dtr/h&d joint venture1 radio frequency exposure and compliance issues for a shortwave may 2008...
TRANSCRIPT
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 Venture
A 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
dTR/H&D Joint Venture
Presentation Outline
• Scope of Work• Exposure Standards• Analytical Work• Measurement Program• Findings
dTR/H&D Joint Venture
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 – [email protected]
Stephen Lockwood - [email protected]
www.dlr.com & www.hatdaw.com