[32 F.R. 12041, Aug. 22, 1967, as amended at 36 F.R. 12487, July 1, 1971] § 21.505 Antenna height-power limit for base stations. In view of the fact that the predominant need for mobile communication service can usually be met by base sta tions within the classification set forth in § 21.502, and because widespread coverage is undesirable in areas where no substantial need exists for mobile communication service through a distant base station, base stations will not be MILES authorized to employ transmitting antennas in excess of 500 feet above average terrain unless the effective radiated power of the base station is reduced below 500 watts by not less than the amount as shown in the chart below en titled "Required Reduction in Effective Radiated Power for Antenna Heights in Excess of 500 Feet Above Average Terrain". This antenna height-power limit does not apply to base stations in the frequency band 470-512 MHZ. ANTENNA HEIGHT IN FEET ABOVE AVERAGE TERRAIN 1500 (See 21.505) [28 F.R. 13002, Dec. 5, 1963, as amended at 36 F.R. 12487, July 1, 1971] EFFECTIVE DATE: Pending further action, the effective date of the amendment at 36 F.R. 12487, which revised the introductory text of § 21.505, was postponed at 36 F.R. 15121, Aug. 13, 1971. For the convenience of the user the superseded introductory text follows here: § 21.505 Antenna height-power limit for base stations. In view of the fact that the predominant need for mobile communication service can usually be met by base stations within the classification set forth in § 21.502, and because widespread coverage is undesirable in areas where no substantial need exists for mobile communication service through a distant base station, base stations will not be authorized to employ transmitting antennas in excess of 500 feet above average terrain unless the effective radiated power of the base station is reduced below 500 watts by not less than the amount shown in the following chart entitled "Required Reduction in Effective Radiated Power for Antenna Heights in Excess of 500 Feet Above Average Terrain". § 21.506 Power limitations. (a) Stations in this service (other than base stations in the frequency band 470512 MHz) shall not be permitted to exceed 500 watts effective radiated power and shall not be authorized to use transmitters having a rated power output in excess of the limits set forth in § 21.107 (b): Provided, however, That the effective radiated power of dispatch stations, and auxiliary test stations and base stations operating on frequencies specified in § 21.521 shall not exceed 100 watts: Provided, further, That the rated power output of transmitters used on frequencies specified in § 21.521 shall not exceed 25 watts and that the transmitter output power of airborne stations operating on such frequencies shall not be less than 4 watts. A base station standby transmitter having a rated power output in excess of that of the main transmitter of the base station with which it is associated and will not be authorized. For stations in the 470-512 MHz frequency band see section 21.501(1). (b) Under idle traffic conditions, a base station assigned frequencies specified in § 21.521 shall radiate continuously on its working channel(s) a tone modulated carrier reduced in power by at least 10 decibels, but not more than 20 decibels, below its normal power. (See also § 21.508(b).) [35 F.R. 429, Jan. 13, 1970, as amended at 36 F.R. 12487, July 1, 1971] 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 convenience of the user the superseded text of (a) follows here: (a) Stations in this service shall not be permitted to exceed 500 watts effective radiated power and shall not be authorized to use transmitters having a rated power output in excess of the limits set forth in § 21.107 (b): Provided, however, That the effective radiated power of dispatch stations, and auxiliary test stations and base stations operating on frequencies specified in § 21.521 shall not exceed 100 watts: Provided, further, That the rated power output of transmitters used on frequencies specified in § 21.521 shall not exceed 25 watts and that the transmitter output power of airborne stations operating on such frequencies shall not be less than 4 watts. A base station standby transmitter having a rated power output in excess of that of the main transmitter of the base station with which it is associated will not be authorized. § 21.507 Bandwidth and emission limitations. (a) Stations in the Domestic Public Land Mobile Radio Service shall normally be authorized to use only type A3 or F3 emission for radiotelephony, and type A1, A2, F1, or F2 emission for selective signaling. The authorization to use type A3 or F3 emission for radiotelephony shall be construed to include the use of tone signals or signaling devices the sole function of which is to establish and maintain communication. Stations providing one-way signaling service by means of selective signaling which is not associated with a voice message are required to be authorized to employ telegraph type emission appropriate to the type of transmission employed. The use of types A0 or Fo emission in the 72–76 MHz band will not be authorized, except for temporary or short periods necessary for testing incident to the construction or maintenance of a radio station. (Further reference should be made to §§ 21.103 to 21.105, inclusive.) (b) The maximum authorized bandwidth of emission and, for the cases of frequency or phase modulated emissions, the maximum authorized frequency deviation shall be as follows: In the frequency band 450 to 470 MHz, radio facilities using frequency modulated or phase modulated emission, authorized prior to June 1, 1968, will continue to be authorized with bandwidth of 40 kHz until Nov. 1, 1971, provided that the frequency deviation is reduced to 5 kHz by June 1, 1968. 2 In the frequency bands 72.0-73.0 and 75.4-76.0 MHz, radio facilities using frequency modulated or phase modulated emission will be authorized with maximum bandwidth of 20 kHz and maximum frequency deviation of 5 kHz. Radio facilities which were authorized for operation on Dec. 1, 1961, in the frequency band 73.0-74.6 MHz may continue to be authorized without change and with bandwidth of 40 kHz and frequency deviation of 15 kHz. New or modified facilities in the frequency band 73.0-74.6 MHz will not be authorized. (c) On frequencies above 512 MHz, the bandwidth authorized shall not exceed 400 kHz for each derived communication channel and may be restricted to lesser bandwidth when appropriate to the type of operation involved in any particular case. (d) Other types of emission or bandwidth in excess of those specified in paragraph (b) of this section may be authorized upon an adequate showing of need therefor. An application requesting such authorization shall fully describe the modulation characteristics (for FM include maximum modulating frequency and maximum frequency deviation) emission and bandwidth desired, shall specify the bandwidth to be occupied, and shall state the reasons why such emission or bandwidth is required. 25-50 Mc/s (e) The authorization to employ any of the various types of modulated emission in this service shall be construed to include authority to employ unmodulated emission only for temporary or short periods necessary for equipment testing incident to the construction and maintenance of a radio station. [28 F.R. 13002, Dec. 5, 1963, as amended at 36 F.R. 12488, July 1, 1971] EFFECTIVE DATE: Pending further action, the effective date of the amendment at 36 F.R. 12488, which revised (b) and (c), was postponed at 36 F.R. 15121, Aug. 13, 1971. For the convenience of the user the superseded text of (b) and (c) follows here: (b) The maximum authorized bandwidth of emission and, for the cases of frequency or phase modulated emissions, the maximum authorized frequency deviation shall be as follows: Al.. A2. A3. F1. F2. F3. 1 In the frequency band 450 to 470 Mc/s, radio facilities using frequency modulated or phase modulated emission authorized prior to June 1, 1968, will continue to be authorized with bandwidth of 40 kc/s until November 1, 1971, provided that, frequency deviation is reduced to 5 kc/s by June 1, 1968. 2 In the frequency bands 72.0-73.0 and 75.4-76.0 Mc/s, radio facilities using frequency modulated or phase modulated emission will be authorized with maximum bandwidth of 20 kc/s and maximum frequency deviation of 5 kc/s. Radio facilities which were authorized for operation on December 1, 1961, in the frequency band 73.0-74.6 Mc/s may continue to be authorized without change and with bandwidth of 40 kc/s and frequency deviation of 15 kc/s. New or modified facilities in the frequency band 73.0-74.6 Mc/s will not be authorized. (c) On frequencies above 500 Mc/s, the bandwidth authorized shall not exceed 400 kc/s for each derived communication chan nel and may be restricted to lesser bandwidth when appropriate to the type of operation involved in any particular case. § 21.508 Modulation requirements. (a) The use of modulating frequencies higher than 3000 hertz for radiotelephony for tone signaling is not authorized on frequencies below 512 MHz. (b) During idle traffic conditions, the working channel carrier of a base station on frequencies specified in § 21.521 shall be modulated continuously with a distinctive tone except during periods required for station identification. (c) When amplitude modulation is used, the modulation percentage shall be sufficient to provide efficient communication and shall normally be maintained above 70 percent on peaks, but shall not exceed 100 percent on negative peaks. (d) When phase or frequency modulation is used for single channel operation on frequencies below 512 MHz, the deviation arising from modulation shall not exceed the limits specified in § 21.507(b). (e) Each transmitter, which has more than 3 watts plate power input to the final radio frequency stage and was initially authorized or installed at the station in this service after July 1, 1950, employing type A3 or F3 emission shall be equipped with a device which will automatically prevent greater than normal audio level from modulating in excess of the limits specified in paragraphs (c) and (d) of this section. (f) Each transmitter, which operates on frequencies below 450 MHz and employs type A3 or F3 emission, shall be equipped with a modulation limiter in accordance with the provisions of paragraph (e) of this section and also shall be equipped with a low-pass audio filter installed between the modulation limiter and the modulated stage. At audiofrequencies between 3 kHz and 15 kHz, the filter shall have an attenuation greater than the attenuation of 1 kHz by at least: 40 log1 (1/3) decibels where "f" is the audiofrequency in kilohertz per second. At audiofrequencies above 15 kHz, the attenuation shall be at least 28 decibels greater than the attenuation at 1 kHz. (g) Each transmitter which operates on frequencies between 450 and 512 MHz and employs type A3 or F3 emission, shall be equipped with a modulation limiter in accordance with the provisions of paragraph (e) of this section and also shall be equipped with a low-pass audio filter installed between the modulation limiter and the modulated stage. At audiofrequencies between 3 kHz and 20 kHz, the filter shall have an attenuation greater than the attenuation at 1 kHz by at least: 60 log10 (1/3) decibels where "f" is the audiofrequency in kilohertz. At audiofrequencies above 20 kHz, the attenuation shall be at least 50 decibels greater than the attenuation at 1 kHz: Provided, however, That in lieu of such filter, transmitters authorized to operate between 450 and 470 prior to June 1, 1968, may continue to operate until November 1, 1971, with a filter meeting the requirements prescribed in paragraph (f) of this section. (h) Each airborne station shall use suitable means to prevent impairment of transmission by the ambient noise present when the aircraft is in operation. Ambient noise in excess of 95 decibels Reference Acoustical Pressure (flat weighting) shall require use of a noisecancelling type of microphone, or suitable environmental acoustic treatment to reduce the ambient noise level to 95 decibels RAP or less. [28 F.R. 13002, Dec. 5, 1963, as amended at 33 F.R. 4578, Mar. 15, 1968; 35 F.R. 429, Jan. 13, 1970; 36 F.R. 12488, July 1, 1971] EFFECTIVE DATE: Pending further action, the effective date of the amendment at 36 F.R. 12488, which revised (a), (d) and (g), was postponed at 36 F.R. 15121, Aug. 13, 1971. For the convenience of the user the superseded text of (a), (d) and (g) follows here: (a) The use of modulating frequencies higher than 3000 cycles per second for radiotelephony or tone signaling is not authorized on frequencies below 500 Mc/s. (d) When phase or frequency modulation is used for single channel operation on frequencies below 500 Mc/s, the deviation arising from modulation shall not exceed the limits specified in § 21.507(b). (g) Each transmitter which operates on frequencies between 450 Mc/s and 470 Mc/s and employs type A3 or F3 emission, shall be equipped with a modulation limiter in accordance with the provisions of paragraph (e) of this section and also shall be equipped with a low-pass audio filter installed between the modulation limiter and the modulated stage. At audiofrequencies between 3 kc/s and 20 kc/s, the filter shall have an attenuation greater than the attenuation at 1 kc/s by at least: 60 log10 (1/3) decibels where "f" is the audio frequency in kilocycles per second. At audio frequencies above 20 |