Base Stations and Masts Base Stations and Masts What Is A Mast? Radio base stations are commonly called masts. The terms are used interchangeably, but they are in fact two different things. A mast is a freestanding structure (the same as a telegraph pole) which supports antennas at a height where they can transmit and receive radio waves. A mast is typically 15m high and plays no part in the transmission of radio waves. To minimise the environmental impact, more slim line versions with smaller head frames are now in place. These can be painted to blend in with their surroundings, disguised as trees or used in conjunction with street lighting. Radio base stations are sites that enable mobile phones to work. They can be big or small and have transmitters and receivers in a cabin or cabinet connected to antennas. They can be mounted on a large mast or tower, an existing building, rooftops or street furniture such as street lamps. Without base stations, mobiles will not work. There were approximately 52,500 base station sites in the UK. How It All Works A mobile phone is a low-powered two-way radio - converting human voice and data messages into radio waves.

When making a call, these radio signals are transmitted from the mobile phone to the nearest base station. Once a signal reaches a base station it is then transmitted to the main telephone network where it is transferred to the network of the person receiving the call. What Is A Cell? In order to enable millions of people across the country to make calls, each of the five mobile phone operators divides the UK into thousands of individual geographic areas known as 'cells'. At the heart of each cell is a base station. The cells overlap at the edges to prevent holes in coverage. If the radio base stations are too far apart, calls cannot be handed over from one area to another and are interrupted or 'dropped' when mobile users are on the move. There are three types of cells: macrocells, microcells and picocells. A macrocell provides the main coverage in a mobile network. The antennas for macrocells are mounted on ground-based masts, rooftops and other existing structures. They must be positioned at a height that is not obstructed by surrounding buildings and terrain. Macrocell base stations have a typical power output of tens of watts. Microcellsprovide infill radio coverage and additional capacity where there are high numbers of users within macrocells.

The antennas for microcells are mounted at street level, typically on the external walls of existing structures, lamp posts and other street furniture. The antennas are smaller than macro cell antennas and, when mounted on existing structures, often blend in with building features to minimise visual impact. Typically, microcells provide radio coverage across smaller distances and are placed 300m-1000m apart. They have lower outputs than macrocells, usually a few watts. A picocell provides more localised coverage than a microcell. They are normally found inside buildings where coverage is poor or where there are a high number of users, such as airport terminals, train stations or shopping centres. The size of a cell depends on: current and future customer call use because each base station can only support a limited number of calls simultaneously the physical terrain of an area as radio signals are blocked by man-made and natural obstacles such as buildings, trees and hills the frequency band in which the network operates can affect cell size - normally the higher the radio frequency (as in 3G technology) the smaller the cell The cells in the third generation (3G) network are smaller because 3G uses a higher radio frequency.

These cells also expand and contract in size depending on the number of simultaneous calls being made. For this reason, 3G cells have to overlap more than 2G cells. Expanding The Mobile Network More base stations were built to enhance the infrastructure for 2G and 3G mobile phone networks; operators are using the existing base station network as far as possible for 4G antennas, although some additional sites will be needed in rural areas. New base stations are required as each cell can only support a finite number of mobile phone calls at any one time. If there is a high customer demand in a cell, greater capacity is needed to enable more calls to be made. This can be done by placing another mast in between the existing cells and creating additional smaller cells. 3G networks use smaller cells because they have to support the transmission of large amounts of information and operate at a higher frequency. 3G cells also expand and contract in size depending on the number of simultaneous calls being made. For this reason, 3G cells overlap more than 2G cells. 4G networks operate on 800MHz, 1800MHz and 2600MHz.

Site Sharing Site sharing is when two or more mobile phone operators agree to put their base station antennas on the same structure, such as water tower or roof-top. Mast sharing is when the antennas are put on the same mast. Operators try to share sites whenever possible. However, it is not always a viable option. Shared masts are normally taller and have more impact on the environment because they have to accommodate two or more sets of antennas. The more antennas that are clustered together, the higher the overall radio frequency emissions are likely to be. Further, the radio frequencies that different mobile network operators use are not always compatible and could interfere with existing antennas. Bluetooth Technology Bluetooth is a technology specification designed to eliminate the cables and infrared links used to connect disparate devices. Its aim is to provide small design, low-cost, short range wireless interconnectivity between, for example, laptop computers, mobile phones, headsets, watches, digital cameras and cars. It also enables close-range applications in public areas like e-cash transactions. Based on low power radio frequency technology using 2.4 GHz spectrum and a power level of 10mW, the data rate is almost 1Mbit per second and the range is approximately 10 metres.

The technology enables users to connect a wide range of computing and telecommunications devices easily and simply, without the need to buy, carry, or connect cables. It also delivers opportunities for rapid ad hoc connections, and the possibility of automatic, unconscious, connections between devices. It will virtually eliminate the need to purchase additional or proprietary cabling to connect individual devices. Because Bluetooth can be used for a variety of purposes, it will potentially replace multiple cable connections via a single radio link. 89.9 Million Mobile Subscriptions Mobile telecommunications are vital for the UK’s economic competitiveness and in promoting social inclusion. There are now 89.9 million subscriptions in the UK. In Q1 2015 61% of UK adults used their mobile phone for internet access. Tablet ownership is 54% of UK households. Operators are working with Ofcom to extend the benefits of mobile communications as widely as possible; 99.7% of UK premises (homes and businesses) had outdoor 2G coverage from at least one operator; 3G coverage is slightly lower at 99.3% and 4G has reached 89.5%.

Smartphone ownership Two thirds of all adults (66%) now own a smartphone, this is on a par with laptop ownership. The proportion of adults that accessed the internet on a mobile handset increased to 61%. Over half of households (54%) had a tablet computer. Twenty eight percent of individuals now own an e-reader. mobile telephone | Definition & History | Britannica.com Telefónica SA Mobile telephone, also called mobile phone, portable device for connecting to a telecommunications network in order to transmit and receive voice, video, or other data. Mobile phones typically connect to the public switched telephone network (PSTN) through one of two categories: cellular telephone systems or global satellite-based telephony. People can quickly and easily communicate with one another over long distances using computers and … Kevin Dodge/Corbis Cellular telephones Cellular telephones, or simply cell phones, are portable devices that may be used in motor vehicles or by pedestrians. Communicating by radio waves, they permit a significant degree of mobility within a defined serving region that may range in area from a few city blocks to hundreds of square kilometres. The first mobile and portable subscriber units for cellular systems were large and heavy.

With significant advances in component technology, though, the weight and size of portable transceivers have been significantly reduced. In this section, the concept of cell phones and the development of cellular systems are discussed. Three students at the University of Cincinnati, Ohio, talking on cell phones between classes. Cell … AP Open Door policy The increasing demands placed on mobile telephones to handle even more data than 3G could led to the development of 4G technology. In 2008 the ITU set forward a list of requirements for what it called IMT-Advanced, or 4G; these requirements included data rates of 1 gigabit per second for a stationary user and 100 megabits per second for a moving user. The ITU in 2010 decided that two technologies, LTE-Advanced (Long Term Evolution; LTE) and WirelessMan-Advanced (also called WiMAX), met the requirements. The Swedish telephone company TeliaSonera introduced the first 4G LTE network in Stockholm in 2009. Airborne cellular systems In addition to the terrestrial cellular phone systems described above, there also exist several systems that permit the placement of telephone calls to the PSTN by passengers on commercial aircraft.

These in-flight telephones, known by the generic name aeronautical public correspondence (APC) systems, are of two types: terrestrial-based, in which telephone calls are placed directly from an aircraft to an en route ground station; and satellite-based, in which telephone calls are relayed via satellite to a ground station. In the United States the North American terrestrial system (NATS) was introduced by GTE Corporation in 1984. Within a decade the system was installed in more than 1,700 aircraft, with ground stations in the United States providing coverage over most of the United States and southern Canada. A second-generation system, GTE Airfone GenStar, employed digital modulation. In Europe the European Telecommunications Standards Institute (ETSI) adopted a terrestrial APC system known as the terrestrial flight telephone system (TFTS) in 1992. This system employs digital modulation methods and operates in the 1,670–1,675- and 1,800–1,805-megahertz bands. In order to cover most of Europe, the ground stations must be spaced every 50 to 700 km (30 to 435 miles).

Satellite-based telephone communication In order to augment the terrestrial and aircraft-based mobile telephone systems, several satellite-based systems have been put into operation. The goal of these systems is to permit ready connection to the PSTN from anywhere on Earth’s surface, especially in areas not presently covered by cellular telephone service. A form of satellite-based mobile communication has been available for some time in airborne cellular systems that utilize Inmarsat satellites. However, the Inmarsat satellites are geostationary, remaining approximately 35,000 km (22,000 miles) above a single location on Earth’s surface. Because of this high-altitude orbit, Earth-based communication transceivers require high transmitting power, large communication antennas, or both in order to communicate with the satellite. In addition, such a long communication path introduces a noticeable delay, on the order of a quarter-second, in two-way voice conversations. One viable alternative to geostationary satellites would be a larger system of satellites in low Earth orbit (LEO). Orbiting less than 1,600 km (1,000 miles) above Earth, LEO satellites are not geostationary and therefore cannot provide constant coverage of specific areas on Earth.

Nevertheless, by allowing radio communications with a mobile instrument to be handed off between satellites, an entire constellation of satellites can assure that no call will be dropped simply because a single satellite has moved out of range. The first LEO system intended for commercial service was the Iridium system , designed by Motorola, Inc., and owned by Iridium LLC, a consortium made up of corporations and governments from around the world. The Iridium concept employed a constellation of 66 satellites orbiting in six planes around Earth. They were launched from May 1997 to May 1998, and commercial service began in November 1998. Each satellite, orbiting at an altitude of 778 kilometres (483 miles), had the capability to transmit 48 spot beams to Earth. Meanwhile, all the satellites were in communication with one another via 23-gigahertz radio “crosslinks,” thus permitting ready handoff between satellites when communicating with a fixed or mobile user on Earth. The crosslinks provided an uninterrupted communication path between the satellite serving a user at any particular instant and the satellite connecting the entire constellation with the gateway ground station to the PSTN.

In this way, the 66 satellites provided continuous telephone communication service for subscriber units around the globe. However, the service failed to attract sufficient subscribers, and Iridium LLC went out of business in March 2000. Its assets were acquired by Iridium Satellite LLC, which continued to provide worldwide communication service to the U.S. Department of Defense as well as business and individual users. Another LEO system, Globalstar, consisted of 48 satellites that were launched about the same time as the Iridium constellation. Globalstar began offering service in October 1999, though it too went into bankruptcy, in February 2002; a reorganized Globalstar LP continued to provide service thereafter. Cellular Phone and Base Station Cellular Phone and Base Station Why it is dangerous to have your mobile phone in operation during refueling at a gas station? The following is a quote from the chair of the Cellular Telecommunications Industry Association (dated June 28, 1999): "You may have received inquiries about wireless phones causing fires or explosions at gas stations.

In an abundance of caution, some manufacturers have included language in the owner's manuals for their products that recommends wireless phone users turn off their phones while at refueling points (gas stations). In addition, we have received information that Exxon will begin issuing warning signs at all domestic gas stations advising drivers to turn off all wireless communications devices when entering Exxon gas stations. While wireless phone owners should always consult their owner's manual for information on the use of the phone, we are not aware of any incident that would justify these concerns." Is there any risk for health with the installation of a cellular tower near a community? Radiofrequency (RF) emissions from antennas used for wireless transmissions such as cellular and PCS (personal communication systems) signals result in exposure levels on the ground that are typically thousands of times less than safety limits. These safety limits were adopted by the Federal Communications Commission (FCC) based on the recommendations of expert organizations and endorsed by agencies of the federal government responsible for health and safety. Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents or students. Other antennas, such as those used for radio and television broadcast transmissions, use power levels that are generally higher than those used for cellular and PCS antennas.

Therefore, in some cases there could be a potential for higher levels of exposure on the ground. However, all broadcast stations are required to demonstrate compliance with FCC safety guidelines, and ambient exposures to nearby persons from such stations are typically well below FCC safety limits. The "Minimum Safe Distance" from a mobile phone base antenna is described by the Food and Drug Administration/FCC as follows: "To be exposed to levels at or near the FCC limits for cellular or PCS frequencies an individual would essentially have to remain in the main transmitted radio signal (at the height of the antenna) and within a few feet from the antenna . . . . In addition, for sector-type antennas RF levels to the side and in back are insignificant." Note that the quote about safe distances applies to the actual radiating antenna, not to the tower (or building or structure) the antenna is on. For a mobile phone base station antenna mounted on a tower that is 5+ meters high (about 15 feet), there should be no areas that will come anywhere close to the RF radiation safety guidelines, so the concept of a "minimum safe distance" doesn't really apply to generally occupied areas.

Is it safe to live or work on the top floor of a building that has a mobile phone base station antenna on it? In general this will not be a problem. The roof of the building will absorb large amounts of the RF energy. Typically a roof would be expected to decrease signal strength by a factor of 5 to 10 (or more for a reinforced concrete or metal roof). In addition, the FCC requires RF radiation evaluations of high-power rooftop transmitters. Even a worst-case calculation predicts that power density on the floor below an antenna will meet all current RF safety guidelines, and actual measurements in top-floor apartments and corridors confirm the power density is far below all current RF safety guidelines. Is it true that hands-free cell phone car microphones radiate more than any other instrument used with these phones? Hands-free cell phone car microphones have been tested by the manufacturers and meet the current American National Standards Institute (ANSI)/Institute of Electrical and Electronics Engineers (IEEE) standards for R) radiation safety. These are the same standards that the FCC enforces under the Telecommunications Act of 1996, and they place limits on the specific absorption rate of RF energy in the body.

There has been no substantiated information that the car microphones emit more RF than any other item used with cell phones. I am in a situation where I would like to be able to wear my hands-free cellular kit all day. Does the radiation only exist when I'm actually making a call or just any time the phone is on? Whenever they are turned on, cell phones communicate at infrequent intervals with a nearby base station even when they are not being used for a call. This is necessary to tell the system where the user is in case a call should come in. Thus, even while they are inactive, the phones are a source of (very low) RF energy exposure to the user. Hands-free kits reduce exposure to a user by removing the phone from the vicinity of the head. There is no identifiable health benefit in using the kits, but there is no detriment either, and using them may increase a user's peace of mind. In your case, the cell phone and hands-free kit are clearly an important link to the outside world and I would not hesitate in using them. There may be comfort issues with having the earpiece in place for a long time, but RF radiation exposure should not be a concern at all.

The hands-free kits will reduce exposure below that which you would receive if the phone were kept close to your head. Are there products available to the general public that can be purchased to protect cellular or portable telephone users from radiation? There are a number of opportunistic gadgets on the market to allegedly protect the user from hazards of cellular phones. You can search the Internet to find the latest, ranging from antenna shields to whole-body shielding materials. Most experts believe that these devices take advantage of customers' misunderstanding and unfounded fears to sell products with no real value. First of all, cell phones that operate within the guidelines established by national and international safety panels have never been shown to pose a health risk to the user (see answers to other questions on cell phone safety on this page). Secondly, placing any kind of shield over the antenna of a cell phone will in most cases cause it to increase its RF output as it attempts to compensate for signal loss in the shield and maintain a quality phone call. I need help in gathering published information about the risks posed by cell towers placed on school grounds. Is there information that would enable me to gather/calculate or measure radiation on the specific site? The best single reference is the Federal Communications Commission Website.

Look for: Bulletin 56, "Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields." Bulletin 65, "Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields." "A Local Government Official's Guide to Transmitting Antenna RF Emission Safety: Rules, Procedures, and Practical Guidance." An excellent technical paper with field measurements of cell-tower emissions was published by R.C. Petersen and P.A. Testagrossa in the journal Bioelectromagnetics , volume 13, page 527ff, 1992. Is cell phone use in and around a hospital safe? The issue of banning mobile phone use in hospitals is a subject of some controversy. For a snapshot of the controversy it is useful to look at an article that was published in March 2003 in the British Medical Journal (BMJ 326:460, March 2003). The authors concluded: "Mobile phones in hospitals are not as hazardous as believed and should be allowed at least in nonclinical areas." At least as interesting as the article itself are the online responses to the article.

This is what we know: Mobile phones can interfere with medical equipment. The interference is relatively rare and generally goes away when the phone is turned off or moved away. There appear to be no confirmed reports of life-threatening interference. The two-way radios used by emergency-service personnel and hospital transport aides (porters) are a bigger source of interference than consumer mobile phones. Other sources of RF radiation (for example, digital TV broadcasts and other medical equipment) have also caused interference with medical devices. Many (most?) hospitals ban mobile phones, but the basis for their bans is generally vague, and the bans are often very poorly enforced on visitors or on staff. I am unaware of any general governmental bans on the use of mobile phones in hospitals. In the United States, this would fall under the jurisdiction of the Center for Devices and Radiological Health of the Food and Drug Administration and to date the Food and Drug Administration has not taken a position on the subject. The bottom line is that interference with medical equipment by devices that produce RF radiation is an issue for hospitals and medical-equipment makers, but the source of the problem is not limited to mobile phones. Hospitals do not allow cell phone use due to potential interference.

Last weekend I was in a hospital where the top of the hospital building was studded with cell tower antennas. Why is it that cell phones would cause interference, but cell tower antennas would not? It's a question of signal strength. Interference with medical devices has been observed only very close to transmitting antennas where there is strong signal strength. Interference has been observed in some medical electronics due to hand-held cell phones. Rooftop antennas are some distance away from any susceptible electronics. In addition to proximity, the directionality of the antennas is important. Most rooftop antennas have strong gain in the forward directiontowards the horizonand very low gain in the vertical direction. Finally, there are layers of building materials shielding the interior areas from the rooftop antennas. Proximity, directionality, shieldingall go towards reducing the signal strength inside a building due to the antennas on the roof so that interference is not generally an issue. This does not mean that you cannot receive the signals from the rooftop antennas inside the building; it simply means that the received signals are not strong enough to cause interference. I would like to inquire about the physics principles regarding the use of mobile phones and the development of brain tumors.

I've been through many sites but they can never give an exact answer. Can they really give someone brain tumors or does it have to do with the intensity of the radiation and the distance between the phone and an individual? It is not clear that mobile phones do produce brain tumors, or any serious health effects for that matter. A number of epidemiology studies have been almost completely negative on the issue. See the article by Kenneth Foster and John Moulder in IEEE Spectrum magazine and also Moulder's FAQ on mobile phones and health. There has been a lot of discussion over the years about the possible mechanisms by which microwave energy such as emitted by cell phones might produce biological effects. The one proven mechanism is the heating of tissue, but mobile phones operate at power levels that are too low to cause noticeable heating in the user. Scientists have speculated about other mechanisms, but these theories remain unproven and many of them have been challenged on biophysical grounds. Whatever may be the risks or nonrisks of mobile phone radiation, a hands-free kit is an effective way for the user to reduce his or her exposure to RF energy while using a mobile phone. If you have serious concerns, limited or no use of a cellular phone might be a consideration for you.

The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society. © 2016 Health Physics Society Cellular Phone Towers Sun and Other Types of Radiation Cellular Phone Towers Cellular (cell) phones first became widely available in the United States in the 1990s, but since then their use has increased dramatically. The widespread use of cell phones has led to cell phone towers being placed in many communities. These towers, also called base stations, have electronic equipment and antennas that receive and transmit radiofrequency (RF) signals. How do cellular phone towers work?

Cell phone base stations may be free-standing towers or mounted on existing structures, such as trees, water tanks, or tall buildings. The antennas need to be high enough to adequately cover the area. Base stations are usually from 50-200 feet high. Cell phones communicate with nearby cell towers mainly through radiofrequency (RF) waves, a form of energy in the electromagnetic spectrum between FM radio waves and microwaves. Like FM radio waves, microwaves, visible light, and heat, they are forms of non-ionizing radiation. This means they do not directly damage the DNA inside cells, which is how stronger (ionizing) types of radiation such as x-rays, gamma rays, and ultraviolet (UV) light are thought to be able to cause cancer. At very high levels, RF waves can heat up body tissues. (This is the basis for how microwave ovens work.) But the levels of energy used by cell phones and towers are much lower. When a person makes a cell phone call, a signal is sent from the phone’s antenna to the nearest base station antenna. The base station responds to this signal by assigning it an available radiofrequency channel. RF waves transfer the voice information to the base station.

The voice signals are then sent to a switching center, which transfers the call to its destination. Voice signals are then relayed back and forth during the call. How are people exposed to the energy from cellular phone towers? As people use cell phones to make calls, signals are transmitted back and forth to the base station. The RF waves produced at the base station are given off into the environment, where people can be exposed to them. The energy from a cellular phone tower antenna, like that of other telecommunication antennas, is directed toward the horizon (parallel to the ground), with some downward scatter. Base station antennas use higher power levels than other types of land-mobile antennas, but much lower levels than those from radio and television broadcast stations. The amount of energy decreases rapidly as the distance from the antenna increases. As a result, the level of exposure to radio waves at ground level is very low compared to the level close to the antenna. Public exposure to radio waves from cell phone tower antennas is slight for several reasons. The power levels are relatively low, the antennas are mounted high above ground level, and the signals are transmitted intermittently, rather than constantly.

At ground level near typical cellular base stations, the amount of RF energy is thousands of times less than the limits for safe exposure set by the US Federal Communication Commission (FCC) and other regulatory authorities. It is very unlikely that a person could be exposed to RF levels in excess of these limits just by being near a cell phone tower. When a cellular antenna is mounted on a roof, it is possible that a person on the roof could be exposed to RF levels greater than those typically encountered on the ground. But even then, exposure levels approaching or exceeding the FCC safety guidelines are only likely to be found very close to and directly in front of the antennas. If this is the case, access to these areas should be limited. The level of RF energy inside buildings where a base station is mounted is typically much lower than the level outside, depending on the construction materials of the building. Wood or cement block reduces the exposure level of RF radiation by a factor of about 10. The energy level behind an antenna is hundreds to thousands of times lower than in front. Therefore, if an antenna is mounted on the side of a building, the exposure level in the room directly behind the wall is typically well below the recommended exposure limits. Do cellular phone towers cause cancer?

Some people have expressed concern that living, working, or going to school near a cell phone tower might increase the risk of cancer or other health problems. At this time, there is very little evidence to support this idea. In theory, there are some important points that would argue against cellular phone towers being able to cause cancer. First, the energy level of radiofrequency (RF) waves is relatively low, especially when compared with the types of radiation that are known to increase cancer risk, such as gamma rays, x-rays, and ultraviolet (UV) light. The energy of RF waves given off by cell phone towers is not enough to break chemical bonds in DNA molecules, which is how these stronger forms of radiation may lead to cancer. A second issue has to do with wavelength. RF waves have long wavelengths, which can only be concentrated to about an inch or two in size. This makes it unlikely that the energy from RF waves could be concentrated enough to affect individual cells in the body. Third, even if RF waves were somehow able to affect cells in the body at higher doses, the level of RF waves present at ground level is very low – well below the recommended limits.

Levels of energy from RF waves near cell phone towers are not significantly different from the background levels of RF radiation in urban areas from other sources, such as radio and television broadcast stations. Studies in people Very few human studies have focused specifically on cellular phone towers and cancer risk. In one large study, British researchers compared a group of more than 1,000 families of young children with cancer against a similar group of families of children without cancer. They found no link between a mother’s exposure to the towers during pregnancy (based on the distance from the home to the nearest tower and on the amount of energy given off by nearby towers) and the risk of early childhood cancer. In another study, researchers compared a group of more than 2,600 children with cancer to a group of similar children without cancer. They found that those who lived in a town that could have exposed them to higher than average RF radiation from cellular phone towers in the previous 5 years had a slightly higher risk of cancer, although not of any certain type of cancer (like leukemia or brain tumors). This study estimated the children’s possible exposure based on the number of towers in their town and how strong the signals were from the towers.

It did not look at actual exposure of any individual child based on how far their home or school was from a tower. This limitation reduces confidence in the results of the study. One study looked for signs of DNA and cell damage in blood cells as a possible indicator of cancer-causing potential. They found that the damage was no worse in people who lived near a cell phone tower as compared with those didn’t. The amount of exposure from living near a cell phone tower is typically many times lower than the exposure from using a cell phone. About 30 studies have looked at possible links between cell phone use and tumors in people. Most studies to date have not found a link between cell phone use and the development of tumors, although these studies have had some important limitations. This is an area of active research. For more information, see Cellular Phones . Studies done in the lab Laboratory studies have looked at whether the types of RF waves used in cell phone communication can cause DNA damage. Most of these studies have supported the idea that the RF waves given off by cell phones and towers don't have enough energy to damage DNA directly. Because of this, it’s not clear how cell phones and towers might be able to cause cancer, but research in this area continues.

Some scientists have reported that RF waves may produc e other effects in human cells (in lab dishes) that might possibly help tumors grow. However, these studies have not been verified, and these effects weren’t seen in a study that looked at the blood cells from people living near a cellular phone tower. Several studies in rats and mice have looked at whether RF energy might promote the development of tumors caused by other known carcinogens (cancer-causing agents). These studies did not find evidence of tumor promotion, but this is still an area of research. A large study by the US National Toxicology Program (NTP) exposed groups of lab rats and mice to RF energy over their entire bodies for about 9 hours a day, starting before birth and continuing for up to 2 years. The NTP recently released partial findings from this study, which found increased (although still low) risks of brain and heart tumors in male rats exposed to RF radiation, although there was no increased risk among female rats. Some aspects this study, such as the high doses of RF radiation and the long amount of time the rats were exposed to it, make it hard to know just how well these results might be applied to people.

Still, the results add evidence to the idea that the signals used in cell phone communication might potentially impact human health. What expert agencies say About cell phone towers The 3 expert agencies that usually classify cancer-causing exposures (carcinogens) – the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (EPA) – have not classified cell phone towers specifically as to their cancer-causing potential. The US Federal Communications Commission (FCC) has said this about cell phone towers near homes or schools: “Radiofrequency emissions from antennas used for cellular and PCS [personal communications service] transmissions result in exposure levels on the ground that are typically thousands of times below safety limits. These safety limits were adopted by the FCC based on the recommendations of expert organizations and endorsed by agencies of the Federal Government responsible for health and safety. Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents or students.” About RF radiation Some of the agencies that classify cancer-causing exposures have, however, made statements about radiofrequency radiation.

The International Agency for Research on Cancer (IARC) has classified RF fields as “possibly carcinogenic to humans,” based on limited evidence of a possible increase in risk for brain tumors among cell phone users, and inadequate evidence for other types of cancer. (For more information on the IARC classification system, see Known and Probable Human Carcinogens .) IARC also noted that exposure to the brain from RF fields from cell phone base stations (mounted on roofs or towers) is less than 1/100th the exposure to the brain from mobile devices such as cell phones. The Environmental Protection Agency (EPA) states: “At very high levels, RF energy is dangerous. It can heat the body's tissues rapidly. However, such high levels are found only near certain equipment, such as powerful long-distance transmitters. Cellphones and wireless networks produce RF, but not at levels that cause significant heating. In addition, RF energy decreases quickly over distance. At ground level, exposure to RF from sources like cellphone towers is usually very low. Some people are concerned about potential health effects, especially on the developing brains and bodies of children. Some studies suggest that heavy long-term use of cellphones could have health effects.

Other studies don't find any health effects from cellphone use. Long-term studies on animals exposed to the RF found in wireless networks (Wi-Fi) have, so far, found no health effects. Scientists continue to study the effects of long-term exposure to low levels of RF.” Can I limit my exposure? Cell phone towers are not known to cause any health effects. But if you are concerned about possible exposure from a cell phone tower near your home or office, you can ask a government agency or private firm to measure the RF field strength near the tower (where a person could be exposed) to ensure that it is within the acceptable range. What should I do if I’ve been exposed to cellular phone towers? There is no test to measure whether you have been exposed to RF radiation from cellular phone towers. But as noted above, most researchers and regulatory authorities do not believe that cell phone towers pose health risks under ordinary conditions. If you have additional health concerns, you might want to talk with your doctor. Story tracker: Mobile phone masts and cancer | Science | The Guardian Science story trackers Mobile phone masts and cancer A study published in the BMJ on 23 June found no link between childhood cancer and mobile phone masts .

Over the coming days and weeks we will publish updates on this story and links to sources of further information The researchers conclude: 'There is no association between risk of early childhood cancers and estimates of the mother’s exposure to mobile phone base stations during pregnancy'. Photograph: Katie Collins/PA Science desk Wednesday 23 June 2010 07.41 EDT First published on Wednesday 23 June 2010 07.41 EDT Close Story summary Wednesday 12.31pm: Pregnant women who live close to mobile phone masts do not need to move house, scientists said today, following the publication of a study which found no link to early childhood cancers. There has been public concern over the possibility that living near phone masts could raise the cancer risk of small children and clusters of cases around masts have been reported. But a study published in the British Medical Journal – the first to examine possible links between phone masts and childhood cancer across Britain – found no cause for concern.

Wednesday 23 June, 12.40pm: An article in the British Medical Journal today reports a study looking at whether there are any links between children developing leukaemia or a tumour of the brain and whether their mothers lived near mobile phone masts at the time of their birth. Sarah Boseley's write-up in the Guardian makes it clear that "Pregnant women who live close to mobile phone masts do not need to move house". She continues: Researchers from Imperial College London identified 1,397 children under five who were diagnosed with leukaemia or a tumour of the brain or central nervous system between 1999 and 2001. They compared each child with four children of the same gender who were born on the same day but had not developed cancer. The researchers studied the distance of the mother's home at the time of the birth from a phone mast, the total power output for base stations within 700 metres and the power density for base stations within 1,400 metres.

"We found no pattern to suggest that the children of mums living near a base station during pregnancy had a greater risk of developing cancer than those who lived elsewhere," said Professor Paul Elliott, one of the report's authors and director of the MRC-HPA centre for environment and health at Imperial. Press roundup In the Independent, health editor Jeremy Laurance gives some context for the study: The increase in mobile phone use – from 9 million handsets in 1997 to 74 million in 2007 – has raised worries about the effects of exposure to low-frequency radiation. Several studies, including the Interphone study involving more than 10,000 people from 13 countries that was published last month, have found no damaging health effects from mobile phones themselves. Public anxiety about transmitters has grown despite the level of individual exposure from transmitters being much lower than from mobile phones.

The LA Times Booster Shots blog reports some of the ways the researchers thought they might have improved their study : The mothers whose children were diagnosed with cancer lived an average of 1,173 yards from a cellphone tower while they were pregnant – statistically indistinguishable from the 1,211 yards that separated the other pregnant women from their nearest cellphone towers. Tallying up the total power output of all cellphone towers within 766 yards of each pregnant woman's home, they found that both groups had nearly the same exposure – 2.89 kilowatts for the mothers of cancer victims and 3.00 kilowatts for the other mothers. Only one of their models revealed a difference that was statistically significant, though just barely. In that case, higher radio-frequency exposure was associated with a reduced risk of cancer of the brain or central nervous system. (This result calls to mind a mouse study from last year that found that electromagnetic radiation from cellphones actually protected mice from Alzheimer's.) The results were published online Tuesday by the British Medical Journal. The British researchers admitted their study would have been stronger if there had been some way to determine the actual radiation exposure for each pregnant woman instead of relying on mathematical models.

They also would have liked to have tracked the exposure of babies after they were born, but the necessary data weren't available. Still, they said that if the cellphone towers had doubled the risk for these childhood cancers, the odds that their study would have picked up on it were greater than 90%. The Press Associaton , Associated Press , Bloomberg Business Week and Irish Times , and the Washington Post's The Checkup blog also have reports. Wednesday 23 June, 1.30pm: If you only have time to read two things related to the analysis of this story, here they are. NHS Choices cuts through all the complexity with a superb article on its Behind the Headlines pages. It explains how the study was carried out, what the results are and what caveats there might be on the work. One of the limitations to this study design is that the exposures being assessed occurred in the past, and therefore it can be difficult to assess them accurately, particularly if researchers rely only on people's recall of events. However, in this study, researchers did not have to rely on people remembering or estimating their exposure to mobile phone masts, instead they used data on where individuals lived and known locations of mobile phone masts.

This increases the reliability of the information about exposure. Despite any perceived limitations, NHS Choices concludes that the BMJ study "appears well conducted". Funding As well as elucidating the way the research was carried out, Ed Yong's post at the Cancer Research UK blog addresses the issue of funding: It's also worth talking about sources of funding. This study was funded by an independent body called the UK Mobile Telecommunications Health Research Programme (MTHR). The MTHR was set up in 2001 to fund research into any possible health effects of mobile phones, following a recommendation by an independent expert group called the Stewart Committee. The group is jointly funded by the UK Department of Health and the mobile telecommunications industry. It says, "In order to ensure that none of the funding bodies can influence the outcome of the MTHR Programme, it is run by an independent programme management committee." This is a common theme in this area of research – industry funding has always been mediated by an independent third party, such as the International Union for Cancer Control. In addition, CRUK have posted data showing that the rates of malignant brain tumours in the UK have remained stable over the past 10 years.

Expert comment Wednesday 23 June, 2:00pm: Some comments on the BMJ study courtesy of the Science Media Centre in London. Eileen Rubery, former head of the public health prevention department at the UK government's department of health , said: "This is a carefully done study by a highly reputable group of epidemiologists. The size of the sample is large and the approach appropriate. It is reassuring that no adverse effects have been found and this fits with the anticipated and known biological effects from such sites and so is consistent with the physiology and biology." Malcolm Sperrin, director of medical physics at the Royal Berkshire Hospital, said: "This study seems exemplary in its approach. The findings are well concluded and the methodology is thorough. The findings are generally in support of both the current understanding of tissue interactions and also in support of the work done by other similar research groups.

The data is complex and requires some interpretation but the abstract and conclusions are well considered and easy to follow." Wednesday 23 June, 2.33pm: The Institution of Engineering and Technology has issued a response to the BMJ's study, saying that there is "no persuasive evidence that normal mobile phone usage or exposure to pylons and power lines causes harmful health effects". Tony Barker, a fellow of the IET and chairman of its Biological Effects Policy Advisory Group , said: "There is still a huge amount of interest in whether exposure to mobile phones and electricity pylons has harmful health effects. However, over the years the conclusion of most scientific bodies, including the Institution of Engineering and Technology, has remained substantially the same – that there is no persuasive evidence of this. The absence of robust new evidence of harmful health effects in the past two years is reassuring and is consistent with findings over the last two decades." The IET's position statement on the possible harmful effects of low-level electromagnetic fields is worth reading for background. It reviewed 813 scientific papers, of which 44% covered static and low frequencies that are typically associated with power generation and distribution.

46% of the papers dealt with radio-frequency fields, and 64% of these were specifically related to mobile phone frequencies. The IET has also published a factfile on the potential health effects of low-level electromagnetic fields with frequencies of up to 300 gigahertz. Jack Rowley, director of research and sustainability at the GSM Association said that the BMJ's findings should reassure families living near mobile phone base stations. "The results are consistent with the World Health Organisation position that there is no convincing scientific evidence that the weak radio signals from wireless networks cause adverse health effects." He continued: "Some people may have been concerned about claims of disease 'clusters' near radio transmitters. Investigations by health authorities in Australia, Europe and the USA have concluded that there was no evidence to link illness with living near radio transmitters. Diseases such as cancer are distributed randomly in the community. The growth in mobile networks in response to customer demand means that there will be chance instances of apparent increases in disease close to radio transmitters." Thursday 24 June, 2.04pm: The results from the second Eurobarometer survey on Electromagnetic Fields (EMF) were published today.

They suggest that public concern about potential health risks from electromagnetic fields remains high. People were most concerned about power lines, followed by mobile phone masts. Some 46% of Europeans surveyed said they were "very concerned" or "fairly concerned" about the potential health risks of EMF. However, this was a slight reduction compared with the 2006 survey (48%). Dr Jack Rowley, director of research and sustainability at the GSM Association (GSMA) , the international body that represents the mobile communications industry, told the Guardian: "The public appears to be increasingly reassured by the growing body of scientific evidence showing no established health risk from low-level radio signals. GSMA supports adoption of WHO-recommended exposure limits and continuing actions to ensure the public has access to accurate information. The countries with the highest concern have generally adopted precautionary policies. The link between non-science based precautionary policies and increased public concern has been shown by practical experience and academic research. Governments should avoid arbitrary limits and restrictions on where antennas can be located. Such policies cause alarm and provide no health benefits." Thursday 24 June, 2.40pm: Carl Heneghan has written an informative blog assessing the methodology of the BMJ research .

Heneghan, who is deputy director of the Centre for Evidence Based Medicine , a GP and lecturer in clinical medicine at Oxford University, concludes: "Overall this is a well done study and allows us to feel more certain about the evidence base that there is no association between risk of cancer in young children and exposure to mobile phone base stations." Heneghan also observes that the dramatic increase in the use of mobile phones has not been accompanied by an increase in the incidence of brain tumours. Friday 25 June, 10.52am: Katherine Hobson at the The Wall Street Journal's health blog reports the BMJ study as being a narrow piece of research. Obviously, the focus of the study was narrow; these results don't mean that kids won't eventually develop cancer or other health problems, and it says nothing about adults. Other caveats include the fact that individual mothers' personal exposures weren't measured (and might be affected by something inside the home) and that the study looked only at where mothers lived when they gave birth, not throughout the pregnancy. Hobson also refers readers to recent study ( published in May in the International Journal of Epidemiology) that was inconclusive on possible links between mobile phone use and brain cancers.

That seemed to suggest that using cell phones actually protects against two types of brain tumour and, reports the WSJ, the reseachers themselves were unsure what to make of it. Tuesday 29 June 4.10pm: Physicist Bernard Leikind has written an essay for the 9 June issue of eSkeptic about how living tissue absorbs microwave radiation, transfers the energy to the bloodstream and then throughout the body. His conclusion is that the tiny amounts of energy involved – which are dwarfed by the heat transfer associated with other everyday activities – cannot cause cancer by any mechanism, known or unknown. Leikind also proposes an explanation for why the recently published Interphone study found a slight protective effect from moderate mobile phone use on the risk of brain cancer.

Question: Relating to mobile phones, what is the area covered by a base station (or aerial) called?
Answer: A cell