Sec.  74.903   Interference.

   

   (a) Since interference in this service will occur only when an
   unfavorable desired-to-undesired signal ratio exists at the antenna
   input terminals of the affected receiver, the directive properties of
   receiving antennas can be used to minimize the hazard of such
   interference. Interference may also be controlled through the use of
   directive transmitting antennas, geometric arrangement of transmitters
   and receivers, and the use of the minimum power required to provide
   the needed service. Harmful interference will be considered present
   when the reference receiving antenna is oriented to receive the
   maximum desired signal, and a free space calculation determines that
   the desired-to-undesired signal ratio is less than the value specified
   for the respective channel under consideration.

   (1) Cochannel interference is defined as the ratio of the desired
   signal to the undesired signal, at the output of a reference receiving
   antenna oriented to receive the maximum desired signal level. Harmful
   interference will be considered present when a calculation using a
   terrain sensitive signal propagation model determines that this ratio
   is less than 45 dB (or the appropriate value for bandwidths other than
   6 MHz.)

   (2) Adjacent channel interference is defined as the ratio of the
   desired signal to undesired signal present in an adjacent channel, at
   the output of a reference receiving antenna oriented to receive the
   maximum desired signal level.

   (i) Harmful interference will be considered present when a calculation
   using a terrain sensitive signal propagation model determines that
   this ratio is less than 0 dB (or the appropriate value for bandwidths
   other than 6 MHz.)

   (ii) In the alternative, harmful interference will be considered
   present for an ITFS station constructed before May 26, 1983, when a
   calculation using a terrain sensitive signal propagation model
   determines that this ratio is less than 10 dB (or the appropriate
   value for bandwidths other than 6 MHz), unless:

   (A) The individual receive site under consideration has been
   subsequently upgraded with up-to-date reception equipment, in which
   case the ratio shall be less than 0 dB. Absent information presented
   to the contrary, however, the Commission will assume that reception
   equipment installation occurred simultaneously with original station
   equipment; or

   (B) The license for an ITFS station is conditioned on the proffer to
   the affected ITFS station licensee of equipment capable of providing a
   ratio of 0 dB or more at no expense to the ITFS station licensee, and
   also conditioned, if necessary, on the proffer of installation of such
   equipment; and there has been no showing by the affected ITFS station
   licensee demonstrating good cause and that the proposed equipment will
   not provide a ratio of 0 dB or more, or that installation of such
   equipment, at no expense to the ITFS station licensee, is not possible
   or has not been proffered.

   (3) For purposes of this section and except as set forth in Sec. 74.939
   regarding the protection of response station hubs, all interference
   calculations involving receive antenna performance shall use the
   reference antenna characteristics shown in Figure I, Sec. 74.937(a) or, in
   the alternative, utilize the actual pattern characteristics of the
   antenna in use at the receive site under study. If the actual receive
   antenna pattern is utilized, the applicant must submit complete
   details including manufacturer, model number(s), co-polar and
   cross-polar gain patterns, and other pertinent data.

   (4) If an application can demonstrate that the installation of a
   receiving antenna at an existing licensee's site with characteristics
   superior to those of the standard antenna (or, alternatively, the
   appropriate existing antenna in use at the site) will permit the
   applicant to provide service without interference to the existing
   licensee, the application will be considered grantable with the
   condition that the applicant bears all costs of upgrading the existing
   licensee's reception equipment at that site(s). Such a showing should
   include interference calculations for both the existing or reference
   antenna and the proposed antenna. The manufacturer, model number(s),
   co-polar and cross-polar gain patterns of the replacement antenna
   should be supplied as well as an accurate assessment of the expected
   reimbursement costs.

   (5) No receive site more than 35 miles from the transmitter shall be
   entitled to interference protection.

   (6) Notwithstanding the above, main, booster and response stations
   shall use the following formulas, as applicable, for determining
   compliance with: (1) Radiated field contour limits where bandwidths
   other than 6 MHz are employed at stations utilizing digital emissions;
   and (2) Cochannel and adjacent channel D/U ratios where the bandwidths
   in use at the interfering and protected stations are unequal and both
   stations are utilizing digital modulation or one station is utilizing
   digital modulation and the other station is utilizing either 6 MHz
   NTSC analog modulation or 125 kHz analog modulation (I channels only).

   (i) Contour limit: -73 dBW/m2 + 10 log(X/6) dBW/m 2 , where X is the
   bandwidth in MHz of the digital channel.

   (ii) Co-channel D/U: 45 dB + 10 log(X[1]/X[2]) dB, where X[1] is the
   bandwidth in MHz of the protected channel and X[2] is the bandwidth in
   MHz of the interfering channel.

   (iii) Adjacent channel D/U: 0 dB + 10 log(X[1]/X[2]), where X[1] is
   the bandwidth in MHz of the protected channel and X[2] is the
   bandwidth in MHz of the interfering channel.

   (b) All applicants for instructional television fixed stations are
   expected to take full advantage of such directive antenna techniques
   to prevent interference to the reception of any existing or
   previously-proposed operational fixed, multipoint distribution,
   international control or instructional television fixed station at
   authorized receiving locations. Therefore, all applications for new or
   major changes must include an analysis of potential interference to
   all existing and previously-proposed stations in accordance with
   paragraph (a) of this section. An applicant for a new instructional
   television fixed station must include the following technical
   information with the application:

   (1) An analysis of the potential for harmful interference with the
   receive sites registered as of September 17, 1998, and with the
   protected service area, of any authorized or previously-proposed
   cochannel station if:

   (i) The proposed transmitting antenna has an unobstructed electrical
   path to receive site(s) and/or the protected service area of any other
   station that utilizes, or would utilize, the same frequency; or

   (ii) The proposed transmitter is within 80.5 km (50 miles) of the
   coordinates of any such station.

   (2) An analysis of the potential for harmful adjacent channel
   interference with the receive sites registered as of September 17,
   1998, and with the protected service area, of any authorized or
   previously-proposed station if the proposed transmitter is within 80.5
   km (50 miles) of the coordinates of any station that utilizes, or
   would utilize, an adjacent channel frequency.

   (3) An analysis concerning possible adverse impact upon Mexican and
   Canadian communications if the station's transmitting antenna is to be
   located within 80.5 km (50 miles) of the border.

   (4) In lieu of the interference analyses required by paragraphs (b)(1)
   and (2) of this section, an applicant may submit (a) statement(s) from
   the affected cochannel or adjacent channel licensee(s) that any
   resulting interference is acceptable.

   (5) Specific rules relating to response station hubs, booster
   stations, and 125 kHz channels are set forth in Sec. Sec. 21.909, 21.913,
   21.949, 74.939, 74.949 and 74.985. To the extent those specific rules
   are inconsistent with any rules set forth above, those specific rules
   shall control.

   (c) Existing licensees and prospective applicants, including those who
   lease or propose to lease excess capacity pursuant to Sec. 74.931(c) or
   (d), are expected to cooperate fully and in good faith in attempting
   to resolve problems of potential interference before bringing the
   matter to the attention of the Commission.

   (d) Each authorized or previously-proposed applicant, or licensee must
   be protected from harmful electrical interference at each of its
   receive sites registered previously as of September 17, 1998, and
   within a protected service area as defined at Sec. 21.902(d) of this
   chapter and in accordance with the reference receive antenna
   characteristics specified at Sec. 21.902(f) of this chapter. An ITFS
   entity which did not receive protected service area protection prior
   to September 17, 1998 shall be accorded such protection by a cochannel
   or adjacent channel applicant for a new station or station
   modification, including a booster station, response station or
   response station hub, where the applicant is required to prepare an
   analysis, study or demonstration of the potential for harmful
   interference. An ITFS entity receiving interference protection
   provided by this section will continue to receive such protection if
   it elects to swap channels with another ITFS or MDS station as
   specified in Sec. 74.902(f).

   [ 28 FR 13731 , Dec. 14, 1963, as amended at  50 FR 26758 , June 28, 1985;
    51 FR 9799 , Mar. 21, 1986;  58 FR 44951 , Aug. 25, 1993;  60 FR 20246 ,
   Apr. 25, 1995;  60 FR 57368 , Nov. 15, 1995;  63 FR 65114 , Nov. 25, 1998;
    64 FR 63737 , Nov. 22, 1999;  65 FR 46620 , July 31, 2000]