RFX-RMR
Issue 1.0
page 5 of
41
1.1
Health & Safety
Exposure to Non-Ionizing (RF) Radiation/Safe Working Distances
The safe working distance from a transmitting antenna may be calculated from the relationship:
D =
√
P
T
. G
R
4
π
.
w
In which D = safe working distance (meters)
PT = transmitter or combiner power output (watts)
GR = antenna gain ratio = anti log (gain dBi
÷
10)
w = power density (watts/square meter)
The RF power density value is determined by reference to safety guidelines for exposure of the
human body to non-ionizing radiation. It is important to note that the guidelines adopted differ
throughout the world and are from time-to-time re-issued with revised guidelines. For RF Central use,
a maximum power density limit of 1w/m² is to be applied when calculating minimum safe working
distances.
Important Note:
It must be remembered that any transmitting equipment radiating power at
frequencies of 100 kHz and higher, has the potential to produce thermal and athermal effects upon the
human body.
To be safe:
a)
Operators should not stand or walk in front of any antenna, nor should they allow anyone else
to do so.
b)
Operators should not operate any RF transmitter or power amplifier with any of its covers
removed, nor should they allow anyone else to do so.
Worked examples
Antenna
Transmitter Power
Type
Gain (dBi)
Gain Ratio
2W
4W
10W
30W
OMNI
4 2.5
1
1
1.5
2.5
HELIX
20 100 4 5.6
9 15.5
PARABOLIC
DISH
35 3,162
22.5
32
50
87
MINIMUM SAFE DISTANCE (METERS)
