Sec.  101.811   Modulation requirements.

   (a) The use of modulating frequencies higher than 3000 hertz for single
   channel radiotelephony or tone signaling on frequencies below 500 MHz is not
   authorized.

   (b) When amplitude modulation is used, the modulation percentage must be
   sufficient  to  provide  efficient  communication and must normally be
   maintained  above 70 percent on positive peaks, but may not exceed 100
   percent on negative peaks.

   (c)  When  phase  or  frequency  modulation is used for single channel
   radiotelephony on frequencies below 500 MHz, the deviation arising from
   modulation may not exceed plus or minus 15 kHz from the unmodulated carrier.

   (d) Each unmultiplexed radiotelephone transmitter having more than 3 watts
   plate power input to the final radio frequency stage and initially installed
   at the station in this service after September 4, 1956, must be provided
   with a device that will automatically prevent modulation in excess of that
   specified in paragraphs (b) and (c) of this section which may be caused by
   greater than normal audio level.