User's Manual | ACOM 2020S | 1.8-54 MHz Linear Power Amplifier
June 2022
S e c t i o n SPECIFICATIONS | Page 65 of 76
c)
RF Exposure Information
This unit (ACOM 2020S amplifier) complies with the FCC RF Exposure limits for an
uncontrolled environment.
To comply with FCC RF exposure limit requirements, antennas must be operated at a
minimum distance of 818.24 cm or 26.85 feet between the radiator and any person's
body!
Table 8-1 | RF exposure distance chart
is a calculation of distances in
meters
for several different antenna
gains using the guidance in the bulletin. To calculate the distances in feet, please. multiply the distance in
meters by 3.28.
CFR Title 47 Part 97.13(C) (as of Apr. 1, 2020) requires the amateur operator to be in compliance with the
radio frequency exposure requirements.
The
Table 8-2 | Different antenna gain chart
is a representation of some commonly used antenna gains. This
will give you a rough estimation of the safe distance needed from the antenna in the direction of maximum
gain. The chart is worst-case conditions of a continuous carrier for the full time allowed for exposure. The
charts do not take into account the antenna patterns or elevation above the ground. In practice, most
antennas have the maximum gain elevated above the ground. For a better estimate, the actual antenna
would need to be analyzed for direction of maximum gain and gain in the direction of interest.
Controlled environments
apply where people are aware of their exposure and have the ability and
knowledge to control it. Greater MPE levels are permitted in controlled areas.
A good rule of thumb is that the controlled exposure limit can be applied to those areas in which you can
control access. An example of this is your fenced-in backyard. Your own household can also be a controlled
environment if your family or guests have been given instruction about RF exposure and safety.
The uncontrolled environment
applies to areas where people would not normally know they are being
exposed. This includes "public" areas such as your property line or a neighboring apartment.
The actual exposure level is time and power averaged which will usually reduce the total exposure.
For example, the average SSB power is around 20% (if not heavily compressed) of the peak power and will
be averaged for the time of the actual transmission.
For CW the power will be 100% but the transmitter will be transmitting for only about 40% of the total
time. RTTY, FT-8 (also other digital modes), AM and FM, will be 100% duty cycle and last for the length of
the transmission.
These calculations are for the direction of maximum gain. The FCC Office of Engineering and Technology
(OET) Bulletin 65 Supplement B has more information on meeting the requirements.
For details, please, see:
https://www.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65.pdf
https://www.fcc.gov/bureaus/oet/info/documents/bulletins/oet65/oet65b.pdf