G0 RF Safety

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G0RF Safety

• Cant touch this, at least not while its
  transmitting!

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Common Sense will tell you a lot when it comes to
RF Safety.
Common sense saves lives answers a lot of test
questions!
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G0B01 What are the FCC's RF-safety rules designed
to control? A. The maximum RF radiated
electric field strength B. The maximum RF
radiated magnetic field strength C. The
maximum permissible human exposure to all RF
radiated fields D. The maximum RF radiated
power density
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G0A01 Depending on the wavelength of the signal,
the energy density of the RF field, and other
factors, in what way can RF energy affect body
tissue? A. It heats body tissue B. It causes
radiation poisoning C. It causes the blood
count to reach a dangerously low level D. It
cools body tissue
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2 Types of Radiation

• Ionizing
• Gamma and X-ray
• Can cause ionization of atomic structure
• Not good for your DNA
• Non-ionizing
• Radio waves
• Can cause heating of biological tissue
• If sufficient energy is present, can cause burns

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RF Heating

• Radio waves can heat body tissue.
• Works exactly like your microwave oven.
• The area most likely to be injured is the eye as
  it lacks sufficient blood flow for cooling.
• The eye can form cataracts from repeated exposure
  to high levels of RF energy.
• NEVER touch an antenna or other RF source. You
  could be severely burned.

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A little history

• Ham radio is a very safe activity.
• We listen MUCH more than we transmit.
• In 1996, the FCC announced new rules governing
  human exposure to RF
• Added to amateur license exams in 2000.

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And a little science

• Human body natural resonant frequency
• 35 MHz (grounded)
• 70 MHz (insulated from ground)
• 400 MHz (head)
• 1270 MHz (eyes)
• Specific Absorption Rate (SAR)
• Rate at which body absorbs RF
• Highest at natural frequencies

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G0A07 At what frequencies does the human body
absorb RF energy at a maximum rate? A. The
high-frequency (3-30-MHz) range B. The
very-high-frequency (30-300-MHz) range C. The
ultra-high-frequency (300-MHz to 3- GHz) range D.
The super-high-frequency (3-GHz to 30- GHz)
range
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G0A05 RF radiation in which of the following
frequency ranges has the most effect on the human
eyes? A. The 3.5-MHz range B. The 2-MHz
range C. The 50-MHz range D. The 1270-MHz
range
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Controlled and Uncontrolled Environments

• Controlled Environments
• The amateur operators household and property
• Persons here are aware of RF risks, and have
  control of the transmitting equipment.
• Uncontrolled Environments
• Your neighbors household and property
• Persons here are generally not aware of RF risks
  and have NO control over the transmitter.

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Exposure Averaging Times

• Controlled Environments
• The exposure averaging time is
• 6 Minutes
• Uncontrolled Environments
• The exposure averaging time is
• 30 Minutes

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Power Density

• Measured in milli-watts per square centimeter
• The rules are most stringent between 30 MHz and
  300 MHz.

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Maximum Exposure Limits (MPEs)
Taken from ARRL General Class Manual
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G0A08 What does "time averaging" mean when it
applies to RF radiation exposure? A. The
average time of day when the exposure occurs B.
The average time it takes RF radiation to have
any long term effect on the body C. The total
time of the exposure, e.g. 6 minutes or 30
minutes D. The total RF exposure averaged over
a certain time
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Routine Station Evaluations

• FCC relies on us to make our own evaluations to
  ensure compliance.
• Most evaluations are done with comparisons
  against charts.
• OET Bulletin No. 65
• Limits will depend on the following
• Frequency
• Duty Cycle
• Antenna Height

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Exemptions based on power output
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G0C07 Which of the following steps might an
amateur operator take to ensure compliance with
the RF safety regulations? A. Post a copy of
FCC Part 97 in the station B. Post a copy of
OET Bulletin 65 in the station C. Nothing
amateur compliance is voluntary D. Perform a
routine RF exposure evaluation
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G0A09 What guideline is used to determine whether
or not a routine RF evaluation must be performed
for an amateur station? A. If the transmitter's
PEP is 50 watts or more, an evaluation must
always be performed B. If the RF radiation from
the antenna system falls within a controlled
environment, an evaluation must be performed C.
If the RF radiation from the antenna system
falls within an uncontrolled environment, an
evaluation must be performed D. If the
transmitter's PEP and frequency are within
certain limits given in Part 97, an evaluation
must be performed
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G0A10 If you perform a routine RF evaluation on
your station and determine that its RF fields
exceed the FCC's exposure limits in
human-accessible areas, what are you required to
do? A. Take action to prevent human exposure to
the excessive RF fields B. File an
Environmental Impact Statement (EIS- 97) with the
FCC C. Secure written permission from your
neighbors to operate above the controlled MPE
limits D. Nothing simply keep the evaluation
in your station records
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G0B10 Which of the following amateur radio
stations are subject to routine environmental
evaluation? A. Those stations that use
gain-type antennas at HF frequencies B. All
except portable stations C. All except those
stations where no one is exposed to RF
radiation D. Those stations with transmitter
output levels exceeding 500-watts PEP on the
40, 75/80 and 160 meter bands
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Repeater Sites
G0B02 At a site with multiple transmitters, who
must ensure that all FCC RF-safety regulations
are met? A. All licensees contributing more
than 5 of the maximum permissible power density
exposure for that transmitter are equally
responsible B. Only the licensee of the station
producing the strongest RF field is
responsible C. All of the stations at the site
are equally responsible, regardless of any
station's contribution to the total RF field D.
Only the licensees of stations which are
producing an RF field exceeding
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Duty Cycle

• How much of the time is the transmitter
  operating?
• AM 100
• FM 100
• SSB 20
• CW 50

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Field Strength

• Calibrated meter
• Antenna Fields
• Near Field
• ½ wavelength from center
• Far Field
• Boundary determined by
• Physical antenna size
• Signal Wavelength
• Field Strength measured in millivolts per meter

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Antenna Fields
Here, we consider a simple wire antenna.
Antenna
Far (Radiating) Field
Near Field
Reactive Field
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Antenna Field Calculations
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Lets Do One!
You have an 18 MHz Yagi that has a far-field
density of 10 mW / sq. m at 3 wavelengths.
What will the power density be at 6 wavelengths?
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Antenna Field Calculations
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Lets Do Another One!
You have an 10 MHz dipole that has a far-field
strength of 1 millivolt per meter at 5
wavelengths.
What will the field strength be at 10 wavelengths?
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RF Safety for Dummies

• Install your antenna away from people, especially
  your neighbors. The higher the better.
• Make sure your antenna is not near or could fall
  on a power line.
• Keep your hands and other body parts away from
  the antenna and feed lines.
• Lets see how well you can do with these
  questions!

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G0D01 Considering RF safety, what precaution
should you take if you install an indoor
transmitting antenna? A. Locate the antenna
close to your operating position to minimize
feed line losses B. Position the antenna along
the edge of a wall where it meets the floor or
ceiling to reduce parasitic radiation C.
Locate the antenna as far away as possible from
living spaces that will be occupied while you
are operating D. Position the antenna parallel
to electrical power wires to take advantage of
parasitic effects
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G0D03 What is the best reason to place a
protective fence around the base of a
ground-mounted transmitting antenna? A. To
reduce the possibility of persons being exposed
to levels of RF in excess of the maximum
permissible exposure (MPE) limits B. To
reduce the possibility of animals damaging the
antenna C. To reduce the possibility of
persons vandalizing expensive equipment D. To
improve the antenna's grounding system and
thereby reduce the possibility of lightning
damage
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G0D07 Why should directional high-gain antennas
be mounted higher than nearby structures? A. To
eliminate inversion of the major and minor
lobes B. So they will not damage nearby
structures with RF energy C. So they will
receive more sky waves and fewer ground waves D.
So they will not direct excessive amounts of
RF energy toward people in nearby structures
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G0D11 Why should you avoid using attic-mounted
antennas? A. They may expose people in the
house to strong, near field RF energy B. The
attic may not have adequate thermal insulation
for the antenna C. People moving around in the
house might detune the antenna D. All of these
choices are correct
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Congratulations!
You are not a dummy!
And, to reiterate, when it comes to RF safety,
common sense rules!
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Like we said, common sense when it comes to RF
safety!