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