Sec.  21.122   Microwave digital modulation.

   

   (a) Microwave transmitters employing digital modulation techniques and
   operating below 15 GHz shall, with appropriate multiplex equipment,
   comply with the following additional requirement: The bit rate, in
   bits per second, shall be equal to or greater than the bandwidth
   specified by the emission designator in Hertz (e.g., to be acceptable,
   equipment transmitting at a 6 Mb/s rate must not require a bandwidth
   of greater than 6 MHz), except the bandwidth used to calculate the
   minimum rate shall not include any authorized guard band.

   (b) For purposes of compliance with the emission limitation
   requirements of Sec. 21.106(a)(2) of this part and the requirements of
   paragraph (a) of this section, digital modulation techniques are
   considered as being employed when digital modulation contributes 50
   percent or more to the total peak frequency deviation of a transmitted
   radio frequency carrier. The total peak frequency deviation shall be
   determined by adding the deviation produced by the digital modulation
   signal and the deviation produced by any frequency division multiplex
   (FDM) modulation used. The deviation (D) produced by the FDM signal
   shall be determined in accordance with Sec. 2.202(f) of part 2 of this
   chapter.

   (c) Transmitters employing digital modulation techniques shall
   effectively eliminate carrier spikes or single frequency tones in the
   output signal to the degree which would be obtained without repetitive
   patterns occurring in the signal.

   [ 44 FR 60534 , Oct. 19, 1979, as amended at  46 FR 23451 , Apr. 27, 1981;
    49 FR 37775 , Sept. 26, 1984;  58 FR 49226 , Sept. 22, 1993;  61 FR 26676 ,
   May 28, 1996]

Subpart D--Technical Operation