Sec.  73.72   Operating during the experimental period.

   (a) An AM station may operate during the experimental period (the time
   between midnight and sunrise, local time) on its assigned frequency and with
   its  authorized  power  for the routine testing and maintenance of its
   transmitting  system,  and  for  conducting  experimentation  under an
   experimental authorization, provided no interference is caused to other
   stations maintaining a regular operating schedule within such period.

   (b) No station licensed for “daytime” or “specified hours” of operation may
   broadcast any regular or scheduled program during this period.

   (c) The licensee of an AM station shall operate or refrain from operating
   its  station  during the experimental period as directed by the FCC to
   facilitate frequency measurements or for the determination of interference.

   [ 43 FR 32780 , July 28, 1978, as amended at  56 FR 64859 , Dec. 12, 1991]