Transcript Slide 1

Radio and Electricity
Radio works because of
electricity, so to understand radio,
you have to know a little bit about
electricity. In this group, we’ll
get some of the basics of
electricity out of the way. There
are three units we will study
related to electricity in this group
– voltage, current, and power. By
the time you are ready for your
test, you will be very familiar with
all of them.
Release 1.0 – September 2006
1
Static Electricity
If you have ever shuffled across a
carpet and touched a doorknob on a cold
dry day, you probably got a nice little
shock.
You probably also heard the crackle of
an electric spark at your fingertip. If
the room was dark, you may have even seen
the spark. You may have seen the same
thing when you combed your hair, pulled
off a sweater, or slid across a cloth car
seat.
This is called static electricity.
Release 1.0 – September 2006
2
The Source of Static
Electricity
To understand where static electricity
comes from, we first have to learn (or
review) just a little bit of chemistry.
All the stuff around us – solids,
liquids and gases – is called “matter.”
All matter is made of extremely tiny
particles called “atoms.” Atoms are far
too small to be seen, even with the best
microscopes, but we still know quite a bit
about them.
Release 1.0 – September 2006
3
The Helium Atom
Take a look at the helium atom. It has two
protons and two neutrons in its nucleus, with two
electrons spinning around the nucleus.
Release 1.0 – September 2006
4
Atoms
Like the helium atom, all atoms are made of a
tightly packed center called a “nucleus” that is
made up of even smaller particles called “protons”
and “neutrons.” The proton has a positive charge
and the neutron has a neutral charge. Buzzing
around this nucleus of protons and neutrons are
particles that are many times smaller than even
the protons and neutrons. These particles are
called “electrons” and have a negative charge.
Electrons circle around the nucleus in paths that
are called “orbits.”
Don’t worry too much about all this charge
business just yet, but do try to remember that
protons have a positive charge, electrons have a
negative charge, and neutrons have a neutral
charge
Release 1.0 – September 2006
5
Kinds of Atoms
The number of protons in an atom determines what
kind of atom it is. For example, a copper atom, shown
here in diagram form, has exactly 29 protons represented
by the “+” in the nucleus or center. A typical copper
atom will also have 34 neutrons, but that number can
vary. The 29 protons are matched by 29 electrons in the
shells or orbits surrounding the nucleus.
Release 1.0 – September 2006
6
Electron Charges = Static
Electricity
A long time ago, people
figured out that if you rubbed
certain substances together such as fur and rubber - a
charge would be produced, just
like the charge produced by
your shuffle across a carpet on
a cold day.
Release 1.0 – September 2006
7
Electron Charges
It turns out that this charge is simply a bunch of
loose electrons that have no place to go. In some
atoms, electrons are not held very tightly and can
easily be removed. When a rubber rod is rubbed with
fur, electrons are removed from the fur and build up on
the rubber rod as static electricity.
Release 1.0 – September 2006
8
Static Electricity
So static electricity is just
a bunch of electrons looking
for some place to go. When you
shuffle across a carpet, you
pick up loose electrons. When
you get to a metal doorknob,
these electrons are attracted
to that metal and – ZAP!
Release 1.0 – September 2006
9
Cute, But No Good For
Radio
Static electricity is interesting to play
with. It’s fun to shock someone else instead of
the doorknob. (Come on, admit it. You know
you’ve done that!) It is also interesting to see
the sparks fly when you pull off your sweater in a
darkened room. And it is really cool to watch the
ultimate static electricity spark – a lightning
bolt!
However, static electricity is no good for
radio. So why did we bother with it? Because you
need to understand that electricity is electrons.
Let me say that again. Electricity is electrons!
So let’s get on to electricity we can use!
Release 1.0 – September 2006
10
The Humble Flashlight
A simple flashlight is
nothing more than a bulb, one
or more batteries, and a switch
to turn it on or off.
Release 1.0 – September 2006
11
Inside the Flashlight
Look inside the flashlight and you will
see that the end of the bulb tip touches
the tip of one battery, and that the side
of the bulb touches metal – usually the
metal reflector. This reflector comes in
contact with the switch. If you look
carefully, you will see that the this
switch is connected to the bare metal
spring at the bottom of the flashlight,
and that spring touches the bottom of the
other battery. Finally, the tip of the
bottom battery touches the bottom of the
top battery.
Release 1.0 – September 2006
12
Flashlight – Schematic
Diagram
If you diagram the flashlight, it
looks something like this:
Release 1.0 – September 2006
13
Schematic Diagram
Notice the symbols that are used to represent the
switch, bulb and batteries. These are “schematic
symbols.”
Also notice that there is a continuous loop from the
bulb to the switch to the batteries and back to the
bulb. This loop is called a circuit.
When the switch is open, the circuit is broken. We
call that an “open circuit.” When the switch is closed,
there is an unbroken loop. We say that the circuit is
now “closed” because of this unbroken loop.
When the circuit is closed, electricity can begin to
move through this closed loop from the batteries,
through the bulb, through the closed switch, and back to
the batteries at the other end.
Release 1.0 – September 2006
14
Simple Light Circuit
This may be a little bit easier to see if we
connect everything together with wires. Here you
see a bulb from a Christmas tree light set
connected to two batteries and a crude switch. As
pictured, the switch is open and the light is off.
Release 1.0 – September 2006
15
Simple Light Circuit
Press the switch and the light
comes on.
Release 1.0 – September 2006
16
So what’s Happening?
When you press the switch, the circuit is
closed and electricity (electrons) begins to flow
from the negative (-) end of the battery where
they are stored up, through the wire loop to the
bulb, and back into the positive (+) end of the
other battery where the battery is hungry for all
those extra electrons. As the electricity flows
through the bulb, some of the energy of this flow
lights up the bulb.
Unlike static electricity, which is just a
bunch of electrons that will jump ship and make a
spark at the first chance they get, this kind of
electricity is a nice flow of electrons through a
circuit that can actually do some useful work.
Release 1.0 – September 2006
17
Conductors
Some substances, including most metals,
provide an easy path for electrons to move through
them. Any substance that allows electrons to flow
freely through it is called a “conductor.” One
excellent conductor is copper. Shown below is a
piece of stranded copper wire. (“Stranded” means
that the wire is actually made up of a number of
smaller wires twisted together.)
Release 1.0 – September 2006
18
Insulators
Other substances do not allow electrons to
flow through them. They are called “insulators.”
One excellent electrical insulator is glass.
Other insulators include rubber, wood and plastic.
Insulators, such as the black plastic shown here
surrounding the copper wire, helps to prevent
electric shock by not allowing electrons to pass
through.
Release 1.0 – September 2006
19
Current
Now with all of that
information, here is the first
big idea. This orderly flow of
electrons in an electric
circuit is called current. It
is this electric current that
is the workhorse of radio and
electronics!
Release 1.0 – September 2006
20
Current Is Measured In
Amperes (Or Amps)
We need to measure just how
much current we have flowing
through a circuit. Electrical
current is measured in a unit
called amperes. This unit is
often abbreviated to “amps.”
Release 1.0 – September 2006
21
How Do We Measure Amps?
The instrument used
to measure the flow
of current in an
electrical circuit is
called an ammeter.
The one shown here
measures in
“milliamperes”
(milliamps) or
thousandths of an
ampere
Release 1.0 – September 2006
22
Voltage and Volts
Sometimes we need to know just how hard
current is being pushed through a circuit.
Imagine a water hose, and imagine that the
water in that hose is like electrons
flowing through a wire. Now suppose this
hose passes a gallon of water every
minute. If you squeeze the hose, it will
still pass the same amount of water, but
it will pass it out in a smaller and
sharper stream. You haven’t changed the
amount of water flowing, but you have
changed the pressure.
Release 1.0 – September 2006
23
Voltage and Volts
Electric current is like that as
well. Without changing the number
of electrons flowing in the circuit,
we can change the pressure on those
electrons. The pressure placed on
those electrons is called “voltage.”
It is also sometimes called
“electromotive force” or “EMF.”
Regardless of what it is called, it
is measured in units called “volts.”
Release 1.0 – September 2006
24
How Do We Measure Volts?
The instrument
used to measure
Electromotive
Force (EMF) (or
voltage) between
two points such
as the poles of a
battery is called
a voltmeter.
Release 1.0 – September 2006
25
Batteries
We often see
batteries measured
in volts. A
typical AA, AAA, C
or D cell produces
an electrical
pressure of about
1.5 volts. If the
cells are stacked
together “+” end
to “-“ end, we can
add their voltage.
So the total
voltage in our
flashlight, as
well as the simple
light circuit, was
about three volts.
Release 1.0 – September 2006
26
Batteries for Hams
The most useful battery for
hams for field work is the
automobile battery because it
can supply the voltage needed
for most amateur radios we
might want to run in our
vehicles. The typical
automobile battery usually
supplies about 12 volts.
Release 1.0 – September 2006
27
Gel Cell Rechargeables
Today, many hams also use high capacity 12
volt “gel cell” batteries such as the one shown
here. They are relatively inexpensive, but care
must be taken to charge them properly!
Release 1.0 – September 2006
28
Power - Watts
We still have a few more terms to
go. We measure the total electric
power used or produced with a unit
called “watts.” One good example is
the light bulb. Light bulbs are
classified based on the number of
watts they use. (This also gives
some indication of how bright the
bulb will be. We’ll learn more
about power in a bit, but for now,
remember that electrical power is
measured in watts.
Release 1.0 – September 2006
29
“Resistance Is Futile!”
Only if you are the Borg! In
electricity, resistance is very useful.
Consider our simple light circuit. When
electricity flows through a metal wire,
the electrons zip along with very little
to slow them down. But when these
electrons hit something like the tiny
filament inside a bulb, it resists the
flow of these electrons. This resistance
changes some of the electrical energy into
the light we wanted in the first place.
Release 1.0 – September 2006
30
Resistance - Ohms
There are some materials, such as
the filament in the light bulb, that
oppose current flow. The term used
to describe opposition to current
flow is called resistance.
This resistance can also be
measured, and it is very useful to
do so. The basic unit of resistance
is the ohm.
Release 1.0 – September 2006
31
The Multimeter
For the Technician exam, you have
to know that the ammeter measures
current (amps), and the voltmeter
measures electromotive force (or
voltage). You do not have to know
that the ohmmeter is used to measure
resistance. Actually, all three of
these can be measured with a single
meter called a “multimeter.” A good
multimeter is very inexpensive and
extremely useful to have around.
Release 1.0 – September 2006
32
The Multimeter
Here is a typical
multimeter that will
measure voltage,
current and
resistance. It
costs less than ten
dollars, and is a
very useful tool
that no ham should
ever be without!
Release 1.0 – September 2006
33
Direct Current
In our simple light circuit,
electricity leaves the batteries
from one end, flows through the wire
in one direction, and enters the
other end of the batteries. In
other words, the electron flow (or
current) is in one direction only.
Current that flows only in one
direction is called direct current,
and is abbreviated DC.
Release 1.0 – September 2006
34
Alternating Current
Electric current in your home works almost the
same way, but not quite. Because of the way
household electricity is produced, it does not
flow in the same direction all the time. In fact,
it is constantly reversing direction. As far as
doing useful work, it doesn’t matter whether the
electrons are moving in the same direction all the
time or constantly changing direction. As long as
the electrons are moving, the work will get done.
When an electric current reverses direction on
a regular basis, it is called alternating current,
and it is abbreviated AC.
Release 1.0 – September 2006
35
Representing AC
We can represent the flow of
alternating current using a wavy line like
this one, called a sine wave. (Don’t
worry about why it’s called a sine wave.
There’s a good reason, but you don’t need
to know it for the Technician test.)
Release 1.0 – September 2006
36
An Electron Roller Coaster
Now imagine a tiny electron riding along this
sine wave, kind of like a roller coaster. When
the electron goes up the curve, it is traveling in
one direction. When it goes back down the curve,
it has reversed itself and is traveling in the
opposite direction.
Release 1.0 – September 2006
37
Cycle
Let’s say we start at the point on the roller
coaster labeled “A” and time how long it takes for the
electron to get to “B” on the roller coaster. If you
look carefully, you’ll see that the electron went up,
then all the way down, and all the way back up. In
other words, it went through one complete curve of this
roller coaster. We call this complete trip down in one
direction and all the way back in the other “one cycle”
Release 1.0 – September 2006
38
Frequency
With any good roller coaster ride, the
faster the better! So let’s suppose we
want to measure how fast our little
alternating current electron is going up
and down this roller coaster. We want to
know how many times our electron is
reversing directions in one second. If we
time the reverses of direction in U.S.
household alternating current, it turns
out that it reverses about sixty times per
second. Since each complete reversal is
one cycle, we say that alternating
household current reverses at sixty cycles
per second.
Release 1.0 – September 2006
39
Frequency Definition
Frequency is the measure of the number
of cycles per second an alternating
current reverses. It is measured in a
unit called the hertz. One hertz is equal
to one cycle per second, and the Hertz is
the standard unit of frequency.
Based on this, the AC current in a U.S.
household is 60 Hertz.
Whew! That was a lot of stuff to
remember. If you are not sure you
understand it, go back over this section
until you do.
Release 1.0 – September 2006
40
Check-Up Time!
Now let’s try the questions from
this group.
You should make a note of any that
you miss for later review.
Release 1.0 – September 2006
41
T4A01
Electrical current is measured
in which of the following
units?
A.
B.
C.
D.
Volts
Watts
Ohms
Amperes
Release 1.0 – September 2006
42
T4A01 Answer - D
Current is measured in
amperes (or more commonly
amps). It is a measure of the
amount of electrical energy.
Power supply capacity is often
rated by the number of amps it
can produce at a given voltage.
Release 1.0 – September 2006
43
T4A02
Electrical Power is measured in
which of the following units?
A.
B.
C.
D.
Volts
Watts
Ohms
Amperes
Release 1.0 – September 2006
44
T4A02 Answer - B
Overall electrical power is
generally measured in watts.
Transmitter power output is
often measured in watts. So
are many common home appliances
and light bulbs.
Release 1.0 – September 2006
45
T4A03
What is the name for the flow
of electrons in an electric
circuit?
A.
B.
C.
D.
Voltage
Resistance
Capacitance
Current
Release 1.0 – September 2006
46
T4A03 Answer - D
Current is the amount of
electron flow in a circuit.
The greater the amount of
electron flow, the higher the
current.
Release 1.0 – September 2006
47
T4A04
What is the name of a current
that flows only in one
direction?
A.
B.
C.
D.
An alternating current
A direct current
A normal current
A smooth current
Release 1.0 – September 2006
48
T4A04 Answer - B
Direct current flows through
a circuit in one direction
only.
Release 1.0 – September 2006
49
T4A05
What is the standard unit of
frequency?
A. The megacycle
B. The Hertz
C. One thousand cycles per
second
D. The electromagnetic force
Release 1.0 – September 2006
50
T4A05 Answer - B
The basic unit of frequency
is the Hertz. One Hertz equals
one cycle per second.
Release 1.0 – September 2006
51
T4A06
How much voltage does an
automobile battery usually
supply?
A.
B.
C.
D.
About
About
About
About
Release 1.0 – September 2006
12 volts
30 volts
120 volts
240 volts
52
T4A06 Answer - A
Most amateur equipment is
designed to be powered by a 12
volt supply. This is so
primarily because most car
batteries are 12 volt
batteries.
Release 1.0 – September 2006
53
T4A07
What is the basic unit of
resistance?
A.
B.
C.
D.
The
The
The
The
volt
watt
ampere
ohm
Release 1.0 – September 2006
54
T4A07 Answer - D
Resistance is the opposition
to current flow and it is
measured in ohms. Whenever
electricity passes through a
wire or any other component and
it either begins to glow or
generate heat or both, that is
due to resistance.
Release 1.0 – September 2006
55
T4A08
What is the name of a current
that reverses direction on a
regular basis?
A.
B.
C.
D.
An alternating current
A direct current
A circular current
A vertical current
Release 1.0 – September 2006
56
T4A08 Answer - A
Alternating current flows first
in one direction and then in the
opposite direction, usually in a
very regular cycle. The alternating
current in U.S. households changes
direction 120 times per second.
Each two changes in direction (down
and back up) is one cycle, creating
60 complete cycles every second, so
we say that electric current has a
frequency of 60 cycles per second or
60 Hertz.
Release 1.0 – September 2006
57
T4A09
Which of the following is a
good electrical conductor?
A.
B.
C.
D.
Glass
Wood
Copper
Rubber
Release 1.0 – September 2006
58
T4A09 Answer - C
Metals are generally good
conductors of electricity. A
conductor is a substance that
allows electrons to flow
through it easily.
Release 1.0 – September 2006
59
T4A10
Which of the following is a
good electrical insulator?
A.
B.
C.
D.
Copper
Glass
Aluminum
Mercury
Release 1.0 – September 2006
60
T4A10 Answer - B
Non-metals do not allow
electrons to move through them
very readily, so they make good
insulators.
Release 1.0 – September 2006
61
T4A11
What is the term used to
describe opposition to current
flow in ordinary conductors
such as wires?
A.
B.
C.
D.
Inductance
Resistance
Counter EMF
Magnetism
Release 1.0 – September 2006
62
T4A11 Answer - B
Even the best conductors
offer some resistance to
current flow, but this
resistance is not enough to
make much difference unless the
conductor is very long, such as
a long strand of wire.
Release 1.0 – September 2006
63
T4A12
What instrument is used to
measure the flow of current in
an electrical circuit?
A.
B.
C.
D.
Frequency meter
SWR meter
Ammeter
Voltmeter
Release 1.0 – September 2006
64
T4A12 Answer - C
If you remember that current
is measured in amps, the answer
to this question should be
easy!
Release 1.0 – September 2006
65
T4A13
What instrument is used to
measure Electromotive Force
(EMF) between two points such
as the poles of a battery?
A.
B.
C.
D.
Magnetometer
Voltmeter
Ammeter
Ohmmeter
Release 1.0 – September 2006
66
T4A13 Answer - B
Electromotive force is the
fancy name for voltage, and
voltage is measured with a
voltmeter.
Release 1.0 – September 2006
67
Group T4B
Group T4B covers the relationship
between frequency and wavelength,
identification of amateur radio
bands, names of frequency ranges,
and types of radio waves .
Release 1.0 – September 2006
68
Radio Waves
Radio waves are a kind of energy that
carries your voice and data from your
transmitter to another ham’s receiver. We
can’t see a radio wave, but we don’t have
to actually see it to understand it.
Remember our electron roller coaster,
better known as a sine wave? It turns out
that a sine wave is a pretty good model to
explain radio waves, so let’s take a
closer look.
Release 1.0 – September 2006
69
Waves
If you have ever dropped a stone into a pool
or pond, you know what happens. You get a series
of ripples that spread out in circles. The energy
from that falling rock is transferred to the water
and spreads out in the form of these little
ripples or waves.
Release 1.0 – September 2006
70
Waves – A Closer Look
Release 1.0 – September 2006
71
Wave Form
If you look at the cross section
of the waves on the diagram in the
previous slide, you can see that it
looks a lot like our sine wave.
That’s because it is a sine wave,
and you can imagine the moving curve
as the waves spread out from where
the stone was dropped. Unlike our
electron roller coaster, it is the
wave that moves, and not something
moving along the wave.
Release 1.0 – September 2006
72
Wavelength
Here is a plain sine wave. If we
measure from Point A to Point B, the
distance is the length of one complete
wave or cycle. We call this the
wavelength. The name for the distance a
radio wave travels during one complete
cycle is wavelength.
Release 1.0 – September 2006
73
Frequency
Remember that the frequency
of alternating current is a
measure of the number of cycles
per second that alternating
current reverses. So the
number of times that an
alternating current flows back
and forth per second is its
frequency.
Release 1.0 – September 2006
74
Measuring Frequency
As you saw in the last group of
questions, frequency is measured in
a unit called the Hertz. Hertz is
the standard unit of frequency, and
one hertz is equal to one cycle per
second.
Since the frequency of AC house
current is 60 Hertz, we say it goes
through 60 cycles per second.
Release 1.0 – September 2006
75
Radio Waves
Now 60 cycles per second (or 60 Hertz) seems
pretty fast. But imagine the ripples on the pond
moving out at a speed of 20,000 times a second.
That’s 20,000 waves lapping up against the shore
every single second.
Obviously, water waves cannot do that, but
radio waves can. They are waves of energy that
act a little like electric waves, and a little
like magnetic waves. Radio waves are types of
waves known as “electromagnetic waves.” Radio
waves “oscillate” (or reverse direction) at a
frequency of at least 20,000 Hertz.
Electromagnetic waves that oscillate more than
20,000 times per second as they travel through
space are generally referred to as radio waves.
Release 1.0 – September 2006
76
How Fast Do Radio Waves
Move?
If radio waves oscillate more than
20,000 times a second, just how fast do
they move? It turns out they move pretty
darn fast. In fact, radio waves travel
through space at the speed of light. And
in case you didn’t know, the speed of
light is (approximately) a whopping
186,000 miles per second. At that speed a
light beam will cover a distance equal to
over seven times around the world in less
than a second!
Release 1.0 – September 2006
77
Wavelength, Frequency and
the Speed of Light
The wavelength and frequency are
directly related to each other and
to the speed of light. We won’t
bore you with the stuff you don’t
need to know about that. However,
there are some things you are going
to have to know to understand this
stuff, so let’s get to it.
Release 1.0 – September 2006
78
Wavelength Revisited
Take another look at the diagram of the sine
wave. You should remember that the distance from
Point A to Point B is the wavelength. In the
radio world, wavelength is measured in meters.
Release 1.0 – September 2006
79
Frequency Revisited
You should also remember that the
frequency of a wave is the measure
of the number of cycles it completes
in one second. One cycle per second
is one Hertz.
But we saw that the lowest
frequency of a radio wave is 20,000
Hertz, and it goes way up from
there. Radio wave frequencies can go
into the millions of Hertz!
Release 1.0 – September 2006
80
So how do we Handle the
Big Numbers?
Let’s take the lowest
frequency radio wave at 20,000
Hertz. It is sometimes easier
to use larger units to deal
with numbers as large as this.
In the radio business, we use
two different units to help us
deal with large numbers.
Release 1.0 – September 2006
81
Kilohertz (KHz)
The first unit we use is the
“kilohertz.” One kilohertz is equal
to 1000 Hertz. Kilohertz is
abbreviated “KHz.”
Using this unit, 20,000 Hertz
equals 20 Kilohertz (or 20 KHz).
It may not be any simpler, but it
is a little shorter.
Release 1.0 – September 2006
82
Megahertz (MHz)
When the frequency of a radio wave gets into
the millions, the numbers get really big. One
popular amateur band, the 2 meter band, starts at
a frequency of 144,000,000 Hertz. As you can see,
144 million is a pretty large number, so we use
our second unit to make things a little easier to
manage.
So the second unit we use is the “megahertz.”
One megahertz equals 1,000,000 Hertz. Megahertz
is abbreviated “MHz.”
Using this unit, 144,000,000 Hertz becomes 144
megahertz (or 144 MHz).
Release 1.0 – September 2006
83
Is Your Head Spinning Yet?
We promised we would explain a
little more about the amateur bands,
so here goes. You now know that the
2 meter band begins at 144 MHz. Do
you know why the call it the 2 meter
band?
Here’s a hint. Remember that the
wavelength of a radio wave measured
in meters.
Release 1.0 – September 2006
84
Aha!
That’s right! This band is called the 2 meter
band because 2 meters is the approximate
wavelength of the waves in this band.
That’s the same reason we call the other ham
bands what we do. The 6 meter band has radio
wavelengths of about 6 meters, the 1.25 meter band
has radio wavelengths of about 1.25 meters, and
the 70 centimeter band has radio wavelengths of
about .7 meters. (Sneaked that last one in on
you, didn’t we?)
So remember that the property of a radio wave
often used to identify the different bands amateur
radio operators use is the physical length of the
wave, or simply the wavelength
Release 1.0 – September 2006
85
Formulas to Forget
OK, we’re going to give you two
formulas that show you how frequency and
wavelength are related, and here they
are...
300
Wavelength (in meters) = ----------------Frequency (in MHz)
300
Frequency (in MHz) = --------------------Wavelength (in meters)
Release 1.0 – September 2006
86
What’s Important!
These two formulas show the math
whizzes among us what the rest of us
will just have to memorize. The
wavelength of a radio wave relates
to its frequency in that the
wavelength gets shorter as the
frequency increases, and the
wavelength gets longer as the
frequency decreases. The same is
true for frequency.
Release 1.0 – September 2006
87
Frequency Ranges of
Several Bands
OK, now that you know all about how frequency
and wavelength are related, and you also know that
amateur bands are often described by their average
wavelength, it’s time to learn some really useful
stuff. Below are the frequency ranges of several
ham bands that you can use as a Technician.
There’s no way around it, you’ll need to memorize
them to “ace” the exam!
Frequency range of the 2 meter band in the U.S. 144 to 148 MHz
Frequency range of the 6 meter band in the U.S. 50 to 54 MHz
Frequency range of the 70 centimeter band in the
U.S. - 420 to 450 MHz
Release 1.0 – September 2006
88
Sound Waves
Sound also travels in waves, but unlike radio
waves, sound waves cannot travel through space.
Sound waves can only travel through air or some
other type of matter. However, like radio waves,
sound waves also have a range of frequencies as
well.
Generally, the higher the frequency, the
higher pitched the sound.
Sound waves in the range between 300 and 3000
Hertz are the frequencies of the average human
voice. These frequencies are important because
hams are trying to transmit their voices all the
time, and they want to use microphones that have a
good frequency response in the human voice range.
Release 1.0 – September 2006
89
Check-Up Time!
Now let’s try the questions from
this group.
You should make a note of any that
you miss for later review.
Release 1.0 – September 2006
90
T4B01
What is the name for the
distance a radio wave travels
during one complete cycle?
A.
B.
C.
D.
Wave speed
Waveform
Wavelength
Wave spread
Release 1.0 – September 2006
91
T4B01 Answer - C
The distance a radio wave
travels in one cycle is its
wavelength. Amateur bands are
often identified by the average
wavelength of the radio waves
within that band, such as the 2
meter band, or more often, just
"2 meters."
Release 1.0 – September 2006
92
T4B02
What term describes the number
of times that an alternating
current flows back and forth
per second?
A.
B.
C.
D.
Pulse rate
Speed
Wavelength
Frequency
Release 1.0 – September 2006
93
T4B02 Answer - D
Frequency is the number of times an
alternating current, such as a radio wave,
travels back and forth in one second.
Each cycle is one Hertz. In the case of
AC house current, the frequency is
relatively low – only 60 cycles per
second.
However, as you will soon see, the
frequencies of radio waves are much
higher, and depending on the frequency,
they are measured in either kilohertz
(1000 hertz) or megahertz (1 million
hertz).
Release 1.0 – September 2006
94
T4B03
What does 60 hertz (Hz) mean?
A.
B.
C.
D.
6000 cycles per second
60 cycles per second
6000 meters per second
60 meters per second
Release 1.0 – September 2006
95
T4B03 Answer - B
Hertz means "cycles per
second."
Release 1.0 – September 2006
96
T4B04
Electromagnetic waves that oscillate
more than 20,000 times per second as
they travel through space are
generally referred to as what?
A.
B.
C.
D.
Gravity waves
Sound waves
Radio waves
Gamma radiation
Release 1.0 – September 2006
97
T4B04 Answer - C
Radio waves are waves of
electromagnetic energy that
have a frequency of more than
20,000 hertz (or 20 kilohertz).
An electromagnetic wave is a
wave of energy with electrical
and magnetic components.
Release 1.0 – September 2006
98
T4B05
How fast does a radio wave
travel through space?
A. At the speed of light
B. At the speed of sound
C. Its speed is inversely
proportional to its wavelength
D. Its speed increases as the
frequency increases
Release 1.0 – September 2006
99
T4B05 Answer - A
All electromagnetic waves
travel through space at the
speed of light - about 186,000
miles per second!
Release 1.0 – September 2006
100
T4B06
How does the wavelength of a radio
wave relate to its frequency?
A. The wavelength gets longer as the
frequency increases
B. The wavelength gets shorter as the
frequency increases
C. There is no relationship between
wavelength and frequency
D. The wavelength depends on the
bandwidth of the signal
Release 1.0 – September 2006
101
T4B06 Answer - B
As frequency increases, the
wavelength gets shorter. As
frequency decreases, the
wavelength gets shorter. For
you math whizzes, frequency and
wavelength are inversely
proportional. (No, that’s not
on the test.)
Release 1.0 – September 2006
102
T4B07
What is the formula for converting
frequency to wavelength in meters?
A. Wavelength in meters equals
Hertz multiplied by 300
B. Wavelength in meters equals
Hertz divided by 300
C. Wavelength in meters equals
megahertz divided by 300
D. Wavelength in meters equals
by frequency in megahertz
Release 1.0 – September 2006
frequency in
frequency in
frequency in
300 divided
103
T4B07 Answer - D
Wavelength
(Meters)
Release 1.0 – September 2006
=
300
--------------Frequency (MHz)
104
T4B08
What are sound waves in the
range between 300 and 3000
Hertz called?
A.
B.
C.
D.
Test signals
Ultrasonic waves
Voice frequencies
Radio frequencies
Release 1.0 – September 2006
105
T4B08 Answer - C
Knowing where the voice
frequencies are concentrated is
very useful when adjusting for
the best possible audio from
your microphone.
Release 1.0 – September 2006
106
T4B09
What property of a radio wave is
often used to identify the different
bands amateur radio operators use?
A. The physical length of the wave
B. The magnetic intensity of the wave
C. The time it takes for the wave to
travel one mile
D. The voltage standing wave ratio of
the wave
Release 1.0 – September 2006
107
T4B09 Answer - A
Amateurs often refer to the
various bands by their
approximate wavelength, such as
80 meters, 20 meters, 10 meters
or 2 meters.
Release 1.0 – September 2006
108
T4B10
What is the frequency range of
the 2 meter band in the United
States?
A.
B.
C.
D.
144 to 148 MHz
222 to 225 MHz
420 to 450 MHz
50 to 54 MHz
Release 1.0 – September 2006
109
T4B10 Answer - A
You will almost certainly get
at least one question on your
exam about the frequency of a
particular band or sub-band.
The bad news is they just have
to be memorized. The good news
is that this is information you
will use as long as you are a
ham.
Release 1.0 – September 2006
110
T4B11
What is the frequency range of
the 6 meter band in the United
States?
A.
B.
C.
D.
144 to 148 MHz
222 to 225 MHz
420 to 450 MHz
50 to 54 MHz
Release 1.0 – September 2006
111
T4B11 Answer - D
Next to 2 meters, 6 meters is
probably the most popular band
for Technician licensees. When
this band is open, you can work
some real DX (long distance
contacts)!
Release 1.0 – September 2006
112
T4B12
What is the frequency range of
the 70 centimeter band in the
United States?
A.
B.
C.
D.
144 to 148 MHz
222 to 225 MHz
420 to 450 MHz
50 to 54 MHz
Release 1.0 – September 2006
113
T4B12 Answer - C
There are really only three
bands you’ll need to know the
frequencies for – 6 meters, 2
meters, and 70 centimeters.
They are important to you
because they are all bands open
to you as a Technician
licensee.
Release 1.0 – September 2006
114
Group T4C
Group T4C covers how radio works. It
also covers receivers, transmitters,
transceivers, amplifiers, power
supplies, and types of batteries and
their service life .
Release 1.0 – September 2006
115
Radio Equipment
After all of that heavy
theory about radio waves, we’re
going to take a look at some
very basic information about
what different radio components
do.
Release 1.0 – September 2006
116
Radio Receiver
The radio receiver is a
device used to convert radio
signals into sounds we can
hear. You should be very
familiar with radio receivers.
You use them to listen to your
favorite radio stations. The
receivers hams use do the very
same thing, except we use them
to listen to other hams.
Release 1.0 – September 2006
117
Radio Transmitter
A radio transmitter is used
to convert sounds from our
voice into radio signals that
are then sent out over the air
to the other ham’s radio
receiver.
Release 1.0 – September 2006
118
Transceiver
Back in the early days of amateur
radio, every ham had to have two
separate pieces of equipment – a
transmitter and a receiver. The
transmitter was used to generate the
signal sent out over the air, and
the receiver was used to receive the
other ham’s signal. However, for
many years now, the transmitter and
receiver have been combined into a
single unit called a transceiver
Release 1.0 – September 2006
119
Transceiver
In a transceiver, the transmitter and
receiver are combined into a single unit.
This eliminates the need for having to
have the two separate units and it makes
tuning much easier as well.
Release 1.0 – September 2006
120
Power Supply
Most modern radios require 12 volts DC
as a power source. This allows them to be
operated mobile using car batteries. The
voltage coming from the plugs in U.S.
homes is 110-120 volts AC. To get the
proper voltage to use these radios in your
home, you need a device called a “power
supply.” The power supply is a device is
used to convert the alternating current
from a wall outlet into low-voltage direct
current. The output of a power supply
used for amateur radio is usually about 12
volts.
Release 1.0 – September 2006
121
RF Amplifier
Sometimes a ham may need or
want more output power than the
radio is capable of generating.
An RF (radio frequency)
amplifier is used to increase
the output of a radio to a
higher power. For example, you
could use an amplifier to boost
the power of a 10 watt radio to
100 watts.
Release 1.0 – September 2006
122
Batteries
Most handhelds are powered by
batteries, and there are a number of
different types. For example, there
are lead-acid batteries, alkaline
batteries, nickel-cadmium batteries
and lithium-ion batteries. Of these,
the lithium-ion battery offers the
longest life when used with a handheld radio, assuming each battery is
the same physical size. You
probably already know this if you
use a digital camera.
Release 1.0 – September 2006
123
Nickel-Cadmium Batteries
Most fully charged AA, AAA, C or D batteries
have a charge of about 1.5 volts. However, a
fully charged nickel-cadmium battery has a nominal
voltage per cell of about 1.2 volts. This voltage
is lower than most other types of batteries, but
the advantage of a nickel-cadmium cell is that it
is relatively inexpensive and rechargeable, and
that can save a lot of money.
Release 1.0 – September 2006
124
Carbon-Zinc Batteries
Carbon-zinc batteries are the
common AA, AAA, C or D batteries you
find at the local store. They are
usually the most inexpensive
batteries, but they have one
distinct disadvantage that makes
them fairly expensive in the long
run. Unlike nickel-cadmium, leadacid or, lithium-ion batteries,
carbon-zinc batteries are not
designed to be re-charged.
Release 1.0 – September 2006
125
Battery Care
As a Technician, you will almost certainly use
some sort of rechargeable batteries with your
equipment. Regardless of the type of rechargeable
you use, there are several things you should do to
keep rechargeable batteries in good condition and
ready for emergencies.
They should be inspected for physical damage
and replaced if necessary
They should be stored in a cool and dry
location
They must be given a maintenance recharge at
least every 6 months
Release 1.0 – September 2006
126
Battery Use
Regardless of the kind of
battery you use, the best way
to get the most amount of
energy from a battery is to
draw current from the battery
at the slowest rate needed.
This will help your battery to
last much longer.
Release 1.0 – September 2006
127
Check-Up Time!
Now let’s try the questions from
this group.
You should make a note of any that
you miss for later review.
Release 1.0 – September 2006
128
T4C01
What is used to convert radio
signals into sounds we can
hear?
A.
B.
C.
D.
Transmitter
Receiver
Microphone
Antenna
Release 1.0 – September 2006
129
T4C01 Answer - B
Radio signals are received
and changed into sound by a
receiver. Radio signals are
produced by a transmitter.
When the transmitter and
receiver are combined into a
single unit, as is almost
always the case with modern
radios, the combination is
called a transceiver.
Release 1.0 – September 2006
130
T4C02
What is used to convert sounds
from our voice into radio
signals?
A.
B.
C.
D.
Transmitter
Receiver
Speaker
Antenna
Release 1.0 – September 2006
131
T4C02 Answer - A
Radio signals are produced by
a transmitter. Radio signals
are received and changed into
sound by a receiver. When the
transmitter and receiver are
combined into a single unit, as
is almost always the case with
modern radios, the combination
is called a transceiver.
Release 1.0 – September 2006
132
T4C03
What two devices are combined
into one unit in a transceiver?
A.
B.
C.
D.
Receiver, transmitter
Receiver, transformer
Receiver, transistor
Transmitter, deceiver
Release 1.0 – September 2006
133
T4C03 Answer - A
In the early days of amateur
radio, even up to the 1960s, the
transmitter and receiver were
usually two separate units.
However, beginning in the mid 1960s,
the two units were combined to make
a transceiver. Almost all
commercially produced amateur gear
is of the transceiver type, with the
exception of a few simple kits.
Release 1.0 – September 2006
134
T4C04
What device is used to convert
the alternating current from a
wall outlet into low-voltage
direct current?
A.
B.
C.
D.
Inverter
Compressor
Power Supply
Demodulator
Release 1.0 – September 2006
135
T4C04 Answer - C
Most amateur gear requires 12
volts direct current (DC).
When amateur gear is used in
the home, a power supply is
required to convert the 110
volt alternating current (AC)
from the wall socket to the 12
volt direct current (DC)
required (or any other DC
voltage that may be required).
Release 1.0 – September 2006
136
T4C05
What device is used to increase
the output of a 10 watt radio
to 100 watts?
A.
B.
C.
D.
Amplifier
Power supply
Antenna
Attenuator
Release 1.0 – September 2006
137
T4C05 Answer - A
An amplifier is a device that
is used to amplify or increase
the power of a signal. An
amplifier may be used to
increase RF (radio frequency)
power. Other amplifiers may be
used to increase the power of a
sound signal such as a guitar
amplifier.
Release 1.0 – September 2006
138
T4C06
Which of the battery types listed
below offers the longest life when
used with a hand-held radio,
assuming each battery is the same
physical size?
A.
B.
C.
D.
Lead-acid
Alkaline
Nickel-cadmium
Lithium-ion
Release 1.0 – September 2006
139
T4C06 Answer - D
Lithium-ion batteries have a
high storage capacity for their
size, so they last longer.
They are generally more
expensive. (You may already
know that lithium-ion digital
camera batteries last longer
than any other kind. If you
do, you also already know they
are more expensive.)
Release 1.0 – September 2006
140
T4C07
What is the nominal voltage per
cell of a fully charged nickelcadmium battery?
A.
B.
C.
D.
1.0
1.2
1.5
2.2
volts
volts
volts
volts
Release 1.0 – September 2006
141
T4C07 Answer - B
Although nickel-cadmium
batteries, more commonly known
as nicads, have a lower voltage
than a typical alkaline battery
of the same type, the
difference is not that great,
and they are rechargeable many
times. For that reason, most
handheld radios use nicads as a
power source.
Release 1.0 – September 2006
142
T4C08
What battery type on this list
is not designed to be recharged?
A.
B.
C.
D.
Nickel-cadmium
Carbon-zinc
Lead-acid
Lithium-ion
Release 1.0 – September 2006
143
T4C08 Answer - B
Carbon-zinc batteries are the
least expensive batteries, and
they are the most common.
However, they are designed for
only a single use, and
generally cannot be recharged.
Release 1.0 – September 2006
144
T4C09
What is required to keep rechargeable
batteries in good condition and ready for
emergencies?
A. They must be inspected for physical
damage and replaced if necessary
B. They should be stored in a cool and dry
location
C. They must be given a maintenance recharge
at least every 6 months
D. All of these answers are correct
Release 1.0 – September 2006
145
T4C09 Answer - D
Amateur operators are often
called on to provide communications
in an emergency. Many emergencies
result in a loss of commercial
power. If you want to help, you
need to insure that your batteries
are properly stored, charged and
maintained so that you can be ready
to deploy at a moment's notice.
Release 1.0 – September 2006
146
T4C10
What is the best way to get the most
amount of energy from a battery?
A. Draw current from the battery as
rapidly as possible
B. Draw current from the battery at
the slowest rate needed
C. Reverse the leads when the battery
reaches the 1/2 charge level
D. Charge the battery as frequently
as possible
Release 1.0 – September 2006
147
T4C10 Answer - B
Drawing only the current you
need will make the most of your
battery's charge. Whatever you
do, NEVER, NEVER, NEVER reverse
the leads on a battery. This
can seriously damage your
equipment!
Release 1.0 – September 2006
148
Group T4D
Group T4D covers the most
important Ohm’s Law
relationships .
Release 1.0 – September 2006
149
Important (But Confusing)
Abbreviations
We’re about to look at something called “Ohms
law.” Ohms law is a very important mathematical
formula that shows how voltage, current and
resistance are related to each other. But before
we can study the law, we need to look at the
abbreviations for each of these values, and they
are not what you would expect. They are:
Voltage – E
Current – I
Resistance – R
You would expect that voltage should be
abbreviated V and current should be C, but they
are not. You’ll need to learn these three for
what comes next.
Release 1.0 – September 2006
150
Ohm’s Law
Ohms law ties voltage, current
and resistance all together in one
neat package. If you know any two
of them, you can easily figure out
the third. If you know a little
algebra, you’ll only need to
remember one formula. If you don’t,
you’ll either need to remember three
formulas or a little memory aide
you’ll see in just a bit.
Release 1.0 – September 2006
151
Ohms Law – Voltage Unknown
Remember our little flashlight circuit?
Suppose you know the current and
resistance in that circuit and you want to
know the voltage. Use this formula:
Voltage (E) equals current (I) multiplied
by resistance (R)
If you use the abbreviations, it is
simply:
E = I x R
We’ll see how you actually use this in
just a bit.
152
Release 1.0 – September 2006
Ohms Law – Current Unknown
Using the same circuit, suppose you know the
voltage and the resistance, but you don’t know the
current. If so, the formula you use is:
Current (I) equals voltage (E) divided by
resistance (R)
Using just the abbreviations, the formula is:
E
I = --R
We’ll use this one shortly, too!
Release 1.0 – September 2006
153
Ohms Law - Resistance
Unknown
Finally, using the same flashlight circuit one
more time, suppose you know the current and the
voltage, but you need to know the resistance. If
so, the formula is:
Resistance (R) equals voltage (E) divided by
current (I)
Using just the abbreviations, the formula is:
E
R = --I
Release 1.0 – September 2006
154
A Simple Solution!
If you know algebra, you can take E = I x R
and come up with the other two equations. But, if
you don’t know algebra and you don’t want to
remember three different equations, there is
another solution - it’s the Ohm’s Law Circle!
Release 1.0 – September 2006
155
Ohm’s Law Circle
The Ohm’s Law circle is really easy to use.
on a piece of paper and keep it handy.
Draw it out
To use the circle, you will cover the value you don’t know
with your hand. If the two values you know are beside each
other, you multiply them together. If one is over the other,
divide the lower value into the upper value.
(Don’t panic! All will be explained…)
Release 1.0 – September 2006
156
Ohm’s Law Problems
We promised all would be explained, so here
goes. Grab a piece of paper and let’s rumble!
OK, all these formulas and this circle might
seem a little confusing, so let’s see how they
work by going through a few problems. That should
clear up any confusion you might have.
We’ll work each problem two ways. First,
we’ll show you how to do it using the formula, and
then we’ll work the same problem using the circle.
It doesn’t matter which one you use to get the
answer, so long as you can get the right answer.
Release 1.0 – September 2006
157
Ohms Law Problem # 1 –
Voltage Unknown
What is the voltage across the
resistor if a current of 0.5 amperes
flows through a 2 ohm resistor?
Solution:
E = I x R
E = 0.5 x 2 = 1 volt
Or...
Release 1.0 – September 2006
158
Ohms Law Problem # 1 –
Voltage Unknown
Using the circle, cover the E. You now
have to multiply I times R to get the
right answer of 1 volt.
Release 1.0 – September 2006
159
Ohms Law Problem # 2 –
Voltage Unknown
What is the voltage across the resistor
if a current of 1 ampere flows through a
10 ohm resistor?
Solution:
E = I x R
E = 1 x 10 = 10 volts
Or, using the circle, cover the E. You
now have to multiply I times R to get the
right answer of 10 volts.
Release 1.0 – September 2006
160
Ohms Law Problem # 3 –
Voltage Unknown
What is the voltage across the resistor
if a current of 2 amperes flows through a
10 ohm resistor?
Solution:
E = I x R
E = 2 x 10 = 20 volts
Or, using the circle, cover the E. You
now have to multiply I times R to get the
right answer of 20 volts.
Release 1.0 – September 2006
161
Ohms Law Problem # 4 –
Current Unknown
What is the current flow in a circuit with an
applied voltage of 120 volts and a resistance of
80 ohms?
Solution:
E
I = --R
120
I = --- = 1.5 amps
80
Or...
Release 1.0 – September 2006
162
Ohms Law Problem # 4 –
Current Unknown
Using the circle, cover the I. You now
have to divide E by R to get the right
answer of 1.5 amps.
Release 1.0 – September 2006
163
Ohms Law Problem # 5 –
Current Unknown
What is the current flowing through a 100 ohm
resistor connected across 200 volts?
Solution:
E
I = --R
200
I = --- = 2 amps
100
Or, using the circle, cover the I. You now have to
divide E by R to get the right answer of 2 amps.
Release 1.0 – September 2006
164
Ohms Law Problem # 6 –
Current Unknown
What is the current flowing through a 24 ohm
resistor connected across 240 volts?
Solution:
E
I = --R
240
I = --- = 10 amps
24
or, using the circle, cover the I. You now
have to divide E by R to get the right answer of
10 amps.
Release 1.0 – September 2006
165
Ohms Law Problem # 7 –
Resistance Unknown
What is the resistance of a circuit when a
current of 3 amperes flows through a resistor
connected to 90 volts?
Solution:
E
R = --I
90
R = --- = 30 ohms
3
Or...
Release 1.0 – September 2006
166
Ohms Law Problem # 7 –
Resistance Unknown
Using the circle, cover the R. You now
have to divide E by I to get the right
answer of 30 ohms.
Release 1.0 – September 2006
167
Ohms Law Problem # 8 –
Resistance Unknown
What is the resistance in a circuit where the
applied voltage is 12 volts and the current flow is 1.5
amperes?
Solution:
E
R = --I
12
R = --- = 8 ohms
1.5
Or, using the circle, cover the R. You now have to
divide E by I to get the right answer of 8 ohms.
Release 1.0 – September 2006
168
Check-Up Time!
Now let’s try the questions from
this group.
You should make a note of any that
you miss for later review.
Release 1.0 – September 2006
169
T4D01
What formula is used to calculate
current in a circuit?
A. Current (I) equals voltage (E)
multiplied by resistance (R)
B. Current (I) equals voltage (E)
divided by resistance (R)
C. Current (I) equals voltage (E)
added to resistance (R)
D. Current (I) equals voltage (E)
minus resistance (R)
Release 1.0 – September 2006
170
T4D01 Answer - B
There are three possible
equations for Ohm's Law. There is
also a great memory aid for those
who don't like to remember
equations. We’ll look at that
later. First, here is the Ohm’s Law
equation to find current (I):
E
I = --R
Release 1.0 – September 2006
171
T4D02
What formula is used to calculate
voltage in a circuit?
A. Voltage (E) equals current (I)
multiplied by resistance (R)
B. Voltage (E) equals current (I)
divided by resistance (R)
C. Voltage (E) equals current (I)
added to resistance (R)
D. Voltage (E) equals current (I)
minus resistance (R)
Release 1.0 – September 2006
172
T4D02 Answer - A
Here is the Ohm’s Law
equation for determining
voltage:
E = I x R
Release 1.0 – September 2006
173
T4D03
What formula is used to calculate
resistance in a circuit?
A. Resistance (R) equals voltage
multiplied by current (I)
B. Resistance (R) equals voltage
divided by current (I)
C. Resistance (R) equals voltage
added to current (I)
D. Resistance (R) equals voltage
minus current (I)
Release 1.0 – September 2006
174
(E)
(E)
(E)
(E)
T4D03 Answer - B
Here is the Ohm’s Law
equation to solve for current:
E
R = --I
Release 1.0 – September 2006
175
T4D04
What is the resistance of a
circuit when a current of 3
amperes flows through a
resistor connected to 90 volts?
A.
B.
C.
D.
3 ohms
30 ohms
93 ohms
270 ohms
Release 1.0 – September 2006
176
T4D04 Answer - B
You can solve this by using this
formula:
E
R = --I
E
90
R = --- = --- = 30 Ohms
I
3
Release 1.0 – September 2006
177
Or You Can Use the Ohm’s
Law Circle
Release 1.0 – September 2006
178
For Resistance...
Cover the R (resistance), and
divide E (voltage) by I (current):
Release 1.0 – September 2006
179
T4D05
What is
circuit
voltage
current
A.
B.
C.
D.
the resistance in a
where the applied
is 12 volts and the
flow is 1.5 amperes?
18 ohms
0.125 ohms
8 ohms
13.5 ohms
Release 1.0 – September 2006
180
T4D05 Answer - C
You can solve this by using this
formula:
E
R = --I
E
12
R = --- = --- =
I
1.5
Release 1.0 – September 2006
8 Ohms
181
Or for Resistance...
Cover the R (resistance), and
divide E (voltage) by I (current)
Release 1.0 – September 2006
182
T4D06
What is the current flow in a
circuit with an applied voltage
of 120 volts and a resistance
of 80 ohms?
A.
B.
C.
D.
9600 amperes
200 amperes
0.667 amperes
1.5 amperes
Release 1.0 – September 2006
183
T4D06 Answer - D
You can solve this one by using the
formula:
E
I = --R
E
120
I = --- = --- = 1.5 amperes
R
80
Release 1.0 – September 2006
184
Or for Current...
Cover the I (current), and divide
E (voltage) by R (resistance)
Release 1.0 – September 2006
185
T4D07
What is the voltage across the
resistor if a current of 0.5
amperes flows through a 2 ohm
resistor?
A.
B.
C.
D.
1 volt
0.25 volts
2.5 volts
1.5 volts
Release 1.0 – September 2006
186
T4D07 Answer - A
You can solve this one by
using the formula:
E = I x R
E = I x R = 0.5 x 2 = 1 volt
Release 1.0 – September 2006
187
Or for Voltage...
Cover the E (voltage), and
multiply I (current) times R
(resistance)
Release 1.0 – September 2006
188
T4D08
What is the voltage across the
resistor if a current of 1
ampere flows through a 10 ohm
resistor?
A.
B.
C.
D.
10 volts
1 volt
11 volts
9 volts
Release 1.0 – September 2006
189
T4D08 Answer - A
You can solve this one by
using the formula:
E = I x R
E = I x R = 1 x 10 = 10 volts
Release 1.0 – September 2006
190
Or for Voltage...
Cover the E (voltage), and
multiply I (current) times R
(resistance)
Release 1.0 – September 2006
191
T4D09
What is the voltage across the
resistor if a current of 2
amperes flows through a 10 ohm
resistor?
A.
B.
C.
D.
20 volts
0.2 volts
12 volts
8 volts
Release 1.0 – September 2006
192
T4D09 Answer - A
You can solve this one by
using the formula:
E = I x R
E = I x R = 2 x 10 = 20
Release 1.0 – September 2006
193
Or for Voltage...
Cover the E (voltage), and
multiply I (current) times R
(resistance)
Release 1.0 – September 2006
194
T4D10
What is the current flowing
through a 100 ohm resistor
connected across 200 volts?
A.
B.
C.
D.
20,000 amperes
0.5 amperes
2 amperes
100 amperes
Release 1.0 – September 2006
195
T4D10 Answer - C
You can solve this one by using
the formula:
E
I = --R
E
200
I = --- = --- = 2 amperes
R
100
Release 1.0 – September 2006
196
Or for Current...
Cover the I (current), and divide
E (voltage) by R (resistance)
Release 1.0 – September 2006
197
T4D11
What is the current flowing
through a 24 ohm resistor
connected across 240 volts?
A.
B.
C.
D.
24,000 amperes
0.1 amperes
10 amperes
216 amperes
Release 1.0 – September 2006
198
T4D11 Answer - C
You can solve this one by using
the formula:
E
I = --R
E
240
I = --- = --- = 10 amperes
R
24
Release 1.0 – September 2006
199
Or for Current...
Cover the I (current), and divide
E (voltage) by R (resistance)
Release 1.0 – September 2006
200
Group T4E
Group T4E covers how to calculate
power, as well as some of the
common units used in electronics kilo, mega, milli, and micro.
Release 1.0 – September 2006
201
“I’ve got the Power!”
Now that you have Ohms law
all figured out, power should
be really easy. First, you
need to remember that the unit
used to describe electrical
power is the watt. When we
measure the amount of
electrical power used or
produced, the watt is always
our basic unit.
Release 1.0 – September 2006
202
The Power Formula
The formula used to calculate electrical power
in a DC circuit is:
Power (P) equals voltage (E) multiplied by current
(I)
You already know the abbreviations for current
and voltages, but now we add a new one – P for
power. Using this abbreviation, you can rewrite
the formula as:
P = E x I
But the old pros change the order of E and I
around slightly so that the short formula becomes
a real “pie” job:
P = I x E or
Release 1.0 – September 2006
P=IE (Get it?)
203
Power – Making Things
Complicated!
OK, just like Ohms law, you have three
different things to worry about – power,
voltage, and current. If you know any two
of them, you can figure out the third.
Also like Ohms law, if you know algebra,
you can take P = E x I (or P = I x E) and
get formulas for figuring out either E or
I.
And as with Ohms law, if you don’t know
algebra, you’ll either have to memorize
three equations or use the power circle.
(Yes, Virginia, there IS a power circle!)
Release 1.0 – September 2006
204
The Other Equations –
Voltage Unknown
Suppose you know the power
and the current, but you don’t
know the voltage. In that
case, the formula is:
P
E = --I
Release 1.0 – September 2006
205
The Other Equations –
Current Unknown
Suppose you know the power
and the voltage, but you don’t
know the current. In that
case, the formula is:
P
I = --E
Release 1.0 – September 2006
206
The Power Circle
The power circle looks very
similar to the Ohms law circle:
Release 1.0 – September 2006
207
The Power Circle
It works the same way as well. Cover the value you
don’t know with your hand. If the two values you know
are beside each other, multiply them together. If one
is over the other, divide the lower value into the upper
value.
Release 1.0 – September 2006
208
Power Problems
Now let’s look at some power
problems. We’ll look at two
solutions – one with the
formula, and one using the
circle.
Release 1.0 – September 2006
209
Power Problem # 1 – Power
Unknown
How much power is represented by a
voltage of 13.8 volts DC and a current of
10 amperes?
Solution:
P = E x I
(Or you can use P = I x E)
P = 13.8 x 10 = 138 watts
Or...
Release 1.0 – September 2006
210
Power Problem # 1 – Power
Unknown
Using the circle, when you cover P, you
see that you have to multiply I times E to
get the correct answer of 138 watts.
Release 1.0 – September 2006
211
Power Problem # 2 – Power
Unknown
How much power is being used in a
circuit when the voltage is 120 volts DC
and the current is 2.5 amperes?
Solution:
P = E x I
(Or you can use P = I x E)
P = 120 x 2.5 = 300 watts
Or, using the circle, when you cover P,
you see that you have to multiply I times
E to get the correct answer of 300 watts.
Release 1.0 – September 2006
212
Power Problem # 3 –
Current Unknown
How many amperes are flowing in a circuit when the
applied voltage is 120 volts DC and the load is 1200
watts?
Here, we need one of the other formulas, and the
solution is:
P
I = --V
1200
I = ---- = 10 amps
120
Or...
Release 1.0 – September 2006
213
Power Problem # 3 –
Current Unknown
Using the circle, when you cover I, you
see that you have to divide P by E to get
the correct answer of 10 amps.
Release 1.0 – September 2006
214
Power Problem – Practical
Application
How can you determine how many watts are being
drawn by your transceiver when you are
transmitting?
Solution:
If you need to know power, the formula you use
is P = E x I (or P = I x E)
But in order to get the power, you need to
know the voltage and current. To do that, you’ll
have to measure them. You can measure the DC
voltage at the transceiver using a voltmeter or
multimeter. Then you need to measure the current
drawn when you transmit using an ammeter or
multimeter. Once you have those two values, you
multiply voltage times the current
Release 1.0 – September 2006
215
Important Unit Prefixes
We are almost done with the math for a bit,
but we still need to learn some important number
prefixes. Sometimes, we have numbers that are
really large or really small, and they become hard
to work with. We have already seen two of them
used in measuring radio frequencies – kilohertz
and megahertz. Remember that one kilohertz (KHz)
equals 1000 Hertz, and that one megahertz (MHz)
equals one million Hertz. The prefix “kilo” means
one thousand, and the prefix “mega” means one
million.
Lets look at a few more...
Release 1.0 – September 2006
216
MilliThe prefix “milli-“ means one onethousandth. We use it with units such as
watts, amperes, and volts.
1 milliwatt = 1/1000 of a watt
1000 millwatts = 1 watt
1 milliampere = 1/1000 of an ampere
1000 milliamperes = 1 ampere
Release 1.0 – September 2006
217
Example
With that in mind, how many
milliamperes is the same as 1.5
amperes?
Solution:
Since there are 1000 milliamperes
in 1 ampere, there are 1500
milliamperes in 1.5 amperes.
Release 1.0 – September 2006
218
An Example using
Milliwatts
How many watts does a hand-held
transceiver put out if the output
power is 500 milliwatts?
Solution:
Since there are 1000 milliwatts
in 1 watt, 500 milliwatts would be
half that, or .5 watts.
Release 1.0 – September 2006
219
Micro“Micro-“ is another important
prefix. It is also used with
watts, amperes and volts as
needed. Micro- means one onemillionth.
1 microvolt = 1/1,000,000 volt
1,000,000 microvolts = 1 volt
Release 1.0 – September 2006
220
Example – KiloWhat is another way to specify
the frequency of a radio signal that
is oscillating at 1,500,000 Hertz?
Solution:
Since 1 kilohertz (KHz) equals
1000 Hertz, if you divide 1,500,000
by 1000, you’ll get 1500 kilohertz
(KHz)
Release 1.0 – September 2006
221
Another Example – KiloHow many volts are equal to one
kilovolt?
Since “kilo-“ means one thousand, there
are one thousand volts in a kilovolt.
Whew!
Breathe a big sigh of relief. You have
now done almost all the math you need for
the Technician exam!
Release 1.0 – September 2006
222
Check-Up Time!
Now let’s try the questions from
this group.
You should make a note of any that
you miss for later review.
Release 1.0 – September 2006
223
T4E01
What unit is used to describe
electrical power?
A.
B.
C.
D.
Ohm
Farad
Volt
Watt
Release 1.0 – September 2006
224
T4E01 Answer - D
The basic unit of electrical
power is the watt. Watts may
measure power produced, such as
the output of a transmitter, or
power consumed, such as the
power required by a 100 watt
light bulb.
Release 1.0 – September 2006
225
T4E02
What is the formula used to calculate
electrical power in a DC circuit?
A. Power (P) equals
by current (I)
B. Power (P) equals
current (I)
C. Power (P) equals
current (I)
D. Power (P) equals
(I)
Release 1.0 – September 2006
voltage (E) multiplied
voltage (E) divided by
voltage (E) minus
voltage (E) plus current
226
T4E02 Answer - A
The formula for power is:
P
=
I
x
E
(watts)
(amperes)
(voltage)
But if you don’t like
formulas, power calculations
can also be done with a memory
aid.
Release 1.0 – September 2006
227
T4E03
How much power is represented
by a voltage of 13.8 volts DC
and a current of 10 amperes?
A.
B.
C.
D.
138 watts
0.7 watts
23.8 watts
3.8 watts
Release 1.0 – September 2006
228
T4E03 Answer - A
Using the formula:
P = I x E
P = 10 x 13.8 = 138 watts
Or, if you prefer a memory aid,
the memory aid for power looks
similar to the one for Ohm’s Law and
works exactly the same way...
Release 1.0 – September 2006
229
Memory Aid for Power
To calculate a missing value, cover
that value with your hand and multiply or
divide the two remaining values as
indicated.
Release 1.0 – September 2006
230
For this Problem...
Cover the P (power) and multiply
I (current) times E (voltage)
Release 1.0 – September 2006
231
T4E04
How much power is being used in
a circuit when the voltage is
120 volts DC and the current is
2.5 amperes?
A.
B.
C.
D.
1440 watts
300 watts
48 watts
30 watts
Release 1.0 – September 2006
232
T4E04 Answer - B
To solve this problem:
P = I x E = 2.5 x 120 =
300 watts
Or, if you use the memory
aid...
Release 1.0 – September 2006
233
For this Problem...
Cover the P (power) and multiply
I (current) times E (voltage)
Release 1.0 – September 2006
234
T4E05
How can you determine how many watts are
being drawn by your transceiver when you
are transmitting?
A. Measure the DC voltage and divide it by
60 Hz
B. Check the fuse in the power leads to see
what size it is
C. Look in the Radio Amateur's Handbook
D. Measure the DC voltage at the transceiver
and multiply by the current drawn when you
transmit
Release 1.0 – September 2006
235
T4E05 Answer - D
This is a practical
application of P = I x E.
First you measure the voltage
going to the transmitter and
the current drawn (or used)
when the transmitting. Then,
using the formula, you multiply
current times voltage to get
the number of watts drawn.
Release 1.0 – September 2006
236
T4E06
How many amperes are flowing in
a circuit when the applied
voltage is 120 volts DC and the
load is 1200 watts?
A.
B.
C.
D.
20 amperes
10 amperes
120 amperes
5 amperes
Release 1.0 – September 2006
237
T4E06 Answer - B
If you are a math whiz, you can figure this
one out by changing the formula around to:
P
I = --E
1200
I = ---- = 10 amperes
120
0r...
Release 1.0 – September 2006
238
Use the Memory Aid
Cover the I (current) and divide
P (power) by E (voltage)
Release 1.0 – September 2006
239
T4E07
How many milliamperes is the
same as 1.5 amperes?
A.
B.
C.
D.
15 milliamperes
150 milliamperes
1500 milliamperes
15000 milliamperes
Release 1.0 – September 2006
240
T4E07 Answer - C
The prefix “milli” means
1/1000, so 1000 milliamperes
equals one ampere. To find out
how many there are in 1.5
amperes, you multiply 1.5 times
1000.
1.5 amperes x 1000 =
1500 milliamperes
Release 1.0 – September 2006
241
T4E08
What is another way to specify
the frequency of a radio signal
that is oscillating at
1,500,000 Hertz?
A.
B.
C.
D.
1500 kHz
1500 MHz
15 GHz
150 kHz
Release 1.0 – September 2006
242
T4E08 Answer - A
One kiloHertz (kHz) equals
1000 Hertz. If you divide the
frequency in Hertz by 1000,
you’ll get the frequency in
kHz:
1,500,000
--------- = 1,500 kHz
1,000
Release 1.0 – September 2006
243
T4E09
How many volts are equal to one
kilovolt?
A.
B.
C.
D.
one
one
one
one
one-thousandth of a volt
hundred volts
thousand volts
million volts
Release 1.0 – September 2006
244
T4E09 Answer - C
The prefix “kilo” means 1000,
so there are 1000 volts in one
kilovolt.
Release 1.0 – September 2006
245
T4E10
How many volts are equal to one
microvolt?
A.
B.
C.
D.
one
one
one
one
one-millionth of a volt
million volts
thousand kilovolts
one-thousandth of a volt
Release 1.0 – September 2006
246
T4E10 Answer - A
The prefix “micro” means onemillionth, so 1 microvolt = 1
one-millionth of a volt.
Release 1.0 – September 2006
247
T4E11
How many watts does a hand-held
transceiver put out if the
output power is 500 milliwatts?
A.
B.
C.
D.
0.02 watts
0.5 watts
5 watts
50 watts
Release 1.0 – September 2006
248
T4E11 Answer - B
1000 milliwatts equals 1
watt, so 500 milliwatts equals
½ watt or .5 watts.
Release 1.0 – September 2006
249
Four Down, Six to Go!
This concludes Study Guide # 4.
Once you are satisfied that you can answer
80% of the questions in this Sub-element, you
are ready to move on to Study Guide # 5.
Release 1.0 – September 2006
250