Amateurs are required to perform a routine evaluation of the strength of
the RF fields around their stations, subject to certain exemptions based on
peak envelope power (PEP) levels at the various amateur bands. However,
the FCC regulations on permissible RF exposure are not based on peak envelope
power (PEP), but on average power over a 30 minute time period for
uncontrolled environments, or a 6 minute time period for controlled
environments. The part of the regulations that determine whether a station
operator must perform a periodic evaluation, however, is based on PEP.
Operating Mode 
Duty Factor 
Morse code (CW)

40%

SSB phone

20%

FM

100%

RTTY/Digital

100%

AM

100%


To estimate your average power, first start with your Peak Envelope Power
(PEP). Multiply that by the duty factor for the mode you
are using, then by the maximum percentage of time you expect to operate within
the averaging period.
For example, if you operate a 1500 watt PEP SSB phone station that is on
for 10 minutes, off for 10 minutes and on for 10 minutes, you are operating
with 200 watts average power (1500 watts PEP * 20% * 67% = 200 watts average
power) over a 30 minute period. If you operate a 1500 watt Morse Code (CW)
station over the same time period, you have 1500 watts PEP * 40% * 67%, or
400 watts average power.
In most cases for the 6 minute controlled environment
exposure estimate, 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 controlledexposure calculations. An RTTY or
digital bulletin station, or FM repeater transmitter, would probably be on for
the full 30 minute time period, so the RTTY bulletin station or FM repeater
would be 1500 watts average power. If it operated 10 minutes on, 10 minutes
off and 10 minutes on, it would have 1000 watts average power over 30 minutes.
