Radio transmitters operate at different frequencies and powers depending on their application. Broadcast AM and FM radio and TV transmitters operate at comparatively high powers (several thousands of watts). Mobile phone base stations operate at moderate to low power. Microwave systems used for point to point communications and mobile phones operate at low power.
Source: Health Protection Agency (UK)
As the chart shows, there are many radio sources in the community and exposures from mobile communications are comparable to broadcast radio and TV. The WHO says that recent surveys show that the RF exposures from base stations typically range from 0.002% to 2% of the levels of international exposure guidelines. It is only in areas close to the antennas that the recommended limits may be exceeded. The network operator will take steps to prevent public access to these areas by placing the antennas near the top of the mast or high on a building.
The strength of the radio signals is greatest near the source and reduces rapidly with distance. Typical exposures in publicly accessible areas are usually thousands of times below international guidelines. As the radio signals are directed outwards from the antennas, exposures directly below the antennas are typically very low.
Some non-scientific policies have been proposed, such as distance based exclusions zones around community facilities, such as schools, hospitals or childcare facilities. As the chart above shows, distance from a base station is not an accurate estimate of exposure at ground level. The European Commission has said of such policies:
‘The distance between a residential area and an antenna is not a proper indicator of its effect on the overall exposure of the public and scientific evidence does not support the assumption according to which an antenna within 300 metres would have adverse effects on public health. As long as factual exposure remains below the recommended levels, the health of the citizens is to our best knowledge well protected.’
The UK NRPB (now Health Protection Agency) also states:
‘…there is no scientific basis for establishing minimal distances between base stations and areas of public occupancy, as has been suggested in some countries. There are many sources of exposure to RF fields, and it would in practice have little impact on people’s overall exposure.’
0 Comments