FCC's website by approximately 10:00 AM each day, Eastern time.  These zipped files are available at the following locations (include capital letters and underscores as shown):

The data is contained in one large file:

The file contains data for active records (licenses, construction permits, applications) as shown in the FM Query.  Please note that AM broadcast service contour data is not presently available, and we have no time frame for posting this information.  See TV Service Contour Data Points for broadcast television service contours.

Using the FCC's F(50,50) propagation curves, distances to the FM service contours are generated from the effective radiated power in a given direction, and the radial antenna height above the average elevation of that same radial.  See FM Propagation Curves and Antenna Height Above Average Terrain (HAAT) Calculations for additional information on this process.

USERS TAKE NOTE: The files are LARGE!  We recommend using a broadband connection, making sure your system has enough disk space to handle these files.  Current data files, unzipped, may be on the order of 220 MB in size.

Because of its large size and layout, it can be difficult to find a viewer capable of displaying the entire text file at one time.  However, the structure of the file is straightforward.  Each line of these formatted text files is constructed as follows:

707       |FM|KAXE  BLED-1533                    |47.25472 ,-93.43417 |
... (359 lat lon points, then) ... |47.76079 ,-93.44731 |^

where the leftmost number represents the application ID number of the CDBS/FM Query record.  The station's service is listed in the next field, followed by the description (call sign and application file number) in effect at the time the service contour data was initially generated. This is followed by the NAD83 coordinates |latitude, longitude| of the station's or application's transmitter site.  Then there are 360 |latitude, longitude| pairs, with the first coordinate pair corresponding to the contour location at 0 degrees (true north) from the transmitter site, and continuing clockwise at 1 degree intervals to 359 degrees.  An end of record character "^" finishes the line (to help users detect broken lines).  This makes each line 7,633 characters long.  Code to read these lines should be written with the long record length in mind.  West longitudes and south latitudes are referenced by negative numbers -- in keeping with the conventions of most GIS systems.  Regretfully, we cannot honor requests to provide this data in alternative formats.

To associate specific service contour records with the proper station or application data, match the application ID number of the record with the corresponding application ID number from CDBS' application.dat table.  Alternatively, (and certainly much easier than deciphering the CDBS tables structures) use the FM Query with the output type set to create a "pipe-delimited text file" -- that output can then be parsed in accordance with the fields description file at http://transition.fcc.gov/mb/audio/newsite/datafiles/am_fm_tv_textlist_key.txt to obtain the data most commonly sought by users.  Using the FM Query searches also has the advantage of allowing users to winnow out unwanted station records.  For example, an FM Query search for all the licensed Low Power FM (LPFM) stations (service code FL) in Arkansas will exclude station records in other states and services, as well as construction permits and application records.

It must be noted that the station contours here do not always reflect the same predicted field strength value. For FM stations, the following table may help:

Channels 201 to 220
Noncommercial educational [NCE] FM stations
60 dBu (1 mV/m)
Channels 221 to 300
Commercial FM stations, and occasional NCE stations, Zone II
60 dBu (1 mV/m)
Channels 221 to 300
Commercial FM stations, occasional NCE stations,
and Class B station in Zones I, I-A
54 dBu
Channels 221 to 300
Commercial FM stations, occasional NCE stations, and all Class B1 stations in Zones I, I-A
57 dBu
Channels 200 to 300
LPFM stations [FL], translator [FX],
and auxiliary (backup) stations [FS]
60 dBu (1 mV/m)
All Canadian stations in the database54 dBu

For more information about FM station classes, see the FM Classes page.

FM service contours usually do not define the outer limit of service.  In most cases, a radio station may be received at locations outside (and sometimes well outside) the service contours given in these files.  Within the service contour, reception is generally protected from interference caused by other stations on the same channel or adjacent channels or frequencies.  Outside of that contour, interference may occur from other stations.  It simply is not possible to protect each station out to the point at which it cannot be heard by anyone.  Doing so would result in far fewer stations available to listeners.  The Commission's rules represent a balance between very few stations with no interference between them, and great numbers of stations with small service areas and severe mutual interference.

Finally, USE OF THESE CONTOUR DATA FILES IS AT THE USERS' SOLE RISK, and the FCC nor the Federal Government is responsible for errors or omissions, late posting of data, or any consequences thereof.  No restrictions are set on the use of this data.  The FCC does not guarantee that the contour data here will correspond to the contour data considered during the processing of given applications.  Users should take note that this contour data is only generated once for each application ID number, shortly after the application is posted to the FM Query, so that the possibility exists that subsequent corrections to the CDBS database might not be reflected in the service contours herein.  (However, amendments to electronically filed applications will have a new application ID number, and so new contour data will be generated for that amendment.)  Archived records will not be corrected, as they are retained for reference purposes only.  Lastly, FM interfering contours will not be generated.

Dale Bickel dale.bickel@fcc.gov
Senior Electronics Engineer
Audio Division, Media Bureau
Federal Communications Commission


FCC > Media Bureau > Audio Division


Updated: January 29, 2014
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