Sec. 74.638  Frequency coordination.

    (a) Channels in Band D are shared with certain Private Operational 
Fixed Stations authorized under Part 94, Sec. 94.93 after September 9, 
1983. After this date all Broadcast Auxiliary use of these bands is 
subject to coordination using the following procedure:
    (1) Before filing an application for new or modified facilities 
under this part the applicant must perform a frequency engineering 
analysis to ensure that the proposed facilities will not cause 
interference to existing or previously applied for stations in this band 
of a magnitude greater than that specified below.
    (2) The general criteria for determining allowable adjacent or co-
channel interference protection to be afforded, regardless of system 
length or type of modulation, multiplexing or frequency band, shall be 
such that the interfering signal shall not produce more than 1.0 dB 
degradation of the practical threshold of the protected receiver. 
Degradation is determined by calculating the ratio in dB between the 
desired carrier signal and undesired interfering signal (C/I ratio) 
appearing at the input to the receiver under investigation (the victim 
receiver). The development of the C/I ratios from the criteria for 
maximum allowable interference level per exposure and the methods used 
to perform path calculations shall follow generally acceptable good 
engineering practices. Procedures as may be developed by the Electronics 
Industries Association (EIA), the Institute of Electrical and 
Electronics Engineers, Inc. (IEEE), the American National Standards 
Institute (ANSI) or any other recognized authority will be acceptable to 
the FCC.
    (3) Where the development of the carrier to interference ratio (C/I) 
is not covered by generally acceptable procedures or where the applicant 
does not wish to develop the carrier to interference ratio, the 
applicant shall employ the following C/I protection ratios.
    (i) Co-channel interference: For both sideband and carrier-beat, 
(applicable to all bands), the previously authorized system shall be 
afforded a carrier to interfering signal protection ratio of at least 90 
dB.
    (ii) Adjacent channel interference: The existing or previously 
authorized system shall be afforded a carrier to

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interfering signal protection ratio of at least 56 dB.
    (b) Coordination of assignments in the 6425-6525 MHz and 17.7-19.7 
GHz bands will be in accordance with the procedure established in 
Sec. 21.100(d) except that the prior coordination process for mobile 
(temporary fixed) assignments may be completed orally and the period 
allowed for response to a coordination notification may be less than 30 
days if the parties agree.

[ 49 FR 50734 , Nov. 3, 1983, as amended at  52 FR 7142 , Mar. 9, 1987]