§ 18.305   Field strength limits.

   (a) ISM equipment operating on a frequency specified in § 18.301 is permitted
   unlimited radiated energy in the band specified for that frequency.

   (b) The field strength levels of emissions which lie outside the bands
   specified in § 18.301, unless otherwise indicated, shall not exceed the
   following:
   Equipment Operating frequency RF Power generated by equipment (watts) Field
   strength limit (uV/m) Distance (meters)
   Any type unless otherwise specified (miscellaneous) Any ISM frequency Below
   500
   500 or more 25
   25 × SQRT(power/500) 300
   ^1300
       Any non-ISM frequency Below 500
   500 or more 15
   15 × SQRT(power/500) 300
   ^1300
   Industrial heaters and RF stabilized arc welders On or below 5,725 MHz
   Above 5,725 MHz Any
   Any 10
   (^2) 1,600
   (^2)
   Medical diathermy Any ISM frequency
   Any non-ISM frequency Any
   Any 25
   15 300
   300
   Ultrasonic Below 490 kHz Below 500
   500 or more 2,400/F(kHz)
   2,400/F(kHz) × SQRT(power/500) 300
   ^3300
       490 to 1,600 kHz
   Above 1,600 kHz Any
   Any 24,000/F(kHz)
   15 30
   30
   Induction cooking ranges Below 90 kHz
   On or above 90 kHz Any
   Any 1,500
   300 ^430
   ^430

   ^1Field strength may not exceed 10 μV/m at 1600 meters. Consumer equipment
   operating below 1000 MHz is not permitted the increase in field strength
   otherwise permitted here for power over 500 watts.

   ^2Reduced to the greatest extent possible.

   ^3Field strength may not exceed 10 μV/m at 1600 meters. Consumer equipment
   is not permitted the increase in field strength otherwise permitted here for
   over 500 watts.

   ^4Induction cooking ranges manufactured prior to February 1, 1980, shall be
   subject to the field strength limits for miscellaneous ISM equipment.

   (c)  The  field  strength  limits for RF lighting devices shall be the
   following:
       Frequency (MHz)     Field strength limit at 30 meters (μV/m)
   Non-consumer equipment:
   30-88                                                         30
   88-216                                                        50
   216-1000                                                      70
   Consumer equipment:    
   30-88                                                         10
   88-216                                                        15
   216-1000                                                      20

Notes

   1. The tighter limit shall apply at the boundary between two frequency
   ranges.

   2. Testing for compliance with these limits may be made at closer distances,
   provided a sufficient number of measurements are taken to plot the radiation
   pattern, to determine the major lobes of radiation, and to determine the
   expected field strength level at 30, 300, or 1600 meters. Alternatively, if
   measurements  are  made  at  only  one closer fixed distance, then the
   permissible  field  strength  limits shall be adjusted using 1/d as an
   attenuation factor.

   [ 50 FR 36070 , Sept. 5, 1985, as amended at  51 FR 17970 , May 16, 1986;  52 FR 43197 , Nov. 10, 1987]

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