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 antenna input terminals of the 
affected receiver, when the ratio is less than 45 dB.
    (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. Harmful interference will be considered 
present when a free space calculation determines that this ratio is less 
than 0 dB. In the alternative, harmful interference will be considered 
present for an Instructional Television Fixed Service (ITFS) station 
constructed before May 26, 1983, when a free space calculation 
determines that this ratio is less than 10 dB, unless the individual 
receive site under consideration has been subsequently upgraded with up-
to-date reception equipment,

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in which case the ratio shall be less than 0 dB, or unless 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 affected ITFS station licensee, and also 
conditioned, if necessary, on installation of such equipment, absent a 
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. Absent information presented to the 
contrary, the Commission will assume that reception equipment 
installation occurred simultaneously with original station equipment.
    (3) For purposes of this section, all interference calculations 
involving receive antenna performance shall use the reference antenna 
characteristics shown in Figure 1, of 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.
    (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 operational fixed, 
multichannel 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 Sec. 74.903(a). An 
applicant for a new instructional television fixed station or for 
changes in an existing ITFS facility for a construction permit must 
include the following technical information with the application:
    (1) An analysis of the potential for harmful cochannel interference 
with any authorized or previously proposed station if:
    (i) The proposed transmitting antenna has an unobstructed electrical 
path to receive sites(s) of any other station(s) that utilize(s), 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 any authorized or previously proposed station(s) if 
the proposed transmitter is within 80.5 km (50 miles) of the coordinates 
of any other station(s) that utilize(s), 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 (b)(2) of this Section for any authorized or previously 
proposed station(s), an applicant may submit a statement(s) from the 
affected ITFS licensee(s) or permittee(s) that any resulting 
interference is acceptable.

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    (5) An analysis of the potential for harmful interference within the 
protected service area, as defined in paragraph (d) of this section, of 
any authorized or previously proposed station(s) described in paragraph 
(d) of this section.
    (c) Existing licensees and prospective applicants are expected to 
cooperate fully 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, construction 
permittee, or licensee who proposes to lease excess capacity to a 
``wireless cable'' operator pursuant to Sec. 74.931(e)(2) must be 
protected from harmful electrical interference for the hours of such 
transmissions within a protected service area as defined at 
Sec. 21.902(d) of this chapter. Alternatively, an applicant, permittee, 
or licensee may select a 56.33 km (35 mile) circular protected area 
centered at the geographic latitude and longitude of the transmitting 
antenna site. Applicants are expected to cooperate fully and in good 
faith with an authorized or previously-proposed applicant, construction 
permittee, or licensee who leases or proposes to lease excess capacity 
to a ``wireless cable'' operator pursuant to Sec. 74.931(e)(2), in 
attempting to resolve problems of potential interference to such 
operations before bringing the matter to the attention of the 
Commission.
    (e) Each ITSF applicant, permittee, or licensee who wishes to claim 
the protection described at paragraph (d) of this section must request 
such protection in writing in its initial application for a new station, 
in an application amendment, or by modification application. Such 
protection shall be applied solely with regard to applications filed 
subsequent to the request for a protected service area.
    (f) With respect to protected service area proposals, two 
applications will be regarded as mutually exclusive if they are:
    (1) Submitted during the same filing window;
    (2) Otherwise grantable;
    (3) Mutually exclusive only because either or both applicants 
request a protected service area. However, if an applicant in such a 
situation shows that the resulting interference would occur solely over 
water, the applications will not be considered to be mutually exclusive.

[ 28 FR 13731 , Dec. 14, 1963, as amended at  50 FR 26758 , June 28, 1985; 
 51 FR 9799 , Mar. 21, 1986;  55 FR 46013 , Oct. 31, 1990;  56 FR 57600 , Nov. 
13, 1991;  58 FR 44951 , Aug. 25, 1993;  60 FR 20246 , Apr. 25, 1995;  60 FR 57368 , Nov. 15, 1995]