FAQs - Transmitters and Base Stations
People living near transmitters have no choice in the matter and there is growing opposition to mast siting. Why is this, if the technology is safe?
The reasons for public concern about transmitter siting are complex and embrace both health issues and environmental concerns such as visual amenity and consequent concerns about potential effects on property prices.
Such concerns are often exacerbated by sensational media coverage and by the pronouncements of some theorists who claim to be experts. In addition, no-one likes dealing with uncertainty, and people often ask for categorical assurances of absolute safety, which, for good reason, cannot be given.
Why are so many transmitters needed?
A TETRA system for the emergency services has to provide coverage everywhere it is needed as well as adequate capacity. It is not acceptable to the emergency services to have gaps where professional users are unable to communicate. By comparison, mobile telephony networks cater for average capacity and it is not uncommon to find areas where there is no coverage.
TETRA also allows multiple professional users on a single network. This means that the network can be shared by emergency services such as the police, ambulance and fire and rescue, all of whom have signed up to use the TETRA-based service in the UK. This provides a considerable environmental advantage over three or more separate networks even though a few additional transmitters may need to be added to accommodate the coverage needs of new user communities.
The TETRA base stations are also low powered, compared with, for example, those used for radio and TV transmission. Each TETRA base station is not just transmitting, as a radio or TV transmitter would be, but has to handle both-way communication with around 16 different handsets.
The more base stations there are, the lower the power of each one needs to be, as the ability of radio signals to travel is dependent on distance and terrain.
How is the decision made on where to site TETRA transmitters?
Radio network planning is very similar to planning lighting. To avoid shadows or dark areas you need to plan the locations of the lights carefully. Similarly, when planning a radio network, the locations of the base stations and antenna need to be planned carefully to avoid places where there is patchy, unreliable, or non-existent communication.
For any radio system the strength of the signal diminishes rapidly as distance from the transmitter increases and many factors affect the distance that radio waves can travel; for example the distance is reduced by obstacles such as trees, hills or buildings.
It is not acceptable to the emergency services to have places where there is no coverage. So TETRA base stations are placed where emergency services users need to communicate, and are sited to provide seamless coverage. Siting also depends on the willingness of a landowner or building freeholder to accommodate a transmitter.
Why does the industry take no notice of people living near proposed transmitter sites?
As with the siting of any telecommunications equipment, the siting of TETRA transmitters always complies fully with planning requirements, including certification of ICNIRP compliance and consultation with those immediately affected by a planning application.
The planning regime was not designed to encompass effective and timely communication with the community at large and there is a broad range of interested stakeholders – mobile operators, site owners, local authorities, users of mobile services and members of the public. With that in mind, companies in the wireless industry signed up to a Code of Practice following the Stewart Inquiry. This provides for earlier and more transparent communications with a wider range of community interests when considering siting.
While it is rarely possible to please everyone, through improved communication and consultation, the industry is attempting to strike a better balance of interests. Where possible, network operators share existing masts to avoid the need to erect new ones, and attempt to site transmitters sensitively. In open rural areas and National Parks transmitters can sometimes be disguised as trees or concealed in barns or in steeples.
Do TETRA transmitters (base stations) pulse?
The simple answer is that although handsets do pulse, transmitters don’t. TETRA base stations emit a continuous signal. Base station transmitter is in contact with four handsets and is using all four of its available time slots to transmit continuously. If there is no need to transmit or receive data during one of those time slots a dummy transmission is slotted in. There is some quiet time occurring after most slots, when the RF signal is not ‘jumping up and down’ sending digitized information. This is the frequency control channel which sends out a pure signal to enable the handset to tune to it. The power output during that period is around the average emitted power and it does not drop to zero. Mathematical analysis of the signal (called Fourier analysis) shows that within experimental error or 1% TETRA base stations do not pulse.
A statement to this effect was included in the January 2004 AGNIR report, which referred back to the comprehensive report published by AGNIR in 2001. That report stated “It is notable that the signals from TETRA base stations are not pulsed whereas those from mobile terminals and repeaters are” and “The measurements confirm that, to within the limitations of the measurement technique (less than 1%), TETRA base station signals are continuous and not pulsed over time intervals that could cause amplitude and therefore power modulation at frequencies between 1 and 200Hz." Further information is available via the Radiation page of the Public Health England's web site - click here.
How much power do base stations emit?
TETRA base station equipment is low powered and typically operates at tiny fractions of the emission levels allowed by the safety standards and all sites are designed to be safe and tested for compliance when the equipment is installed. Many measurements have been made, both in the laboratory and in situ, of the RF field strength around TETRA transmitters. The level of RF falls away rapidly with distance from the transmitter and the intensity at ground level is very small - 10m away at ground level it is 1000 times below the ICNIRP standard, at 50m away it is 1300 times below, at 100m away (the levels are higher here as this is where a down-tilted beam would hit the ground) it is 365 times below, and at 300m it is 3500 times below the safety standard.
Is it safe to work or live in a building with a TETRA base station on the roof?
Yes it is. The exposure to RF for occupants of buildings is very small. Hardly any signal goes directly downwards into the building and what little does would be generally absorbed by the roof.
If someone climbed onto a roof that housed a base station they would find a clearly labelled exclusion zone with a physical barrier, within which the RF could exceed guideline levels and be hazardous. The maintenance engineers responsible for the base station would switch off the base station before entering this zone.
What are the implications of the Control of Electromagnetic Fields at Work Regulations 2016 (“the CEMFAW Regulations”)?
Employers have a duty to take reasonable steps to prevent harm in the workplace and this duty includes considering any risks arising from exposure to electromagnetic fields (EMFs).
Employers’ duties under the CEMFAW Regulations, which came into force on 1st July 2016, are explained in a guide issued by the Health and Safety Executive (HSG281). This guide may be viewed here and the Regulations themselves, Statutory Instrument 2016 No. 588, may be viewed here.