2
A05-0473-010
1
1
2
2
d
2 x d
RF Signal Attenuation
In addition to this square law attenuation, signal strengths inside a
building will also vary from place to place owing to destructive and
constructive interference caused by signals arriving with different
phases, resulting from different path lengths
(see Figure 2)
.
The Agile™ 200 Series RF devices have a typical transmission
range in free air of up to 500m, but within an office or factory
environment, signals can come into contact with many objects in
a range of materials such as ceilings, floors and walls at different
angles, desks, filing cabinets and a variety of plant and machinery.
There are numerous opportunities for reflection, refraction and
absorption and all these things will probably reduce the effective
range, even in an open plan environment, to not much more than
about 100m.
Some common building materials are listed in
Table 1
together
with typical energy loss figures which can be expected. A normal
double brick wall, for example, can reduce a signal’s strength
by up to a third or more. All these factors will contribute to the
occurrence in a building of areas of varying signal strengths and
reception characteristics.
Figure 1: Relationship Between Distance and RF-Power
SURFACE AT DISTANCE
2d
SURFACE AT DISTANCE
d
SURFACE MEASURES 1M
2
AT DISTANCE d
SURFACE MEASURES 4M
2
AT DISTANCE 2d
WHEN THE DISTANCE IS DOUBLED, THE FIELD
STRENGTH IS REDUCED BY A FACTOR OF 4
RADIO GATEWAY
Figure 2: Different RF Signal Paths
Table 1: Energy Loss with Different Materials
Designing and installing an RF system in areas with large radio
field absorption, e.g. with metallic lattice partitions, large metal
vessels or with tall metallic storage racks may be very challenging.
Material Type
Energy Loss
Wood and plasterboard
0 – 10%
Solid brick
5 – 35%
Steel reinforced concrete
30 – 90%
Metal plates, under floor heating 90 – 100%