Download 3.0 Operating Procedures

CNIB
1929 BAYVIEW AVENUE
TORONTO ONTARIO
M4G 3E8
AMATEUR RADIO PROGRAM
AMATEUR RADIO COURSE
Second Edition April 2004
VE7TBC Terrance Berscheid
VE3WRN Randy Nelson
French Translation
Pierre Mainville VA3PM
Claude Paquet VE2OCP
First Edition September 1992
VE3JQY Frank Walke
COPYRIGHT 2004 by the CNIB Amateur Radio Program
Copyright by the CNIB Amateur Radio Program and may not be
reproduced in any form without the written permission of the
Amateur Radio Program except for duplication in written, Braille,
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tape or computer formats in the course of providing instruction to
those with vision loss.
Some material is copyright by Radio Amateurs of Canada in their
volumes "RAC Study Guide for the Basic Exam" and "The RAC
Operating Manual". The CNIB Amateur Radio Program gratefully
acknowledges with thanks their valuable contribution to this
course.
In the event you find this course useful and feel a donation to our
Program is appropriate, our Program would be pleased to accept
such a donation. Our work with people with vision loss across
Canada is sponsored by CNIB but we raise our own funds. Please
make your cheque payable to “CNIB Amateur Radio Program” and
mail to 1929 Bayview Ave, Toronto, ON M4G 3E8. Many thanks in
advance.
Section numbers are now used. Please refer to a section number
such as #21.8 then use CONTROL F to “find” a section. All section
numbers are preceded by a # sign to aid computer searches.
#0.0 is the Table of Contents. This is a good starting point when
you are searching for a specific topic.
Forward to the Second Edition
On behalf of the Board of Directors of the CNIB Amateur Radio
Program, I would like to welcome you to Amateur Radio and your
decision to ask the Amateur Radio Program for assistance. This
course is designed for students with vision loss to use in DAISY,
Braille, tape, large print and computer text formats.
It is not intended to be a self-study guide. Please feel free to ask
questions of your instructor or helper. Your instructor/helper will
have access to various models and samples to illustrate concepts
and components used. There are occasions when sighted help
may be needed to operate your station. Antenna erection and
programming some features in modern transceivers are two
examples. You may have heard the word “sponsor”, who is an
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individual who offers you help. We now prefer to call them
“Helpers”.
The Amateur Radio Program strongly recommends that you join a
local Amateur Radio club. They will be better equipped to help
you rather than relying on one individual.
Helpers should be developed as friends, not as servants. Ensure
that you have completed all that can be done before you seek
help. A radio not plugged in or the house fuse blown should not
require a call to a helper. Do these simple checks yourself. Ask
for assistance over the phone first before asking a helper to come
to your home. Ensure that it is convenient for them.
In summary, treat your helpers as you would your best friend.
I would appreciate your feedback on the value of this course and
your suggestions for improvements are welcomed and
encouraged.
George Fanjoy VE3PEB February 2004
Chairman, Board of Directors
416 207 0797
[email protected]
Preface
When an Amateur Operator's Certificate is issued to an individual,
certain rights and privileges are conveyed to the individual as well
as certain responsibilities. By passing the tests, the operator has
demonstrated that he or she is qualified to possess that
certificate and understands the responsibilities, theory, operating
skills and possibly Morse code.
The rights and privileges are that the individual has the legal right
to transmit radio signals from an Amateur Radio station within
the rules and regulations administered by Industry Canada.
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The responsibilities imposed on each radio Amateur are many.
Each Amateur must know, understand and follow the rules and
regulations including amendments and changes as they occur.
Each Amateur must recognize that Amateur Radio has long been
known for its public service and all Amateurs are expected to
conduct their activities appropriately. This will reflect their desire
to be of service to the public wherever possible. Providing
communications on a volunteer basis for public events is one
example.
Amateur radio renders assistance in times of emergency or
national disaster. Each Amateur operator is expected to make
him or herself or their stations available if needed. They are also
expected to maintain radio silence if an emergency
communication is underway.
Each Amateur needs to continuously recognize that Amateur
Radio has long been known and praised as a self policing service.
As a consequence, the Amateur bands are used in an orderly
way, with courtesy, without profane language and in a helpful
way to new operators. The need for courtesy and helpfulness
cannot be overemphasized.
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#0.0 Table of Contents
Forward to the Second Edition .............................................. 2
Preface.............................................................................. 3
#0.0 Table of Contents ........................................................ 5
#1.0 Introduction ............................................................... 7
#2.0 Regulations ................................................................ 7
#3.0 Operating Procedures ................................................. 10
#3.1 Common Terms ....................................................... 11
#3.2 Canadian Callsigns ................................................... 11
#3.3 Station Classifications ............................................... 12
#3.4 VHF/UHF Call Procedure ............................................ 12
#3.5 HF Call Procedures ................................................... 13
#3.6 Morse code Procedures ............................................. 14
#3.7 Q codes .................................................................. 14
#3.8 International Phonetic Alphabet.................................. 15
#3.9 Universal Time Coordinated ....................................... 16
#3.10 Phone Procedure Words .......................................... 16
#3.11 Repeater Operations ............................................... 16
#3.12 Testing Equipment ................................................. 18
#3.13 Log Keeping .......................................................... 19
#3.14 QSL Cards ............................................................. 19
#4.0 Theory...................................................................... 19
#4.1 Electricity ............................................................... 19
#4.2 Atoms .................................................................... 20
#4.3 Voltage .................................................................. 21
#4.4 Current .................................................................. 22
#4.5 Conductors ............................................................. 22
#4.6 Insulators ............................................................... 23
#4.7 Resistance .............................................................. 23
#4.8 Ohm's Law .............................................................. 25
#4.9 Electrical Power ....................................................... 26
#4.10 Capacitance, Electrostatic Field................................. 26
#4.11 Capacitors in Series and Parallel ............................... 27
#4.12 Inductance and Magnetic Fields ................................ 28
#4.13 Inductors, Series and Parallel ................................... 29
#4.14 Directions of Electrons and Current ........................... 29
#4.15 Alternating Current ................................................. 30
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#4.16 Capacitors and Inductors in AC Circuits ..................... 32
#4.17 Impedance ............................................................ 33
#4.18 Resonance ............................................................ 33
#4.19 Transformers ......................................................... 35
#4.20 Transformer Construction ........................................ 36
#4.21 The Amplifier ......................................................... 37
#4.22 Rectification: AC to DC ............................................ 38
#4.23 Filters................................................................... 39
#4.24 Low and High Pass Filters ........................................ 39
#4.25 Prefixes ................................................................ 40
#4.26 Transmission Lines ................................................. 41
#4.27 The Antenna .......................................................... 42
#4.28 Types of Antennas .................................................. 44
#4.29 Impedance Matching and Reflected Waves ................. 45
#4.30 Baluns and Traps ................................................... 46
#4.31 Antenna Polarization ............................................... 47
#4.32 Propagation ........................................................... 47
#4.33 Sunspot Cycles ...................................................... 50
#4.34 Atmospherics......................................................... 50
#4.35 Transmitters and Receivers...................................... 51
#4.36 Oscillators ............................................................. 51
#4.37 Modulation ............................................................ 52
#4.38 Selectivity, Sensitivity and Stability........................... 54
#4.39 Decibels................................................................ 55
#4.40 AGC Automatic Gain Control .................................... 55
#5.0 Your Amateur Radio Station ......................................... 56
#6.0 Conclusion ................................................................ 57
#7.0 Attachment “A” .......................................................... 58
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#1.0 Introduction
The Basic Qualification is your first step on the way to becoming
an Amateur Radio Operator. Those who want to operate on high
frequency HF bands will need to acquire a Morse code
Qualification of 5 words per minute (w.p.m.). The third and last is
the Advanced Qualification. This text provides you with the
necessary information to operate at the Basic level. Please refer
to our Morse code tapes for instruction on Morse code. The
Amateur Radio Program does not recommend and does not
provide training or training materials for those who want the
Advanced qualification. Please consult your local club and/or
helper for more information.
#2.0 Regulations
This section summarizes the regulations applicable to the CNIB
Amateur Radio Program. To the best of our ability they include all
aspects of interest to us. However readers should be aware that
they are subject to all laws and regulations administered by
Industry Canada. Reference to RIC-2, “Standards for the
Operation of Radio Stations in the Amateur Radio Service” and
RIC-3: Information on the Amateur Radio Service.” is suggested.
Part of the Basic qualification examination is devoted to
regulations. These are subject to change. Only the main features
are offered here. Your helper will have the most recent changes
and will explain them.
There is no fee for an Amateur Radio Operator Certificate which is
valid for life.
This certificate covers both your personal
qualification and authority to install and operate your transmitter.
There is no age limit or citizenship need to hold an Amateur radio
Operator Certificate.
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A Basic examination must be passed before an Amateur Radio
Operator Certificate is issued. Local accredited examiners can
administer the examination. Such examiners should contact the
Amateur Radio Program to determine our methods of conducting
this exam for candidates with vision loss.
After a candidate has passed the Basic qualification he or she
may be examined for 5 w.p.m. or Advanced in any order.
Authority to make "Radiocommunication Regulations" is derived
from the Radiocommunication Act administered by Industry
Canada.
You must notify Industry Canada of address changes within 30
days.
The holder of an Amateur Radio Operator Certificate may operate
an Amateur station anywhere in Canada and in countries with
whom reciprocal operating agreements exist.
Out of Amateur band transmissions are not allowed. Amateur
equipment is not approved to transmit outside the Amateur bands
such as General Radio Service (GRS), Citizens Band (CB) or
Family Radio Service (FRS).
If an Amateur pretends there is an emergency and transmits the
word "MAYDAY," this is a false or deceptive signal.
Your Amateur radio Certificate must be posted in a conspicuous
place in your station and protected from theft.
The owner of an Amateur station may permit any person to
operate the station under the supervision and in the presence of
the holder of the Amateur Operator Certificate.
The holder of the Basic or Basic plus Morse code qualification may
only transmit with unmodified commercially manufactured
equipment at powers to the final amplifier less than 250 watts.
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He or she may not hold the call sign for a repeater. Building or
transmitting with “home built” equipment and operating at higher
powers requires the Advanced qualification.
No person may operate his or her equipment so that it will
interfere with any radio station or private receiving station.
The operator of any Amateur station shall transmit the station’s
call sign in English or in French at the beginning and end of each
period of exchange of communication or test transmission and at
intervals of not more than
30 minutes.
The frequency, bandwidth, type of emission and power of an
Amateur radio station must be as authorized. The key bands and
bandwidths of interest to the Amateur Radio Program are in
Attachment “A”. There are other bands and reference must be
made to RIC-2, “Standards for the Operation of Radio Stations in
the Amateur Radio Service.”
No person shall transmit or make a signal containing profane or
obscene words or language.
You can communicate only with other Amateur stations in Canada
and world wide.
Communication is limited to messages of a technical or personal
nature. No secret code or cipher is permitted nor is
communication
that
could
be
construed
as
business
communication permitted. You cannot accept payment for
passing messages.
The use of abbreviations or procedural signals is permitted if they
do not obscure the meaning of a message.
To keep your station from retransmitting music or signals from a
non-Amateur station you must turn down the volume of
background audio.
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If you hear distress traffic and are unable to render assistance,
you are to maintain watch until you are certain that assistance is
forthcoming. If radio silence is requested by a station rendering
distress assistance, you shall maintain radio silence.
If you hear an unanswered distress signal on an Amateur band
where you do not have privileges to communicate, you should
offer assistance.
Amateur third party communications is the transmission of noncommercial or personal messages to or on behalf of a third party.
You may not communicate with a country that has notified the
International Telecommunications Union that it objects to such
communications. Your instructor will let you know the current
countries that have so indicated.
Your instructor will cover how to identify your station when
operating away from your home location. Some alternatives are:
VE3??? Portable if on foot
VE3??? Mobile if in a car
VE3???/W4 Portable in Florida
#3.0 Operating Procedures
As an Amateur Radio operator, you will be required to learn the
following Operating Procedures. Procedures cannot be taught well
in a classroom environment. Your instructor may provide on air
practice, further experience will be obtained by doing a lot of
listening before you transmit. After listening do not be afraid to
transmit. Your fellow Amateurs will help when they discover you
are new.
Your helper will assist in ensuring your station is safe to operate.
The high voltage generated when transmitting and hazards
caused by atmospheric lightning in thunderstorm conditions are
of particular concern. Lightening can enter your station via two
routes. Through your antenna system or your household electrical
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supply. Your helper will assist in balancing the risks and the cost
of lightning protection devices.
To improve your CW, SSB and VHF/UHF operating procedures,
your helper will discuss the protocol used when making a contact
with another Amateur as well as the meanings of the
abbreviations used. You will learn about the various frequencies
to use and the best times of day when communicating are
possible.
Your helper will advise what antenna and equipment selection
and installation possibilities are available. All aspects may be
discussed including voice communication, Amateur television,
computer use, satellites, and nets and contests.
#3.1 Common Terms
The term ‘working’ is often heard in Amateur radio. It generally
means that you are using the frequency.
Remember that the actual frequency you are transmitting is
about 2 kHz above or below the frequency set on your rig. Stay
away from band edges.
#3.2 Canadian Call Signs
The Canadian call signs are:
VE1-VA1
VE2-VA2
VE3-VA3
VE4-VA4
VE5-VA5
VE6-VA6
VE7-VA7
Nova Scotia including some New Brunswick stations
Quebec
Ontario
Manitoba
Saskatchewan
Alberta
British Columbia
VA7 British Columbia
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VE8 North West Territories
VE9 New Brunswick
VE0* Maritime
VO1 Newfoundland
VO2 Labrador
VY0 Nunavut
VY1 Yukon
VY2 Prince Edward Island
* VE0 call signs are only intended for use when the amateur radio
station is operated from vessels that make international voyages
Your helper will explain the call signs of other countries.
#3.3 Station Classifications
Your instructor will explain the following
Base station
Portable station
Mobile station land, marine and air
HF transmitter
VHF and UHF transmitters
QRP
#3.4 VHF/UHF Call Procedure
To call someone in the telephony or voice mode is simple. For
example, we'll use the Toronto VE3NIB call sign. On the VHF or
UHF repeaters, the quality of communications is normally
excellent. After listening for a couple of minutes to ensure the
frequency is not in use, simply say "VE3NIB listening". If
someone wants to talk to you, they'll reply. It is not necessary to
repeat the call or call more than once.
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If you want to call a specific station e.g. VE3AW, after listening to
ensure the frequency is clear say, “VE3AW this is VE3NIB”, it is
usually not necessary to repeat this. If VE3AW is there they will
respond.
#3.5 HF Call Procedures
On high frequency, you must provide time for the receiving
station to tune to you. Listen to the selected frequency for a
couple of minutes. If it is quiet ask, "Is this frequency in use, this
is VE3NIB over?" Ask twice. The reason for this is that someone
may be listening to a party that you cannot hear. When the
frequency is clear say, "CQ CQ CQ this is Victor Echo 3 November
India Bravo Victor Echo 3 November India Bravo". Repeat this
three times without stopping and finish with "over". Listen; try
two or three times if you wish. If you wish to speak to a specific
location then say “VE3ZW”, “CQ Halifax” or “CQ France”. This will
limit responses to the particular station or those locations. Do not
send a long CQ without waiting for a reply. The sentence above,
spoken slowly and distinctly is sufficient.
When each transmission is finished, send "over". This means I am
finished and I want to hear from you. Do not over identify your
station. It is sufficient to identify your call sign every 10 to 30
minutes. If you are using a repeater, do not be a hog. Others
may be waiting. When you are finished send "VE3NIB clear"
indicating that you are finished.
One piece of information that is almost universally exchanged is
signal reports. A standard system of reporting signals covering
readability, strength and tone has been developed to describe a
CW signal. Naturally it is called the RST system. R stands for
readability, S for strength and T for tone with a scale of 1 to 5 for
R and 1 to 9 for S and T, where 1 is bad and 5 or 9 is good. A CW
report of 368 would be interpreted as, your signal has a slight
trace of modulation, they are readable with difficulty, and have
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good strength. The tone report is a useful indication
transmitter performance.
of
On phone the tone report is not used. Signal reports are given as
readability and strength. A very good signal is 59.
#3.6 Morse code Procedures
CW is similar. Listen, use "QRL?" (Is the frequency busy?) to
determine if the frequency is clear. Send "CQ CQ CQ de VE3NIB
VE3NIB VE3NIB" three times finishing with "K". The letters de
mean from, the letter K means over and I wish to hear from
anyone. Do not send faster than you can copy. When your
communication starts sign off your transmissions with "KN" sent
without a space between letters. This means you only want a
reply from the station to which you are talking. When your
conversation is complete, sign off with your call sign followed by
"CL" to indicate that you are finished.
#3.7 Q codes
In the days when Morse code was used by railways, ships and
telegraph, it was and still is important to use as little time
transmitting as possible. Q-codes were developed to assist. It is
much quicker to say “QRM”, for example, than transmit in Morse
“Are you being interfered with by any other signals?”
The following are key Q codes:
QRM - I am being interfered with by man-made signals
QRN - I am being interfered with by man-made signals
QSO - A communication between people
QSL – I understand; confirmation
QTH - My location is…
QSY – Change to (another) frequency…
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Note that a question mark after any “Q” code changes it from a
statement to a question. “QTH?” Means “What is your location?”
It is suggested that the Q codes not be used in radiotelephony.
It is not time consuming to simply say I live in Edmonton and
avoid the jargon.
#3.8 International Phonetic Alphabet
Differences in accents throughout the world together with
marginal communications quality may result in unclear reception.
It is standard procedure to use the International Phonetic
Alphabet as follows:
A
B
C
D
E
F
G
H
I
J
K
L
M
Alpha
Bravo
Charlie
Delta
Echo
Foxtrot
Golf
Hotel
India
Juliette
Kilo
Lima
Mike
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
November
Oscar
Papa
Quebec
Romeo
Sierra
Tango
Uniform
Victor
Whisky
X-ray
Yankee
Zulu
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#3.9 Universal Time Coordinated
Keeping track of time can be confusing when we talk all over the
world. Radio amateurs, the airlines and many others Use
universal Time Coordinated, called UTC which is the time at
Greenwich England. Time is expressed as a 24 hour clock from
0000 hours, to 2400 hours. Each day runs over that 24 hour
period from midnight in the morning to midnight at the end of the
day.
The letter Z denotes UTC time. Therefore 0010 Z, 1992 January 2
denotes 10 minutes after midnight on 1992 January 2 at
Greenwich, England. It would have been 1910 hours standard
time 1992 January 1 in Toronto at this time. Get to know how to
tell time in UTC for your area. You may find it easier to have a
clock at your operating position set to UTC.
#3.10 Phone Procedure Words
Like all activities there are some jargon words you will hear. This
is intended to be a very brief list. Your instructor will cover their
use:
OVER - I am finished and wish to hear from you
CLEAR - I am finished and do not expect to hear from you
AFFIRMATIVE and NEGATIVE
ROGER - I understand
SAY AGAIN - self evident
73 - “My best to you and yours”.
88 - Love and Kisses – Only used with Amateurs you know
well or used by women to greet each other.
#3.11 Repeater Operations
“Simplex” operations means that an Amateur Radio Operator
attempts to contact another Amateur Radio Operator within the
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transmitting range of his radio equipment. A base station, with a
fixed antenna normally has a greater range than mobile (inside a
vehicle, boat, aircraft, etc.) or portable (hand-held) equipment.
In VHF/UHF bands, the general rule is ‘line-of-sight’. In the HF
bands, propagation might extend the range beyond ‘line-of-sight’.
A repeater, in comparison, is a ‘system’ whereby an Amateur
Radio operator can call a station or place a ‘general call’ to other
Amateur Radio stations on a specific frequency. The radio at the
receiving station, the ’repeater station’ (generally unattended,
but monitored by the repeater owner or his designate) will then
re-transmit that call on another frequency (often 600 Hz above or
below the receiving frequency). The effect is that the original call
can be transmitted over a geographical range that may be
greater than the range that could be achieved by the originating
station. For example, you might call a repeater in your city which
is in range of your radio signal, and then that signal would be retransmitted on another frequency to other stations monitoring the
repeater operations. Those stations may be outside of the range
of your station’s transmission capabilities.
Whenever possible, the Amateur Radio Operator should only use
the repeater frequencies when simplex communication is not
possible, or results in poor readability. This alleviates pressure on
the repeater systems.
REMEMBER: Users of Amateur repeaters are responsible for the
content of communications relayed by the repeater. You must
identify your station at the beginning and end of your
communication and at intervals of no more than 30 minutes in
long conversations.
When using a repeater, remember that many other Amateur
Radio Operators also use that frequency for communications; so
keep your conversations as brief as possible, and if the
conversation becomes lengthy, invite other Amateur Radio
Operators to break in for either a call to a different station, or to
join in the discussion. Remember, you share the repeater with
many others.
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One final point about repeaters; there is usually a tone which
announces that one station has completed his communication and
the repeater is available to either the current receiving operator
to anyone else who wishes to use the repeater. Common courtesy
is to pause for a couple of seconds before beginning so that
another station who wishes to join in or to make a separate call
can have that chance. If you have just completed your
transmission and hear a “double” (two stations transmitting at
the same time) it is common practice for you to transmit to the
original receiving station that a “double” has occurred and to
invite the third station to re-transmit his message or call.
#3.12 Testing Equipment
Testing equipment, particularly transceiver/antenna matches is
permitted; however, it is your responsibility to ensure that your
test transmissions comply with the relevant Radiocommunication
Regulations and in particular that you do not interfere with
communications between other amateurs. There is probably
nothing more frustrating to many amateurs than to have
someone tuning up his transceiver on the same frequency.
The use of a “dummy load” is recommended when testing
equipment. This piece of equipment replaces the antenna system.
The transmitter can be tested without interference to other
stations, as no signal is transmitted to air.
When a dummy load is unavailable, and when using an antenna
or feeder system, “use the minimum power that will give readings
or indications on the measuring equipment. For example, one
watt from a transmitter and a good field strength meter will give
plenty of indication of field strength for lining up elements on a
high frequency beam antenna”.
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#3.13 Log Keeping
Log keeping is no longer a regulatory requirement; however,
many amateurs keep a log in order to record contacts, equipment
changes, and other information that seems appropriate to the
operation of the station. If an Amateur decides to keep a log,
contacts should be entered in the log as they occur, not from
memory several hours later.
A well-kept log is an asset to any radio station and can assist in
the investigation of an interference complaint.
#3.14 QSL Cards
In the early days of Amateur radio when contacts were few and
far between, amateurs started the practice of exchanging written
confirmation of their contacts, usually in the form of a postcard.
Although a letter or postcard is still sufficient to confirm a
contact, amateurs often use a specially designed card, called a
QSL Card, to confirm their contacts. It is also possible now to
send and receive QSL cards electronically via the Internet. A
station operator is not required to send and collect QSL cards.
#4.0 Theory
#4.1 Electricity
We can associate electricity with many things with which we are
familiar. When it is untamed, it is lightning. Lightning ruptures or
breaks down air between clouds and earth. Cars and homes use a
more controlled form. We can associate this with the movement
of electricity through a liquid or gas, even a vacuum. An example
would be through the electrolyte or fluid of the cells of a car
battery, or the electricity across a spark gap that ignites the
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gasoline in your car’s engine. The type that flows through a
copper wire is most common. This type of current also exists in
our body where it acts as a messenger to carry information from
the brain to the muscles, enabling us to move our arms and legs,
even to feel pain.
#4.2 Atoms
Electricity flows through air, liquids and solids. These are three
different substances so they must have something in common to
permit the flow of electricity. The common particle is the electron.
We do not want to get in to atomic theory but we should
understand that one of the particles in each atom is an electron.
Some atoms hold some of their electrons loosely. An electric
pressure will allow them to move resulting in the flow of
electricity. These atoms we call conductors.
Other atoms hold their electrons tightly and electric pressure will
not move them. These atoms we call insulators.
Have you ever tried to push the north poles of two magnets
together? You would find that there is a soft but firm pressure
holding them apart. Similar poles in magnets repel each other.
Opposite poles of a magnet attract each other. Charged particles
behave in a way similar to the two magnets.
A positively charged particle and a negatively charged particle
attract each other. Two positive or two negative particles repel
each other. Like repels like, opposites attract.
But why do electrons flow? There are many similarities between
electricity flowing in a wire and water flowing through a pipe. How
does the town water system work? Chances are that there is a
large supply of water in a nearby lake, river, well or reservoirs.
Pumps are used to push water through pipes to a reservoir high
on a hill or to a tank atop a tower. Gravity is used to push the
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water down from the tank or reservoir, through a system of pipes
to the house. The force of gravity is pushing down on all of the
water exerting pressure on the water in the pipes. The water will
flow out of the taps in the house with some force. So a pump
takes water from the large supply and puts it in a storage tank
and the force of gravity is used to push the water through the
pipes.
We can think of electrons flowing through a wire in a way similar
to water flowing through a pipe. If we understand that some force
is required to make water flow through a pipe, one wonders what
force exerts pressure to make electrons flow through a wire.
#4.3 Voltage
The amount of pressure that it takes to make water flow to a
house depends mainly on how far the house is from the reservoir
and on any hills or resistance that the water has to flow over on
the way.
The amount of pressure that it takes to make electrons flow in an
electrical circuit also depends upon the opposition or resistance
that the electrons must overcome. There can be no definite flow
of electrons or flow of electricity without the application of
electromotive force. Electromotive force is sometimes called
electrical pressure since it causes the flow of electrons.
Electromotive force or EMF is similar to water pressure. The more
pressure there is the more water that flows. The greater the EMF,
the greater the flow of electrons. EMF is measured in a unit called
the volt, so we sometimes refer to the EMF as the voltage. The
more voltage applied to the circuit, the more electrons will flow
through the circuit.
Another way to think about electromotive force or voltage
pushing electrons through a circuit is to remember that like
charges repel. So, if we have a large group of electrons, the
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negative charge of these electrons will act to repel or push other
electrons through the circuit.
Because there are two types of electric charge, positive and
negative, there are also two polarities, positive and negative
associated with voltage. A voltage source has two terminals, the
positive and the negative. The negative repels electrons, the
positive attracts electrons. If a piece of wire is connected between
the two terminals of a voltage source, electrons will flow through
the wire. We call this an electrical current.
#4.4 Current
You have probably heard the term current used to describe the
flow of water in a stream or a river. Water flow can also be called
a current. Similarly, the flow of electrons in an electric circuit is
called electric current. When water flows we describe the flow as
liters per minute. When current flows we use the term Amperes,
thus we have amperes of electric current.
#4.5 Conductors
Some atoms do not have a firm grip on their electrons. The
materials whose atoms do not hold their electrons firmly are
called conductors of electricity. Certain materials like copper,
gold, aluminum and other metals and certain solutions will readily
permit the passage of electric current through them.
The more easily the electrons can be moved from the atom in a
given material, the better the current conducting qualities of that
material. Its resistance to current flow is said to be low. Good
conductors such as copper, aluminum and brass are used
extensively in electrical and electronic circuits.
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#4.6 Insulators
Materials in which atoms hold on to their electrons very strongly,
so that it is difficult to free any electrons and make them flow in a
definite direction, are known as nonconductors or insulators.
There is no sharp distinction between conductors and insulators.
Materials such as glass, rubber, plastic, ceramic, wood and even
air are poor conductors. Materials that are poor conductors are
called insulators.
It is fortunate that certain substances do not conduct electricity
freely and may therefore be used as insulators, for if this were
not so, we would find it impossible to conduct electricity from one
place to another through metallic conductors.
If we did not have insulators, we would not be able to isolate one
electric circuit from another.
#4.7 Resistance
Some materials release their electrons easily, others hold their
electrons strongly, and that there is no definite distinction
between a conductor and an insulator. All materials have
electrical resistance. There is always opposition to the flow of
electrons through any material, although the resistance of
different materials varies widely.
Between the extremes of a very good conductor and a very good
insulator we can make devices with a range of opposition to the
flow of electrons in a circuit. Resistance of a body varies with its
length, its cross section area and the type of material.
The basic unit of resistance is called the ohm. The devices that
we make to control the flow of electrons are called resistors. The
greater the resistance, the greater the reduction of the current
that can flow. To reduce the current flow with a resistor requires
that a price be paid in the form of energy lost by the electrons as
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they flow through a resistor.
This energy is converted into heat and the resistor gets warm.
The resistor must therefore be able to dissipate the heat safely.
Resistors are rated by the amount of their resistance in ohms and
their ability to dissipate heat in watts, and are usually made of
carbon or wire.
Sometimes it is necessary to calculate the total resistance of
resistors in a series circuit, end to end like a string of sausages,
or a parallel circuit, side by side like the boards in a picket fence.
When resistors are connected in series the total resistance is
simply the sum of the values of each of the resistors.
For example, if there are two resistors in series in a circuit having
a value of 10 ohms and 15 ohms, the total value would be 10
plus 15 equals 25 ohms. The total resistance of a string of
resistors in series will always be greater than the individual
resistors in the string. All of the current flows through each
resistor in a series circuit.
In a parallel circuit, the conditions are different. When two
resistors are connected in parallel the formula is more
complicated. One divided by the total resistance equals one
divided by the resistance of resistor one plus one divided by the
resistance of resistor two.
If there are two resistors in a parallel circuit having a value 10
ohms and 15 ohms, the total resistance is found as follows. One
divided by the total resistance equals one divided by 10 plus one
divided by 15. Therefore one divided by the total resistance
equals 3 divided by 30 plus 2 divided by 30. One divided by the
total equals 5 divided by 30. The total resistance equals 30
divided by 5. Therefore the parallel circuit resistance is 6 ohms.
When two or more resistors are connected in parallel, there is
more than one path for the current to flow in the circuit.
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More electrons flow which means there is greater current. The
total value of the resistance of a parallel system will always be
less than the smallest valued resistor in the system.
#4.8 Ohm's Law
We have now been introduced to three essential electrical terms.
The volt, abbreviated by the capital letter E, which is the
electromotive force applied across a circuit to cause electrons to
flow through that circuit. The Ampere abbreviated by the capital
letter I, which is the rate at which electrons, or current flows
through a circuit when an electromotive force is applied to it. The
ohm, abbreviated by the capital letter R, which is the basic
measurement of resistance in a circuit to the flow of current when
an electromotive force is applied to it. If the voltage remains
constant and the resistance is increased, less current will flow.
Dr. George Ohm, who lived in Germany 150 years ago, first
demonstrated this effect and the formula evolved by him became
known as Ohm's Law.
Ohm's Law states that the intensity of current in any circuit is
equal to the electromotive force divided by the resistance of the
circuit. Ohm's law is an important mathematical relationship. A
simple way to remember the equations of Ohm's Law can be done
with Ohm's law circle. Think of a circle with a horizontal line
drawn through the middle, making two equal halves and now in
the lower part place a vertical line from the centre of the circle to
the outer edge of the circle. In the top part place the capital letter
E. In the left lower side place the capital letter I and in the lower
right side, the capital letter R.
Given a circuit having a resistance of 5 ohms, with a voltage of
10 volts applied across it, what current will flow in amperes?
Cover the letter I, the current which is unknown and note that E
is above R. The current is therefore E divided by R or 10 divided
by 5. Thus 2 amperes flows through the circuit.
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To find the voltage applied across the circuit having a resistance
of 5 ohms with 2 amperes flowing, cover the letter E, the
unknown voltage and note that I is beside R. The voltage is I
times R or 5 times 2. Thus 10 volts is applied across the circuit.
To find the resistance of a circuit through which a current of 2
amperes is flowing when a voltage of 10 volts is applied across
the circuit, cover the unknown R and note that E is above I. The
resistance is 10 divided by 2. Thus the resistance of the circuit is
5 ohms.
#4.9 Electrical Power
Electricity flowing through a conductor is a source of power
because it can be made to do work, if it is made to flow through a
suitable apparatus. A familiar application of this is in the use of
electricity to drive an electric motor, to toast bread or to boil
water in a kettle. Power is the rate of doing work. It requires
more power to do a certain amount of work in a short interval of
time than in a longer time.
The unit of electric power is the watt. Its symbol is the capital
letter P. Power is also defined in terms of electromotive force and
the rate of electron flow. The formula therefore is power equals
volts times amperes.
Going back to our circuit of 5 ohms resistance and a voltage of 10
volts across it with 2 amperes flowing through it, we find that
power in the circuit is found as 10 volts multiplied by 2 amperes
or 20 watts. The resistor will dissipate 20 watts.
#4.10 Capacitance, Electrostatic Field
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A capacitor is another device that is used to develop an electronic
circuit that can perform a function.
A capacitor is made by separating two conductive plates with an
insulating material, called a dielectric. If we can connect one plate
to the positive terminal of a voltage source and the other plate to
the negative terminal, we can build up a surplus of electrons on
one plate. At some point, the voltage across the capacitor will be
equal to the applied voltage, and the capacitor is said to be
charged. If we then connect a load, such as our 5 ohm resistor,
across the terminals of the capacitor it will discharge through the
resistor, releasing the stored energy. The basic property of a
capacitor is this ability to store a charge in an electrostatic field.
It is important to understand that in charging and discharging the
capacitor, electrons do not flow across the dielectric, which is an
insulator. The electrons moved around the external circuit.
The basic unit of capacitance is the farad usually represented by
the capital letter C. However the farad is too large a unit for
practical purposes and the microfarad, which is one millionth of a
farad, is used.
There are three factors affecting the capacitance value of a
capacitor. They are, the area of the plates, the distance between
the plates and the dielectric material.
Increasing the area of the plates, reducing the spacing between
them or using a better dielectric will increase the capacitance.
#4.11 Capacitors in Series and Parallel
We can increase the value of capacitance in a circuit by increasing
the total plate area and we can effectively increase the total plate
area by connecting two capacitors in parallel. Two parallel
connected capacitors act like one large capacitor. The total
capacitance is simply the sum of all the values added together.
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Connecting capacitors in series has the effect of increasing the
distance between the plates, thereby reducing the total
capacitance. For capacitors in series we use a formula similar to
one we used for resistors in parallel. One divided by the total
capacitance equals one divided by capacitor one plus one divided
by capacitor two. The total capacitance of capacitors in series is
less than the capacitance of the smallest capacitor.
#4.12 Inductance and Magnetic Fields
Every radio circuit is merely a combination of resistors, capacitors
and inductors arranged to produce certain desired characteristics.
We have dealt with resistors and capacitors and will now consider
inductors. An inductor is a coil of wire made up of a few or many
turns wound on a core of insulating material or of iron.
Whenever an electric current flows through a wire, there is a
magnetic field produced around the wire. The intensity of the
magnetic field depends upon the strength of the current. When
the conductor is a piece of wire, the force produced by this
magnetic field is negligible compared to the force if the same wire
is formed into a coil. In coils, the magnetic field around each turn
affects the other turns. Together the combined forces produce
one large magnetic field. Much of the energy in the magnetic field
is concentrated in the centre of the core. In much the same way
that a capacitor stores energy in an electrostatic field an inductor
stores energy in a magnetic field.
When a DC voltage is first applied to an inductor, as when a
switch is closed, the smallest amount of current that starts to
flow produces a change in the magnetic field which generates an
opposing or counter electromotive force. The counter EMF or
voltage opposes any change in current flow, either increasing or
decreasing. This is the basic property of inductors. They oppose
any change in current flowing through them. This opposition
produces a delay in time before the current reaches a steady
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value through an inductor. Likewise if the voltage source is
removed from the inductor there is a delay time until the current
returns to zero.
The inductor has a property known as inductance. The unit of
inductance is the henry abbreviated to the capital letter H. The
electronic abbreviation for inductance is the capital letter L. The
more common sizes of inductors have values smaller than the
henry such as millihenry which is one thousandth of a henry.
Since back EMF depends on a change in current, it is readily
realized that inductance will be a significant factor where
alternating current is flowing.
Four factors that affect inductance are the number of turns used,
the type of core material, for example air or iron, the length of
the coil and the diameter of the coil.
#4.13 Inductors, Series and Parallel
In circuits, inductances combine like resistors. The total
inductance of several inductors in series is the sum of all of the
inductors.
For parallel connected inductors the total is the sum of the
inverses, as it is for resistors. One divided by the total inductance
equals one divided by inductor one plus one divided by inductor
two.
#4.14 Directions of Electrons and Current
So far we have been discussing electron flow in direct current
circuits consisting of resistors, capacitors and inductors.
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We know that the electrons move continuously from the negative
terminal of the electricity source around through the circuit to the
positive terminal and through the source to the negative terminal.
It is unfortunate, however, that in early experiments with primary
batteries before the electron theory was thought of, the electric
current was thought of as a fluid such as water. It was arbitrarily
said, at the time, that the flow was from the positive terminal,
the point of high pressure or level to the negative terminal, the
point of low pressure or level. This purely arbitrary terminology
has been carried down and is in universal use. We know that the
electron flow, which is really current, is actually from the negative
terminal around to the positive terminal of the potential source.
This apparent discrepancy should not cause any serious difficulty
if you will keep in mind the electron theory and remember how
and why the terminology of current flow originated.
#4.15 Alternating Current
It is possible to have a voltage source that periodically reverses
polarity. With this kind of voltage, the current flows first in one
direction and then in the opposite direction. Such voltage is called
an alternating voltage and the current is called alternating
current, abbreviated AC. The reversals may occur at any rate
from less than one per second, one hertz, up to several billion per
second, several gigahertz.
With the application of an AC voltage to a circuit, the current
starts at zero. It smoothly increases in amplitude until it reaches
its maximum positive amplitude, or peak value: then it decreases
slowly until it drops to zero once more. At this moment the
direction of the current increases in amplitude in the negative
direction until it reaches its negative maximum amplitude or peak
value. Then the amplitude decreases until it finally returns to zero
and the direction reverses once more.
This type of smoothly varying alternating current is known as a
sine wave.
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Ask your instructor/helper to prepare for you the shape of two
sine waves of AC, by bending some rigid wire to show you how
the current flow varies as described. These sine waves will help in
the discussion of peak voltage, peak to peak voltage, positive and
negative half cycle and the complete cycle whether or not the
current and voltage are in step or phase.
Because the wave is constantly changing and is not in a steady
state as DC voltage there is no one value we can point to and say
that is the value of the voltage.
If we pass DC through a resistor it will get warm. Also if we pass
AC through a resistor it will get warm. The AC voltage that will
heat a resistor to the same temperature as an applied 10 volt DC
is said to have an effective voltage of 10 volts AC.
The effective voltage is also called the root mean square or RMS
value of the wave. The root mean square describes the actual
process of calculating the effective voltage. Your wall outlets
provide 120 volts RMS or effective AC. If we plug a toaster into a
source of 120 volts DC, it will get just as hot as it will if we plug it
into the wall outlet. However, in order for the AC voltage to have
the same effect as DC voltage its peak value must be higher. For
a sine wave to have the same heating effect as a DC voltage the
AC peak voltage equals 1.414 times DC voltage.
To obtain the equivalent effect of a sine wave voltage to that of
10 volts DC we would have to have an AC Peak voltage of 1.414
times 10 which is 14.14 volts.
As we mentioned the wall outlet voltage of 120 volts AC is the
effective or RMS voltage. The peak voltage is 1.414 times this or
169.68 volts.
Sources of alternating current voltages are hydroelectric, coal and
nuclear generators which supply large cities and populated urban
areas. There is also another source known as an electronic
oscillator which will produce alternating current voltages at higher
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frequencies. The effects of alternating currents on capacitors and
inductors when used alone in a circuit, or in combinations with
each other permit us to create many interesting phenomena in
electronic circuits.
#4.16 Capacitors and Inductors in AC Circuits
When a capacitor is connected to an alternating current circuit a
periodic transfer of electrons takes place from one plate around
the circuit toward the other plate and back again, many times
every second. In a purely capacitive circuit, when the flow of
alternating current starts, the current or rate of flow of electrons
is greatest when the applied voltage is near the zero value and
slows down to zero when the EMF approaches maximum. In other
words the current variations lead the EMF variations by 90
electrical degrees. Have your instructor explain this to you with
the two sine waves. The greater the capacitance of a capacitor,
the more electrons will be transferred around the external circuit.
Also, the more rapidly the applied voltage changes, the greater
are the total flow of electrons around through the circuit in one
second.
If the effects of capacitance and frequency are lumped together,
they form a quantity that plays a similar part to that of resistance
in Ohm's Law. This quantity is called capacitive reactance, and
the unit for it is the ohm, just as in the case of resistance.
Although the unit of capacitive reactance is the ohm, there is no
heat dissipation in reactance. Energy is stored and returned with
each alternate variation of current.
Whenever an electric current flows through a conductor, a
magnetic field is produced around it. If an alternating current
flows through a conductor the magnetic field will be changing
periodically both in direction and strength, consequently a
counter or self-induced EMF will be set up in the conductor. If the
conductor is wound into the shape of a coil or inductor the effect
is greater because the magnetic field is concentrated in a smaller
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space and the magnetic field of every turn affects every other
turn.
When alternating current voltage is applied to an inductor the
current flow is immediately impeded because of the counter EMF
that is set up. It takes a definite time for the current to reach
some steady value. The current variations lag the EMF variations
by 90 electrical degrees.
The effect of the counter EMF in impeding the flow of current is
known as inductive reactance and is measured in ohms.
Inductive reactance of an inductor depends upon the frequency of
the applied voltage and the size of the inductor. Inductive
reactance becomes larger as one or the other or both are
increased.
#4.17 Impedance
Many circuits consist of resistors, capacitors and inductors. These
circuits are a combination of both resistance and reactance and
the total effective reactance will depend upon the frequency of
the current being applied to the circuit. The total reactance,
comprised of the true resistance and reactance, is known as
impedance. Impedance is measured in ohms and it is shown in
formulae by the capital letter Z.
#4.18 Resonance
We have said in our discussion on capacitive and inductive
reactances, that when the frequency of an applied voltage is
increased, the inductive reactance increases and the capacitive
reactance decreases. It was also said that current flowing through
a capacitor and an inductor at a given frequency produced
reactances that were opposite. That is, the current through a
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capacitor leads the voltage while the current through the inductor
lags the voltage.
In a circuit that includes both a capacitor and an inductor, of
selected values; at any given frequency there may be a high
degree of inductive reactance with a corresponding low degree of
capacitive reactance. By varying the amount of inductive and
capacitive reactance at a given frequency, we can achieve a
condition where the two reactances are equal. When the two are
equal, they cancel each other, leaving a total reactance of zero.
Therefore, the only restriction to the flow of electrons is the pure
resistance of the conductor.
The condition where capacitive reactance equals inductive
reactance is known as resonance. At other frequencies, however,
there will be a considerable amount of reactance thus electrons
will not flow. The condition where capacitive reactance equals
inductive reactance is known as resonance.
Inductors and capacitors can be connected in a series or a
parallel arrangement in a circuit.
When a condition of resonance exists in a series arrangement,
the capacitive and inductive reactances cancel each other. There
is a maximum flow of electrons at the resonant frequency.
When a capacitor and inductor are connected in parallel and a
condition of resonance exists, electrons will flow back and forth
between the inductor and the capacitor at resonant frequency
and will not flow through the circuit. However, electrons at other
frequencies will flow through either the inductor or capacitor.
Thus, a series resonant circuit will pass a desired frequency. The
parallel resonant circuit will restrict a desired frequency. These
circuits have many applications in radio receiver and transmitter
circuits.
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#4.19 Transformers
In our discussion on inductors it was said that when a current
flows through a coil that a concentrated magnetic field is set up in
the coil. If the current is alternating the magnetic field is also
alternating. It is also said that the alternating current set up an
induced electromotive force or EMF.
If two coils are arranged with their axes on the same line and an
alternating current is caused to flow through one coil, a magnetic
field is produced that will pass through the adjacent coil.
Consequently an electromotive force, EMF, has been induced in
the adjacent coil. This induced EMF is similar to the self-induced
EMF in the energized coil but since it appears in the adjacent coil
because of the current flowing in the first, it is a mutual effect
and results from mutual inductance between the two coils.
When two coils are arranged so that a changing current in one
induces a voltage in the other, the combination of windings is
called a transformer. Every transformer has a primary and a
secondary winding. The primary winding is connected to the
source and the secondary winding is connected to the load.
With a transformer, electrical energy can be transferred from one
circuit to another without direct connection. In the process, the
input voltage in the primary can be readily changed to a different
level in the secondary.
For a given magnetic field, the voltage induced in a coil will be
proportional to the number of turns in the coil. It follows
therefore, that if the primary and secondary windings of a
transformer have the same number of turns and if we ignore
losses in the coils, we would expect the full primary voltage to be
induced into the secondary.
If the secondary has fewer turns than the primary, the voltage
induced in the secondary will be less than the primary voltage,
and the transformer is called a step down transformer. If the
secondary has more turns than the primary, the secondary
35
voltage will be greater than the primary voltage and the
transformer is a step up transformer.
If you know the number of turns on the primary and secondary
windings of a transformer and you know the applied voltage, it is
easy to calculate the secondary voltage. The secondary voltage
equals the number of secondary turns divided by the number of
primary turns times the primary voltage.
If we have a transformer with 10 turns in the secondary winding
and 100 turns in the primary winding, what secondary voltage
will be produced with 120 volts on the primary?
The secondary voltage would be 10 divided by 100 times 120; or
12 volts.
The transformer can not create power; it can only transfer it and
change the EMF. Therefore, if the primary winding has 100 turns
and capable of letting 1 ampere flow at an applied voltage of 100
volts, which is 100 watts, the secondary with 10 windings will
produce 10 volts at 10 amperes, which is 100 watts.
Transformers have two major applications, first raising or
lowering AC voltages in power amplifiers; and second, impedance
matching.
In both cases the transformer isolates the input from the output,
because no direct electrical connection exists between the
primary and the secondary. A magnetic connection exists through
the core but there is no direct electrical connection.
#4.20 Transformer Construction
Transformer coils are usually wound on a core of magnetic
material. This increases the inductance of the coils so that a
relatively small number of turns may be used to induce a given
value of voltage in the secondary. A closed core with a continuous
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magnetic path is used to insure that practically all of the
magnetic field set up in the primary coil will induce a voltage in
the entire secondary coil. For low frequencies such as 60 hertz
and audio frequencies, a core made of thin sheets of silicon steel
is used. These are separated from each other by a thin layer of
varnish to prevent the flow of electricity within the core which
would cause the core to heat up.
As the frequencies approach the RF, radio frequency range, the
layers of steel are no longer thin enough. To accommodate RF,
powdered iron is used, which is suspended and bound in plastic
filler or glue called ‘ferromagnetic material’. Most transformers
are wound on a ferromagnetic material such as powdered iron.
Sometimes transformers and coils for RF application are wound
on a doughnut shape form, called a toroid. This shape has the
advantage that the entire magnetic field is contained within the
toroid, and no shielding is required.
#4.21 The Amplifier
There are vacuum tube circuits and transistor circuits that will
take a small signal and increase its power to a larger signal.
These circuits are called amplifiers. Describing now vacuum
tubes and transistors do this is beyond the scope of this course.
To put it very simply, a single stage of amplification has three
wires. In a transistor they are called base, collector and emitter.
A small signal across the base and emitter will result in a large
signal across the emitter and collector. Many such single stages
can be wired in series. This is the principle of the amplifier used
in most applications from your kitchen radio, to the most
powerful transmitters.
A few words on transistors may help if only to understand some
of the words. There are transistors that only allow current flow in
one direction. This is rectification which will be covered later.
Most transistors are a sandwich of three substances, such a
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silicon that has had a special impurity added. There are two
types, the PNP or the NPN where N is negative and P positive. To
go further would get very technical.
#4.22 Rectification: AC to DC
In the early days of radio and before the establishment of public
electric supply systems, DC was supplied by large batteries, as it
is today for portable and mobile systems. However, to power our
radio transmitter and receiver today we usually provide power to
it by plugging it into the wall outlet. The power available is AC
and not DC and it is at a voltage not usually suitable for the
circuits of the equipment. The voltage must be raised or lowered
to the desired value. The voltage must be changed from AC to DC
and we have the devices to do it.
Remember the transformer, it is a device to step up or step down
the AC input voltage and we know that the output voltage is
determined by the ‘turns-ratio’ of the transformer. AC is changed
to DC by a process called rectification and the device is called a
‘rectifier’. The vacuum tube diode and the solid state usually
silicon diode.
These devices will pass current in only one
direction, through the tube when the plate or anode is positive
with respect to the cathode and through the silicon diode when
the anode is positive with respect to the cathode. When AC is
applied across the terminals of the rectifier, the vacuum tube or
the silicon diode, current will flow when the anode is positive with
respect to the cathode. We have thus produced a positive
directed wave with the negative portion of the AC wave blocked.
This type of rectification is called half wave rectification.
We would like to use all of the AC voltage and we can do this by
inverting the negative half cycle, that is, make it positive to fill in
the gap between the positive half waves. By inverting the
negative portion of the cycle we now have full wave rectification.
However, we do not have a pure DC voltage; there will be a
ripple in the voltage, caused by the peaks of the AC wave.
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#4.23 Filters
The DC voltage produced by full wave rectification is pulsating
and will cause a hum in the audio circuits of the transmitter and
receiver. If we have rectified a 60 hertz alternating voltage, the
hum produced by full wave rectification will be 120 hertz and it
must be eliminated. We use a capacitor in most low voltage
power supplies; in order to convert the pulsating DC voltage to a
smooth DC voltage. The capacitor is usually large and has a value
of several thousand microfarads. The presence of the capacitor
smoothes out the peaks of the pulsating DC voltage. As a safety
measure, to discharge the capacitor when the power supply is
switched off, a resistor, of several thousand ohms, called a
bleeder resistor, is placed across the capacitor terminals.
Following the filter there is usually a regulating circuit. This circuit
ensures that the voltage remains constant when a heavy demand
is placed on the supply.
#4.24 Low and High Pass Filters
The low pass filter is designed to pass all frequencies below a
specified frequency and block all frequencies above the specified
frequency. A low pass filter installed at the output of an Amateur
HF transmitter will block signals above 30 Megahertz, particularly
the dreaded harmonics that can appear on your neighbours’
favourite TV program. Harmonics result from impurities in the
wave form and occur at multiples of the fundamental frequency.
Another filter is the high pass filter. This filter will pass all
frequencies above a specified frequency and block or reject all
those below the specified frequency.
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#4.25 Prefixes
The base units that we have used so far in our studies are the
volt, the ampere, the ohm, the henry, the farad, the hertz and
the watt.
For quantities larger or smaller than the base units we use
prefixes.
The prefixes for much larger quantities than the base unit that
are most frequently encountered are:
kilo
This means a quantity of one thousand base units. For
example, 1 kilovolt means 1 thousand volts.
mega
This means a quantity of one million base units. For
example, 3 megavolts mean 3 million volts.
The prefixes for much smaller quantities than the base unit that
are most frequently encountered are
milli
This means a quantity of one thousandth of the base
unit. For example 1 millivolt means 1 thousandth of a
volt.
micro
This means a quantity of one millionth of the base unit.
For example 1 microhenry means 1 millionth of a
henry.
Some examples using prefixes are
10,000 ohms is 10 kilohms
3,000,000 Hertz is 3 MegaHertz
8 millionths of a farad is 8 microfarads
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20 thousandths of an ampere is 20 milliamperes
#4.26 Transmission Lines
The system of connecting a transmitter to the antenna is made
up of three parts, the antenna coupler, the transmission line and
the antenna.
One of the concepts of electronics that we have discussed is that
of impedance. The consideration of impedance is very important
when we want to connect the transmitter to the antenna.
The first device in the system is the antenna coupler. The coupler
has two purposes, it matches the impedance of the transmitter to
the impedance of the transmission line, and it acts as a tuned
circuit to prevent the emission of harmonics.
The antenna coupler is sometimes used in conjunction with an
indicating instrument known as a standing wave bridge.
The second device is the transmission line or feeder. The feeder
connects the antenna to the coupler and transmitter. The antenna
may be located some distance from the transmitter and that is
why a feeder or feed line is used. The feed line is necessary to
carry RF power from the coupler and transmitter without radiating
radio waves. There are two types of feed line in common use
today, one is the coaxial cable, and the other is the parallel
conductor.
The coaxial cable consists of a centre conductor surrounded by an
insulating material. Around this insulating material is wrapped
another conductor in the form of a tube or sheath and an
insulating material is wrapped around the complete assembly.
This type of cable is usually called coax and has several
advantages as a feed line. It is readily available, it is flexible, and
it is quite resistant to weathering and can be buried in the ground
41
if necessary. It also has a characteristic impedance in the range
of most Amateur radio transmitters.
The other popular feed line is the parallel conductor twin lead.
The most familiar example of this type of feed line is the TV lead
in wire which has an impedance of 300 ohms. It has two
insulated parallel conductors separated by a strip of insulation.
Twin lead can also be constructed of bare wire, with plastic
spacers placed every 15 to 30 centimetres to maintain a required
distance between them. This is usually called a "ladder line"
because it resembles a rope ladder with wooden steps as was
used on sailing ships. The main advantage of the ladder line is its
low loss.
A transmission line, whether it is a coax or a ladder line contains
two conductors arranged parallel to one another. As a result of
this arrangement there is a capacitance due to the proximity of
the conductors and an impedance because of the length of the
conductors. Both of the characteristics are distributed properties
and present a finite series of small inductors connected to parallel
capacitors. The resulting circuit offers a reactance to any RF
passing along the line.
Because of the relationship of the capacitive reactance and the
inductive reactance the impedance of the transmission line stays
near the same value over a wide range of frequencies. The
impedance of a transmission line is not affected by its length.
Coaxial cable is provided with characteristic impedances of 52
and 72 ohms. The normal characteristic impedance of twin lead
transmission lines is 300 ohms. The ladder line is usually 300 or
450 ohm impedances.
#4.27 The Antenna
The third device is the antenna which radiates the RF energy from
the transmitter into space. Radio waves travel in space at the
42
same speed as light which is 300 million metres per second, or
300 megametres per second. For an antenna to do its job
efficiently its length should be related to the length of the wave it
is radiating. The length of the antenna is very important. It must
form a tuned or resonant circuit.
The length in free space of a complete cycle is its wave length.
Remember the model of a complete cycle. It has both a positive
peak and a negative peak. The more hertz or cycles per second
the higher is the frequency, thus the wavelength is shorter.
Radio waves travel at 300 megametres per second, so we can
determine the wavelength in metres of any frequency. This is
equal to 300 divided by frequency in megahertz.
The wavelength in metres equals 300 divided by the frequency in
megahertz.
If we know the wavelength of the radio frequency that we want to
transmit we can construct the proper antenna. A general rule is
that an antenna length should be some multiple of a quarterwavelength.
Following is a list of the HF Amateur bands with their frequencies
and nominal wavelengths:
1.8 to 2.0 megahertz
160 metres
3.5 to 4.0
80
7.0 to 7.3
40
14.00 to 14.35
20
21.00 to 21.45
15
28.0 to 29.7 MegaHertz 10 metres
144 to 148 MegHertz
2 metres
440 to 450 MegaHertz
70 centimetres
An antenna to be used on 40 metres to be a half wavelength
would be 20 metres long. The conductor which forms the antenna
has inductance because of its diameter and length and
capacitance due to the nearby earth. An antenna made to the
43
correct length for the frequency is a tuned circuit. At that length
it will provide the proper load to the transmitter.
The antenna will not only radiate radio waves, it will also work in
reverse. When a radio wave in space passes across an antenna, a
voltage is generated in it which is enough to make two way
communications possible.
#4.28 Types of Antennas
The Vertical or Marconi
For a vertical antenna to operate efficiently it is essential that a
good ground be provided. With this ground the radio waves act as
if the ground were a mirror. With a quarter wave antenna above
the ground the radio waves act as if it were a half wave antenna
with the other quarter wave below ground, the mirror effect. This
type of antenna is successfully used as a whip antenna on
automobiles because the body of the car replaces the ground.
The quarter-wave vertical antenna has a characteristic impedance
of 52 ohms and can readily be connected to a coax feed line
having the same impedance. This antenna takes up very little
space, is non-directional and inexpensive. However, it is
susceptible to man made noise.
The Half-Wave Dipole or Hertzian Antenna
A common antenna is a wire cut to one-half wavelength of the
operating frequency and attached to the feed line at its centre.
The half-wave dipole must be supported at each end using
insulators to tie it to the supports. The centre is cut and an
insulator is inserted between the two ends with the feed line
connected across the insulator. The impedance of the half-wave
dipole is 72 to 75 ohms.
44
The Half-Wave Folded Dipole
This antenna is a full-wave antenna folded back on it so that it is
a half-wave in length. It is easily made from twin TV lead. Each
conductor at the end of the lead is bared and soldered together.
One conductor is cut in the centre and bared and connected to
the feed line which is also twin TV lead. It is supported at each
end using insulators. This antenna requires an antenna tuner or
matching unit because it has an impedance of 300 ohms and
most transceivers used today have an output impedance of 50
ohms. The folded dipole has a broader bandwidth than a dipole
and it does not radiate the second harmonic.
Shortening Effects
The actual length of a resonant half wavelength antenna will not
be exactly equal to the half wavelength in space, but depends on
the thickness of the conductor in relation to the wavelength. An
additional effect occurs with wire antennas supported by
insulators at the ends because of capacitance added by the
insulators. Therefore the antenna must be made slightly shorter
than the exact wavelength.
#4.29 Impedance Matching and Reflected Waves
The output impedance of modern transceivers is 50 ohms. We
have also said that some feed lines have impedances of 52 and
300 ohms. Antennas can also have impedances of 52 ohms, 72
ohms and 300 ohms. It is quite possible therefore to have a
situation where there is a mismatch of impedances. If the
impedances are not the same, then some of the energy will not
be coupled to the antenna, but will be reflected back to the
source. The reflected wave will meet the outgoing wave from the
transmitter. If they meet when both are positive, then a more
45
positive point will be created on the feed line. If one is negative
and the other positive then they will tend to cancel each other.
The combination of forward or outgoing and reflected waves
produces a series of waves that appear to stand still. These are
known as standing waves.
The waves that are passed back and forth on the feed line are not
radiated and result in higher RF currents and voltages in the feed
line resulting in power loss. There will be different currents and
voltages at different points along the transmission line. If the
maximum current or voltage is measured and divided by the
minimum current or voltage measured, a numerical figure
referring to the maximum and minimum currents or voltages
would be obtained. This ratio is known as the standing wave ratio
or SWR. If there is no reflected wave and therefore no SWR the
standing wave ratio would be 1 to 1, which is the ideal condition.
The instrument which is used to detect and measure standing
waves is known as a standing wave bridge. It is connected
between the transmitter and the antenna coupler or tuner. An
antenna tuner and a standing wave bridge are necessary for
operation unless the antenna is specifically tuned for the
frequencies that are going to be used.
#4.30 Baluns and Traps
If you want to join 52 ohm coax feed line to a folded dipole
antenna that has an impedance of 300 ohms you would connect a
balun between the feed line and the antenna. Balun is an
acronym for balanced unbalanced. A balanced circuit has each
side identical, such as a dipole antenna. An unbalanced circuit has
each side different, such as in a coax conductor. A balun is simply
a small transformer that is not frequency sensitive, but each
winding has an impedance that will match the two different
impedances.
46
Many Amateur radio operators are restricted to one antenna, yet
wish to operate on many bands. To accommodate this
requirement an operator can insert traps into the dipole or
vertical antenna. Traps are frequency sensitive and can be
purchased or made.
Trap operation is simple. Let's think of a vertical antenna for two
metres. It will be approximately one-half of a metre long for a
quarter wave antenna. Let's assume the operator wants to also
work the 0.7 metre band or 440 megahertz. Its antenna will be
about 0.2 metres. We buy or make a trap that passes all
frequencies except 440 megahertz and put it 0.2 metres from the
bottom. At 140 megahertz the radio waves pass through the trap,
and the waves think the antenna is half a metre long. At 440
megahertz the radio waves are stopped by the trap which will not
let them through. They are fooled; they think the antenna is 0.2
metres long, just what we want. We have one antenna for two
frequencies.
#4.31 Antenna Polarization
The signal transmitted from an Amateur radio station is
influenced by the type of antenna that is used and its physical
orientation to the earth's surface. A horizontal antenna such as a
dipole which is parallel to the earth or ground will produce a
horizontally polarized signal. A vertical antenna which is
perpendicular to the surface of the earth will produce a vertically
polarized signal. Polarization is critical on the VHF and UHF bands,
but not on the HF bands since HF signals can change their
polarization as they travel through the ionosphere.
#4.32 Propagation
This discussion of propagation is greatly simplified. Many hams
make a lifetime study of propagation and are skilled at using the
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data provided by Canada and other countries to forecast the
conditions tomorrow and next week.
When electrons in a conductor such as an antenna are made to
oscillate back and forth, electromagnetic waves are produced.
These waves radiate outwards from the antenna at the speed of
light which is 300 million metres per second. Light waves and
radio waves are both electromagnetic waves differing only in
frequency.
The electromagnetic waves can be exchanged between two radio
stations directly by line of sight, by ground waves where the
waves follow the ground or by sky waves where the waves reach
the ionosphere and are bent back to earth.
Local communication within say 100 kilometres is mostly line of
sight with a bit of ground wave effect. All frequencies are
useable. Frequencies above 50 megahertz substantially fall in this
category.
Nearly all Amateur radio communication beyond local and below
30 megahertz is by means of sky waves. As the radio waves
travel out from the earth they encounter a region of ionized
particles in the atmosphere. This region is called the ionosphere
and it can bend the radio waves back to the earth. Without the
ionosphere, radio waves would be lost in space. Thus our radio
waves skip off the ionosphere. The skip length can be 400 to
4000 kilometres and multiple skips are possible.
The ionosphere begins about 50 kilometres above the earth's
surface and extends upward about 460 kilometres. In this region
free ions and electrons exist in sufficient quantity to affect the
direction of radio wave travel. Ionization of the ionosphere is
attributed to ultraviolet radiation from the sun. The result is not a
single region, but several layers of varying densities at various
heights surrounding the earth. Each layer has a central region of
relatively dense ionization that tapers off both above and below.
The ionosphere layers have been given letter designations.
48
The layer closest to the earth's crust is the D layer. When sunlight
strikes it, it rapidly forms a dense layer as part of the earth's
atmosphere which is about 50 to 90 kilometres above the surface
of the earth. The D layer actually is ineffective in bending high
frequency signals back to the earth. In fact the major effect the D
layer has on long distance communication is to absorb energy
from the radio waves. Absorption is most pronounced at mid day
and is the principal reason for short daytime communication
ranges in the 160, 80 and 40 meter bands. When the sun sets
the D layer rapidly disappears, allowing long distance
communication.
The E layer, which is the next layer up, exists in the ionosphere
at an altitude of about 100 to 115 kilometres. The E layer can be
used to bend radio waves when there is sunlight. Like the D
layer, the E layer reaches a minimum just before sunrise and a
maximum about midday. Skip distances between two Amateur
stations of approximately 2000 kilometres can be realized
because of the ability of the E layer to turn radio waves back to
the earth. However, since the radio waves can be absorbed by
the D layer, use of the E layer is spotty; but skilled amateurs do
use it.
The next higher layer in the ionosphere is the F layer which is
responsible for almost all long distance communication on the
Amateur HF bands. It is actually a very large region, ranging from
about 210 to 420 kilometres above the earth, depending on the
season, the time of day and the solar activity. The F layer
remains ionized throughout the night and reaches a minimum
just before sunrise.
In summary, long distance communication for 160, 80 and 40
metres is by sky wave after dark. Frequencies above 6 metres
are direct or by ground wave and typically limited to 100
kilometres. The frequencies between 6 and 40 metres exhibit
both properties and can be limited to local distances or avail
themselves of the sky waves. The workhorse of Amateur radio is
49
20 metres and long distance communication is possible during
daylight hours.
#4.33 Sunspot Cycles
For the sun there is a period of about 22 years in which ultra
violet radiation reaches minima and maxima. Ultra violet
radiation is the chief, but not the only source of radiation in the
upper atmosphere. During periods of low ultraviolet emission the
ionization of the atmosphere is low and radio signals with short
wavelengths will pass through and will be lost in space. During
periods of higher ultraviolet emission higher levels of ionization
reflect higher frequencies and shorter wavelengths will propagate
much longer distances.
There are two sunspot maxima and minima in each 22 year cycle,
leading to enhanced and reduced propagation of radio waves
approximately every 11 years.
Solar storms or sun spot activity are very large disturbances on
the sun's surface that create large bursts of energy from the sun.
These have the effect of disturbing the layers in the ionosphere
and have major bad effects on our ability to use the ionosphere
to communicate. We have to wait until the storms stop. HF
communication is difficult and in many cases impossible, except
by ground waves.
#4.34 Atmospherics
Atmospherics is another phenomenon which also affects radio
propagation. This is a name that is given to a wide variety of
effects that originate with weather disturbances. These include
lightning storms and related electrical discharges.
50
#4.35 Transmitters and Receivers
There are many types of transmitters and receivers. This course
will only cover a very simple transmitter and the superheterodyne
receiver by describing the functions of the key blocks within the
equipment. Circuit descriptions within the blocks and descriptions
of actual transmitters and receivers are beyond the scope of this
course.
If you have a well filtered DC power supply, an oscillator tuned to
a specific radio frequency and an amplifier, you would have a
transmitter. The signal that you would get from the amplifier is
called a radio frequency carrier. It would not convey any
information. The emission from the amplifier is classified as an
unmodulated wave.
If you want to transmit information such as Morse code, you
would use a telegraph key as a switch to turn the carrier on and
off in the proper code pattern. You would be able to transmit
telegraphy. However, you will probably want your transmitter to
operate on many frequencies. Therefore, instead of a fixed
frequency oscillator you would use a variable frequency
#4.36 Oscillators
Your basic CW transmitter consists of a DC power supply, a
variable frequency oscillator, or VFO, an intermediate amplifier or
driver, the telegraph key and the power amplifier. Your
transmitter is a sending device and you can transmit a radio
signal as telegraphy. Your antenna will radiate the signal into the
air. Some distance away the signal from your antenna will induce
an RF voltage into a receiving antenna. The RF voltage goes from
the antenna into a receiver which converts the RF energy into
audio frequency energy which one can hear from a loudspeaker.
You will also need a receiver to hear a return message.
51
There are a number of different circuits that are used in radio
receivers. One of the fundamental principles of receiver operation
is mixing and the superheterodyne system is the most popular. In
a superheterodyne receiver all desired incoming signals are
converted to a common frequency. To do this, two signals at
different frequencies are used, one from the antenna and the
other generated by an oscillator in the receiver, a VFO. These two
signals are combined in a mixer circuit. The mixer output will
contain four frequencies, the original two frequencies, the sum of
the two original frequencies and the difference between the two
original frequencies.
A tuned circuit is used to select one of the output frequencies,
usually the difference between the two input frequencies.
This frequency is called the intermediate frequency or IF. The
output of the IF stage goes into a detector stage. The detector
stage will separate the audio frequency from the radio frequency,
if you are receiving a voice signal. The audio signal from the
detector stage is fed into an audio amplifier which is connected to
the speaker.
The basic superheterodyne receiver is a radio frequency amplifier,
a mixer with a variable frequency oscillator feeding it as well as
the radio frequency amplifier output, a number of intermediate
frequency stages, a detector, an audio amplifier plus the output
audio device such as a loudspeaker or earphones.
#4.37 Modulation
Amplitude Modulation
We want to address two radio wave characteristics, amplitude
and frequency. We can modify either characteristic.
To transmit information contained in a human voice it is
necessary to change the form of the radio wave in such a manner
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that when it is received the original voice can be reproduced. One
such method of doing this is called amplitude modulation or AM.
In amplitude modulation the amplitude or wave height of the
carrier signal is made to vary in accordance with the audio signal.
When a carrier signal is modulated by an audio frequency tone,
additional frequencies are produced in the output signal which is
equal to the sum of the carrier and the modulating frequency and
the difference between the two frequencies. Thus the process of
modulation adds additional frequency bands called sidebands,
located above and below the carrier. These are called upper and
lower sidebands, respectively. The upper and lower sidebands
carry duplicate information.
Having said that amplitude modulation produces a transmitter
signal output containing the carrier frequency and the upper and
lower sidebands it seems obvious that redundant information is
being transmitted. The lower and upper sidebands contain the
same amount of power and the same frequencies, although one is
upside down with respect to the other. The carrier too is
redundant as it contains no information at all. It doesn't vary.
The spectrum or space taken by this signal is twice as wide as the
highest modulating frequency. To conserve the spectrum we can
remove one of the sidebands, it does not matter which one. We
now have the carrier and the remaining sideband. To conserve
power we can remove the carrier and transmit the remaining
sideband. Having taken the carrier out the remaining sideband
provides the same amount of information as in the original
amplitude modulation signal. This method of transmission is
called single side band suppressed carrier or SSB. It is the
standard method of radio telephone on the Amateur HF bands.
Frequency Modulation
When the frequency of the carrier signal is varied with the
variations in a modulating signal, the result is frequency
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modulation or FM. Amateurs in the VHF and UHF range use
narrowband FM which has a bandwidth of about 5 kilohertz.
Signal Bandwidth
Any modulated signal occupies a finite space in the radio
spectrum. A signal occupying zero bandwidth can not carry
information. The narrowest signal used by radio amateurs is CW
or Morse code. The narrowest bandwidth is about 250 hertz.
Amplitude modulation uses a bandwidth of twice the highest
modulating frequency. The minimum bandwidth that will carry a
human voice is 6 000 hertz.
Single sideband deletes one of the sidebands before transmission.
Since there is no carrier, there is no base line reference so the
actual occupied spectrum is the same as the difference between
the highest and lowest frequencies involved, which is about 2700
hertz.
The spectrum space occupied by an FM signal is greater and is
about 15 kilohertz wide.
#4.38 Selectivity, Sensitivity and Stability
A receiver is characterized by its ability to separate and decode or
demodulate the desired signal from all other signals in the
spectrum at that time. This includes the modulation technique
involved, the occupied bandwidth and the actual level of the
signal at the antenna terminals.
The work of the receiver is made difficult by other signals on the
same or nearby frequencies, noise both internal and external to
the receiver, and transmission path problems, such as fading.
54
There are three useful terms that are used to describe the
characteristics of a receiver. Sensitivity, selectivity, and stability.
Sensitivity refers to the minimum signal that a receiver can
detect. The greater the receiver's sensitivity is, the weaker the
signal it can receive.
Selectivity is the ability of a receiver to distinguish between two
stations whose frequencies are close together.
Stability refers to the receiver's ability to tune a frequency and
remain on it for a period of time.
#4.39 Decibels
You will find that in most radio communications the received
signal is converted into sound. This being the case it is useful to
appraise signal strength in terms of relative loudness as
registered by the ear. A peculiarity of the ear is that we hear in
decades. You are barely able to discern a difference in loudness
of a factor of two. It takes a factor of ten before you see a
difference. Your ear is capable of hearing over several decades.
In other words, the human ear has a logarithmic response. This
means we hear things in levels of decades.
This fact is the basis for the use of the relative power unit called
the decibel, abbreviated db. Without going into mathematics it is
useful to know:
3 db says that there is a gain in power by a factor of 2.
10 db says that there is a gain in power by a factor of 10.
20 db says that there is a gain in power by a factor of 100.
#4.40 AGC Automatic Gain Control
55
Another term that you will encounter in a discussion on receivers
is AGC or automatic gain control. Automatic gain control is a
characteristic that is designed into a receiver. It is the regulation
of the gain of the receiver in inverse proportion to the signal
strength. AGC is an operating convenience in reception, since it
tends to keep the output level of the receiver constant regardless
of the signal strengths. AGC is accomplished by feeding a portion
of the signal at the detector stage back to preceding amplifiers.
#5.0 Your Amateur Radio Station
Your HF radio station should contain the following items:
The transmitter and receiver or transceiver with a key for Morse
code. The operator must ensure that the station is equipped with
a means of measuring transmitted frequency.
Low pass filter. This device acts as a part of the transmission path
for the RF signal and will eliminate spurious emission from
transmitters operating below 30 megahertz. These often are built
in to modern transceivers.
An SWR meter. The standing wave ratio meter allows the
operator to monitor the amount of power being put into the
antenna.
An antenna tuning unit. This device is also known as an antenna
tuner or an antenna coupler. It is required to match the antenna
to your transmitter or transceiver and is used in conjunction with
the SWR meter.
The dummy load. This unit is connected to the connection
between the SWR meter and the antenna tuning unit. Its use
assures that no unnecessary HF signals are radiated during
tuning of an HF transmitter. Its impedance matches that of the
transmitter output.
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The antenna.
#6.0 Conclusion
Enjoy our hobby, its great fun, and as noted in the preface keep
the spirit of courtesy, helpfulness and public service continuously
alive and well.
For more information or assistance, please call
Randy Nelson VE3WRN
Manager, CNIB Amateur Radio Program
1929 Bayview Avenue
Toronto, ON M4G 3E8
T: (416) 480-7438
F: (416) 480-7677
E: [email protected]
W: www.cnib.ca/amateurradio
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#7.0 Attachment “A”
Amateur Bands and Bandwidths
A summary of the key bands and bandwidths that Amateurs may
use are listed below. For the total list see RIC-2, “Standards for
the Operation of Radio Stations in the Amateur Radio Service”
Band
Frequency
(metres) (MegaHertz)
Bandwidth
(kiloHertz)
Qualification Required
(B Basic 5 wpm Morse)
160
1.80 – 2.00
6
B+5
80
3.50 – 4.00
6
B+5
40
7.00 – 7.30
6
B+5
30
10.10 – 10.15
1
B+5
20
14.00 – 14.35
6
B+5
10
28.00 – 29.70
20
B
6
50.00 – 54.00
30
B
2
144.0 – 148.0
30
B
0.7
430.0 – 450.0
12000
B
58