From SwissExperiment

Contents 1 Legally transmittable WiFi signals 1.1 Path Loss 1.2 EIRP (Equivalent Isotropically Radiated Power) 1.3 Calculations for SwissEx equipment

Legally transmittable WiFi signals

The limitations for WiFi transmission in Switzerland are governed by BAKOM. The details can be found in their RLAN factsheet.

For the units currently used by SwissEx, we are using 27dBi antennae at 5.7GHz and 16dBi or 24dBi antennae at 2.4GHz.

Bakom governs that at 2.4GHz, the maximum transmitted radiation (EIRP max) at (approx!) 15cm from the antenna must not exceed 100mW and at 5.8GHz, must not exceed 1000mW (but must use radio link quality control adaptation). No compensation is allowed for directional antennae.

Path Loss

Path loss is governed by the spherical spreading loss formula: L=20log(4 pi d/lambda)

where d is distance from the antenna and lambda is the wavelength.

At 0.15m, this loss is:

• 31dB @ 5.7GHz
• 29.4dB @ 2.4GHz

EIRP (Equivalent Isotropically Radiated Power)

EIRP is defined as:

EIRP = P_TR - L_c + G_a

where P_TR is the transmitted power ratio, L_c is any system losses (e.g. cables) plus the path loss and G_a is the antenna gain.
EIRP and power ratio are in dBm, losses are in dB and antenna gain is in dBi.

P_R=10 log (1000P_W) =10 log P_W + 30

where P_W is the Power in Watts.
1000mW=30dBm
100mW=20dBm

Calculations for SwissEx equipment

Taking cable losses to be approx. 4dB over 0.5m of high quality cable, we can calculate the maximum allowed transmission power P_T:
5.7GHz, 27dBi antenna:
30 = P_TR - 4 - 31 + 27
P_TR=38dBm
P_T=6.3W

2.4GHz, 16dBi antenna:
30 = P_TR - 4 - 29.4 + 16
P_TR=37.4dBm
P_T=5.5W

2.4GHz, 24dBi antenna:
30 = P_TR - 4 - 29.4 + 24
P_TR=29.4dBm
P_T=871mW

All of the hardware used in SwissEx has a maximum transmission power of 200mW, so the transmissions are well within the legal limits.