How do mobile telecommunications work?

In contrast to other technical equipment such as computers or household appliances in which electromagnetic fields (= radiation) arise as an unnecessary by-product, mobile telecommunica-tions deliberately use these fields to transmit messages. Mobile telephones and telecommuni-cations antenna have basically identical functionality: they send and receive high frequency electromagnetic fields and interact with each other. Despite having the same functionality, they expose the user to different levels of radiation.

The aim of this brochure is to point out to users the most important functionality of GSM mobile telecommunications and the effects resulting from the radiation exposure. Through the imparted knowledge it will also be shown how one can easily reduce one’s personal exposure.

© 2009 • Consumer Behavior • ETH Zurich • Content: Marie-Eve Cousin & Michael Siegrist • Design: Sandro Bösch • Translation: David Bowler

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Electromagnetic fields become disproportionately weaker as the distance from their source incre-ases. This means that when the distance to the source of the radiation is doubled, the radiation is

reduced by more than half. This physical fact is of great importance in respect of the radiation exposure caused by mobile telecommunications.

Although a mobile telephone has a much lower output than a telecommuni-cations antenna, it exposes the user to many times more radiation because it is held directly next to the head. Thus in a telephone conversation lasting just a few minutes approximately the same amount of radiation is released as would result from an average 24 hour exposure to an antenna (1 V/m). A further difference is that a mobile telecommunications antenna radiates the

Mobile telephones and telecommunications antenna emit electromagnetic fields

The electric field strength or intensity of the electromagnetic field is specified in Volts per Metre (V/m).

Radiation intensity:When purchasing a mobile telephone make sure that you buy a handset having the lowest possible radiation. The smaller the stated SAR (Specific Absorption Rate) value, the lower is the radiation absorbed by the head during a telephone conversati-on. Low SAR values are less than 0.6 W/kg.

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Distance from the source of the radiation:Use a “hands-free” set (headphone, headset) with a cable or low-power Bluetooth wireless transceiver to increase the distance from the mobile telephone.

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The intensity of the electromagnetic field transmitted by a mobile telecommunications antenna also reduces with increasing distance. In addition the mobile telecommunica-tions antenna beams radiation in a specified direction like a car headlight. Outside this main beam, although electromagnetic waves are present, they are greatly reduced. (The lower the radiation, the lighter the colour in the diagram).

entire body at a comparatively low level over a long period of time whereas the mobile telephone radiates primarily the head and hand with a strong exposure for a short period. When the telephone is not in use, the mobile telephone only transmits a short signal every few minutes to inform the telecommunications antenna of its current location. To summarise, it is first and foremost the use of a mobile telephone that influences the amount of the individual’s radiation exposure, and thus the possibilities of reducing the radiation exposure relate above all to mobile telephone handsets.

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A network of mobile telecommunications base stations (i.e. an antenna or antennas, a supporting transmitter mast and a power source), is necessary in order for one to be able to communicate to or from a mobile telephone. Usually several antenna are attached to a transmitter mast as each antenna can only transmit in a single direction.

A mobile telecommunications antenna does not transmit at the same strength throughout the day but adjusts its transmitting power to the current use or the number of connections. Thus during the night when nobody telephones, the radiation is much less than that in the late afternoon when many telephone calls are made.

One can envisage mobile telecommunications networks as large honey-combs in which a transmitter mast provides the coverage in each cell. However as a telecommunications antenna can only handle a limited number of calls at the same time, the cells can be of different sizes. For example in urban areas where many persons use mobile telephones, the cells are smaller than in rural areas where only a few persons telephone at the

How does the interaction between the mobile telephone and the telecommunications antenna actually work?

The longish antenna provides the contact to the mobile telephone whilst the round antenna ensures contact to the next base station.

Directional antenna

mobile telecommuni-cations antenna

directional antenna

transmitter mast

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The size of the cells can vary from a few hundred metres up to several kilometres according to the utilization density.

same time. In general, mobile telephones and telecommunications antenna operate with lower transmitter strength in mobile telecommunications networks made up of small cells as they only need to bridge shorter distances to each other. Thus it makes sense to locate telecommunications antenna where persons make telephone calls. If mobile telecommunications antenna, like radio or television transmitters, were located far from built-up areas, mobile telephones would need to radiate more strongly in order to set-up a connec-tion. The result would be increased radiation exposure for the users of mobile telephones.

In order to transmit a call or an SMS (text message) a connection between the mobile telephone and the telecommunications antenna must be made. For this purpose both transmit at full power for a short time until they have found each other. As soon as this happens they reduce the emitted

Establishing a connection: As the connection is being established the radiation from the mobile telephone is greatest. After dialling the number do not hold the handset next to the ear but at some distance from the head until the connection has been made. Avoid telephone conversations made whilst you are travelling long distances.

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Radiation exposure when telephoning

When telephoning the transmitting power and thus the radiation exposure is…

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radiation to the minimum necessary. This procedure also takes place on each occasion that a cell change is necessary when telephoning on the move. During a telephone call the radiation transmission strength is additionally influenced by other factors. The distance between the telecommunications antenna and the mobile telephone as well as possible obstacles to the radiation can play a role. Telephone calls made from indoors, in a car or in a train require the mobile telephone and the telecommunications antenna to transmit at a higher power in order to overcome the walls or vehicle body-work. The same can also apply to so-called shielding products which can be attached to or around the mobile telephone. When these impair the quality of the connection (signal), they force the mobile telephone to transmit at a higher power.

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Mobile telecommunications are extremely popular: over 80% of the adult population of Switzerland use this technolo-gy. Yet time and again que-stions are raised as to the influence of mobile telecom-munications radiation on health.

Previous research has shown that radiation can result in a warming of tissues. In order to eliminate such effects as far as possible, exposure limits have been laid down for both base stations and mobile telephones. The construction and operation of mobile telecommunications antenna are governed by laws which ensure compliance with these limits.

In addition it has been discussed whether exposure to mobile telecommuni-cations radiation below these limits can, over a long period of time, have an influence on human health. Until now the studies available are unable to either substantiate or discount this. Some evidence has been found that mobile telephones can influence brain activity and sleep. Whether these changes result in negative consequences for health is currently under research. It is also unclear whether or not mobile telephones increase the risk of developing a brain tumour.

Harmless to health?

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Only telephone when you have a good connection to the mobile telecommunica-tions antenna as the mobile telephone can then transmit at reduced power. You can verify the signal quality by reference to the bars shown on the handset display. Avoid making telephone calls from rooms underground or from inside metal bodywork.

If you do not want to do without your mobile telephone but nevertheless wish to keep your personal radiation exposure as low as possible, we recommend the following simple steps:

• Use a “hands-free“ (headphone, headset) with a cable or a low-power Bluetooth wireless transceiver to reduce the radiation to the head.

• As the connection is being established do not hold the mobile telephone next to your head.

• As far as possible only telephone when a good connection (signal) quality is available.

• Beware of protective and screening products which claim to reduce the radiation exposure as they can reduce the quality of the connection and thus force the telephone to transmit at a higher output power.

• When purchasing a mobile telephone make sure that the stated SAR value is low.

• Make only short telephone calls or, instead, write an SMS (text message).

Key points