Radio and Electricity

1. Radio and Electricity • Radio works because of electricity, so to understand radio, you have to know a little bit about electricity. In this group, we’ll get some of the basics of electricity out of the way. There are three units we will study related to electricity in this group – voltage, current, and power. By the time you are ready for your test, you will be very familiar with all of them.

2. 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.

3. 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.

4. 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.

5. 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

6. 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.

7. 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.

8. 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.

9. 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!

10. 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!

11. 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.

12. 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.

13. Flashlight – Schematic Diagram • If you diagram the flashlight, it looks something like this:

14. 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.

15. 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.

16. Simple Light Circuit • Press the switch and the light comes on.

17. 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.

18. 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.)

19. 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.

20. 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!

21. 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.”

22. 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

23. 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.

24. 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.”

25. 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.

26. 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.

27. 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.

28. 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!

29. 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.

30. “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.

31. 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.

32. 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.

33. 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!

34. 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.

35. 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.

36. 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.)

37. 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.

38. 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”

39. 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.

40. 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.

41. 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.

42. T4A01 • Electrical current is measured in which of the following units? • A. Volts • B. Watts • C. Ohms • D. Amperes

43. 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.

44. T4A02 • Electrical Power is measured in which of the following units? • A. Volts • B. Watts • C. Ohms • D. Amperes

45. 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.

46. T4A03 • What is the name for the flow of electrons in an electric circuit? • A. Voltage • B. Resistance • C. Capacitance • D. Current

47. T4A03 Answer - D • Current is the amount of electron flow in a circuit. The greater the amount of electron flow, the higher the current.

48. T4A04 • What is the name of a current that flows only in one direction? • A. An alternating current • B. A direct current • C. A normal current • D. A smooth current

49. T4A04 Answer - B • Direct current flows through a circuit in one direction only.

50. T4A05 • What is the standard unit of frequency? • A. The megacycle • B. The Hertz • C. One thousand cycles per second • D. The electromagnetic force