batteries, interference and grounding

Power Supplies
Section 5-3
The most common power supply
converts household ac current into
“smooth “
dc current
by using a
Regulated power supplies
are best because they
prevent voltage
fluctuations from
affecting the functions of
the radio’s sensitive
circuits ( T4A03).
A mobile transceiver can run off of
the car’s regular 12 volt battery.
For safety reasons:
the negative connection
of the transceiver
should connect to the
battery’s negative
terminal or to the
engine’s block ground
strap. (T4A11)
Sometimes others can hear a
high pitched whine that varies
with the speed of your engine.
This is called alternator whine and is
cause by noise in the electrical
system inside your own vehicle.
It can be removed by a dc filter at
your radio. T4A10
Which is a good reason to use a regulated power
supply for communications equipment?
A. It prevents voltage fluctuations from reaching
sensitive circuits
B. A regulated power supply has FCC approval
C. A fuse or circuit breaker regulates the power
D. Power consumption is independent of load
What is the source of a high-pitched whine
that varies with engine speed in a mobile
receive audio?
A. The ignition system
B. The alternator
C. The electric fuel pump
D. Anti-lock braking system controllers
Where should a mobile transceiver’s
power negative connection be made?
A. At the battery or engine block ground strap
B. At the antenna mount
C. To any metal part of the vehicle
D. Through the transceiver’s mounting bracket
How much voltage does a mobile
transceiver usually require?
A. About 12 volts
B. About 30 volts
C. About 120 volts
D. About 240 volts
What type of circuit controls the
amount of voltage from a power
A. Regulator
B. Oscillator
C. Filter
D. Phase inverter
What could be happening if another operator
reports a variable high-pitched whine on the
audio from your mobile transmitter?
A. Your microphone is picking up noise from
an open window
B. You have the volume on your receiver set
too high
C. You need to adjust your squelch control
D. Noise on the vehicle’s electrical system is
being transmitted along with your speech
Batteries supply dc power in place of ac
power supplies.
The chemicals in disposable
batteries can be used only
once and then discarded
(ex: zinc carbon batteries)
In Rechargeable
batteries the chemical
reaction can be
reversed and the
battery is recharged.
(ex: a fully charged
nickel-Cadmium battery
has a 1.2 voltage. )
Storage batteries (deep cycle
marine or RV batteries) store
A LOT of energy. They are often
left connected to
a charger and kept
fully charged with
a “trickle” current.
In an emergency, a 12 v
battery can be recharged
by connecting it to a
vehicle’s battery and
running the engine.
Care must be taken when charging or
discharging a battery, if it is done so too
quickly it can vent flammable hydrogen
gas that can cause an explosion.
(Remember the Hindenberg!
What is the nominal voltage of a
fully charged nickel-cadmium
A. 1.0 volts
B. 1.2 volts
C. 1.5 volts
D. 2.2 volts
Which battery type is not
A. Nickel-cadmium
B. Carbon-zinc
C. Lead-acid
D. Lithium-ion
What is one way to recharge a 12-volt
lead-acid station battery if the
commercial power is out?
A. Cool the battery in ice for several
B. Add acid to the battery
C. Connect the battery to a car’s
battery and run the engine
D. All of these choices are correct
What kind of hazard is presented by a
conventional 12-volt storage battery?
A. It emits ozone which can be harmful to
the atmosphere
B. Shock hazard due to high voltage
C. Explosive gas can collect if not properly
D. All of these choices are correct
What can happen if a lead-acid storage
battery is charged or discharged too
A. The battery could overheat and give off
flammable gas or explode
B. The voltage can become reversed
C. The “memory effect” will reduce the
capacity of the battery
D. All of these choices are correct
RF Interference (RFI)
Section 5.4
As the number of electronic devices
continues to increase so does the
possibility of interference between
them and your amateur station.
Radio frequency interference (RFI)
RFI can occur in either direction---to
or from the Amateur radio equipment
Every transmitter’s RF output
signal contains weak harmonics
of the desired output signal and
other spurious emissions that
can cause interference to
nearby equipment.
To prevent harmonics from being
radiated, a low pass filter must be
installed at the transmitter’s
connection to the antenna feed line.
Filters are an important way to prevent or
eliminate RFI.
Ferrite choke filters
are an example of
one type of filter
used to reduce RF
current flowing
on the outside of cables. (T4A09)
Because cordless telephones are rarely
designed to reject RF signals they
often inadvertently act as a receiver
The best way to reduce RFI
in a cordless phone is to
connect an RF filter
at the telephone jack. (T7B05)
Very Strong signals may overwhelm a
receiver’s ability to reject them. This is
called fundamental overload. (T7B04)
If a TV is receiving RFI due to overload
then a filter at the transmitter will not
solve the problem—the problem is
with the receiver (TV)
Sometimes the interfering signal’s
frequency is close to the desired signal's
frequency, (for example a 2 meter signal
from a transmitter is interfering with
broadcast TV channels 2-13.)
In this case a band–reject filter will filter
only the 2 meter signals without filtering
out the desired TV broadcast signals
Part 15 of the FCC rules governs
the responsibilities of owners of
unlicensed devices that use RF
1. They can’t cause a licensed
station a problem
2. They must accept interferences
caused by a licensed station
If there is an interference problem with a
neighbor you should:
Make sure your station is operating properly
Make sure that your station is not causing
interference with your unlicensed devices (TV
and phone)
Work with the other owner to determine the
cause of the problem.
If the problem cannot be eliminated then
inform your neighbor of the rules.
Where must a filter be installed to
reduce harmonic emissions?
A. Between the transmitter and the
B. Between the receiver and the
C. At the station power supply
D. At the microphone
What type of filter should be connected to
a TV receiver as the first step in trying to
prevent RF overload from a nearby 2
meter transmitter?
A. Low-pass filter
B. High-pass filter
C. Band-pass filter
D. Band-reject filter
Which would you use to reduce RF
current flowing on the shield of an
audio cable?
A. Band-pass filter
B. Low-pass filter
C. Preamplifier
D. Ferrite choke
What is meant by fundamental overload in
reference to a receiver?
A. Too much voltage from the power supply
B. Too much current from the power supply
C. Interference caused by very strong
D. Interference caused by turning the
volume up too high
Which of the following may be a
cause of radio frequency
A. Fundamental overload
B. Harmonics
C. Spurious emissions
D. All of these choices are correct
What is the most likely cause of
interference to a non-cordless telephone
from a nearby transmitter?
A. Harmonics from the transmitter
B. The telephone is inadvertently acting as
a radio receiver
C. Poor station grounding
D. Improper transmitter adjustment
What is a logical first step when attempting
to cure a radio frequency interference
problem in a nearby telephone?
A. Install a low-pass filter at the transmitter
B. Install a high-pass filter at the transmitter
C. Install an RF filter at the telephone
D. Improve station grounding
What should you do first if someone tells you that your
station’s transmissions are interfering with their radio or
TV reception?
A. Make sure that your station is functioning properly
and that it does not cause interference to
your own television
B. Immediately turn off your transmitter and contact
the nearest FCC office for assistance
C. Tell them that your license gives you the right to
transmit and nothing can be done to reduce the
D. Continue operating normally because your
equipment cannot possibly cause any interference
Which of the following may be
useful in correcting a radio
frequency interference problem?
A. Snap-on ferrite chokes
B. Low-pass and high-pass filters
C. Band-reject and band-pass filters
D. All of these choices are correct
What should you do if a “Part 15” device in your
neighbor’s home is causing harmful interference
to your amateur station?
A. Work with your neighbor to identify the offending
B. Politely inform your neighbor about the rules that
require him to stop using the device if it causes
C. Check your station and make sure it meets the
standards of good amateur practice
D. All of these choices are correct
RF Grounding
Section 5.5
RF Grounding refers to keeping
all the radio equipment at the
same RF voltage.
The goal is to prevent current
from flowing between the
different pieces of equipment.
RF current flowing in sensitive
audio or data cables causes
interference with the normal
function of the station.
RF feedback, which causes garbled
distorted or unintelligible
transmissions, is an example of this
type of interference.
The best way to RF ground your equipment is to
bond them together to a common ground bus, then
connect the ground bus to your household ground
rod with a short, wide (flat) strap.
Which type of conductor is best
to use for RF grounding?
A. Round stranded wire
B. Round copper-clad steel wire
C. Twisted-pair cable
D. Flat strap
What is a symptom of RF feedback in a
transmitter or transceiver?
A. Excessive SWR at the antenna
B. The transmitter will not stay on the
desired frequency
C. Reports of garbled, distorted, or
unintelligible transmissions
D. Frequent blowing of power supply

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