Appendix
Operating Instructions SCALANCE W78x
C79000-G8976-C184-07
265
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(4π * 2m / λ) + 20 * log(4πd / λ)
c
d
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:
UDistanceU UCoupling lossU
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.
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