§  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)(i) Except as noted in paragraph (a)(7) of this section, the payload
   capacity of equipment shall meet the following minimum efficiency
   standards:
   Frequency Emission bandwidth <=5 MHz Emission bandwidth >5 MHz and <=20
   MHz Emission bandwidth >20 MHz
   3,700-10,550 MHz 2.4 bits/second/Hertz 4.4 bits/second/Hertz 4.4
   bits/second/Hertz.
   10,550-13,250 MHz 2.4 bits/second/Hertz 4.4 bits/second/Hertz 3.0
   bits/second/Hertz.

   (ii) Traffic loading payload shall exceed 50 percent of payload
   capacity within 30 months of licensing. During anomalous signal fading,
   licensees subject to the capacity and loading requirements may adjust
   to a modulation specified in their authorization if such modulation is
   necessary to allow licensees to maintain communications, even if the
   modulation will not comply with the capacity and loading requirements
   specified in this paragraph. Links that must comply with the capacity
   and loading requirements that use equipment capable of adjusting
   modulation must be designed using generally accepted multipath fading
   and rain fading models to meet the specified capacity and loading
   requirements at least 99.95% of the time, in the aggregate of both
   directions in a two-way link.

   (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 at least 50 percent of their total
   capacity is being used. For purposes of this subsection, a Fixed
   Service channel is being used if it is attached to a communications
   system that is capable of providing data to it at a rate that is
   sufficient to occupy at least 50 percent of the payload capacity of the
   Fixed Service channel, after header compression is applied.

   (7) Equipment placed in service after June 1, 1997 and prior to October
   5, 2012 may comply with the provisions of § 101.141(a)(3) in effect as
   of the date the equipment was placed in service.

   (b) For purposes of compliance with the emission limitation
   requirements of § 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 § 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.
   Frequency band (MHz) Minimum number of voice 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;  76 FR 59572 , Sept. 27, 2011;  77 FR 54433 , Sept. 5, 2012]