Appendix
A.2 Designing and calculating wireless systems (for example RCoax)
SCALANCE W786-xPRO
Operating Instructions, Release 08/2007, C79000-G8976-C221-02
237
IEC 61196-4
Values for coupling losses according to IEC 61196-4 already include spatial attenuation of 2
m. To calculate the actual coupling loss, a spatial attenuation for the distance of 2 m must be
deducted from this value. The coupling loss for a specified distance between the RCoax
cable and the antenna of the communication partner is therefore calculated according to the
following formula:
c
d
= c
95
- 20 * log(4
π
* 2m /
λ
) + 20 * log(4
π
d /
λ
)
cd Coupling loss of the cable in dB for a specified distance between cable and
antenna.
c
95
c
95
value of the coupling loss (specified in the data sheet of the cable)
λ
Wavelength of the electromagnetic oscillation in m; at a frequency of 2.4 GHz, the
wavelength is 0.125 m.
d Distance between cable and antenna in m.
For a frequency of 2.4 GHz, you can also calculate with the following equation in which you
must specify the distance d in meters:
c
d 2.4 GHz
= c
95
- 46 dB + 20 * log(100 * d)
For a SIEMENS SIMATIC NET IWLAN RCoax Cable PE 1/2'' 2.4 GHz (c
95
= 69 dB at 2.4
GHz), for example, this results in the following coupling losses:
Distance Coupling loss
1 m
63 dB
2 m
69 dB
5 m
77 dB
10 m
83 dB
100 m
103 dB
Note
The formula is valid only for the 2.4 GHz RCoax cable.
Losses due to power splitters
Normally. when a double power splitter is used (one input, two outputs, for example, RCoax
N-Connect Female Power Splitter 2-Way) a loss of 3 dB must be taken into account.
Receiver sensitivity
The receiver sensitivity is the minimum power that must be fed to a receiver to allow
communication to take place. The receiver sensitivity is a device-specific property and
depends on the transmission technique and data rate. The information in the following tables
applies to the following SIMATIC NET products:
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Access Point SCALANCE W786-1PRO
