Section 73.504 - Channel assignments in the Mexican border area(a) NCE-FM stations within 199 miles (320 km) of the United States-Mexican border shall comply with the separation requirements and other provisions of the "Agreement between the United States of America and the United Mexican States Concerning Frequency Modulation Broadcasting in the 88 to 108 MHz Band" as amended.(b) Applicants for noncommercial educational FM stations within 199 miles (320 km) of the United States-Mexican border shall propose at least Class A minimum facilities (see § 73.211(a) ). However, existing Class D noncommercial educational stations may apply to change frequency within the educational portion of the FM band in accordance with the requirements set forth in § 73.512 .(c) Section 73.208 of this chapter shall be complied with as to the determination of reference points and distance computations used in applications for new or changed facilities. However, if it is necessary to consider a Mexican channel assignment or authorization, the computation of distance will be determined as follows: if a transmitter site has been established, on the basis of the coordinates of the site; if a transmitter site has not been established, on the basis of the reference coordinates of the community, town, or city.52 FR 43765, Nov. 16, 1987