RF exposure evaluator
Find out whether your station is exempt from a routine RF exposure evaluation, how far people need to be from your antenna, and what to change if they are too close. Add every band and antenna you use to a worksheet you can keep.
Your station
Set to 14.35 MHz, where the limits in this band are strictest.
Loss between the radio and the antenna at this frequency. Leaving it at 0 is the conservative choice.
Use the maximum gain from the manufacturer. dBd is gain over a dipole: dBi = dBd + 2.15.
The percentage is the mode duty factor: average power during a transmission.
Reflections can add to the field near the ground or a roof. Use none only for people in the main beam well away from reflecting surfaces.
Where people can be
About 2 m when standing on the ground (OET Bulletin 65 Supplement B). Raise it for an upstairs room. Distances run to the nearest part of the body, as the FCC defines separation distance.
Exempt from routine evaluation
Time-averaged ERP is 10.7 W; the exemption threshold at the closest person (7.3 m) is 888 W. Exempt stations must still stay within the limits, and this estimate agrees that they do.
- Controlled limit met beyond 0.3 m
- Uncontrolled limit met beyond 0.6 m
- Drag the antenna, the household member or the neighbor, or use the sliders.
- Average power at the antenna
- 13.3 W 6 min
10.7 W 30 min - ERP, 30 minute average
- 10.7 W EIRP 17.5 W
- Household needs (uncontrolled)
- 0.6 m is 7.3 m away
- Neighbor needs (uncontrolled)
- 0.6 m is 12 m away
How exposure falls with distance
Power density falls with the square of the distance from the antenna. Each line is your station's power density averaged over one of the two averaging times; where it crosses its limit is the minimum distance for that tier.
- Averaged over 6 minutes
- Controlled limit
- Averaged over 30 minutes
- Uncontrolled limit
Why frequency matters
The same power needs more distance on some bands than others, because the limits change with frequency.
- Controlled limit
- Uncontrolled limit
Time averaging
The limits apply to exposure averaged over 6 minutes (controlled) or 30 minutes (uncontrolled), so the mode and how long you transmit both count. OET Bulletin 65 Supplement B uses the busiest 6 or 30 minutes of operating. Its 2 minutes on, 2 off example counts 4 of every 6 minutes, which gives 20 of 30; a cycle that strictly repeats 2 on and 2 off has at most 16 minutes on in any 30, which is what this page uses.
Try this
Each button sets up the evaluator above and tells you what to change and what to watch for.
Apply it to your station
Add each band, antenna and mode you use to the worksheet. The row with the least distance to spare is your station's worst case. The worksheet lives in this page's address, so copy the link or print the page to keep it with your station records.
Your worksheet is empty. Set up a band and antenna above, then press Add to worksheet.
- Every station must be assessed: either show that it qualifies for an exemption, or evaluate it (47 CFR 1.1307(b)(1), 97.13(c)(1)).
- If people could be exposed above the limits where they can go, you must act to prevent it (97.13(c)(2)): move or raise the antenna (T0C08), use less power (97.313(a) asks for the minimum necessary anyway), transmit less of the time or use a lower duty cycle mode, and keep a beam pointed away from people when they are present (G0A10).
- Re-evaluate whenever you change the transmitter or antenna system (T0C09).
- The FCC can ask for the technical basis of an exemption or evaluation (1.1307(b)(1)(ii)), so keep the worksheet link or a printout.
- Several transmitters on the air in the same averaging period count together: they are exempt only if the fractions of each one's threshold add up to no more than 1 (1.1307(b)(3)(ii)(B)). A larger sum means the station needs an evaluation, not that it exceeds the limits.
Limits of this estimate
- The far-field formula over-predicts power density close to most antennas, so it is conservative there (OET Bulletin 65, Supplement B).
- Small transmitting loops are the exception: very close to them the field is much higher than the formula predicts. The ARRL also says not to use this kind of calculation for antennas less than 20 cm (8 inches) from a person (ARRL).
- The circles assume the antenna's maximum gain in every direction. For a directional antenna, the ARRL suggests evaluating each direction of interest with the gain in that direction (ARRL).
- A hand-held radio held against the body is a portable device evaluated by absorption (SAR), not by these power density limits (1.1310(d)(2)).
- The exemption table applies only at least λ/2π from the antenna (3.4 m at 14 MHz). For a band, λ/2π is largest at the bottom of the band, so that is where the exemption is checked, while the limits use the edge where they are strictest.
Result: exempt from routine evaluation
How it works
- Limits come from Table 1 of 47 CFR 1.1310, which covers 0.3 MHz to 100 GHz. Household members who have had RF exposure training and information may be evaluated against the controlled limits; everyone else gets the uncontrolled limits (47 CFR 97.13(c)(1)). Because the rule allows either tier for a trained household, the evaluator uses whichever needs less distance.
- A station is exempt from routine evaluation when its time-averaged ERP (gain relative to a dipole) is no more than the threshold in 47 CFR 1.1307(b)(3)(i)(C) for its frequency and the separation distance R, which must be at least one wavelength divided by 2π. For a whole band, the threshold is taken at the band edge where it is strictest and λ/2π at the bottom of the band, where it is largest. A source of 1 mW or less is always exempt. An exemption removes the duty to evaluate, not the duty to stay within the limits.
- Power density uses the far-field formula from FCC OET Bulletin 65, Supplement B: S = F × EIRP / (4πR²), where F is 2.56 for typical ground reflection, 4 for total reflection and 1 for none. Close to most antennas it over-predicts, so it errs on the safe side; small transmitting loops are an exception.
- Average power is the transmitter PEP, less feed line loss, times the mode duty factor, times the share of the busiest 6 minutes (controlled) or 30 minutes (uncontrolled) spent transmitting, as in Supplement B. Duty factors are from Supplement B Table 2, with the ARRL calculator adding AM and unknown modes at 100 percent.
- The calculation reproduces the compliance distance tables in Supplement B (Tables 4a and 4b) and its worked repeater example. Antenna presets are the ARRL’s approximate gains; use your antenna’s actual maximum gain when you know it.
Learn more: RF exposure and your station
Sources: 47 CFR 1.1310, Radiofrequency radiation exposure limits (eCFR); 47 CFR 1.1307, Actions that may have a significant environmental effect (eCFR); 47 CFR 97.13, Restrictions on station location (eCFR); OET Bulletin 65, Supplement B: Additional Information for Amateur Radio Stations (FCC Office of Engineering and Technology); Human Exposure to Radiofrequency Electromagnetic Fields (85 FR 18131) (Federal Register); RF Safety FAQ (FCC Office of Engineering and Technology); RF Exposure Calculator (ARRL); RF Exposure Calculator instructions (antenna gains) (ARRL); 47 CFR 97.313, Transmitter power standards (eCFR); WSJT-X User Guide (FT8 timing and audio on SSB) (WSJT Development Team); 2026-2030 Technician question pool (NCVEC Question Pool Committee); 2023-2027 General question pool (NCVEC Question Pool Committee)
Practice the exam questions: T0 Safety (Technician), G0 Electrical and RF Safety (General), E0 Safety (Amateur Extra)
Found something wrong or out of date? Report a problem with this tool on GitHub (a public issue; nothing is sent until you submit it there).