Sec.  90.735   Station identification.

   (a)  Except for nationwide systems authorized in the 220–222 MHz band,
   station identification is required pursuant to  Sec. 90.425 of this part.

   (b) Trunked systems shall employ an automatic device to transmit the call
   sign of the base station at 30 minute intervals. The identification shall be
   made on the lowest frequency in the base station trunked group assigned to
   the licensee. If this frequency is in use at the time identification is
   required,  the  identification  may  be made at the termination of the
   communication in progress on this frequency.

   (c) Station identification may be by voice or International Morse Code. If
   the call sign is transmitted in International Morse Code, it must be at a
   rate of between 15 to 20 words per minute, and by means of tone modulation
   of the transmitter, with the tone frequency being between 800 and 1000
   hertz.

   (d) Digital transmissions may also be identified by digital transmission of
   the station call sign. A licensee that identifies its station in this manner
   must provide the Commission, upon its request, information (such as digital
   codes  and algorithms) sufficient to decipher the data transmission to
   ascertain the call sign transmitted.

   [ 56 FR 19603 , Apr. 29, 1991, as amended at  62 FR 15997 , Apr. 3, 1997]