Sec.  90.241   Radio call box operations.

   (a) The frequencies in the 72–76 MHz band listed in  Sec. 90.257(a)(1) may be
   assigned in the Public Safety Pool for operation of radio call boxes to be
   used by the public to request fire, police, ambulance, road service, and
   other  emergency  assistance,  subject to the following conditions and
   limitations:

   (1) Maximum transmitter power will be either 2.5 watts plate input to the
   final stage or 1 watt output.

   (2) Antenna gain shall not exceed zero dBd (referred to a half-wave dipole)
   in any horizontal direction.

   (3) Only vertical polarization of antennas shall be permitted.

   (4) The antenna and its supporting structure must not exceed 6.1 m (20 feet)
   in height above the ground.

   (5) Only A1D, A2D, F1D, F2D, G1D, or G2D emission shall be authorized.

   (6) The transmitter frequency tolerance shall be 0.005 percent.

   (7) Except for test purposes, each transmission must be limited to a maximum
   of two seconds and shall not be automatically repeated more than two times
   at  spaced  intervals within the following 30 seconds. Thereafter, the
   authorized cycle may not be reactivated for one minute.

   (8) All transmitters installed after December 10, 1970, shall be furnished
   with an automatic means to deactivate the transmitter in the event the
   carrier remains on for a period in excess of three minutes. The automatic
   cutoff system must be designed so the transmitter can be only manually
   reactivated.

   (9) Frequency selection must be made with regard to reception of television
   stations on channels 4 (66–72 MHz) and 5 (76–82 MHz) and should maintain the
   greatest  possible  frequency  separation from either or both of these
   channels, if they are assigned in the area.

   (b) [Reserved]

   (c) Frequencies in the 450–470 MHz band which are designated as available
   for assignment to central control stations and radio call box installations
   in  Sec. 90.20(c) or  Sec. 90.20(d)(58) may be assigned in the Public Safety Pool for
   highway call box systems subject to the following requirements:

   (1) Call box transmitters shall be installed only on limited access highways
   and may communicate only with central control stations of the licensee.

   (2) Maximum transmitter power for call boxes will be either 2.5 watts input
   to the final amplifier stage or one watt output. The central control station
   shall not exceed 25 watts effective radiated power (ERP).

   (3) The height of a call box antenna may not exceed 6.1 meters (20 feet)
   above the ground, the natural formation, or the existing man-made structure
   (other than an antenna supporting structure) on which it is mounted. A
   central station transmitting antenna, together with its supporting structure
   shall not exceed 15 m. (50 ft.) above the ground surface.

   (4) Only F1D, F2D, F3E, G1D, G2D, or G3E, emission may be authorized for
   nonvoice signaling, radiotelephony, and multiplexed voice and nonvoice use.
   The provisions in this part applicable to the use of F3E or G3E emission are
   also applicable to the use of F1D, F2D, G1D or G2D emission for call box
   transmitters.

   (5) The station identification required by  Sec. 90.425 shall be by voice and may
   be transmitted for the system from the central control station. Means shall
   be  provided at each central control station location to automatically
   indicate the call box unit identifier when a call box unit is activated.

   (6) Call box installations must be so designed that their unit identifier is
   automatically transmitted when the handset is lifted.

   (7) Each application for a call box system must contain information on the
   nonvoice transmitting equipment, including the character structure, bit
   rate, modulating tone frequencies, identification codes, and the method of
   modulation (i.e., frequency shift, tone shift, or tone phase shift).

   (8) Call box installations may be used secondarily for the transmission of
   information from roadside sensors. Central control station transmitters may
   be used secondarily to interrogate call box roadside sensors and for the
   transmission of signals to activate roadside signs.

   (9) Each call box transmitter must be provided with a timer which will
   automatically deactivate the transmitter after 2 minutes unless the central
   control station operator reactivates the timer cycle.

   (10) The central control station must include facilities that permit direct
   control of any call box in the system.

   (11) Call box transmitter frequency tolerance shall be 0.001 percent.

   (12)  Transmitters  certificated under this part for use of F3E or G3E
   emission may be used for F1D, F2B, G2B or G2D emission provided that the
   audio tones or digital data bits are passed through the low pass audio
   filter required to be provided in the transmitter for F3E or G3E emission.
   The transmitter must be adjusted and operated so that the instantaneous
   frequency deviation does not exceed the maximum value allowed for F3E or G3E
   emission.

   (d) In addition to the frequencies available pursuant to  Sec. 90.20(c) the
   frequencies set forth in  Sec. 90.20(d)(58) may be used for central control
   station and call box installations in areas where such frequencies are
   available for fixed system use subject to the requirements and limitations
   of that section and subject to the provisions of paragraphs (c) (1), (4),
   (5), (6), (7), (8), (9), (10), and (12) of this section.

   (e) In accordance with subpart Q of this part, the frequencies available
   pursuant to  Sec. 90.20(c) or  Sec. 90.20(d)(58) for central control station and call
   box installations may be assigned for developmental operation as part of a
   highway safety communication program which is designed to provide radio
   communications directly with motorists to and from their motor vehicles.

   [ 43 FR 54791 , Nov. 22, 1978;  44 FR 32219 , June 5, 1979;  49 FR 48712 , Dec.
   14, 1984;  50 FR 39680 , Sept. 30, 1985;  50 FR 40976 , Oct. 8, 1985;  54 FR 38681 , Sept. 20, 1989;  54 FR 45891 , Oct. 31, 1989;  58 FR 44957 , Aug. 25,
   1993;  62 FR 18927 , Apr. 17, 1997;  63 FR 36610 , July 7, 1998;  63 FR 68965 ,
   Dec. 14, 1998;  72 FR 35195 , June 27, 2007]