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Safe distance from an antenna calculator

The Ukrainian limits are a hundred times stricter

ICNIRP allows the general public two watts per square metre; DSanPiN allows twenty-five milliwatts, eighty times less. In terms of distance that is a difference of about nine times. So the calculator uses the Ukrainian limit by default: it is the one in force here, and it is the one the sanitary service applies.

dlimit
In the near field the calculation from gain does not work — there you need measurements
Transmitter power (W)
Antenna gain (dBi)
Standard
Mode
Fraction of time transmitting
Frequency (MHz)
Largest antenna dimension (m)
Result
Time-averaged power
Safe distance
Field strength at the boundary
Far-field boundary (2D²/λ)
Standards: DSanPiN 3.3.6.096-2002 (Ukraine), ICNIRP 2020, FCC OET Bulletin 65. The calculator gives an estimate, not the finding of a safety survey.

📐 The formulas​

Power density in the far field:

S = P · G / (4π·d²)          →     d = √( P·G / (4π·S) )

Field strength:

E = √(377 · S)      [V/m]

The far-field boundary:

d_far = 2·D² / λ          D is the largest antenna dimension

Time averaging:

P_average = P · (fraction of time transmitting) · (duty cycle of the mode)
SSB ≈ 0.2      CW ≈ 0.4      FM, RTTY, FT8 = 1.0

A check point:​

100 W, 6 dBi, a limit of 2 W/m² (ICNIRP) → 3.98 m, E = 27.5 V/m. The same antenna under DSanPiN (0.025 W/m²) → 35.6 m.

Where this calculator stops:
  • The formula holds in the far field only. For an HF antenna in a garden the far field begins tens of metres away, and the calculator warns you
  • Reflections from the ground and from objects are not accounted for, and they can double the field at particular points
  • This is an estimate, not the finding of a sanitary inspection: an official document needs measurements
  • The gain is taken in the direction of the main lobe — the worst case, which is the right assumption for a safety estimate

🎯 In practice​

  • Where an antenna may go relative to the neighbours' windows and your own operating position.
  • Making the case to neighbours or a residents' association, with a reference to the standard in force.
  • Choosing a mast height: raising the antenna is often easier than reducing the power.
Practical advice:
  1. Time averaging is legitimate and it matters: SSB with its pauses gives an average power five times lower than FM.
  2. The simplest measure is to raise the antenna and turn the main lobe away from people.
  3. The near field is not a reason to shrug but a reason not to use this formula: there you need measurements.
  4. On HF with wire antennas the critical issue is usually not the far field but the possibility of touching the wire.

© 2026 UR3PKI · CyberDev.Space · Content licensed under CC BY-NC-SA 4.0.

How to cite this calculator
UR3PKI. «Safe distance from an antenna calculator». CyberDev.Space. https://cyberdev.space/en/radio/calculators/others/rf_safety (licence CC BY-NC-SA 4.0).

The licence lets you use this material freely, including in teaching materials, but only with attribution to the author and a link to the source.

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