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 or 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

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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 include a 
description of the nonvoice transmitting equipment. This description 
shall specify 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 type accepted 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

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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]

    Effective Date Note: At  62 FR 18927 , Apr. 17, 1997, Sec. 90.241 was 
amended by revising the introductory text of paragraphs (a) and (c) and 
revising paragraphs (d) and (e), effective Oct. 17, 1997.