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Chapter 9
Electrical and RF Safety
Basic Safety
• Have a master on/off switch for your
station.
• Don’t work on “live” equipment. Check
with a meter first.
• Discharge capacitors before working on
equipment.
• Solder in a well ventilated area. Wash
your hands after soldering to remove any
lead and flux residue.
– Some newer solders do not contain lead
Electrical Shock
• Current is what is felt when shocked – but
it takes a high enough voltage to push that
current through your skin and body.
– Voltages as low as 30 volts can be dangerous
depending on your body’s resistance.
– A current of more than a few milliamperes can
be dangerous.
Wiring and Safety Grounding
• The National Electrical Code (NEC)
provides the information of how to safely
handle AC wiring.
• Always use a 3-prong plug and ground the
metal chassis or cabinet of equipment to
ensure no hazardous voltages appear on
the cabinet.
• A 20 A circuit requires 12 AWG wire.
• A 15 A circuit requires 14 AWG wire.
Protective Equipment
• Fuses break a circuit that is carrying an
excessive amount of current. Slow-blow fuses
can handle some surges beyond their rated limit.
• Circuit breakers are like fuses, but are
resettable.
• Never replace a fuse or circuit breaker with a
larger value!
• Only place a fuse or circuit breaker on a hot wire
– never on a neutral wire.
– One exception: if you wire a radio directly to a battery
in a car you should put fuses on both the hot (+) and
neutral (-).
• A safety interlock switch on equipment will
de-energize the circuit whenever a cabinet
is opened.
• A ground fault circuit interrupter (GFCI)
senses a current imbalance of a few mA
indicating an electrical shock hazard. The
GFCI will break the circuit when this
occurs.
Generator Safety
• Never operate a generator in an enclosed
space. Always have adequate ventilation.
• Carbon Monoxide (CO) is in the exhaust of
a gasoline or diesel generator. Install a
CO detector if you use a generator
regularly.
• A ground rod should be connected to the
metal frame of a generator.
• If you connect the generator to your home
you must have a transfer switch installed.
Lightning
• The best protection is to disconnect all external
cables (antenna, rotator, etc.), unplug
equipment power cords, and telephones.
• Surge protectors or DC ground on antennas will
help prevent strikes by bleeding off charges.
• All towers and antenna mounts should be
grounded.
– Grounding wires should be short and direct.
– Do not solder ground wires. Use mechanical clamps
or welds.
– Lightning grounds should be bonded to other
grounds.
RF Exposure
• Low lever RF exposure is not dangerous.
– Factors for exposure are power level, frequency,
average exposure time, and transmission duty cycle.
• Heating of body tissue occurs when the body
tissue absorbs the RF radiation. This is how a
microwave oven works.
• RF radiation is non-ionizing, which means that
the RF does not have enough energy to ionize
(remove electrons) from material. Note, the
energy of the RF is different from its power. The
energy is the energy of one RF photon.
• The specific absorption rate (SAR) is the
rate at which tissue absorbs the energy of
the incident RF.
• SAR’s are greatest between 30 and 1500
MHz.
• Maximum Permissible Exposure (MPE)
rates also vary with frequency.
• Time averaging is an average of the RF
exposure over a fixed time interval.
• Controlled environments are where
exposure to RF energy is controlled by
access restriction or other measures.
– The averaging period for controlled
environments is 6 minutes.
• Uncontrolled environments are areas with
public access where people may not be
aware of the RF exposure.
– The averaging period of uncontrolled
environments is 30 minutes.
• Duty cycle is the ratio of time the
transmitter is on to the total time.
– If you listen half the time and transmit the
other half, then the duty cycle is 50%.
– A lower transmission duty cycle permits
greater short term exposure for a given
average exposure.
• Emission duty cycle is the average
transmitter power during modulation.
– SSB has an emission duty cycle of ~20%
– FM has an emission duty cycle of 100%
• Average output power = Duty Cycle X
Emission Duty Cycle X Transmitter PEP
Power.
– Example: A 100 W PEP SSB transmitter is
operated during a contest with a 50% duty
cycle. What is the average output power?
• 100 x 20% x 50% = 10 W
• Antenna gain in the direction of the
exposure area must be taken into account.
• All amateurs operating a fixed station must
evaluate the RF exposure caused by their
station.
• RF exposure must be measured only if
transmitter power output exceeds the values
given in Table 8-5 (p. 8-10).
– RF exposure can be measured with a calibrated field
strength meter, or by using a table or online calculator
(http://www.arrl.org/rf-exposure)
• If your evaluation of the RF exposure exceeds
the MPE you can;
– Locate the antenna further away from people. Fence
the area around the antenna.
– Point beam antennas away from people.
– Lower average transmit power.
– Raise the antenna higher.
– Indoor antennas should be evaluated to ensure that
MPE limits are not being exceeded.
Outdoor Safety
• Never place antennas or feed lines near power
lines.
• Before climbing a tower;
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Check tower guying and support hardware.
Crank-up towers must be fully collapsed.
Check all belts and lanyards.
Check ropes and pulleys (for pulling up antennas).
Turn off and secure all equipment. Lock the circuits if
possible.
• Use a climbing belt
– Carabiners on climbing gear should be fully closed.
– Latching hooks should close away from the tower.
– Always use a safety lanyard or redundant lanyard.