* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 3.0 Operating Procedures
Superheterodyne receiver wikipedia , lookup
Power MOSFET wikipedia , lookup
Telecommunication wikipedia , lookup
Power electronics wikipedia , lookup
Yagi–Uda antenna wikipedia , lookup
Battle of the Beams wikipedia , lookup
Surge protector wikipedia , lookup
Cellular repeater wikipedia , lookup
Radio direction finder wikipedia , lookup
Amateur radio repeater wikipedia , lookup
Opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
RLC circuit wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Standing wave ratio wikipedia , lookup
Regenerative circuit wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Rectiverter wikipedia , lookup
Mathematics of radio engineering wikipedia , lookup
Crystal radio wikipedia , lookup
Valve RF amplifier wikipedia , lookup
Direction finding wikipedia , lookup
Antenna tuner wikipedia , lookup
Bellini–Tosi direction finder wikipedia , lookup
High-frequency direction finding wikipedia , lookup
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, 1 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 2 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. 3 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. 4 #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 5 #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 6 #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. 7 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. 8 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. 9 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 10 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 11 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. 12 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 13 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… 14 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 15 #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 16 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. 17 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”. 18 #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 19 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 20 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 21 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. 22 #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 23 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. 24 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. 25 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 26 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. 27 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 28 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. 29 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. 30 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 31 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 32 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 33 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. 34 #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 36 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 37 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. 38 #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. 39 #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 40 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 47 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 52 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 53 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. 56 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 57 #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