§  73.683   Field strength contours and presumptive determination of field
strength at individual locations.

   (a) In the authorization of TV stations, two field strength contours
   are considered. These are specified as Grade A and Grade B and indicate
   the approximate extent of coverage over average terrain in the absence
   of interference from other television stations. Under actual
   conditions, the true coverage may vary greatly from these estimates
   because the terrain over any specific path is expected to be different
   from the average terrain on which the field strength charts were based.
   The required field strength, F (50,50), in dB above one micro-volt per
   meter (dBu) for the Grade A and Grade B contours are as follows:
                  Grade A (dBu) Grade B (dBu)
   Channels 2-6              68            47
   Channels 7-13             71            56
   Channels 14-69            74            64

   (b) It should be realized that the F (50,50) curves when used for
   Channels 14-69 are not based on measured data at distances beyond about
   48.3 kilometers (30 miles). Theory would indicate that the field
   strengths for Channels 14-69 should decrease more rapidly with distance
   beyond the horizon than for Channels 2-6, and modification of the
   curves for Channels 14-69 may be expected as a result of measurements
   to be made at a later date. For these reasons, the curves should be
   used with appreciation of their limitations in estimating levels of
   field strength. Further, the actual extent of service will usually be
   less than indicated by these estimates due to interference from other
   stations. Because of these factors, the predicted field strength
   contours give no assurance of service to any specific percentage of
   receiver locations within the distances indicated. In licensing
   proceedings these variations will not be considered.

   (c) The field strength contours will be considered for the following
   purposes only:

   (1) In the estimation of coverage resulting from the selection of a
   particular transmitter site by an applicant for a TV station.

   (2) In connection with problems of coverage arising out of application
   of § 73.3555.

   (3) In determining compliance with § 73.685(a) concerning the minimum
   field strength to be provided over the principal community to be
   served.

   (d) For purposes of determining the eligibility of individual
   households for satellite retransmission of distant network signals
   under the copyright law provisions of 17 U.S.C. 119(d)(10)(A), field
   strength shall be determined by the Individual Location Longley-Rice
   (ILLR) propagation prediction model. Such eligibility determinations
   shall consider only the signals of network stations located in the
   subscriber's Designated Market Area. Guidance for use of the ILLR model
   in predicting the field strength of analog television signals for such
   determinations is provided in OET Bulletin No. 72 (stations operating
   with analog signals include some Class A stations licensed under part
   73 of this chapter and some licensed low power TV and TV translator
   stations that operate under part 74 of this chapter). Guidance for use
   of the ILLR model in predicting the field strength of digital
   television signals for such determinations is provided in OET Bulletin
   No. 73 (stations operating with digital signals include all full
   service stations and some Class A stations that operate under part 73
   of this chapter and some low power TV and TV translator stations that
   operate under Part 74 of this chapter). OET Bulletin No. 72 and OET
   Bulletin No. 73 are available at the Federal Communications
   Commission's Reference Information Center, located at the address of
   the FCC's main office indicated in 47 CFR 0.401(a), or at the FCC's
   Office of Engineering and Technology (OET) website:
   http://www.fcc.gov/oet/info/documents/bulletins/.

   (e) If a location was predicted to be unserved by a local network
   station using a version of the ILLR model specified in OET Bulletin No.
   72 or OET Bulletin No. 73, as appropriate, and the satellite subscriber
   at that location is receiving a distant signal affiliated with the same
   network from its satellite provider, the satellite subscriber shall
   remain eligible for receiving the distant signal from its satellite
   provider if that location is subsequently predicted to be served by the
   local station due to either a change in the ILLR model or a change in
   the station's operations that change its coverage.

   (f) A satellite carrier is exempt from the verification requirements of
   47 U.S.C. 339(c)(4)(A) with respect to a test requested by a satellite
   subscriber to whom the retransmission of the signals of local broadcast
   stations is available under 47 U.S.C. 338 from such carrier. The
   definitions of satellite carrier, subscriber, and local market
   contained in 47 CFR 76.66(a) apply to this paragraph (f).

   [ 44 FR 36039 , June 20, 1979, as amended at  47 FR 35990 , Aug. 18, 1982;
    50 FR 23699 , June 5, 1985;  50 FR 32416 , Aug. 12, 1985;  65 FR 36641 ,
   June 9, 2000;  70 FR 21670 , Apr. 27, 2005;  75 FR 80363 , Dec. 22, 2010;
    85 FR 64408 , Oct. 13, 2020]