Section 74.551 - Equipment changes(a) Modifications may be made to an existing authorization in accordance with §§ 1.929 and 1.947 of this chapter.(b) Permissible changes in equipment operating in the bands 18.3-18.58, 18.76-18.82 GHz and 19.1-19.16 GHz. Notwithstanding other provisions of this section, licensees of stations that remain co-primary under the provisions of § 74.502(c) may not make modifications to their systems that increase interference to satellite earth stations, or result in a facility that would be more costly to relocate.28 FR 13716, Dec. 14, 1963, as amended at 38 FR 6827, Mar. 13, 1973; 47 FR 54448, Dec. 3, 1982; 49 FR 7130, Feb. 27, 1984; 50 FR 48599, Nov. 26, 1985; 58 FR 19775, Apr. 16, 1993; 61 FR 4368, Feb. 6, 1996; 65 FR 54172, Sept. 7, 2000; 68 FR 12768, Mar. 17, 2003; 68 FR 16967, Apr. 8, 2003; 68 FR 20225, Apr. 24, 2003; 69 FR 43772, July 22, 2004