Project engineering
27
Building Technologies
009865_b_en_--.doc
Fire Safety & Security Systems
11.2007
6.2 Transmission
field
In free environmental conditions, the field strenght decreases by 1/r²; i.e. with
double distance the attenuation increases by 6 dB. In buildings this factor is, as a
first approximation, 1/r
5
, i.e. with double distance the attenuation increases by
approx. 16 to 17 dB.
The following table shows the correlation between the distance and attenuation in
case of intervisibility in the building.
Distance [m]
40
30 25 20 15 10 5
Attenuation [dB] 90
83 79 74 67 57 40
Maximum values: Distance 40 m / Attenuation 90 dB
Table for the conversion to linear values
Attenuation factor
1 4 10 50 100
1000
Attenuation [dB]
0 6 10 17 20 30
The transmission field in the building is influenced by walls or obstacles. To be able to make a
statement on the attenuation, construction elements such as walls, ceilings, etc. must be exactly
analysed.
Fig. 8
Radio attenuation when penetrating obstacles
