Sec. 101.141  Microwave modulation.

    (a) Microwave transmitters employing digital modulation techniques 
and operating below 19.7 GHz and in the 24.25-25.25 GHz 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.

    Note to (a)(1): Systems authorized prior to December 1, 1988, may 
install equipment after that date with no minimum bit rate.

    (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).

[[Page 773]]

Where type accepted 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

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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)........................          
------------------------------------------------------------------------

[61 900 FR 26677 , May 28, 1996, as amended at  62 FR 24583 , May 6, 1997]