Title 47
SECTION 18.305
18.305 Field strength limits.
§ 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 |
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]