- How Base Stations Operate
- Mobile Phone Base Stations and Safety
- Radiofrequency in the Environment
- How do Base Stations compare to other sources of RF EME?
- Where Base Stations are Located
- Safety Standards for Base Stations
- Telstra's Compliance with Safety Standards
- Independent Testing of Base Stations
How Base Stations Operate
A mobile communications network is made up of a patchwork of cells, each relying on its own base station. Each base station provides coverage to a small local area, or "cell". When you make a call, your mobile phone will always "talk" to the nearest base station antennas to you. As you move around, the phone will "talk" to different base stations, which ever is the closest, or the least congested.
Each base station can only handle a finite number of calls at any one time - typically fewer than 100 simultaneous calls. When a base station is congested with calls, a mobile phone will try to communicate with the surrounding base stations if they are close enough to maintain a signal.
This is referred to as network capacity. In order to provide reliable, continuous network coverage, which is the basic expectation of our customers and of any mobile phone user, we need to install many low-powered antennas across the city to pick up phone signals.
Insufficient network capacity in areas of high call demand can cause poor service. Other factors that can affect network performance include:
- being too far away from antennas to pick up a phone signal
- large objects such as hills, tall buildings or even trees blocking network signals,
- the network's depth of coverage - or the ability to make calls inside buildings.
Mobile Phone Base Stations and Safety
The World Health Organization (WHO) states that the research has found no adverse health effects from the weak RF signals emitted by mobile network base stations.
"From all evidence accumulated so far, no adverse short- or long-term health effects have been shown to occur from the RF signals produced by base stations... Considering the very low exposure levels and research results collected to date, there is no convincing scientific evidence that the weak RF signals from base stations and wireless networks cause adverse health effects."
WHO Fact Sheet: Electromagnetic fields and public health - base stations and wireless technologies, 2006
Radiofrequency in the Environment
Mobile network base stations emit radiofrequency electromagnetic energy (EME) as "radio waves". Other radio wave signals transmitted by communications facilities include TV signals, AM and FM radio signals, taxi service signals, paging network signals, emergency service communications, police two-way radio and cordless phones.
Radiofrequency EME is something we've been living with for generations - literally since the invention of "the wireless".
Source http://www.emfexplained.info/?ID=25186
This picture shows the typical power of the radio services in the community when transmitting
How do Base Stations compare to other sources of RF EME?
Mobile network base stations contribute a very small fraction of radiofrequency energy in the environment, because the transceivers themselves are extremely low powered, and provide coverage to relatively small areas (typically several kilometres).
Telstra's antennas typically require about 50 Watts of power to operate - less than many household light globes. By comparison, a commercial AM radio transmitter requires 100,000 Watts of power to operate.
Independent testing of radiofrequency EME levels in the environment has repeatedly found that mobile network base stations contribute very little radiofrequency EME, often much less than other sources such as radio and television broadcast signals.
Below are the results of independent tests completed in 2006 at Geelong in Victoria and Caloundra in Queensland. The pie chart shows a break down in percentage (%) of the radio frequency EME levels measured at Richmond Oval in Geelong as part of the environmental EME testing. Radio frequency EME (at 57%) from AM radio stations was the most dominant signal measured.
(click for larger image)
Geelong EME Survey pie chart showing the % of radio
signal levels measured at Richmond Oval in Geelong
(click for larger image)
(click for larger image)
Point Cartwright EME Survey pie chart (above) and spectrum plot showing the of radio signal levels measured at Point Cartwright in Caloundra QLD
These local test results are in keeping with the advice of public health authorities on how mobile network base stations compare to other sources of radiofrequency EME in the environment.
The WHO advises:
"Until mobile phones became widely used, members of the public were mainly exposed to radiofrequency emissions from radio and TV stations. Even today, the phone towers themselves add little to our total exposure, as signal strengths in places of public access are normally similar to or lower than those from distant radio and TV stations."
WHO website fact sheet: What are electromagnetic fields - typical exposure levels at home and in the environment, 2007
The Australian Communications and Media Authority (ACMA) also puts mobile network base stations into perspective with common sources of radiofrequency energy:
"The EME emission levels produced by 3G transmitters are considered low, with an average radiated power of around 3 watts. This is significantly lower than the power levels of some other common types of transmitters, such as two-way radios used by taxis and emergency services."
ACMA Website Consumer Fact Sheet: Electromagnetic Energy and 3G Phones, 2007
Where Base Stations are Located
Base Stations are located in a patchwork of cells across the metropolitan and regional areas of Australia. They are located close to mobile phone users to ensure that users can rely on high quality, continuous coverage. There are currently more than 16,000 mobile network base stations in Australia.
The number of base stations required to provide network coverage to an area is greatly affected by the number of users in that area.
In dense urban areas such as a city central business district, small micro-cell antennas can be located only hundreds of metres apart to ensure that there is enough network capacity to cater for the large number of people making calls on their mobiles at any one time. In suburban settings, antennas are typically several kilometres apart, and in regional areas they can be as much as 30 kilometres apart.
Some commercial buildings such as shopping centres and office blocks are also fitted with small "in-building" base stations that provide coverage to specifically that building.
Base stations can be found in just about every urban setting. They are located on apartment buildings, commercial buildings and industrial estates, on existing utility structures such as light poles and high voltage electricity towers, on hospitals, university campuses, shopping centres and corner stores, at clubs and sports complexes, and in local parks.
Base Station located on apartment building rooftop lift motor room. Antennas are
mounted behind colour matched screening
Microcell base station mounted on street light pole
Base station located on suburban street to visually blend with street scape
Base station antennas located in a church's cross structure
Base station and outdoor equipment cabinet located on a main road.
Telstra tries hard to strike a balance between providing services that we know people use every day and finding good local solutions for our equipment. No mobile network can provide reliable, continuous coverage across the metropolitan area and at all times avoid residential areas.
However, Telstra always endeavours to locate antennas in industrial or built-up commercial areas wherever possible. Telstra also seeks to co-locate antennas on existing telecommunications poles to minimise the impact and disturbance of our infrastructure as best as we can.
Safety Standards for Base Stations
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has adopted the radiofrequency safety standard recommended by the World Health Organization (WHO).
The safety standards are developed using all available scientific literature and are designed to offer protection against identified health effects of EME with a large in-built safety margin.
Radiofrequency transmitters, including mobile network base stations and commercial radio and TV broadcast towers, are regulated for their environmental EME levels. Specifically, regulations are in place to limit the strength or level of the radiofrequency signals in the environment from all radio transmitters including Telstra's mobile network base stations. They are not based on distance, or creating "exclusion zones" for residential or other sensitive areas.
That is why from a public health perspective telecommunications facilities are permissible in any environment, including on apartment buildings and hospitals, and even within schools grounds.
The safety standard limits the network signal strength to a level low enough to protect all people, in all environments, 24-hours a day. The safety limit itself, recommended by the WHO, has a significant safety margin, or precautionary approach built into it.
The concept of "exclusion zones" for schools and residential areas is not supported by the WHO or ARPANSA as an effective precautionary measure to reduce the general public's exposure to radiofrequency EME. ARPANSA advises that exclusions zones do not provide precautionary protection to the community:
"It is important to note that exclusion zones would not necessarily reflect a precautionary approach, for example, a base station sited further from a school may need to operate at a higher power level in order to operate effectively and this could result in higher exposures at the school."
ARPANSA Fact Sheet for NSW Parents & Citizens Association, 2003
Telstra's Compliance with Safety Standards
Telstra and all other mobile network carriers in Australia must demonstrate that they comply with national RF EME safety limits when proposing a new base station.
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) created a compliance report that all carriers must produce for each proposed new base station. These reports are publicly available on the Radio Frequency National Site Archive.
The compliance report predicts the maximum signal strength from the proposed facility - assuming that it is handling the maximum number of phone calls possible 24-hours a day. The maximum power of the proposed base station is presented as a percentage of the standard.
In reality, mobile base stations are designed to operate at the lowest possible power - lower than the maximum capacity demonstrated in the compliance report. Once a call has been established, the base station and handset reduce their power automatically to the lowest level required to maintain a connection.
However, ARPANSA requires all network carriers to show the maximum signal strength of a proposed new facility to give the community peace of mind about the greatest possible impact that the antennas could have on the environment.
Operating at their maximum capacity, the signal strength transmitted by Telstra's network antennas is typically less than 1 per cent of the power we are permitted to transmit in any environment 24-hours a day, 7-days a week.
In other words, Telstra's network facilities operate at power levels that are typically thousands of times below national public health and safety limits, which have been recommended by the World Health Organization (WHO).
Independent Testing of Base Stations
Telstra has commissioned independent surveys of the cumulative RF EME in the environment from all sources, including AM and FM radio, TV broadcast signals, emergency service signals and mobile network base stations.
The survey results are in keeping with the World Health Organization (WHO) advice. Namely that cumulative RF EME levels found in the environment are very low and significantly below international safety guidelines.
Magnified view of the environmental EME levels measured at Richmond Oval in Geelong on 24th Oct 06 showing a comparison to the ARPANSA general public EME safety standard. 100 per cent is the general public maximum exposure limit on a continuous basis.
The measured levels in this example are well below 1 per cent of the exposure
limit.
The low power levels of Telstra's base stations are not unusual for
mobile networks. The WHO advises that independent testing of mobile network base
stations around the world has found that they operate at very low power levels.
"Recent surveys have indicated that RF exposures from base stations and wireless technologies in publicly accessible areas (including schools and hospitals) are normally thousands of times below international standards."
WHO Fact Sheet: Electromagnetic fields and public health - base stations and wireless technologies, 2006
The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has also conducted a spot-audit of base stations throughout Australia and published the results of its testing in June 2000. ARPANSA describes the radiofrequency EME levels found near base stations it tested as "extremely low".
"The highest daily average level, taking into account the measurements from all sites we surveyed, was ten thousand times lower than the ACA [now ACMA] limit. Even the highest daily average level recorded for one of the sites was still three thousand times lower than the limit... It was interesting to note that the levels of radiofrequency radiation from AM and FM radio or television were significantly higher than those from the base stations."
ARPANSA Media Release, Low Emissions from Mobile Phone Towers, 2000
The results of the ARPANSA survey are published on their website.
