Sec.  101.141   Microwave modulation.

   (a) Microwave transmitters employing digital modulation techniques and
   operating below 25.25 GHz (except for MVDDS stations in the 12,200–12,700
   MHz band) must, with appropriate multiplex equipment, comply with the
   following additional requirements:

   (1) The bit rate, in bits per second, must be equal to or greater than the
   bandwidth specified by the emission designator in Hertz (e.g., to be
   acceptable, equipment transmitting at a 20 Mb/s rate must not require a
   bandwidth of greater than 20 MHz), except the bandwidth used to calculate
   the minimum rate may not include any authorized guard band.

   (i) Stations authorized prior to December 1, 1988 may install equipment
   after that date with no minimum bit rate. Equipment applied for or
   authorized prior to April 1, 2005 in the 21.2–23.6 GHz band may be installed
   with no minimum bit rate.

   (ii) However, any digital equipment applied for after April 1, 2005 and
   equipment replacing existing equipment in the 21.2–23.6 GHz band must meet
   the bit rate standard.

   (2) Equipment to be used for voice transmission placed in service,
   authorized, or applied for on or before June 1, 1997 in the 2110 to 2130 and
   2160 to 2180 MHz bands must be capable of satisfactory operation within the
   authorized bandwidth to encode at least 96 voice channels. Equipment placed
   in service, authorized, or applied for on or before June 1, 1997 in the
   3700–4200, 5925–6425 (30 MHz bandwidth), and 10,700–11,700 MHz (30 and 40
   MHz bandwidths) bands must be capable of satisfactory operation within the
   authorized bandwidth to encode at least 1152 voice channels. These required
   loading levels may be reduced by a factor of 1/N provided that N
   transmitters may be operated satisfactorily, over the same radio path,
   within an authorized bandwidth less than, or equal to, the maximum
   authorizable bandwidth (e.g., the 1152 channel requirement may be reduced to
   576 if two transmitters can be satisfactorily operated over the same path
   within the maximum bandwidth). Where certificated equipment is designed to
   operate on the same frequency in a cross polarized configuration to meet the
   above capacity requirements, the Commission will require, at the time
   additional transmitters are authorized, that both polarizations of a
   frequency be used before a new frequency assignment is made, unless a single
   transmitter installation was found to be justified by the Commission at the
   time it authorized the first transmitter.

   (3) The following capacity and loading requirements must be met for
   equipment applied for, authorized, and placed in service after June 1, 1997
   in the 3700–4200 MHz (4 GHz), 5925–6425 and 6525–6875 MHz (6 GHz),
   10,550–10,680 MHz (10 GHz), and 10,700–11,700 MHz (11 GHz) bands:


------------------------------------------------------------------------
                                             Minimum
                                             traffic
                                  Minimum    loading
                                  payload    payload
   Nominal channel bandwidth     capacity      (as          Typical
             (MHz)               (Mbits/s)   percent    utilization \2\
                                    \1\         of
                                             payload
                                            capacity)
------------------------------------------------------------------------
0.400.........................        1.54        N/A  1 DS-1
0.800.........................        3.08        N/A  2 DS-1
1.25..........................        3.08        N/A  2 DS-1
1.60..........................        6.17        N/A  4 DS-1
2.50..........................        6.17        N/A  4 DS-1
3.75..........................       12.3         N/A  8 DS-1
5.0...........................       18.5         N/A  12 DS-1
10.0..........................       44.7      \3\ 50  1 DS-3/STS-1
20.0..........................       89.4      \3\ 50  2 DS-3/STS-1
30.0 (11 GHz).................       89.4      \3\ 50  2 DS-3/STS-1
30.0 (6 GHz)..................      134.1      \3\ 50  3 DS-3/STS-1
40.0..........................      134.1      \3\ 50  3 DS-3/STS-1
------------------------------------------------------------------------
\1\ Per polarization
\2\ DS and STS refer to the number of voice circuits a channel can
  accommodate. 1 DS-1 = 24 voice circuits; 2 DS-1 = 48; 4 DS-1 = 96; 8
  DS-1 = 192; 12 DS-1 = 288; 1 DS-3/STS-1 = 672; 2 DS-3/STS-1 = 1344; 3
  DS-3/STS-1 = 2016.
\3\ This loading requirement must be met within 30 months of licensing.
  If two transmitters simultaneously operate on the same frequency over
  the same path, the requirement is reduced to 25 percent.

   (4) If a transmitter is authorized to operate in a bandwidth that is not
   listed in paragraph (a)(3) of this section, it must meet the minimum payload
   capacity and traffic loading requirements of the next largest channel
   bandwidth listed in the table; e.g., if the authorized bandwidth is 3.5 MHz,
   the minimum payload capacity must be 12.3 Mbits/s.

   (5) Transmitters carrying digital motion video motion material are exempt
   from the requirements specified in paragraphs (a)(2) and (a)(3) of this
   section, provided that at least 50 percent of the payload is digital video
   motion material and the minimum bit rate specified in paragraph (a)(1) of
   this section is met. In the 6, 10, and 11 GHz bands, concatenation of
   multiple contiguous channels is permitted for channels of equal bandwidth on
   center frequencies, provided no other channels are available and the minimum
   payload capacity requirements are met.

   (6) Digital systems using bandwidths of 10 MHz or larger will be considered
   50 percent loaded when the following condition is met: at least 50 percent
   of their total DS–1 capacity is being used. A DS–1 channel is being used
   when it has been connected to a DS–0/DS–1 multiplexer. For non-DS–0
   services, such as, but not limited to, video or broadband data transmission,
   the next largest DS–1 equivalent will be considered for the computation of a
   loading percentage.

   (7) For digital systems, minimum payload capacities shall be expressed in
   numbers of DS–1s, DS–3s or STS–1s. The payload capacity required by the
   Commission shall correspond to commercially available equipment.

   (b) For purposes of compliance with the emission limitation requirements of
    Sec. 101.111(a)(2) and the requirements of paragraph (a) of this section,
   digital modulation techniques are considered as being employed when digital
   modulation occupies 50 percent or more to the total peak frequency deviation
   of a transmitted radio frequency carrier. The total peak frequency deviation
   will 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 must be determined in accordance with  Sec. 2.202(f) of this chapter.

   (c) Analog Modulation. Except for video transmission, an application for an
   initial working channel for a given route will not be accepted for filing
   where the anticipated loading (within five years for voice, or other period
   subject to reasonable projection) is less than the minimum specified for the
   following frequency bands. Absent extraordinary circumstances, applications
   proposing additional frequencies over existing routes will not be granted
   unless it is shown that the traffic load will shortly exhaust the capacity
   of the existing equipment. Where no construction of radio facilities is
   requested, licensees must submit this evidence with their filing of any
   necessary authority required pursuant to section 214 of the Communications
   Act and part 63 of this chapter.


------------------------------------------------------------------------
                                                               Minimum
                                                              number of
                                                                voice
                    Frequency band (MHz)                     channels (4
                                                                KHz or
                                                             equivalent)
------------------------------------------------------------------------
3700 to 4200 (20 MHz bandwidth)............................          900
5925 to 6425 (10 MHz bandwidth)............................          300
5925 to 6425 (20 MHz bandwidth)............................          600
5925 to 6425 (30 MHz bandwidth)............................          900
6525 to 6875 (10 MHz bandwidth)............................          300
10,700 to 11,700 (10 MHz bandwidth)........................          300
10,700 to 11,700 (20 MHz bandwidth)........................          600
10,700 to 11,700 (30 MHz bandwidth)........................          900
10,700 to 11,700 (40 MHz bandwidth)........................          900
------------------------------------------------------------------------

   [ 61 FR 26677 , May 28, 1996, as amended at  62 FR 24583 , May 6, 1997;  63 FR 36611 , July 7, 1998;  65 FR 59358 , Oct. 5, 2000;  67 FR 43039 , June 26, 2002;
    68 FR 4958 , Jan. 31, 2003]