RF Exposure Limits

Subject: RF Radiation Limit Calculations

I assumed the following things in the calculations:

1) The radiating structure has a gain of 0 dB, and is non-directional
in design.

2) The equipment is being modulated 100%. That is, the RF carrier is
turned completely off on the negative portion of the modulation
cycle, and reaches full power during the positive portion of the
modulation cycle. This causes the AVERAGE power level to be 50% of
the PEAK power level. (Note that according to FCC regulations, these
calculations require the use of the average RF power level.)

3) The modulating signal is a symmetrical square wave.

4) The equipment is radiating into the air 10 watts of average RF power
from the tube and connecting wires. (This represents a radiation
loss of 10% for a system with an output of 100 watts average
power, 200 watts peak power. (I think this is pretty much a
worst-case scenario; I would expect between 1 and 3% to be radiated
at most, if the unit is well constructed.)

5) 100% of the RF energy hitting the ground is reflected back towards
the subject, and so adds to the total RF energy absorbed. (In most
cases, this is an over estimation. A large part of the RF will
generally be absorbed rather than reflected because the ground is
not a perfect conductor, and surrounding objects may affect the
reflection and absorption of the RF energy.)

6) The RF carrier frequency is 27.120 mHz, +/- 163 kHz. (ISM band)


Further;

According to the current FCC rules, a Controlled Environment is
considered to be the case when the person(s) being exposed to the RF
signal have full knowledge of the exposure and may control whether or
not they wish to stay within the RF field.

This category includes the operator of the RF generating equipment,
and the person(s) who willingly expose themselves to the radiated
energy.

And;

According to the current FCC rules, an Uncontrolled Environment is
considered to be the case when the person(s) being exposed to the RF
signal do NOT have have full knowledge of the exposure and/or are NOT
able to control whether or not they wish to stay within the RF field.

This category includes the general public.


Results:

The calculations show that for the values given above, the closest
distance that a person should approach the tube during operation is:

Controlled Environment = 1.39 feet
Uncontrolled Environment = 3.04 feet

Note that these distances considered to be the safe (government
approved) distances for continuous exposures i.e., 24 hours a day.


In conclusion, it is apparent from these calculations that a properly
constructed and operated Rife/Bare system should be safe for both the
operator and general public under almost any circumstances.

Ralph Hartwell W5JGV

Member, Society of Broadcast Engineers