Sec. 21.118  Transmitter construction and installation.

    (a) The equipment at the operating and transmitting positions shall 
be so installed and protected that it is not accessible to, or capable 
of being operated by, persons other than those duly authorized by the 
licensee.
    (b) In any case where the maximum modulating frequency of a 
transmitter is prescribed by the Commission, the transmitter shall be 
equipped with a low-pass or band-pass modulation filter of suitable 
performance characteristics. In those cases where a modulation limiter 
is employed, the modulation filter shall be installed between the 
transmitter stage in which limiting is effected and the modulated stage 
of the transmitter.
    (c) Each transmitter employed in these services shall be equipped 
with an appropriately labeled pilot lamp or meter which will provide 
continuous visual indication at the transmitter when its control 
circuits have been placed in a condition to activate the transmitter. In 
addition, facilities shall be provided at each transmitter to permit the 
transmitter to be turned on and off independently of any remote control 
circuits associated therewith.
    (d) [Reserved]
    (e) At each transmitter control point the following facilities shall 
be installed:
    (1) A carrier operated device which will provide continuous visual 
indication when the transmitter is radiating, or, in lieu thereof, a 
pilot lamp or meter which will provide continuous visual indication when 
the transmitter control circuits have been placed in a condition to 
activate the transmitter.
    (2) Facilities which will permit the operator to turn transmitter 
carrier on and off at will.
    (f) Transmitter control circuits from any control point shall be so 
installed that grounding or shorting any line in the control circuit 
will not cause the transmitter to radiate: Provided, however, That this 
provision shall not be applicable to control circuits of stations which 
normally operate with continuous radiation or to control circuits which 
are under the effective operational control of responsible operating 
personnel 24 hours per day.
[ 44 FR 60534 , Oct. 19, 1979, as amended at  52 FR 37783 , Oct. 9, 1987]