[28 F.R. 13002, Dec. 5, 1963, as amended at 31 F.R. 10361, Aug. 2, 1966; 33 F.R. 4577, Mar. 15, 1968; 33 F.R. 7238, May 16, 1968; 35 F.R. 428, Jan. 13, 1970; 35 F.R. 10445 June 26, 1970; 36 F.R. 12485, July 1, 1971; 36 F.R. 18652, Sept. 18, 1971]

EFFECTIVE DATE: Pending further action, the effective date of the amendment at 36 F.R. 12485, which added (k) and (1), was postponed at 36 F.R. 15121, Aug. 13, 1971. § 21.502 Classification of base stations.

Base stations in the Domestic Public Land Mobile Radio Service shall be classified, as set forth below, according to their transmitting antenna height above average terrain in any particular direction and according to their effective radiated power in the horizontal plane of the antenna in that direction. This classification is not applicable to base stations in the frequency bands 454.6625-455.000 MHz, 459.6625-460.000 MHz, and 570-512 MHz.

C

60 120 250 500 Effective radiated power (watts).

[35 F.R. 429, Jan. 13, 1970]

§ 21.503 Geographical separation of cochannel stations.

(a) Base stations engaged in two-way communications, employing frequency modulation or phase modulation and operating co-channel in this service, shall normally be separated by not less than the distances shown below:

A.

B.

C.

D.

E

B.

C.

D.

E

500

Class of station in the band 35-44 MHz

Class of station in the band 152-162 MHz

Effective radiated power (watts).

57

E.

3480

C

Class of station

(b) In any particular case, where it appears that unusual radio wave propa

gation conditions are involved, the Commission may require greater separation than indicated in the tables in paragraph (a) of this section, or make assignments at lesser station spacing. Reference may be made to § 73.611(d) of this chapter for methods of computing mileage separation between station locations. [32 F.R. 12041, Aug. 23, 1967]

§ 21.504 Service area of base station.

(a) The limits of reliable service area of a base station engaged in two-way communication service with mobile stations are considered to be described by a field strength contour of 31 decibels above 1 microvolt per meter for stations operating on frequencies in the 35.44 MHz band, 37 decibels above 1 microvolt per meter for stations operating on frequencies in the 152-162 MHz band, and 39 decibels above 1 microvolt per meter for stations operating on frequencies in the 450-460 MHz and 470-512 MHz bands. The limits of reliable service area of base station engaged in one-way signaling service is considered to be 43 decibels above 1 microvolt per meter. Service within such areas is generally expected to have an average reliability of not less than 90 percent.

EFFECTIVE DATE: Pending further action, the effective date of the amendment at 36 F.R. 12487, which revised (a), was postponed at 36 F.R. 15121, Aug. 13, 1971. For the con

venience of the user the superseded text of (a) follows here:

(a) The limits of reliable service area of a base station engaged in two-way communication service with mobile stations are considered to be described by a field strength contour of 31 decibels above one microvolt per meter for stations operating on frequencies in the 35-44 Mc/s band, 37 decibels above one microvolt per meter for stations operating on frequencies in the 152–162 Mc/s band, and 39 decibels above one microvolt per meter for stations operating on frequencies in the 450-460 Mc/s band. The limits of reliable service area of a base station engaged in one-way signaling service is considered to be 43 decibels above one microvolt per meter. Service within such areas is generally expected to have an average reliability of not less than 90 percent.

(b) The field strength contours described in paragraph (a) of this section shall be regarded as determining the limits of the reliable service area of the related base stations for the purpose of providing protection to such stations from co-channel electrical harmful interference and defining the area within which consideration will be accorded claims of economic competitive injury. The following F(50,50) radio wave propagation charts shall be used in connection with making such determinations, and shall be used in combination with the following F(50,10) radio wave propagation charts in the determination of areas of harmful interference between co-channel stations: