Sec. 90.475  Operation of internal transmitter control systems in 
          specially equipped systems.

    (a) An internal transmitter control system need not be designed to 
meet the requirements of Sec. 90.473 if it meets the following 
requirements:
    (1) All operating positions must be located on premises controlled 
by the licensee.
    (2) An internal transmitter control system may be used in 
conjunction with other approved methods of transmitter control and 
interconnection so long as the internal transmitter control system, 
itself, is neither accessed from telephone positions in the public 
switched telephone network, nor used dial-up circuits in the public 
switched telephone network. Licensees with complex communications 
systems involving fixed systems whose base stations are controlled by 
such systems may automatically access these base stations through the 
microwave or operational fixed systems from positions in the PSTN, so 
long as the base stations and mobile units meet the requirements of 
Sec. 90.483 and if a separate circuit is provided for each mode of 
transmitter operation (i.e., conventional, dial-up or internal).
    (3) The system must be designed so that upon completion of a 
transmission, the base station transmitter(s) will close down 
automatically within 3 seconds.
    (4) To guard against malfunctions, the system must also be designed 
so that the base station(s) will be deactivated by an automatic timing 
device when a modulated signal is not transmitted for a period of three 
(3) consecutive minutes.
    (5) The system must include automatic monitoring equipment, 
installed at the base station transmitter site(s), which will prevent 
the activation of the system when signals of other co-channel stations 
are present.
    (b) [Reserved]
[ 43 FR 54791 , Nov. 22, 1978, as amended at  44 FR 67125 , Nov. 23, 1979; 
 47 FR 17521 , Apr. 23, 1982]

                         Interconnected Systems