radio interference EMI


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A lot of "interference" problems that afflict communities using cellular, PCS, microwave, satellite or other systems have their origins in events that originated outside the premises of the communicator, but the proximity to disseminate or other high power RF installations. An increasing number of communication services is also crowded places with high ambient electromagnetic RF generated by a high concentration of lower power radio transmitters. It wasexpected that about 100,000 new transmission and reception will be needed in coming years to meet demand for new wireless services. The pressure on the availability of the site is forcing the implementation of many services, and the problems of EMI are ubiquitous. Unless stated and properly treated, these problems can seriously hinder the deployment of wireless systems and expensive operation.

Despite EMI may occur dramatically, as the accidentsystems together, his touch is generally more subtle. Victims often suffer from significant degradation of the system before realizing that it is a problem that concerns us. This often occurs during the operation, repair or repair events. Typical signs of interference EMI are:

* Character unusual equipment defective test.
* Problems intermittent power regulator.
* Temporary, unwanted audio, video or digital noise signals superimposed.
* The high rate of unexplained signalsinterruptions.
* Poor or coverage of certain sites unreliable.
* General "malaise" in a particular site.

Many wireless media have always been built in a well-placed, with high-power FM and TV antennas. It is not uncommon for FM signals over 100,000 W or television signals to exceed five million W.

In such situations, there is a real threat that high levels of RF signal will brute force interference problems in wirelessprovide or support the team. The potential for overloading the receiver desensitization, the receipt and harmonic intermodulation interference is important. There are even cases where ambient levels of field strength limits at the approach of radiation risk for staff, including shelters and buildings.

close to AM broadcast stations with effective radiated power up to 250,000 sites W can be subjected to intense electric and magnetic fields, which are coupledteam through the coaxial cables, telephone lines, and grounding and power cables. fundamental and harmonic frequencies of AM stations and modulation of the audio components of overlap case of common data, T-carrier and the spectrum clock. The potential disruption of the system is enormous. Torres commonly associated with mobile sites effectively "concentrate" the signal of AM broadcasting to local values and above the forecasts in space.

Even in places that are not close to broadcasting, areoften miscalculated so there is a significant intervention of the EMI. Although wireless is not generally considered "great power", the concentration of chains on a site can not compete with the power of television. For example, 32 channels maximum power PCS FCC may extend about 50,000 W. A group of eight channels of research can accumulate more than 25,000 W. An installation of wireless cable with 32 channels can contribute more than 200,000 watts in the 2 GHz band.

At these power densities, not only the RFengineer is interested in attitudes EMI, as intermodulation and desensitization, but also the enforcement staff and the direct input signal RF equipment. Perhaps recognizing this potential RF bathroom, the FCC requires that all PCS transmission facility to be inspected and certified free of RF compliance.

Intentional interference EMI RF transmitters is not the whole problem. The mass conversion of the radio equipment room for digital architectures has led toan environment rich in step signals radiated site. As digital signals tend to be square waves with a rich harmonic spectrum, and convergence of clock frequencies in the VHF range, wireless carriers are increasingly finding that they are producing energy right combs EMI through its own and their neighbors are receiving benefits. This problem is compounded as the antennas down. Even the digital equipment that complies with FCC Class "A" specifications can interact with receptorsseveral hundred meters, if not properly protected.

EMI containment management and challenges of the resolution is not as simple as it seems. Action must begin with a clear institutional policy for carrying out the procedures for electromagnetic compatibility in the process of developing the site (often a critical factor is missing). Just as the loss of revenue of a scrambling system of balls is a concern of businesses and should also be a system of dynamic programming free of interference.

Athe more frustrating is trying to define, let alone maintain, a steady state RF situation everywhere. In fact, the electromagnetic environment on the site is better controlled in constant evolution. Most mobile sources are by nature "explosions" and unpredictable in their operating cycle. Even the stations to change the modes and observing irregular hours they operate.

new transmitters, channels and modes of operation can be calculated emission or near the siteand incompatible with existing systems. Identification of new operators is further complicated by the policies of the FCC license on the market and, consequently, there can be no trace of all the exact positions of the transmitter.

Space does not permit a thorough discussion of techniques for solving such problems known as intermodulation and desensitization. However, there are some basic approaches that can help contain or resolve equipment worth less input EMIchallenges

Site analysis *. acquisition of business management, site and design of all systems engineers must consider EMI refers to in his post. Clearly, the ideal scenario would be to select all sites at a sufficient distance external EMI and keep them sterile. In reality, however, system developers must choose sites with respect to the "clean" EMI environment and establish an appropriate legal basis and control of site structureelectromagnetic environment, including the ability to eliminate the sources of worry if the sign consolidation efforts fail.

In general, many potential troublemakers can be identified early in the process of site selection of adequate protection can be designed efficiently in the new system. A careful study of problems, including field measurements where necessary, must be made to identify and document risks, and anticipate the future. (The diagnostic measures mayfor the preparation of the existing zone.) These studies should use proven electromagnetic parametric models and spatial data such as consulting firms specializing in this field.

* Protection against RF. It is not uncommon for a high-level RF site must be occupied, despite the best efforts of the site evaluation, which requires that the site team is surrounded by a virtual "box", designed to block more signals outside the RF input as possible from sensitive circuits.However, a perfectly insulated container is neither practical nor cost effective. There should always be the penetration of the shield box to account for the transmission lines of the antenna, the main power connection, telephone lines, doors, ground wires, air conditioners and water pipes and sewer. The trick is to restrict the passage of the RF by these ideas, too.

Most of the needs of the wireless industry can be met by the shield of innovative applications of the architecture of protection of advanced materials. Fibermitigation compounds, suspensions and coating more traditional techniques can produce an attenuation of 40 dB or more in existing buildings. Even if no "military secret" rules, such mitigation will often be sufficient to prevent the ingress of unwanted RF electromagnetic destructive, and potential hazards of radiation to the site personnel of the team.

In addition to creating the case with any test, other techniques are needed to adequately meetpenetrations, such as the use of filters for power lines and transmission lines and blocking RF signals from the offender's door, air conditioning and other openings. complete identification of the best way to meet this challenge must be exercised for each site. Importantly, the implementation of a comprehensive technical analysis since the beginning of the project will measure and determine the extent of potential problems caused by RF and identify alternatives to ensure effective controlcompatibility of systems and the environment.

Based on these data and other support, shielding and other protective RF may be selected to complement and influence the architectural planning and construction. In some cases it may be necessary to modify the standard electronic designs to ensure that existing facilities and future expansion of the site will remain resistant to RF interference.

Site operators should recognize that the shield "systems" anti-RF input on your computer,and this system is an integral part of the real activity of the site air conditioning or power systems. They must recognize that its system of protection must be cautious. Too often, out of sight, the attitude of mind on the shield components allows future violation of the effectiveness of the protection system.

* Measures of the evidence. test measurements should be incorporated into the overall design process to include baseline measures on suspicion of "threat" of frequencyprotective equipment and new facilities are in place. These data, move a baseline to support future maintenance of prevention, which must be done on a regular basis, and solving problems. Whatever the installation of equipment and site selection process is planned and executed, and not the invariable "unauthorized entry" Wall of cable TV, air conditioning or replacement of any other change that would EMI shield damage or other preventive procedures.

Wheninteference deal with EMI, it is a pay me now or pay later, my world, and the latter option is almost always more expensive. It is never too early to plan for the effective reduction of RF interference. The actions of the first analysis of the RF environment, shielding and other RF interference prevention should be taken into account the principle of site selection, building design or material selection and updating process . It is important to realize that the reduction is a prerequisite for a life-cycle wirelesssite, careful attention to the demanding requirements of the evolving site that can degrade RF EMI or modify the system performance.

A consultant is qualified and experienced engineering EMI compatibility must be maintained in the design and planning process and maintained throughout the operational phase. An analysis of the electromagnetic environment of a potential site wireless avoid costly surprises in the final product, and ensure compatibility between the site andoperator environments.

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