RF exposure limits chart: MPE by frequency
The full MPE table, plus what to multiply it by for your mode.
The short answer
The FCC maximum permissible exposure limit for an uncontrolled environment is at its strictest between 30 and 300 MHz, where it is 0.2 mW per square centimetre. On 20 metres it is 0.92, on 40 metres 3.67 and on 80 metres 14.9. The controlled environment limit is five times higher, and averaging periods are 30 minutes uncontrolled and 6 minutes controlled.
- Strictest range
- 30 to 300 MHz
- Minimum uncontrolled MPE
- 0.2 mW/cm2
- Controlled multiplier
- 5x
- Uncontrolled averaging
- 30 minutes
- Controlled averaging
- 6 minutes
- Evaluation required
- Every station
Every amateur station must perform its own routine RF exposure evaluation and keep the result, at any power level. This page is the reference table that evaluation is compared against, along with the duty cycle factors and averaging periods that go into the calculation.
The limits come from 47 CFR Part 1 Subpart I, and the amateur obligation is at Part 97.13(c). The official text is at the electronic Code of Federal Regulations. The method for using these numbers is in how to run an RF exposure evaluation, and the arithmetic is done for you by the RF exposure calculator.
Maximum permissible exposure by frequency
MPE
Power density limits, uncontrolled and controlled
| Frequency | Band | Uncontrolled mW/cm2 | Controlled mW/cm2 |
|---|---|---|---|
| 1.8 MHz | 160 m | 100 | 100 |
| 3.5 MHz | 80 m | 14.9 | 74.5 |
| 5.3 MHz | 60 m | 6.50 | 32.5 |
| 7.0 MHz | 40 m | 3.67 | 18.4 |
| 10.1 MHz | 30 m | 1.76 | 8.82 |
| 14.0 MHz | 20 m | 0.92 | 4.59 |
| 18.1 MHz | 17 m | 0.55 | 2.75 |
| 21.0 MHz | 15 m | 0.41 | 2.04 |
| 24.9 MHz | 12 m | 0.29 | 1.45 |
| 28.0 MHz | 10 m | 0.23 | 1.15 |
| 50 MHz | 6 m | 0.20 | 1.00 |
| 144 MHz | 2 m | 0.20 | 1.00 |
| 222 MHz | 1.25 m | 0.20 | 1.00 |
| 440 MHz | 70 cm | 0.29 | 1.47 |
| 902 MHz | 33 cm | 0.60 | 3.01 |
| 1296 MHz | 23 cm | 0.86 | 4.32 |
| 2400 MHz | 13 cm | 1.00 | 5.00 |
Below 30 MHz the uncontrolled limit follows 180 divided by the frequency in MHz squared, and the controlled limit is 900 divided by the same. From 30 to 300 MHz both are flat at their minimum. From 300 to 1500 MHz they rise with frequency, and above 1500 MHz they are flat again.
Controlled versus uncontrolled
- Controlled environment
- People who know they are being exposed and can act on that knowledge. In an amateur context this means you and, in most interpretations, the members of your household who are aware of the station. The limit is five times higher and averages over 6 minutes.
- Uncontrolled environment
- Everybody else. Neighbours, visitors, people on the pavement, and anyone who has no idea your antenna exists. The limit is five times stricter and averages over 30 minutes, which is the number your evaluation must satisfy for anywhere the public can be.
- The practical rule
- Evaluate against the uncontrolled limit for the nearest place any member of the public can stand, and against the controlled limit for your own operating position. If you pass the uncontrolled limit everywhere, you are finished.
Duty cycle factors
Duty cycle
Multipliers for the averaging calculation
| Mode | Duty while transmitting | Typical overall factor |
|---|---|---|
| SSB, no processing | 20 percent | 0.10 |
| SSB, heavy processing | 50 percent | 0.25 |
| AM voice | 100 percent | 0.50 |
| FM voice | 100 percent | 0.50 |
| CW, hand sent | 40 percent | 0.20 |
| CW, keyer at speed | 50 percent | 0.25 |
| RTTY | 100 percent | 0.50 |
| PSK31 | 100 percent | 0.50 |
| FT8 and FT4 | 100 percent | 0.45 |
| DMR, C4FM, D-STAR | 100 percent | 0.50 |
| Contest or net operation | Mode dependent | Up to 0.90 |
The overall factor combines duty while transmitting with the fraction of the averaging window you spend transmitting at all. Evaluate for your busiest realistic operating, not your quietest.
Distance, and why it dominates
Power density falls with the square of distance and only linearly with power. Doubling the distance from an antenna to a person quarters the exposure. Halving the power only halves it. That is why the standard fix for a failed evaluation is height or distance rather than a permanently detuned station.
Distance effect
Relative power density at increasing distance from the same antenna
| Distance | Relative density | Equivalent power reduction |
|---|---|---|
| 1 m | 100 percent | Reference |
| 1.5 m | 44 percent | Same as cutting power to 44 percent |
| 2 m | 25 percent | Same as quartering the power |
| 3 m | 11 percent | Same as running 11 percent power |
| 5 m | 4 percent | Same as running 4 percent power |
| 10 m | 1 percent | Same as running 1 percent power |
This is why an antenna at the far end of a garden on a mast is worth more to an exposure evaluation than any reduction in transmitter output, and why it also happens to make the antenna work better.
What helps you pass
Distance, height and honest measurement
The three things that change an evaluation result.
Easy Up
Easy Up 20 ft telescoping push-up mast
Height is distance. Getting the antenna up and away from the patio is usually the whole fix.
Check price$185.00
Bolton Technical
Bolton400 low-loss coax, 100 ft with PL-259
Low-loss coax lets you site the antenna far from the house without giving away the power that made the distance worthwhile.
Check price$119.95
Surecom
Surecom SW-102 digital VHF/UHF SWR meter
Reads real forward power at the feedline rather than the number on the front panel of the radio.
Check price$57.99
AURSINC
NanoVNA H4 vector network analyzer
Tells you what the antenna is actually doing, which is the input the whole calculation depends on.
Check price$89.90
Threlaco
Threlaco 3-way galvanized guy wire kit, 50 ft
A mast is only as safe as its guying, and an unguyed mast is not a distance solution.
Check price$46.99
Common questions
Questions people ask about this
Which band has the strictest RF exposure limit?
Everything between 30 and 300 MHz shares the strictest limit, 0.2 mW per square centimetre for an uncontrolled environment. That covers 6 metres, 2 metres and the 222 MHz band. The reason is that human tissue absorbs radio frequency energy most efficiently near its own resonance, which lands in that range, so those bands need more care than 80 metres at the same power.
What is the difference between the controlled and uncontrolled limits?
The controlled limit is five times higher and applies to people who know they are being exposed and can act on it, which in an amateur context means you and your household. The uncontrolled limit applies to everybody else, including neighbours and passers-by. Uncontrolled exposure averages over 30 minutes, controlled over 6 minutes.
Do I have to keep a record of my evaluation?
Yes. There is no form to file and nothing to send anywhere, but you must perform the evaluation and retain the result. A single sheet per antenna and band showing power, gain, distance, duty factor, computed density and the applicable limit is exactly what the rule expects, and it is what you would produce if anybody ever asked.
How does duty cycle affect the calculation?
It scales the computed power density directly. A mode at 100 percent duty produces five times the average exposure of SSB at 20 percent duty for the same peak power. That is why a station passing comfortably on voice can fail on FT8 at the same power setting, and why the evaluation should reflect the mode you actually use most.
Does feedline loss count?
Yes, and you should include it. The evaluation is based on power delivered to the antenna, not power leaving the transmitter. On VHF and UHF especially, a long feedline run throws away a substantial fraction of your output before it reaches the antenna, which lowers the power density at the antenna and works in your favour.
Keep going
Related on this site
Keeping your own cut lengths, SWR sweeps and exposure record? The Station Build & Antenna Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.
Disclaimer Researched guidance for planning purposes, not professional engineering, electrical or legal advice. Antenna work, RF exposure, mast and tower work, grounding and battery handling all carry real risk that depends on your specific site and installation. Verify anything safety-critical against current FCC rules, the National Electrical Code and the manufacturer's own documentation, and hire a professional where the job calls for one. We research equipment from published specifications, regulatory documents and verified owner reviews rather than claiming hands-on testing we have not done.