RF Exposure Calculator

FCC has adopted guidelines and procedures for evaluating environmental effects of RF emissions. The new guidelines incorporate two tiers of exposure limits based on whether exposure occurs in an occupational or “controlled” situation or whether the general population is exposed or exposure is in an “uncontrolled” situation. In addition to guidelines for evaluating fixed transmitters, the FCC adopted limits for evaluating exposure from mobile and portable devices, such as cellular telephones and personal communications devices.

To use the RF Exposure Calculator, fill-in the form below with your operating power, antenna gain, and the operating frequency. Depending on how far above ground the RF source is located, you might want to consider ground reflections — and then click “Calculate”.

You may need to run the calculator multiple times to get a complete picture of your situation, i.e. kake into account the antenna’s lobes and directionality.

Click here to get (more) info.

Parameters

  • Power at Antenna: (Need help with this?) (watts)
  • Mode duty cycle:
  • Transmit duty cycle: (time transmitting)
    You transmit for  minutes then receive for  minutes (and repeat).
  • Antenna Gain (dBi):
  • Operating Frequency (MHz):

 Include Effects of Ground Reflections


Results for a controlled environment:

Maximum Allowed Power Density (mw/cm2):
Minimum Safe Distance (feet):


For an uncontrolled environment:

Maximum Allowed Power Density (mw/cm2):
Minimum Safe Distance (feet):


Antenna gain instructions:

One of three conditions will likely apply to you.

  • You could have a detailed antenna model. If so, along each lobe of the model, or direction of interest, use the dBi gain of the antenna derived from the model. This likely will mean running the calculator several times, but it will result in a the most detailed picture of your situation.
  • Or you might have an antenna model from the manufacturer with gain and radiation pattern information. If so, you could use the same process as #1 using the manufacturer’s model. This will give you a good rough picture.
  • Finally, if you have no idea what your antenna’s radiation pattern looks like, use the information below as a first approximation. Refine your picture as you research your situation over time.
Antenna TypeApprox. Gain (dBi) **Directionality *
Half wave dipole2.2 dBiSlightly
0.3m dish22.0 dBiHighly
0.6m dish24.0 dBiHighly
1.0m dish34.0 dBiHighly
1.5m dish38.0 dBiHighly
10 element Yagi15.1 dBiHighly
2 element Yagi5.9 dBiModerately
3 element Yagi8.1 dBiHighly
4 element Yagi9.1 dBiHighly
5 element Yagi10.1 dBiHighly
6 element Yagi 11.1 dBiHighly
8 element Yagi13.1 dBiHighly
Alford Slotg9.0 dBiSlightly
Big Colinear8.2 dBiHighly
Colinear5.2 dBiModerately
Delta5.2 dBiMedium
Flat Panel (typical)24.0 dBiHighly
Four Square5.2 dBiModerately
G5RV1.0 dBiSlightly
Helix14.1 dBiHighly
Hex Beam5.0 dBiModerately
Horn (typical)22.0 dBiHighly
Log Periodic6.0 dBiHighly
Longer Yagi19 dBiHighly
Longwire2.0 dBiSlightly
Moxon6.0 dBiModerately
Quad9.1 dBiHighly
Quarter Wave Vertical1.5 dBiOmni
Slotted Waveguide12.0 dBiHighly
SteppIR7.1 dBiModerately
Vertical Dipole4.2 dBiOmni
Windom (OCD)2.0 dBiSlightly
ZS6BKW (G5RV type)5.0 dBiSlightly
* Source: Informal discussions within our team, aka. The School of Hard Knocks
** Source: RSGB EM Field Exposure web site at https://rsgb.org/main/technical/emc/emf-exposure/
Calculator: RSGB/Ofcom calculator (3.0 MB MS-Excel Worksheet)

Notes:

(1) Antennas with even moderate directionality may need to be evaluated in multiple directions to get a complete picture of their overall RF exposure.

(2) Small mag loops are particularly difficult to calculate their near field RF exposure. See the ARRL Antenna book, Chapter 5 “Loop Antennas”, section 5.3 “Small Transmitting Loops” and Table 5.5 on page 5.19.

Calculation Sources:
FCC’s OST Bulletin 65, originally issued in 1985 and revised in 1997, provides additional guidance for evaluating compliance with the latest FCC policies and guidelines and is available here. A supplement for the Amateur Radio Service (Supplement B) is available here. Likewise a supplement for Mobile and Portable equipment (Supplement C) is available here.

Credits:
The Javascript contained on this page was derived from a public domain BASIC program written by Wayne Overbeck N6NB and published in the January, 1997 issue of CQ VHF, p. 33. Terms: GNU Licence. To view the Javascript that performs the calculation, right-click on this page and select ‘View Page Source’.

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