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theRSGB @theRSGB
1
Ofcom EMF Licence changes - 2020
John Rogers M0JAV
“Implementation of measures to require compliance
with international guidelines for limiting exposure to
electromagnetic fields (EMF)”
theRSGB @theRSGB
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Proposed Licence Condition:
“Licensee shall only establish, install, modify or use Relevant
Radio Equipment if the electromagnetic field exposure levels
produced by the Relevant Radio Equipment are below the basic
restrictions in the relevant tables for general public exposure
identified in the ICNIRP Guidelines in any area that is accessible
to the general public”
Ofcom want to foster a climate of compliance not a “high handed”
enforcement approach, but they would act against reckless individuals
Ofcom proposals for limiting exposure to EMF
theRSGB @theRSGB
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To comply, you perform an assessment using any appropriate combination of the following:
1. Following manufacturers’ guidance/instructions
2. Establishing consistency with pre-assessed compliant configurations
3. Performing desk-top calculations
4. Making sure that people are not present in areas where ICNIRP reference levels are not met, before transmitting
5. Taking measurements
Then keep records of what you have done, and when.
– Aim should be Compliance by Design
How can amateurs Demonstrate Compliance
theRSGB @theRSGB
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• Electromagnetic energy can be absorbed by body and cause a temperature rise, or tingling nerves
• ICNIRP gives guidelines for limiting exposure including:
– Basic restrictions and reference levels for
– two levels of limits Occupational and General Public
– for two types of exposure Local and Whole-body
– for three measures peak, averaged for 6 minutes and for 30 minutes
What is that all about ?
When Transmitting:
Amateurs can be in the occupational
zone
General public outside the
occupational zone in the compliance
zone
Zone shape is antenna dependent
Potential
theRSGB @theRSGB
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How Guideline reference levels are calculated
> 6 minute exposure < 6 minute exposure
41 page document guideline document
theRSGB @theRSGB
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ICNIRP Reference Levels for General Public Exposure
Need to compare Electric
Field, Magnetic Field and
Power Density with
recommended maximum
exposure levels (frequency
dependant) to determine
compliance in near and far
field conditions
Then there are limb
current limits
Ofcom calculator is conservative but if separation maintained you will be Compliant
• Input PEP including feeder losses, antenna gain and EIRP multiplier
• Derives average power including modulation factor and Tx/Rx ratio
• Calculate separation to stay below recommendations at operating power level
• Keep people out of the non compliant zones while transmitting
theRSGB @theRSGB
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Using the Ofcom Calculator - RSGB frontsheet
theRSGB @theRSGB
8 Flowchart to Demonstrate Compliance
Keep a
Record of
results
EMF
Employ
any
Needed
Mitigations
Done
Inherently
Compliant
Normally
Compliant
Compliant
Separation
achievable
?
Are
Exposure
Zones
Accessible
?
Is EIRP <
10W ?
Calculate
Exposure
Zones
Use
RSGB /
Ofcom
Calculator
Y
Y
Y
N
N
N
1 Screening Evaluation
Pre-assessed Configurations,
power, antenna, height, orientation
2 Calculate Separation
needed for compliance – use
RSGB/Ofcom calculator based on
far field so it is
deliberately conservative
3 Advanced methods
near field modelling,
compliant power contours,
other mitigation measures to help
achieve compliance…
Advanced
methods if
needed
theRSGB @theRSGB
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• We should all aim to be “Compliant by Design”
– Follow Manufacturers Instructions and Guidelines
– Follow Ofcom and RSGB advice - Radios will perform better if you do
• Configure/operate station using pre-evaluated guidance
• Run the Ofcom calculator to give compliant separation
• Implement mitigations if required to demonstrate compliance
– Turn down the power
– Adjust antenna type / position / height / limit operating beam headings
– Don’t transmit if a person is in a potential exposure exceedance zone
• If compliance not demonstrated, use advanced modelling
and/or revise mitigations until compliance is demonstrated
Good Practice to achieve Compliance
theRSGB @theRSGB
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Research - V/UHF Compliance Zones, 70cm Yagi
Ofcom calculator vs NEC 5 Clay ground
theRSGB @theRSGB
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• Identify differing ICNIRP compliance requirements over amateur licence frequency range – Exposure assessment is NOT just about field strength at a point
• Develop modelling tools for: – computing electric and magnetic fields (e.g., latest NEC 5)
– analysing data to determine exposure (e.g., Mathematica)
• Establish range of amateur antenna types / configurations to be evaluated
• Apply modelling to establish guidance on achieving ICNIRP (UK), FCC(US) compliance – Contour maps to show exposure from antenna at given power
– Contour map showing max power for compliance at location
– Minimum height / separation guidance
• Prepare guidance on RF Safety with Ofcom / PHE
EMF Guidance & Tools – Research jointly with ARRL
theRSGB @theRSGB
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Thank You!
Any Questions?
theRSGB @theRSGB
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Research - EMF exposure contours for dipole
E Field H Field
Dipole Inverted V
theRSGB @theRSGB
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• Develop an increasing number of pre-assessed off-the-shelf
configurations so compliance is demonstrated by meeting that
configuration: - – HF dipole [beam] – no part of any radiating element less than Z m AGL for W
power [range of X, Y & frequencies]
– Ground mounted vertical – X m separation for W power [range of X, Y &
frequencies]
– Power < W Watts, and you can’t touch antenna with extended arms is Okay
• Good practice – Matching at antenna to limit feeder radiation
– Radiating elements as high as practical
– People not too close to antenna when operating
• Training – Improved syllabus
– Documentation prepared and website updated
Proposed guidelines and training