Download Topic 18 Safety

General Licensing Class
RF & Electrical Safety
• Antenna & tower safety
• RF safety
• AC/DC safety
1
RF & Electrical Safety
While working on an antenna system, turn off the
transmitter and disconnect the feed line from it so
there is absolutely no way that someone could
accidentally transmit while you are making the
repairs.
2
RF & Electrical Safety
To insure that no one starts rotating a beam
antenna using the electric powered rotator,
double check that the rotator control unit is
unplugged and tagged “climber aloft.”
3
RF & Electrical Safety
• Preventing falls from a tower is best achieved with
a safety harness. Always be sure that the belt is
rated for the weight of the climber and is within its
service life. You need a hard hat and safety
glasses, too.
4
RF & Electrical Safety
Performing a routine RF exposure evaluation is a
good idea for all amateurs to ensure compliance
with RF safety regulations and that you and your
neighbors are not being “overexposed” to RF
radiation.
5
RF & Electrical Safety
It is always a good idea to locate an antenna as
far away as possible from living spaces that will
be occupied when you are transmitting. This
will help ensure that Maximum Permissible
Exposure (MPE) limits are not exceeded.
6
RF & Electrical Safety
If RF energy from your antenna system is
concentrated on the human body, it heats the
body tissue just like your microwave oven heats
your leftovers. RF burns are a very real thing.
They include those experienced from poor
grounding of the equipment to those received
from touching or standing too close to an antenna
while someone is transmitting.
7
RF & Electrical Safety
You can determine how your station complies with FCC RF exposure
regulation by:
• Using the tables to estimated safe distances based on FCC OET
Bulletin No. 65,
• By your own calculations based on computer modeling,
• You can use a field-strength meter and measure the power density
level.
8
RF & Electrical Safety
Time-averaging is a method of calculating an
individual’s total exposure to RF radiation over a
given period of time. The premise of timeaveraging is that the human body can tolerate
larger amounts of RF radiation if the exposure is
received in short “bursts” as compared to a
constant exposure at the same high level of RF
radiation.
9
RF & Electrical Safety
Duty cycle is the percentage of time the transmitter
is actually sending out energy. The lower duty cycle
permits greater short-term exposure levels to RF
radiation.
10
RF & Electrical Safety
In Section 97.13, the FCC rules state that if your
station’s RF exceeds permissible limits, you “must
take action to prevent human exposure to such RF
electromagnetic fields.”
11
RF & Electrical Safety
Although a simple field-strength meter can show
the presence of radio frequency emissions, it
takes a precisely calibrated field-strength meter
with a calibrated antenna to make accurate
measurements of the RF field.
12
RF & Electrical Safety
There are all sorts of great 5band trap vertical antennas that
work nicely mounted on the
ground. When you’re looking
for a spot to mount an antenna,
keep in mind maximum
permissible exposure limits.
Install it so that no one can
actually walk up to it or stand
near it when you are
transmitting. This goes for your
pets, too.
13
RF & Electrical Safety
If your calculations indicate that you may be
exposing your neighbors to too much RF, you need
to relocate your entire antenna system, or take
precautions to ensure it cannot be pointed in their
direction when transmitting.
14
RF & Electrical Safety
The National Electrical Code covers electrical
safety standards as they relate to conductors and
wiring inside your ham shack. RF exposure limits
to the human body are covered by ANSI, not by the
NEC.
15
RF & Electrical Safety
Ground fault circuit interrupters are found in
newer electrical plug outlets. They instantly
open a circuit to halt current flow when they
detect current flowing from the hot wire to
ground.
16
RF & Electrical Safety
Good station grounding ensures that no
hazardous or dangerous voltages appear on the
metal chassis of your equipment. Without good
grounding you could be shocked when you
touch a piece of equipment.
17
RF & Electrical Safety
Most ham transceivers run on 12 volts DC. Some
base stations may have their own 110 VAC power
supplies built-in. However, linear amplifiers may
require 240 VAC. For single phase 240 VAC, fuse
both the black and red hot wires. NEVER fuse the
neutral white wire or the neutral ground bare
copper wire. Most amplifiers already have the
fuse circuits built in.
18
RF & Electrical Safety
Based on the American Wire Gauge (AWG)
information shown, 14 gauge wire can handle 15
amperes. The easy way to remember this is with
the “F” for “Fourteen” (14 gauge) wiring will handle
Fifteen (15) amps.
19
RF & Electrical Safety
Based on the American Wire Gauge (AWG)
information shown, 20 amperes of continuous current
requires a wire size of AWG #12.
Thick or thin insulation can be
misleading about the actual wire
size! You need to strip off the
insulation from unmarked wire to
determine which gauge wire you
20
RF & Electrical Safety
Linear amplifiers will have
a power supply interlock
switch. If the equipment
is on and the power supply
door is opened, the
equipment will instantly
power off. This protects
you and the equipment
from a high voltage shock.
21
RF & Electrical Safety
Any time you are working on radio equipment
innards, wash your hands when you finish to
remove any lead that might be contained in that
roll of old solder before you grab a sandwich.
22
RF & Electrical Safety
Good engineering practice for a lightning
ground indicates that all grounds be bonded
together with all other grounds.
23
RF & Electrical Safety
Carefully inspect tower grounding circuits and
you will find that all the ground connections
have been swaged rather than soldered. Solder
might melt on a direct lightning strike destroying
the route to ground.
24
RF & Electrical Safety
In an emergency you might power your house
with your generator. Any time you connect a
generator into your home, you MUST ABSOLUTELY
trip all of the breakers to disconnect the incoming
utility power feed.
This ensures you are not sending voltage back
into the grid through your electrical panel, which
could prove dangerous for anyone working on the
lines.
Disconnecting the utility power feed at the panel
will also prevent damage to the generator when 25
the power is restored.
RF & Electrical Safety
Any time you use a generator for power, make
sure the generator is located in a well-ventilated
area; not where someone could inhale the toxic
exhaust. The generator should be properly
grounded, and always store the generator’s fuel
in a safe place away from any inhabited area.
26
G0A12
What precaution should you take
whenever you make adjustments or
repairs to an antenna?
A. Ensure that you and the antenna structure are
grounded.
B. Turn off the transmitter and disconnect the
feed line.
C. Wear a radiation badge.
D. All of these choices are correct.
27
G0B08
supports
What should be done by any person
preparing to climb a tower that
electrically powered devices?
A. Notify the electric company that a person will
be working on the tower.
B. Make sure all circuits that supply power to the
tower are locked out and tagged.
C. Unground the base of the tower.
D. All of these choices are correct.
28
G0B07
Which of these choices should be
observed when climbing a tower
using a safety belt or harness?
A. Never lean back and rely on the belt alone to
support your weight.
B. Confirm that the belt is rated for the weight of
the climber and that it is within its allowable
service life.
C. Ensure that all heavy tools are securely
fastened to the belt D-ring.
D. All these choices are correct.
29
G0A08
Which of the following steps must an amateur operator
take to ensure compliance with RF safety
regulations when
transmitter power exceeds levels
specified in part 97.13?
A.
B.
C.
D.
Post a copy of FCC Part 97.13 in the station.
Post a copy of OET Bulletin 65 in the station.
Perform a routine RF exposure evaluation.
All of these choices are correct.
30
G0A11 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 radiation.
B. Position the antenna along the edge of a wall to
reduce parasitic radiation.
C. Make sure that MPE limits are not exceeded in
occupied areas.
D. Make sure the antenna is properly shielded.
31
G0A01
What is one way that RF energy can
affect human 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.
32
G0A03
How can you determine that your station
complies with FCC RF exposure
regulations?
A. By calculation based on FCC OET Bulletin 65.
B. By calculation based on computer modeling.
C. By measurement of field strength using
calibrated equipment.
D. All of these choices are correct.
33
G0A04
What does “time averaging” mean in
reference to RF radiation exposure?
A. The average amount of power developed by the
transmitter over a specific 24 hour period.
B. The average time it takes RF radiation to have
any long-term effect on the body.
C. The total time of the exposure.
D. The total RF exposure averaged over a certain
time.
34
G0A07
What effect does transmitter duty cycle
have when evaluating RF exposure?
A. A lower transmitter duty cycle permits greater
short-term exposure levels.
B. A higher transmitter duty cycle permits greater
short-term exposure levels.
C. Low duty cycle transmitters are exempt from RF
exposure evaluation requirements.
D. High duty cycle transmitters are exempt from RF
exposure requirements.
35
G0A02
Which of the following properties is important
in estimating whether an RF signal
exceeds the
maximum permissible exposure
(MPE)?
A.
B.
C.
D.
Its duty cycle.
Its frequency.
Its power density.
All of these choices are correct.
36
G0A05
your
What must you do if an evaluation of your
station shows RF energy radiated from
station exceeds permissible limits?
A. Take action to prevent human exposure to the
excessive RF fields.
B. File an Environmental Impact Statement (EIS97) with the FCC.
C. Secure written permission from your neighbors
to operate above the controlled MPE limits.
D. All of these choices are correct.
37
G0A09
What type of instrument can be used to
accurately measure an RF field?
A. A receiver with an S meter.
B. A calibrated field strength meter with a
calibrated antenna.
C. An SWR meter with a peak-reading function.
D. An oscilloscope with a high-stability crystal
marker generator.
38
G0A06 What precaution should be taken when
installing a ground-mounted antenna?
A. It should not be installed higher than you can
reach.
B. It should not be installed in a wet area.
C. It should limited to 10 feet in height.
D. It should be installed such that it is protected
against unauthorized access.
39
G0A10
directional
What is one thing that can be done if evaluation shows
that a neighbor might receive more than the allowable
limit of RF exposure from the main lobe of a
antenna?
A. Change to a non- polarized antenna with higher
gain.
B. Post a warning sign that is clearly visible to the
neighbor.
C. Use an antenna with a higher front-to-back ratio.
D. Take precautions to ensure that the antenna
cannot be pointed in their direction.
40
G0B14
A.
B.
C.
D.
Which of the following is covered by the
National Electrical Code?
Acceptable bandwidth limits.
Acceptable modulation limits.
Electrical safety inside the ham shack.
RF exposure limits of the human body.
41
G0B05
disconnect
device?
Which of the following conditions will cause a
Ground Fault Circuit Interrupter (GFCI) to
the 120 or 240 Volt AC line power to a
A. Current flowing from one or more of the
voltage-carrying wires to the neutral wire.
B. Current flowing from one or more of the
voltage-carrying wires directly to ground.
C. Over-voltage on the voltage-carrying wire.
D. All of these choices are correct.
42
G0B06
Why must the metal enclosure of every
item of station equipment be
grounded?
A. It prevents blowing of fuses in case of an
internal short circuit.
B. It prevents signal overload.
C. It ensures that the neutral wire is grounded.
D. It ensures that hazardous voltages cannot
appear on the chassis.
43
G0B01
Which wire or wires in a four-conductor connection
should be attached to fuses or circuit breakers in a
device operated from a 240-VAC single phase
source?
A.
B.
C.
D.
Only the two wires carrying voltage.
Only the neutral wire.
Only the ground wire.
All wires.
44
G0B03
that uses
A.
B.
C.
D.
Which size of fuse or circuit breaker would
be appropriate to use with a circuit
AWG
number 14 wiring?
100 amperes.
60 amperes.
30 amperes.
15 amperes.
45
G0B02
to 20
A.
B.
C.
D.
What is the minimum wire size that may be
safely used for a circuit that draws up
amperes of continuous current?
AWG number 20.
AWG number 16.
AWG number 12.
AWG number 8.
46
G0B12
What is the purpose of a transmitter
power supply interlock?
A. To prevent unauthorized changes to the circuit
that would void the manufacturer’s warranty.
B. To shut down the unit if it becomes too hot.
C. To ensure that dangerous voltages are removed
if the cabinet is opened.
D. To shut off the power supply if too much voltage
is produced.
47
G0B10
Which of the following is a danger from
lead-tin solder?
A. Lead can contaminate food if hands are not
washed carefully after handling the solder.
B. High voltages can cause lead-tin solder to
disintegrate suddenly.
C. Tin in the solder can “cold flow” causing shorts
in the circuit.
D. RF energy can convert the lead into a poisonous
gas.
48
G0B11
Which of the following is good practice
for lightning protection grounds?
A. They must be bonded to all buried water and
gas lines.
B. Bends in ground wires must be made as close
as possible to a right angle.
C. Lightning grounds must be connected to all
ungrounded wiring.
D. They must be bonded together with all other
grounds.
49
G0B09
of a
Why should soldered joints not be used
with the wires that connect the base
tower to a system of ground rods?
A. The resistance of solder is too high.
B. Solder flux will prevent a low conductivity
connection.
C. Solder has too high a dielectric constant to
provide adequate lightning protection.
D. A soldered joint will likely be destroyed by the
heat of a lightning strike.
50
reason for not placing a gasolinegenerator inside an occupied
fueled
area?
A.
B.
C.
D.
Danger of carbon monoxide poisoning.
Danger of engine over torque.
Lack of oxygen for adequate combustion.
Lack of nitrogen for adequate
combustion.
51
G0B13
What must you do when powering your
house from an emergency
generator?
A. Disconnect the incoming utility power feed.
B. Insure that the generator is not grounded.
C. Insure that all lightning grounds are
disconnected.
D. All of these choices are correct.
52
G0B15
Which of the following is true of an
emergency generator installation?
A. The generator should be located in a wellventilated area.
B. The generator should be insulated from
ground.
C. Fuel should be stored near the generator for
rapid refueling in case of an emergency.
D. All of these choices are correct.
53