§  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

   ^1 Field 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.

   ^2 Reduced to the greatest extent possible.

   ^3 Field 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.

   ^4 Induction 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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