Appendix
A.2 Designing and calculating wireless systems (for example RCoax)
SCALANCE W786-xPRO
Operating Instructions, Release 08/2007, C79000-G8976-C221-02
239
System calculation based on the example of RCoax
The calculation of the entire system shows whether communication is possible at the desired
transmission rate using the desired components. All losses (longitudinal attenuation, spatial
attenuation, power splitters etc.) are deducted from the transmit power. An antenna gain is
added. The result is the power fed to a receiver. This power must be higher than the receiver
sensitivity. The calculation can be made with the following formula:
P
e
= P
0
- a
rc
- c
d
- a
ps
+ G
ANT
-
Δ
rc
-
Δ
fr
> P
e min
P
e
Receiver input power in dBm
P
0
Transmit power in dBm
a
rc
Longitudinal attenuation of the RCoax cable and the feeder in dB
c
d
Coupling loss for the distance between RCoax cable and communication
partner
a
ps
Power splitter losses in dB
G
ANT
Antenna gain in dB
Δ
rc
Correction value for the longitudinal attenuation in dB. Depending on the concrete
operating conditions, between 5 and 15 dB.
Δ
fr
Correction value for the spatial attenuation in dB. Depending on the concrete
operating conditions, between 0 and 20 dB.
P
e min
Receiver sensitivity in dBm