PART7 RF WAVES

11.11.2009

ANNEX -

occasionally and transmit RF only when the device is communicating. Moreover, some devices such

as mobile phones automatically decrease output power if possible i.e., in

areas where reception is good. Hence, typical exposure from these devices is lower than the theoretical

maximum; 0.1-0.5 and <0.01 of maximum values for GSM and 3G, respectively. Exposure

caused by small-range devices (e.g., cordless DECT phones, Bluetooth devices etc.) is typically only

a few percent of exposure limits.

Exposure to RF caused by a small-size low power transmitter generally decreases rapidly with increasing

distance from the source. A 30 cm gap between the receiving body and the transmitter typically

decreases exposure by a factor 100 when compared to direct contact exposure. Therefore, exposure

concerns mainly the user of the device. The individual exposure from such sources is reduced by

increasing the distance between user and device. This can be easily done by e.g., using hands-free for

voice calls and/or placing baby monitors, WLAN terminals etc such that they are not touching the

individual.

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2.2. Fixed transmitters

Numerous technologies utilise fixed RF transmitters. Signals from WLAN, WiMAX and mobile

phone networks are transmitted by base stations, while TV and voice radio broadcasts are sent via

fixed transmitter antennas in high masts. Transmission powers in these devices range from milliwatt

(mW) to kilowatts (kW).

The antennas transmitting at the highest power levels (kilowatt-range) are the mast-mounted TV and

VHF voice radio transmitters. Power densities measured at ground level are low, however, since the

antennas are mounted 100–300 m above ground. The main RF transmission beam is targeted towards

the horizon; hence virtually all the RF power surpass people living in the vicinity of the mast (see

Fig. 1). Measurements performed around typical broadcasting masts have shown that the field

strengths depend more on the terrain (by factor 1000) than on the distance from the source. The highest

measured values in a normal living environment have been approximately 0.1 mW/m

to measurements in the Nordic countries, though more typical values are between 0.0001 –

0.001 mW/m

due to a lower transmission power being necessary for a single TV program. However, the

number of TV channels will increase and presumably all former frequencies of analogous TV will be

utilised again for digital broadcasts at some time in the future leading to background RF fields being

in the same order of magnitude as before the digitalisation.

2, according2. The introduction of digital TV broadcasting appears to have decreased overall exposure,

Fig.1. Radiowaves from mast-mounted antennas surpasses the people living in the vicinity of the

mast.