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RF Exposure Calc Instructions

Calculator Parameters

Enter the Power at the antenna. This is the radiated power in watts at the antenna. For best results you should account for feedline loss, poor SWR, etc. At VHF/UHF frequencies, the feedline loss with coax can be significant. For example, transmitting 100W into 80 feet of RG-8X coax to an antenna with an SWR of 1.4:1 at 146.52 MHz will result in only 46W of actual power at the antenna. Here is an excellent coax loss calculator. Alternatively you can be conservative and enter the transmitter's output power (which is naturally a higher power than at the antenna) if you cannot determine what that actual power is at the antenna. Try to be as accurate as you can.

Enter the Mode Duty Cycle: based on your usage. This affects the average output power. Mode duty cycles are:

  • Conversational SSB with no speech processing, uses a 20% duty cycle which includes voice characteristics and syllabic duty factor.
  • Conversational SSB with heavy speech processing, uses a 50% duty cycle which includes voice characteristics and syllabic duty factor.
  • Voice FM, uses a 100% duty cycle.
  • FSK or RTTY, uses a 100% duty cycle.
  • AFSK SSB, uses a 100% duty cycle.
  • Conversational CW, uses a 40% duty cycle
  • Carrier always on (e.g. commonly used for tune-up purposes), uses a 100% duty cycle.
  • For all others, or if unknown, uses a 100% duty cycle as a worst case catch-all.

To figure out your percentage of transmitting, enter the number of minutes you transmit, followed with the number of minutes you receive. This affects the average output power.

Enter the Antenna Gain: in dBi. See the Antenna gain instructions at the bottom of the page

Controlled vs Uncontrolled: takes into account whether or not individuals are aware of the RF exposure or not. A Controlled Environment is an area where the persons exposed to RF are aware of the exposure and its effects. An Uncontrolled Environment is an area where the persons exposed to RF are unaware of the exposure and its effects.

For the Effect of ground: parameter, when checked, the effects of signals reflecting off the ground are included in the calculation. Use this setting for low or non-directional antennas. This is a more conservative way of estimating RF exposure.

Antenna Gain Instructions

Use manufacturer's free space gain figures in dBi when available.

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 Type Approx. Gain (dBi) *
Half wave dipole 2.15 dBi
10 element Yagi 15.1 dBi
2 element Yagi 5.9 dBi
3 element Yagi 8.1 dBi
4 element Yagi 9.1 dBi
5 element Yagi 10.1 dBi
6 element Yagi 11.1 dBi
8 element Yagi 13.1 dBi
Delta Loop 5.2 dBi
Four Square 5.2 dBi
G5RV 1.0 dBi
Hex Beam 5.0 dBi
Moxon 6.0 dBi
Quarter Wave Vertical 1.5 dBi
Windom (OCD) 2.0 dBi


* Source: RSGB EM Field Exposure web site at
https://rsgb.org/main/technical/emc/emf-exposure/
 

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.
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