radio frequency exposure and compliance issues for a shortwave may 2008

Radio Frequency Exposure and Compliance Issues for a ShortwaveMay 2008Matthew W. Folkert, MSEEEStephen S. Lockwood, P.E.dTR/H&D Joint VentureA Joint Venture of the Consulting Engineering firms of duTreil Lundin & Rackley and Hatfield & Dawson

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HCJB - Pifo, Equador

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HCJB - Pifo, Equador

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Presentation OutlineScope of WorkExposure StandardsAnalytical WorkMeasurement ProgramFindings

Scope of WorkConduct a Maximum Permissible Exposure Evaluation (MPE) of All IBB Transmitting Facilities16 Shortwave and Mediumwave Stations WorldwideLimited to a SurveySafety Seminar and Plan

IBB Stations Worldwide

Schedule of Site VisitsDelano - 1998Greenville 2001Kavala, Rhodes & Kuwait - 2001Morocco - 2002Sao Tome - 2002Philippines - 2003Botswana - 2003Sri Lanka - 2005Germany 2006Tinian - 2007Thailand - 2008

Analytical WorkModeling Using NEC-2Curtain Antennas with Full Reflecting ScreenRhombic AntennasE and H Field 2 Meters Above Ground

Curtain Antenna : E-Field

Curtain Antenna : H-Field

Exposure StandardsIEEEC95.1-2005ICNIRP(International Committee on Non-Ionizing Radiation Protection)Guidelines For Limiting Exposure To Time-varying Electric, Magnetic and Electromagnetic Fields(up to 300 GHz)OET(FCC Office of Engineering & Tech.)Bulletin 65

IEEE Occupational Standards

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IEEE Public Standards

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RF Exposure MechanismsExposure to radio frequency (RF) fields results in the absorption of energy in the body The mechanism of this energy transfer is the body acting as an antenna or, for contact currents, a semiconductive load for an RF source (i.e.RF source can be a tower, antenna, guy wire, etc)

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RF Exposure Mechanisms (continued)The direct result is RF currents flowing in the body If the currents are large enough the body temperature rises At a certain rate of energy absorption biological effects also occur

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The Electromagnetic Spectrum

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Measurement ProgramIEEE C95.3 Recommended Practice for the Measurements of Potentially Hazardous Electrical Fields RF and MicrowaveSpatial Averaged over vertical line from 0.2 m 2.0 m20 cm from any object

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Spatial AveragingMeasure over the area of a Human Body

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Equipment UsedNARDA Model 8718B Electromagnetic Radiation Survey Meter

E-Field Probe: 8742H-Field Probe: 8732Both shaped probesConforms to IEEE Occupational Standard

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Equipment UsedHoladay Contact Current Meter

Clamp-on Current Transformer: HI-3702System Readout: HI-44161 mA to 1 A100 kHz to 100 MHz

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Contact CurrentPhysical Contact with a Conductive Material

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Typical Data Sheet

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Findings Where would you expect to find high fields at a shortwave broadcasting facility?

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Transmitter Building?

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Control Room?

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Switch Matrix?

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Transmission Lines?

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Baluns?

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Antenna Ground Works?

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Antenna Near Field?

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Warning Signs

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Conclusions Closer to ground of RF conductors the higher exposure levelUnder Baluns -Open Wire Transmission LineAntenna Ground WorksAreas in main beam of antennas for 100 kW or greater within 100 meters

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Questions?Matt Folkert matt@dlr.com Stephen Lockwood - lockwood@hatdaw.comwww.dlr.com & www.hatdaw.com

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