(a) The basis for the rules in this part is the Communications Act of 1934, as amended, and applicable treaties and agreements to which the United States is a party. The rules in this part are issued pursuant to the authority contained in Titles II and III of the Communications Act of 1934, as amended, which vests authority in the Federal Communications Commission to regulate common carriers of interstate and foreign communications and to regulate radio transmissions and issue licenses for radio stations.

(b) The purpose of the rules and regulations in this part is to prescribe the manner in which portions of the radio spectrum may be made available for the use of radio for domestic communication common carrier operations which require transmitting facilities on land.

§ 21.1

Subpart A-Definitions
Definitions.

As used in this part:

Antenna power gain. The square of the ratio of the root-mean-square free space field intensity produced at one mile in the horizontal plane, in millivolts per meter for one kilowatt antenna input power to 137.6 mv/m. This ratio should be expressed in decibels (db). (If specified for a particular direction, antenna power gain is based on the field strength in that direction only.)

Antenna power input. The radio frequency peak or RMS power, as the case may be, supplied to the antenna from the antenna transmission line and its associated impedance matching network.

Antenna structures. The term antenna structures includes the radiating system, its supporting structures, and any surmounting appurtenances.

Assigned frequency. The frequency coinciding with the center of the radio frequency channel in which the station is authorized to work. This frequency does not necessarily correspond to any frequency in an emission.

Authorized frequency. The frequency assigned to a station by the Commission and specified in the instrument of authorization.

Authorized power. The power assigned to a radio station by the Commission and specified in the instrument of authorization. The authorized power does not necessarily correspond to the

power used by the Commission for purposes of its Master Frequency Record (MFR) and notification to the International Telecommunications Union.

Auxiliary test station. A fixed station used for test transmissions only, operating on mobile station frequencies from a specified fixed location, for the purpose of determining the performance of fixed receiving equipment which is remotely located from the base station with which it is associated, or where the receiving equipment is located with the base station and both are remotely located from the control point of the station.

Bandwidth occupied by an emission. The band of frequencies comprising 99 percent of the total radiated power extended to include any discrete frequency on which the power is at least 0.25 percent of the total radiated power.

Base station. A land station in the land mobile service carrying on a service with land mobile stations.

NOTE: In certain cases, also communicates with fixed stations and vessels.

Carrier. In a frequency stabilized system, the sinusoidal component of a modulated wave whose frequency is independent of the modulating wave; or the output of a transmitter when the modulating wave is made zero; or a wave generated at a point in the transmitting system and subsequently modulated by the signal; or a wave generated locally at the receiving terminal which when combined with the side bands in a suitable detector, produces the modulating

wave.

Carrier frequency. The frequency of the carrier.

Central office. A landline termination center used for switching and interconnection of public message communication circuits.

Central office station. A fixed station used for transmitting communications to rural subscriber stations associated therewith.

Communication common carrier. Any person engaged in rendering communication service for hire to the public.

Control point. A control point is an operating position at which an operator responsible for the operation of the transmitter is stationed and which is under the control and supervision of the licensee.

Control station. A fixed station whose transmissions are used to control auto

matically the emissions or operations of another radio station at a specified location, or to transmit automatically to an alarm center telemetering information relative to the operation of such station.

Coordination distance. For the purpose of this part, the expression "coordination distance" means the distance from an earth station, within which there is a possibility of the use of a given transmitting frequency at this earth station causing harmful interference to stations in the fixed or mobile service, sharing the same band, or of the use of a given frequency for reception at this earth station receiving harmful interference from such stations in the fixed or mobile service.

Dispatch communication. Two-way voice communication, normally of not more than one minute's duration, between common carrier base and land mobile stations, or between a common carrier land mobile station and a landline telephone station not connected to a public message telephone system.

Dispatch point. A dispatch point is a base station operating position, operated by a subscriber, which is under the control and supervision of the base station licensee.

Dispatch station. A fixed station, operated by a subscriber, or a group of subscribers, which communicates, under the supervision and control of the base station licensee, through the base station, with the individual subscriber's own mobile station or stations.

Domestic fixed public service. A fixed service, the stations of which are open to public correspondence, for radiocommunications originating and terminating solely at points all of which lie within: (a) the State of Alaska, or (b) the State of Hawail, or (c) the contiguous 48 States and the District of Columbia, or (d) a single possession of the United States. Generally, in cases where service is afforded on frequencies above 72 Mc/s, radiocommunications between the contiguous 48 States (including the District of Columbia) and Canada or Mexico, or radiocommunications between the State of Alaska and Canada, are deemed to be in the domestic fixed public service.

Domestic public land mobile radio service. A public communication service for hire between land mobile stations wherever located and their assoclated base stations which are located within the United States or its posses

sions, or between land mobile stations in the United States and base stations in Canada.

Domestic public radio services. The land mobile and domestic fixed public services the stations of which are open to public correspondence.

NOTE: Parts 81 and 83 of this chapter are applicable to maritime services. Part 87 is applicable to aeronautical services; and Part 85 is applicable to certain Alaskan services.

Earth station. A station in the space service located either on the earth's surface, including on board a ship, or on board an aircraft.

Effective radiated power. The product of the antenna power input and the antenna power gain. This product should be expressed in watts. (If specified for a particular direction, effective radiated power is based on the antenna power gain in that direction only.)

Exchange. A unit of a communication company or companies for the administration of communication service in a specified area, which usually embraces a city, town, or village and its environs, and consisting of one or more central offices, together with the associated plant, used in furnishing communication service in that area.

Exchange area. The geographic area included within the boundaries of an exchange.

Facsimile. A system of telecommunication for the transmission of fixed images with a view to their reception in a permanent form.

Fixed earth station. An earth station intended to be used at a specified fixed point.

Fixed microwave auxiliary station. A fixed station used in connection with (1) the alignment of microwave transmitting and receiving antenna systems and equipment, (2) coordination of microwave radio survey operations, and (3) cue and contact control of television pickup station operations.

Fixed service. A service of radiocommunication between specified fixed points.

Fixed station. A station in the fixed service.

Frequency tolerance. The frequency tolerance, expressed as a percentage or in cycles per second, is the maximum permissible deviation, with respect to the reference frequency of the corresponding characteristic frequency of an emission.