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PHOENIX CONTACT 105542_en_05
General formula: free space attenuation [dB] = 32.4 + 20 x log(f) + 20 x log(d)
Formula for 2.4 GHz: free space attenuation [dB] = 100 + 20 x log(d)
Formula for 868 MHz: free space attenuation [dB] = 91.17 + 20 x log(d)
f = transmission frequency in MHz
d = distance between the antennas in km
The free space attenuation is later included in the system calculation (see Section “Equiva-
lent isotropically radiated power (EIRP)” on page 147).
9000 m - -110.3 dB
10 km - -111.2 dB
11 km - -112 dB
12 km - -112.8 dB
13 km - -113.4 dB
14 km - -114.1 dB
15 km - -114.7 dB
16 km - -115.3 dB
17 km - -115.8 dB
18 km - -116.3 dB
19 km - -116.7 dB
20 km - -117.2 dB
21 km - -117.6 dB
22 km - -118.1 dB
23 km - -118.5 dB
24 km - -118.8 dB
25 km - -119.2 dB
Table 8-6 Free space attenuation
Distance [...] Attenuation at 2.4 GHz [...] Attenuation at 868 MHz [...]