Maximum Permissible RF Exposure

By now you should all be aware that the FCC (since January 1, 1998) now requires us to perform an RF evaluation on our stations to determine if they comply with the Maximum Permissible Exposure regulations. Exposure comes in two flavors. What you do to yourself and the inhabitants of your own house, and what you do to your neighbors. The FCC calls these the controlled and uncontrolled environments.

The FCC document that defines the investigation you need to perform, is known as OET-65B. It can be found at the FCC web site, http://www.fcc.gov/oet/rfsafety/ which contains a list of OET bulletins, or the document itself is found on the download page at http://www.fcc.gov/oet/info/documents/bulletins/#65. The documents themselves are only available in Word Perfect 5.1 or Adobe PDF (portable doc format) formats.

The gist of OET 65-B is that you are exempt from further investigation if the RF power into your antenna is below the level determined to exceed the MPE.

Power Thresholds for Routine Evaluation
of Amateur Radio Stations
Wavelength Band	Evaluation Required if Power* (watts) Exceeds:
MF
160 m	500
HF
80 m	500
75 m	500
40 m	500
30 m	425
20 m	225
17 m	125
15 m	100
12 m	75
10 m	50
VHF (all bands)	50
UHF
70 cm	70
33 cm	150
23 cm	200
13 cm	250
SHF (all bands)	250
EHF (all bands)	250

Note that into your antenna is not what comes out of your rig, it's always less because of losses and even mode of transmission employed! If your radio specification says it's a 40 watt PEP 2m rig, you don't need to go any further with this. If, however, it says it's a 50 watt PEP 2m rig, you do need to at least get through page 1 of the suggested form that's included at the end of OET 65-B. With certainty your station will comply even if it is at the threshold level listed because you are bound to have some feed line loss. However small that is, the RF input to your antenna has to be less than 50 watts. You just declare it on page 1 of the form and now your done!

You need to do a separate form for each band you use. You may need to do multiple forms for each band if you have more than one antenna or rig or amplifier on that band.

To be absolutely safe and certain that you comply with the current law on the FCC's books, FARA strongly recommends that you at least fill in page 1 of the MPE form regardless of what power you are running at home. Mobile installations are tacitly exempt, but it might make you feel better if you had a page 1 of the form for your mobile installation tucked away somewhere just in case somebody starts to "wonder".