RF Safety and Station Evaluation
Amateurs are required to perform a routine evaluation of the strength of the RF fields around their stations, subject to certain exemptions. These and other information can be found on the FCC website as well as the complete text of OET Bulletin Number 65. The exemptions are also part of the Element-3 question pool so any current study guide will have them listed.
While the exemptions are based on your PEP, the FCC regulations base their limits on Average power over a 30 minute period for Uncontrolled Environments and a 6-minute time period for Controlled Environments.
To get you started and to comply with the Form 605 you submitted which certifies that you have evaluated your station and have a copy of the calculations on file.
The first thing you need to do is come up with some measurements of your station, starting with the average power that you will be transmitting. If you run more than one antenna and/or operate on more than one mode (i.e. SSB, CW, RTTY) then you'll want to fill out a sheet for each. Chances are, unless you are running high power, the results will be well within compliance, so just print out the results, file them and go about your business.
Calculating Average Power. You may find the following table which describes the process for finding your average power. Just do the arithmetic.
To estimate your average power, first start with your Peak Envelope Power (PEP) and multiply that by the Duty Factor for the mode you are using, then by the maximum percentage of time you expect to transmit within the averaging period.
For example: If you operate a 1500 Watt PEP SSB phone station that is on for 10 minutes, off for ten minutes, then on for ten minutes you are operating with 200 Watts average power (1500 W (PEP) x 20% x 67% = 200 Watts average power) over a 30 minute time period. If you were operating a 1500 Watt CW station over the same time period, you have 1500W (PEP) x 40% x 67% = 400 Watts average power.
In most cases for the 6-minute controlled environment exposure estimation, you should probably assume that it is possible to operate over the entire 6-minute period so the 1500 Watt PEP SSB Phone station would be 300 Watts average power for controlled exposure calculations.
Now go to the RF Safety Calculator * and input your data. The average power figure you got in the above routine should be entered in the first box.
The 2nd box is the distance to the "area of interest". That is the distance from the center of the antenna (in feet) to the area of interest.
The distance to the area of interest usually will lie in the uncontrolled environment such as a public place or your neighbors back yard.
From the center of the antenna to the ground is the area represents the "Controlled Environment".
The next box asks for the antenna gain. You can get these figures from the manufacturer's data sheet or estimate them. Use 2.2 dB for dipoles and 6 dB for directional antennas. For very high gain far field measurements, use the best information you can find.
The last box, is the frequency of operation. If you plan to operate on 10 or 6 meters use the highest of the frequencies in mHz.
Finally, check the radio button to "Include the effects of ground reflections".
Your evaluation will come back to you immediately. Most likely, unless you are running high power at high duty cycles, you should get a "yes" on both environments and you will be in compliance. If you fail one or both then you will need to adjust the numbers. Raise your antenna, use less gain, or decrease your power and run another calculation.
That's all there is to it. Have fun.
Operating Mode
CW
SSB Phone
eSSB Phone
FM
AM
RTTY / Digital
Duty Factor
100%
100%
100%
40%
30%
20%