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Question #: 258

Question: ARE LIVING QUARTERS IMMEDIATELY BELOW ROOF-TOP CELLULAR TELEPHONE ANTENNA/TRANSMITTERS HAZARDOUS?

Current Solution

There is very little radiofrequency (RF) energy exposure to people inside a building from a cellular base station located on its roof. There are several reasons for this. First, the transmitters operate at low power levels. Second, the antennas are normally mounted near the edges of the roof and are aimed away from the building. Third, most cellular transmitters use "high gain" or panel antennas. Such antennas transmit most of their energy in a narrow beam (in the vertical direction) from their front surfaces, away from the building. They radiate very little energy downwards towards the roof or backwards from their rear surfaces. Finally, building materials absorb a significant fraction of the RF energy passing through them. As a result, the RF signal levels at any location inside the building are invariably low and far below safety limits. The situation might be different in some locations on the roof itself. RF signal levels close to (within a few feet) and directly in front of cellular base station antennas can easily exceed safety limits. Some precautions are needed to prevent people from walking directly in front of the antennas while they are transmitting. This applies also to paging and other systems that use rooftop antennas, some of which transmit at higher power levels than many cellular base stations. Kenneth R. Foster, Ph.D.

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Other Possible Solutions to this Question

  • ARE THERE PRODUCTS AVAILABLE TO THE GENERAL PUBLIC THAT CAN BE PURCHASED PROTECT CELLULAR OR PORTABLE TELEPHONE USERS FROM RADIATION? IF SO, WHERE THESE FOUND?

    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 website). 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. The U.S. Food and Drug Administration published an advisory on cell phones several years ago that said if you are concerned about risks of using a cell phone, then simply use it less. That is still good advice today. Gary Zeman, ScD, CHP Lawrence Berkeley National Laboratory

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    ARE THERE PRODUCTS AVAILABLE TO THE GENERAL PUBLIC THAT CAN BE PURCHASED PROTECT CELLULAR OR PORTABLE TELEPHONE USERS FROM RADIATION? IF SO, WHERE THESE FOUND?

  • THERE ANY STANDARD FOR A DISTANCE BETWEEN CELLULAR BASE STATION AND RESIDENTIAL AREA?

    The two main constraints on siting cellular base stations near residential areas are government exposure limits and local zoning ordinances. Various governments have limits for human exposure to radiofrequency (RF) energy that must be complied with in the siting of cellular base stations and other transmitters. In the United States, the relevant limits are those of the Federal Communications Commission (FCC). Cellular base stations use low-powered transmitters, and RF signal levels are invariably below FCC limits at any distance more than a few feet from the antennas. Thus it is entirely feasible to locate cellular base stations on rooftops of apartment buildings and to locate communications towers within residential areas and indeed these are both common practices. Local zoning ordinances are a different story. Local governments commonly restrict the location of communications towers through zoning ordinances, and they may have provisions that restrict cellular base stations in residential districts. Local attorneys or government officials should be consulted for advice about local requirements, which vary greatly among jurisdictions. Kenneth R. Foster Professor, Department of Bioengineering University of Pennsylvania

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    THERE ANY STANDARD FOR A DISTANCE BETWEEN CELLULAR BASE STATION AND RESIDENTIAL AREA?

  • ARE CELLULAR PHONE HARMFUL?

    Cellular phones are designed to be safe for both the user and anyone standing nearby. Cellular phones are actually small radios that transmit signals to and from base-station antennas located on towers or buildings in the nearby neighborhood. Cellular phones use low-power radio signals, even weaker than CB, police, or fire radios.

    The American National Standards Institute (ANSI) sets safety standards for human exposure to radiofrequency (RF) electromagnetic energy in the United States. Government agencies such as the Federal Communications Commission (FCC), the Occupational Safety and Health Administration (OSHA), and many states recognize and accept the ANSI RF safety standard. Also, the United States standard for RF energy is comparable to those set in other countries.

    Cellular phones and cellular-phone base stations have been shown to meet these RF safety standards. Safety standards for RF energy are threshold standards. Threshold standards define the level of RF energy above which there may be health or safety hazards and below which there have been no reported harmful effects. Unlike ionizing radiation, which many people believe to act cumulatively even at small exposure levels, RF energy at low levels is not considered a cumulative hazard. Therefore the consensus of scientific experts in this area is that RF exposure from cellular phones, meeting the threshold levels set in safety standards, is safe for all.

    The specific answer to the question is that cellular phone technology is safe for all. There is no danger posed by either handheld phone units or by base-station antennas. In both cases, the radio signals transmitted from the antennas are required to meet the ANSI safety standard for RF safety as embodied in FCC regulations governing this technology. For more information:

    The FCC has recently revised and reissued its Bulletin 56 on Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields.

    OSHA provides information and links to more sites on RF safety at its Web page, Radiofrequency/Microwave Radiation.

    Gary Zeman, ScD, CHP Lawrence Berkeley National Laboratory

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    ARE CELLULAR PHONE HARMFUL?

  • WHAT ARE THE HEALTH RISKS OF LIVING NEAR A CELL PHONE TOWER?

    There is very little radiofrequency (RF) energy exposure to people inside a building from a cellular base station located on its roof. There are several reasons for this. First, the transmitters operate at low power levels. Second, the antennas are normally mounted near the edges of the roof and are aimed away from the building. Third, most cellular transmitters use "high gain" or panel antennas. Such antennas transmit most of their energy in a narrow beam (in the vertical direction) from their front surfaces, away from the building. They radiate very little energy downwards towards the roof or backwards from their rear surfaces. Finally, building materials absorb a significant fraction of the RF energy passing through them. As a result, the RF signal levels at any location inside the building are invariably low and far below safety limits. The situation might be different in some locations on the roof itself. RF signal levels close to (within a few feet) and directly in front of cellular base station antennas can easily exceed safety limits. Some precautions are needed to prevent people from walking directly in front of the antennas while they are transmitting. This applies also to paging and other systems that use rooftop antennas, some of which transmit at higher power levels than many cellular base stations. Kenneth R. Foster, Ph.D.

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    WHAT ARE THE HEALTH RISKS OF LIVING NEAR A CELL PHONE TOWER?

  • IT MORE DANGEROUS STAY FOR ONE HOUR AT A TEN-METER DISTANCE FROM CELLULAR ANTENNA OR TALK INTO PHONE THE SAME AMOUNT OF TIME?

    Cellular phones are designed to be safe for both the user and anyone standing nearby. Cellular phones are actually small radios that transmit signals to and from base-station antennas located on towers or buildings in the nearby neighborhood. Cellular phones use low-power radio signals, even weaker than CB, police, or fire radios.

    The American National Standards Institute (ANSI) sets safety standards for human exposure to radiofrequency (RF) electromagnetic energy in the United States. Government agencies such as the Federal Communications Commission (FCC), the Occupational Safety and Health Administration (OSHA), and many states recognize and accept the ANSI RF safety standard. Also, the United States standard for RF energy is comparable to those set in other countries.

    Cellular phones and cellular-phone base stations have been shown to meet these RF safety standards. Safety standards for RF energy are threshold standards. Threshold standards define the level of RF energy above which there may be health or safety hazards and below which there have been no reported harmful effects. Unlike ionizing radiation, which many people believe to act cumulatively even at small exposure levels, RF energy at low levels is not considered a cumulative hazard. Therefore the consensus of scientific experts in this area is that RF exposure from cellular phones, meeting the threshold levels set in safety standards, is safe for all.

    The specific answer to the question is that cellular phone technology is safe for all. There is no danger posed by either handheld phone units or by base-station antennas. In both cases, the radio signals transmitted from the antennas are required to meet the ANSI safety standard for RF safety as embodied in FCC regulations governing this technology. For more information:

    The FCC has recently revised and reissued its Bulletin 56 on Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields.

    OSHA provides information and links to more sites on RF safety at its Web page, Radiofrequency/Microwave Radiation.

    Gary Zeman, ScD, CHP Lawrence Berkeley National Laboratory

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    IT MORE DANGEROUS STAY FOR ONE HOUR AT A TEN-METER DISTANCE FROM CELLULAR ANTENNA OR TALK INTO PHONE THE SAME AMOUNT OF TIME?

  • I'M SEARCHING FOR INFORMATION ABOUT THE HEALTH RISKS OF CELLULAR ANTENNAS' RADIATION. I NEED SCIENTIFIC (SCIENTIFIC PAPERS IN JOURNALS) THIS.

    Cellular telephone base stations are low-powered radiofrequency (RF) transmitters which operate at around 850-900 or 1800-1900 MHz (depending on the technology and region of the world). RF energy in a similar frequency range is used by many other technologies such as microwave ovens, UHF television, other communications systems, and radar. Health and safety issues related to RF energy have been studied for many years and there is an immense literature on the subject. Here are some sources that review health and safety issues related to RF energy from cellular base stations.

    A fact sheet published by the World Health Organization. There is also a Spanish version available on the WHO EMF website.
    Also see the IEEE EMBS Committee on Man and Radiation Report. Other reports are available through its website.
    The International Commission on Nonionizing Radiation Protection (ICNIRP) has published a lot on health and safety of RF energy. See its website. The ICNIRP published an article that describes the ICNIRP exposure limits for RF energy and their scientific rationale. See "Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz)," Health Physics Vol. 74, No 4, pp 494-522, 1998.
    A very detailed assessment of the scientific evidence related to health and safety of mobile telephones and base stations is in the recent (May 2000) report by the Independent Expert Group on Mobile Phones (IEGMP) titled "Mobile Phones and Health" This study concludes "the balance of evidence to date suggests that exposures to RF radiation at levels below [international exposure guidelines] do not cause adverse health effects to the general population" but that "there may be biological effects at exposures below those guidelines." Public exposure to RF energy from cellular base stations is invariably far below the ICNIRP exposure guidelines.

    Kenneth R. Foster
    Professor, Bioengineering
    University of Pennsylvania

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    I'M SEARCHING FOR INFORMATION ABOUT THE HEALTH RISKS OF CELLULAR ANTENNAS' RADIATION. I NEED SCIENTIFIC (SCIENTIFIC PAPERS IN JOURNALS) THIS.

  • THERE´S A CELLULAR PHONE ANTENNA ON THE ROOF OF BUILDING RIGHT OPPOSITE MY WINDOW, LEVEL ABOUT TEN METERS ABOVE HEAD. AM I LIKELY TO BE IN RADIUS RADIATION?

    You will have to contact the cell phone company that operates that particular antenna to obtain the radiation pattern (or emission pattern) of that particular type of antenna. Different models of antennae have different emission patterns to provide coverage of different size and shape geographical areas. For example, many of the antennae are directional, only broadcasting in the forward direction. Most emit very little radiation in the upward and downward directions, although the vertical extent of the beam can be quite different for different antennas. Some are strongly focussed on the horizon, others provide better coverage of nearby areas. Many antennae only broadcasting into a defined geometrical sector of the horizion, often 120 degrees so that three sets of antennae are required to cover the entire horizon. Therefore, to find the type of radiation pattern broadcast by any particular antenna will require local information from the equipment operator. Gary Zeman, ScD

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    THERE´S A CELLULAR PHONE ANTENNA ON THE ROOF OF BUILDING RIGHT OPPOSITE MY WINDOW, LEVEL ABOUT TEN METERS ABOVE HEAD. AM I LIKELY TO BE IN RADIUS RADIATION?

  • IT LIKELY THAT CELLULAR PHONE USAGE COULD EFFECT A CHANGE IN 400 MHZ NMR SPECTROMETER'S MAGNET IF HAS DECENT SHIELDING (TOP-OF-THE-LINE SHIELDING, CA. 1992)?

    Some electronic equipment has been shown to be sensitive to radiofrequency interference from cell phones. I suggest you talk with the manufacturer of the spectrometer for information about it.

    Gary H. Zeman, ScD, CHP

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    IT LIKELY THAT CELLULAR PHONE USAGE COULD EFFECT A CHANGE IN 400 MHZ NMR SPECTROMETER'S MAGNET IF HAS DECENT SHIELDING (TOP-OF-THE-LINE SHIELDING, CA. 1992)?

  • WHAT CAN USE BELOW MY WORKPIECE AS SUBSTRATE IN BLACKTOOTH LASER CUTTER?

    A cutting surface. I bought myself a aluminum 'egg crate' mesh from my local HVAC company. They are used a cover for fluorescent lights and work great for low impact cutting surface. They come in 4'x8' sheets and are easily cut to fit. The other side is if you can find a steel honeycomb cutting bed to fit. These can be quite costly or fairly affordable depending where you are looking. The benefit of a steel honeycomb is you can use high power magnets to hold material down.

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    WHAT CAN USE BELOW MY WORKPIECE AS SUBSTRATE IN BLACKTOOTH LASER CUTTER?

  • IN WHICH ORGANELLE OF A LIVING CELL DNA FOUND?

    Nucleus is the organelle of a living cell DNA is found.

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    Additional Information:
    nucleus


    Additional Information:
    qwertyuio

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    IN WHICH ORGANELLE OF A LIVING CELL DNA FOUND?

  • THEY ARE ASKING FOR THE ACTIVATION CODE AND SERIAL NUMBER USB BOARD. HOW CAN GET THAT INFORMATION?

    To get the activation code, all you need to do is plug the USB board into the computer using a USB cable, go to machine -> firmware -> update. After the firmware is updated the program will present to you a dialog box containing the activation code.

    Additional Information:
    MUAR-QVXU-CAYW-CBWQ


    Additional Information:
    MUIS-RQPB-PTHB-QTTB

    Additional Information:
    MUIH-EERP-IADB-TRIP

    Additional Information:
    9zYWBVf5TxKSK7hEr8gFX3EBw5wa0AMMllQqgftIAnKvZ8DXItLxaPbOB3jWvnpczl/sM/De0scRPHfSxWGmcA==

    Additional Information:
    Key: LUQR-BQYI-SCEW-QVBT

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    Additional Information:
    after i copy the code in the lower case i recived the same message (more than 8 times) ,, this is a evaluation...,, what i need to do to register properly?

    Additional Information:
    MUJR-BISM-KRDN-KKER
    056971

    Additional Information:
    0561234

    Additional Information:
    MURL-QPQU-EGBJ-FNMB

    Additional Information:
    MUCE-LFMQ-WBCW-MLHO

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    Additional Information:
    LUTA-ADVJ-FXTW-FBCE

    Additional Information:
    LUTA-ADVJ-FXTW-FBCE

    Additional Information:
    looking for registration key for MUUK-IBTW-ECTL-CJWD

    Additional Information:
    MUXO-PIYY-KNHD-RKLY

    Additional Information:
    MUUE-YYCR-FCIC-VATK

    Additional Information:
    MUUE-YYCR-FCIC-VATK

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    Additional Information:
    MUEY-YLJU-OBRR-LJBV

    Additional Information:
    MUSP-JFDV-EKGQ-OVLW

    Additional Information:
    MUSP-JFDV-EKGQ-OVLW

    Additional Information:

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    THEY ARE ASKING FOR THE ACTIVATION CODE AND SERIAL NUMBER USB BOARD. HOW CAN GET THAT INFORMATION?

  • ARE THERE RECOMMENDATIONS FOR THE PREVENTION OF INSTITUTIONAL OUTBREAKS INFLUENZA?

    The most important factor in preventing outbreaks is annual vaccination of all occupants of the facility, and all persons in the facility who share the same air as the high-risk occupants. Groups that should be targeted include physicians, nurses, and other personnel in hospitals and outpatient settings who have contact with high-risk patients in all age groups, and providers of home care to high-risk persons (e.g., visiting nurses, volunteers).

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    ARE THERE RECOMMENDATIONS FOR THE PREVENTION OF INSTITUTIONAL OUTBREAKS INFLUENZA?

  • WHAT ARE CURRENT RECOMMENDED IEEE EMF OCCUPATIONAL EXPOSURE LEVELS AND GUIDELINES FOR RADIO BASE STATION ANTENNAS?

    The following answer assumes "radio Base Station Antennas" refers to base stations used for personal wireless communications services such as cellular telephone, Personnel Communications Services (PCS), and Enhanced Specialized Mobile radio (ESMR). In the United States, the frequency band allocated for base stations used for personal wireless communications is 869-894 MHz for cellular service, 851-866 MHz for ESMR, and 1930-1990 MHz for PCS. The IEEE exposure limits (maximum permissible exposure—MPE) for occupational exposure (controlled environments where exposures may be incurred by persons who are aware of the potential for exposure) are frequency dependent and are expressed in terms of incident power density. The appropriate value to compare with the MPE is the incident power density averaged over the vertical cross-section of the human body. The occupational exposure limits are also time-averaged over any six-minute interval. The IEEE C95.1-1991 MPE values are shown in the table below:
    IEEE C95.1-1991 Maximum Permissible Exposure (MPE) Values
    Frequency Band Power Density
    General mw/cm2 W/cm2
    851-866 MHz f/300 mW/cm2 2.84-2.88 28.4-28.8
    869-894 MHz f/300 mW/cm2 2.90-2.98 29.0-29.8
    1930-1990 MHz f/300 mW/cm2 6.43-6.63 64.3-66.3
    NOTE: f is in MHz
    As indicated above, these values are for continuous exposure (t > 6 minutes) and are to be compared with the spatial average of the incident power density. all base stations used for personal wireless telecommunications services in the United States are required to comply with the FCC limits (as mandated by the Telecommunications Act of 1996). The FCC limits are based on a hybrid of the IEEE limits and the 1986 recommendations of the National Council on Radiation Protection and Measurements. The FCC MPEs are the same as the IEEE values for frequencies below 1500 MHz but are capped at 5 mW/cm2 (50 W/cm2) for frequencies greater than 1500 MHz.

    Both the FCC and IEEE MPEs for exposure of the public (uncontrolled environments) are one-fifth of the above values. As above, the value to compare with the MPE is the incident power density averaged over the vertical cross-section of the human body. The averaging time for the general public is 30 minutes. Thus, for transient exposures lasting six minutes or less, the MPEs for occupational exposure and exposure of the general public MPEs are the same. For cases of simultaneous exposure from antennas operating in different frequency bands, the ratio of the spatially averaged incident power density in each frequency band to the corresponding MPE for that band is determined and the sum of all such ratios must be less than unity in order to comply.

    R. C. Petersen
    Manager, Wireless and Optical
    Technologies Safety Department

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    WHAT ARE CURRENT RECOMMENDED IEEE EMF OCCUPATIONAL EXPOSURE LEVELS AND GUIDELINES FOR RADIO BASE STATION ANTENNAS?

  • HAVE THERE BEEN ANY STUDIES OF POSSIBLE RADIATION DANGER FROM HEADSETS USED WITH HANDSETS CORDED TELEPHONES? I A TELEPHONE BATTERY-POWERED HANDSET. THIS HANDSET HAS JACK FOR HEADSET, SO YOU CAN WALK AROUND THE HOUSE AND YARD ON YOUR BELT WHILE TALK INTO HEADSET. EITHER OR HEADSET GIVING OFF RADIATION, LIKE CELLULAR PHONE? DANGEROUS AMOUNT RADIATION?

    Headsets have been tested by the manufacturers and meet the current ANSI/IEEE standards for RF safety, the same standards that the Federal Communications Commission enforces under the Telecommunications Act of 1996. These standards place limits on the specific absorption rate (SAR) of radiofrequency (RF) energy in the body. Recent inflamatory articles in British press were not substantiated by testing in ISO-accredited testing facilities at Motorola. Manufacturers of cellular phones are required under FCC regulations to assure that their products meet the SAR limits on both hand-held and hands-free units. Further information may be available from the FDA or from the FCC. Ron Petersen, Lucent C.K. Chou, Motorola

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    HAVE THERE BEEN ANY STUDIES OF POSSIBLE RADIATION DANGER FROM HEADSETS USED WITH HANDSETS CORDED TELEPHONES? I A TELEPHONE BATTERY-POWERED HANDSET. THIS HANDSET HAS JACK FOR HEADSET, SO YOU CAN WALK AROUND THE HOUSE AND YARD ON YOUR BELT WHILE TALK INTO HEADSET. EITHER OR HEADSET GIVING OFF RADIATION, LIKE CELLULAR PHONE? DANGEROUS AMOUNT RADIATION?

  • WHAT ARE SOME USEFUL MODIFICATIONS CAN APPLY TO THE BLACKTOOTH LASER CUTTER?

    Temperature probe monitor. Very valuable. This keeps you up to date on your coolant temperature levels.

    Voltage meter. This will tell you the exact level of voltage/power you are running telling the laser to run at instead of an arbitrary mark on a drawn wheel around your POT.

    Ammeter sensitive to 1mA. This will be sure your not over driving your tube and reducing it's life significantly.

    Hour meter. This will tell you exactly how long your system has been 'on' giving you a more accurate bead on the length of your tubes life.

    Exhaust fan upgrade. The current fan included is 100CFM. You can buy 120mm fans that push 250CFM and I have included a guide on how to go about doing this here. http://buildyourtools.com/phpBB3/viewto ... 8cdd1802bf

    To push the exhaust fan even further, if you have the room/power, I would highly recommend investing in a 600+ CFM "Dust Collector" system. 250CFM is still not suffice to draw all the smoke that can come off of 3mm or 1/8 MDF cutting job.

    A cutting surface. I bought myself a aluminum 'egg crate' mesh from my local HVAC company. They are used a cover for fluorescent lights and work great for low impact cutting surface. They come in 4'x8' sheets and are easily cut to fit. The other side is if you can find a steel honeycomb cutting bed to fit. These can be quite costly or fairly affordable depending where you are looking. The benefit of a steel honeycomb is you can use high power magnets to hold material down.

    Click the link to add information to this solution:
    WHAT ARE SOME USEFUL MODIFICATIONS CAN APPLY TO THE BLACKTOOTH LASER CUTTER?

  • WHAT ARE THE SPINDLE INVERTERS (VFD) INPUT AC CONNECTIONS FROM WALL OUTLET?

    Input to VFD:
    240V Active - R
    240V Neutral - S
    Ground - E

    Additional Information:

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    WHAT ARE THE SPINDLE INVERTERS (VFD) INPUT AC CONNECTIONS FROM WALL OUTLET?

  • WHERE ARE THE WIRING DIAGRAMS FOR BLACKTOOTH LASER CUTTER IN INSTRUCTIONS?

    You can find the wiring diagrams for the blackTooth on step 105 and 106 on the list of instructions on the blackTooth page. Step 105 pertains to the parallel breakout board and step 106 pertains to the USB interface board.

    Additional Information:
    wire size

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    WHERE ARE THE WIRING DIAGRAMS FOR BLACKTOOTH LASER CUTTER IN INSTRUCTIONS?

  • ARE WE SUPPOSED TO GIVE INFANTS PRESERVATIVE-FREE INFLUENZA VACCINE?

    No. CDC and ACIP express no preference for preservative-free vaccine for infants or any other group of vaccine recipients. See page 22 of the 2010–11 ACIP influenza recommendations: www.cdc.gov/mmwr/pdf/rr/rr5908.pdf.

    No scientific evidence exists that thimerosal in vaccines, including influenza vaccines, is a cause of adverse events, unless the patient has a systemic allergy to thimerosal. However, some states have enacted legislation that restricts the use of thimerosal-containing vaccines. Check with your state immunization manager to see if your state is one of them (www.immunize.org/coordinators).

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    ARE WE SUPPOSED TO GIVE INFANTS PRESERVATIVE-FREE INFLUENZA VACCINE?

  • WHAT ARE THE BLACKTOOTH LENS SIZES AND FOCAL LENGTH SPECIFICATIONS?

    The lens is 20mm wide and a 50.6mm focal length (the one included). This lens will stand up to at least 30PSI air assist.

    The mirrors are 25mm wide mirrors.

    Focal length is the distance from the lens to the material for the laser converge into the best focal point. If a lens is listed as 2". You measure 2" from the lens to the material, this will be the tightest point the laser can go before it starts to re-expand again losing focus.

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    WHAT ARE THE BLACKTOOTH LENS SIZES AND FOCAL LENGTH SPECIFICATIONS?

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