Technical Resources

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RF Exposure Limits – Resources for Evaluation of Maximum Permissible Exposure Limit

The FCC has revised the rules and regulations concerning human exposure from radio transmitting stations.  The new rules went into effect June 1, 2020.  However changes to the existing rules were delayed until May 3, 2021 and existing stations have until May 3, 2023 to comply.  New stations must comply after May 3, 2021.

Before the new rules went into effect, most amateurs were able to use a Categorical Exclusion to the FCC requirement, to evaluate if a station fell under the Maximum Permissible Exposure limit.  The new rules replaced the Categorical Exclusions with a new mechanism called Exemptions to Routine Evaluation.  The Exemptions are based upon frequency, power and distance.

Steve Moreen, KA6UGS, has developed an on-line worksheet which allows an amateur to determine if a station meets the Exemption to Routine Evaluation and the maximum station power allowed under the Exemption.

The on-line calculator is available here. (Link will open in a new tab)

Exemption Minimum Distances (λ/π2)

The distances shown below are the required minimum distance, between any part of the antenna and human exposure, for an Exemption to Routine Environmental Evaluation to apply.  (Use the Amateur Radio RF Environment Evaluation Exemption Calculator to determine the allowed maximum Effective Radiated Power (ERP).

160 m (1.8-2.0 MHz) ………….. 82.8 feet

80 m (3.5-3.75 MHz) ………….. 41.3 feet

75 m (3.75-4.0 MHz) ………….. 38.8 feet

40 m (7.0-7.3 MHz) ……………. 20.7 feet

30 m (10.1-10.15 MHz) ………. 15.5 feet

20 m (14.0-14.35 MHz) ………. 10.3 feet

17 m (18.068-18.168 MHz) …… 8.8 feet

15 m (21.0-21.45 MHz) ………… 7.8 feet

12 m (24.89-24.99 MHz) ………. 6.2 feet

10 m (28.0-29.7 MHz) ………….. 5.2 feet

6 m (50-54 MHz) …………………. 3.1 feet

2 m (140-144 MHz) …………….… 1.0 feet

1.25 m (222-225 MHz) …………. 7.8 inches

For higher frequencies, λ/2π is less than 20 cm

SAR Exemption or Testing is required.

70 cm (420-450 MHz) ………….. 4.3 inches

33 cm (902-928 MHz) ………….. 2.0 inches

Additional web resources:

Here is the ARRL page on FCC Exposure Rules: FCC RF-Exposure Regulations — the Station Evaluation

ARRL page on setting up the exposure calculator. This has information about how to set up the calculator – including coax loss calculations and a list showing gains for common antenna configurations, and duty cycles for common operating modes.

The actual Exposure Calculator is here.

For a more sophisticated loss line calculator see the coax loss calculator from KV5R here.

…and if you really want all the nitty-gritty, here is the official FCC page on Radio Frequency Safety. This page includes links to all the FCC documents relating to RF Safety.