Goto Section: 18.303 | 18.307 | Table of Contents
Revised as of September 1, 2021
Goto Year:2020 |
§ 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
(b) The field strength levels of emissions which lie outside the bands
specified in § 18.301, unless otherwise indicated, shall not exceed the
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
500 or more 25
25 × SQRT(power/500) 300
Any non-ISM frequency Below 500
500 or more 15
15 × SQRT(power/500) 300
Industrial heaters and RF stabilized arc welders On or below 5,725 MHz
Above 5,725 MHz Any
Medical diathermy Any ISM frequency
Any non-ISM frequency Any
Ultrasonic Below 490 kHz Below 500
500 or more 2,400/F(kHz)
2,400/F(kHz) × SQRT(power/500) 300
490 to 1,600 kHz
Above 1,600 kHz Any
Induction cooking ranges Below 90 kHz
On or above 90 kHz Any
^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
(c) The field strength limits for RF lighting devices shall be the
Frequency (MHz) Field strength limit at 30 meters (μV/m)
1. The tighter limit shall apply at the boundary between two frequency
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]
Goto Section: 18.303 | 18.307
Goto Year: 2020 |
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