§  90.539   Frequency stability.

   Transmitters designed to operate in 769–775 MHz and 799–805 MHz
   frequency bands must meet the frequency stability requirements in this
   section.

   (a) Mobile, portable and control transmitters must normally use
   automatic frequency control (AFC) to lock on to the base station
   signal.

   (b) The frequency stability of base transmitters operating in the
   narrowband segment must be 100 parts per billion or better.

   (c) The frequency stability of mobile, portable, and control
   transmitters operating in the narrowband segment must be 400 parts per
   billion or better when AFC is locked to the base station. When AFC is
   not locked to the base station, the frequency stability must be at
   least 1.0 ppm for 6.25 kHz, 1.5 ppm for 12.5 kHz (2 channel aggregate),
   and 2.5 ppm for 25 kHz (4 channel aggregate).

   (d) The frequency stability of base transmitters operating in the
   wideband segment must be 1 part per million or better.

   (e) The frequency stability of mobile, portable and control
   transmitters operating in the wideband segment must be 1.25 parts per
   million or better when AFC is locked to a base station, and 5 parts per
   million or better when AFC is not locked.

   [ 63 FR 58651 , Nov. 2, 1998, as amended at  65 FR 53646 , Sept. 5, 2000;
    72 FR 48861 , Aug. 24, 2007]