[Code of Federal Regulations] [Title 47, Volume 5] [Revised as of October 1, 2006] From the U.S. Government Printing Office via GPO Access [CITE: 47CFR80.74] [Page 29] TITLE 47--TELECOMMUNICATION CHAPTER I--FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) PART 80_STATIONS IN THE MARITIME SERVICES--Table of Contents Subpart C_Operating Requirements and Procedures Sec. 80.74 Public coast station facilities for a telephony busy signal. A ``busy'' signal, when used by a public coast station in accordance with the provisions of Sec. 80.111(d), must consist of the transmission of a single audio frequency regularly interrupted, as follows: (a) Audio frequency: Not less than 100 nor more than 1100 Hertz, provided the frequency used for this purpose will not cause auto alarms or selective-ringing devices to be operated. (b) Rate of interruption: 60 times per minute 10%. (c) Duration of each interruption: 0.5 second 10%.