(b) Explanation of assignment limitations appearing in the frequency tabulation of this section:

(1) Limited to developmental operation only with the assigned frequency and particulars of operation specified in each authorization.

(2) Available only on a shared basis with stations in other services, and subJect to no protection from interference due to the operation of industrial, scientific, or medical devices.

(3) Use of this frequency is subject to the condition that no harmful interference will be caused to the reception of television channels 4 or 5. Assignments will be made only in accordance with the criteria set forth in § 91.8.

(4) This frequency will be assigned only for the specific purpose of transmitting hydrological or meteorological data. The use of this frequency is subject to the condition that harmful interference will not be caused to Federal Government stations, and further, that the hydrological or meteorological data being handled is made available to interested governmental agencies. Other provisions of this part notwithstanding, an operational fixed station operating on this frequency shall not engage in communications with any station in the mobile service unless written authorization to do so has been obtained from the Commission. Persons who desire to operate stations on this frequency should communicate with the Commission for instructions concerning the procedure to be followed in filing formal application.

(5) Use of this frequency is limited to stations located in the States of Pennsylvania and West Virginia only and is subject to no protection from interference due to the operation of industrial, scientific, or medical devices on this frequency.

(6) This frequency is intended for use primarily by fixed relay stations.

(7) This frequency will not be assigned to base stations.

(8) Other provisions of this part notwithstanding, this frequency may be authorized for use with any type of emission which does not exceed an occupied bandwidth of 8 kc/s, for intermittent transmission; further, authorizations may be issued to permit operation on this frequency by selfactuating or other electrical or mechanical means not under the direct control of any individual. All operations on this frequency are limited to a maximum plate power input of 30 watts to the final radio frequency stage.

(9) Control stations associated with mobile relay stations may be authorized to operate on the land mobile service frequency assigned to the associated mobile station. However, when located less than 75 miles from the center of any urbanized area of 200,000 or more population such stations must employ directional antennas having a front-to-back ratio of at least 15 db and may radiate a signal that, when measured at the antenna terminals of the mobile relay station receiver, does not exceed the signal strength of a mobile station operating from the control station location by more than 6 db. To make this measurement the mobile station may be moved no more than one-fourth mile away from the control location if necessary to provide a satisfactory signal at the mobile relay receiver. An engineering statement attesting to compliance with this signal level limitation shall accompany each control station application. Urbanized areas of 200,000 or more population are defined in the U.S. Census of Population, 1960, vol. 1, table 23, pages 1-50. The centers of urbanized areas are determined from the appendix, page 226

(28) This frequency will not be assigned to stations for use at temporary unspecified locations.

(29) This frequency band is available on a shared basis with other Industrial Radio Services and may be used for lowpower mobile operations for the purpose of remote control and telemetering. The maximum power output of the transmitter may not exceed 1 watt. A1, A2, F1, or F2 emission may be authorized and mobile stations used to control remote objects and devices may be operated in the continuous transmit mode.

(30) For FM transmitters the sum of the highest modulating frequency in c/s and the amount of frequency deviation or swing in c/s may not exceed 2800 c/s, and the maximum frequency deviation may not exceed 2.5 kc/s. For AM transmitters the highest modulating frequency may not exceed 2000 c/s. The carrier frequency must be maintained within 0.0005 percent of the center of the frequency band, and the authorized bandwidth may not exceed 6 kc/s.

(31) For FM transmitters the sum of the highest modulating frequency in c/s and the amount of frequency deviation or swing in c/s may not exceed 1700 c/s, and the maximum frequency deviation may not exceed 1.2 kc/s. For AM transmitters the highest modulating frequency may not exceed 1500 c/s. The carrier frequency must be maintained within 0.0005 percent of the center of the frequency band, and the authorized bandwidth may not exceed 3 kc/s.

(32) Within the boundaries of urbanized areas of 200,000 or more population defined in the U.S. Census of Population, 1960, vol. 1, table 23, pages 1-50, this frequency may be assigned only to persons rendering a central station commercial protection service. Central station commercial protection service is defined as those electrical protection and supervisory services rendered from and by a central station approved by one or more of the recognized rating agencies and/or the Underwriters' Laboratories, Inc. (UL).

(33) This frequency may not be used aboard aircraft in flight.

(34) This frequency will be assigned for mobile operations within normal twoway communications range of any associated base stations.

(35) For two-frequency systems, separation between base and mobile transmit frequencies is 5 Mc/s, however, a mobile station may be assigned the

frequency of an associated base station. (Such operation may, however, subject the single-frequency system to interference that would not occur to a twofrequency system).

(36) This frequency is available for assignment to stations located on or near airports serving urbanized areas of 200,000 or more population, U.S. Census of Population, 1960, vol. 1, table 23, pages 1-50, and may be assigned only to persons engaged in furnishing commercial air transportation service, or to a nonprofit corporation or association for the purpose of furnishing radio communications service to persons so engaged on a nonprofit cost-sharing basis. Stations on this frequency may be used only in connection with the servicing and supplying of aircraft at the airport.

(37) This frequency is available for assignment to stations in the Business Radio Service for use at locations removed by 75 or more miles from the boundaries of airports in urbanized areas of 200,000 or more population, U.S. Census of Population, 1960, vol. 1, table 23, pages 1-50. Maximum permissible plate power input is 180 watts.

(38) This frequency may be assigned to fixed stations in the Business Radio Service. All use of these frequencies by fixed stations is limited to locations 100 or more miles from the center of any urbanized area of 200,000 or more population, except that the distance may be 75 miles if the plate power input does not exceed 30 watts. All fixed systems are limited to a maximum of two frequencies and must employ directional antennas with a front-to-back ratio of at least 15 db. For two-frequency systems separation between transmit-receive frequencies is 5 Mc/s. Urbanized areas of 200,000 or more population are defined in the U.S. Census of Population, 1960, vol. 1, table 23, pages 1-50. The centers of urbanized areas are determined from the appendix, page 226, of the U.S. Commerce publication "Air Line Distance Between Cities in the United States."

(39) This frequency will be assigned only to stations operated with local control. Maximum plate power input to the final radiofrequency stage may not exceed 180 watts. Overall height of antenna above ground may not exceed 100 feet. Control point location to be within one-half air mile of the transmitter location.

(40) This frequency may be assigned to low-power (3 watts or less) stations in