Section 74.501 - Classes of aural broadcast auxiliary stations(a)Aural broadcast STL station. A fixed station for the transmission of aural program material between the studio and the transmitter of a broadcasting station other than an international broadcasting station.(b)Aural broadcast intercity relay (ICR) station. A fixed station for the transmission of aural program material between radio broadcast stations, other than international broadcast stations, between FM radio broadcast stations and their co-owned FM booster stations, between noncommercial educational FM radio stations and their co-owned noncommercial educational FM translator stations assigned to reserved channels (Channels 201 to 220), between FM radio stations and FM translator stations operating within the coverage contour of their primary stations, or for such other purposes as authorized in § 74.531 .(c)Aural broadcast microwave booster station. A fixed station in the broadcast auxiliary service that receives and amplifies signals of an aural broadcast STL or intercity relay station and retransmits them on the same frequency.28 FR 13716, Dec. 14, 1963, as amended at 49 FR 7129, Feb. 27, 1984; 53 FR 4169, Feb. 12, 1988; 55 FR 50692, Dec. 10, 1990; 57 FR 41111, Sept. 9, 1992