dTR/H&D Joint Venture 1

Radio Frequency Exposure and Compliance Issues for a Shortwave

May 2008

Matthew 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 Outline

• Scope of Work• Exposure Standards• Analytical Work• Measurement Program• Findings

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Scope of Work

• Conduct a Maximum Permissible Exposure Evaluation (MPE) of All IBB Transmitting Facilities– 16 Shortwave and Mediumwave Stations

Worldwide– Limited to a Survey

• Safety Seminar and Plan

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IBB Stations Worldwide

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

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Analytical Work

• Modeling Using NEC-2• Curtain Antennas with Full Reflecting

Screen• Rhombic Antennas• E and H Field 2 Meters Above Ground

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Curtain Antenna : E-Field

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Curtain Antenna : H-Field

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Exposure Standards

• IEEE– C95.1-2005

• ICNIRP(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

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IEEE Occupational Standards

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IEEE Public Standards

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RF Exposure Mechanisms

• Exposure 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 Program

• IEEE C95.3 Recommended Practice for the Measurements of Potentially Hazardous Electrical Fields – RF and Microwave

• Spatial Averaged over vertical line from 0.2 m – 2.0 m

• 20 cm from any object

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Spatial Averaging

Measure over the area of a Human

Body

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Equipment Used

•NARDA Model 8718B Electromagnetic Radiation Survey Meter

•E-Field Probe: 8742•H-Field Probe: 8732•Both “shaped” probes•Conforms to IEEE Occupational Standard

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Equipment Used

•Holaday Contact Current Meter

•Clamp-on Current Transformer: HI-3702•System Readout: HI-4416•1 mA to 1 A•100 kHz to 100 MHz

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Contact Current

Physical 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 level– Under Baluns -– Open Wire Transmission Line– Antenna Ground Works

• Areas 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.com

www.dlr.com & www.hatdaw.com