Alternating current—Abbreviation, AC. Electrical current that reverses direction at regular intervals. In the United States and some other countries, standard utility AC reverses direction every 1/120 of a second, so it goes through 60 complete cycles per second. In many countries, standard utility AC reverses direction every 1/100 of a second, so it goes through 50 complete cycles per second.
Alternator—A small electric generator used in motor vehicles to provide power to electrical and electronic devices, and to keep the battery charged up. The alternator in a car or light truck can generate several amperes of current when the engine runs at normal driving speed.
Alternator whine—Interference to mobile two-way radio reception caused by the electrical activity in the vehicle’s alternator. Usually sounds like an audio “tone” whose pitch varies depending on the speed of the engine. Sometimes this whine can appear on a transmitted signal, too.
Amateur radio—Also called “ham radio.” A popular worldwide electronics hobby. In most countries of the world, people need government-issued licenses to operate ham radio transmitters. Some operators communicate over wireless media at various frequencies by talking, sending Morse code, or typing on computer terminals. Others prefer to experiment with electronic circuits. Of course, any individual “ham operator” can do both of these things, as well as contribute to emergency communications preparedness.
Ampere—The standard unit of electrical current. Mathematically it can be considered the equivalent of a volt per ohm in a simple DC circuit.
Analog television—Also known as fast-scan TV (FSTV) or National Television System Committee (NTSC) TV. In most of the world, broadcasters no longer use this mode; it was pretty much done away with worldwide by 2011. Nevertheless, if you have an old TV set, it was probably designed for analog TV and won’t work nowadays unless you get a digital-to-analog converter box.
Audio mixer—A hi-fi sound system component that allows you to connect the outputs of multiple audio devices to a single channel input for an amplifier. The mixer isolates the amplifier’s inputs from each other, so you don’t have to worry about any possible mismatch or “competition” among the source devices. In addition, you can adjust the signal level (gain) for each device without affecting the behavior of any other device.
Automotive battery—A large, heavy battery about half the size of a concrete cinder block. In the United States, a standard automotive battery produces 12.6 V at full charge with no load. It contains six 2.1-V lead-acid cells connected in series.
Baffle—An object, usually a flat piece of wood or other sound-reflective material, used to modify the way that sound waves propagate in a speaker cabinet, room, or auditorium. Properly used, baffles can enhance the quality of sound from a high-end audio system.
Balance control—A single control, or a pair of controls, intended for adjusting the relative volume levels of the sounds coming from the left and right channels in a stereo hi-fi system. This control can compensate for variations in speaker placement, relative loudness in the channels, and the acoustical characteristics of the room in which the equipment is installed.
Banana connector—A convenient single-pin plug-and-receptacle combination. Used with single-wire conductors to make temporary connections.
Bar code tag—A simple possession-based access control technology. Also used for item labeling. The tag has parallel bands of various widths. More sophisticated tags have complicated patterns of black shapes on a white background. A laser rapidly scans the pattern. The dark regions absorb the laser light, while the white regions reflect the light back to a sensor. The sensor, thereby, receives a binary data signal unique to the pattern on the tag.
Battery—A combination of electricity-producing cells that produces a higher voltage, or that can deliver a higher current, than an individual cell can do all by itself.
Binary digital signal—Signals that occur in either of two states called bits (a contraction of “binary digits”) that represent the number 1 and the number 0, but nothing else. These signals are, in fact, rapidly fluctuating direct currents. Commonly used in computer communications.
Biometric access control—A property protection technology that acts on certain biological characteristics of people authorized to enter. For example, it might employ a camera along with a pattern recognition computer program to check a person’s facial contours against information in a gigantic database. The machine might use speech recognition to identify people by breaking down the waveforms of their voices. It might record a hand print, fingerprint, or iris print. It might even employ a combination of all these things. A computer analyzes the data obtained by the sensors, and determines whether or not the person has authorization to enter the premises.
Bit—A single element in a binary digital signal. It can exist in either of two states, but only those two states, called 1 (high) and 0 (low).
Breaker—See Circuit breaker.
Cassegrain dish—A satellite TV or satellite Internet dish antenna whose geometry resembles that of a Schmidt-Cassegrain reflecting telescope. Sometimes found in more remote areas where a larger antenna is necessary. This type of dish can sometimes measure more than two meters in diameter. The signal arrives along the dish axis, reflects from the spherical or paraboloidal surface, and comes to a focus at a second, smaller reflector. The second reflector causes the incoming microwaves to travel straight back to the center of the dish, where the energy enters the feed horn and frequency converter assembly through a small hole.
Catastrophic failure—An equipment malfunction in which the entire device or system becomes useless. Often takes place suddenly, and can happen without warning.
Cell—A device that produces DC electricity from chemical reactions, visible light radiation, or other processes. A cell can’t be broken down into anything more elementary; it’s the simplest possible arrangement for producing DC electricity. Compare Battery. Sometimes a cell is imprecisely called a “battery.”
CFL—See Compact fluorescent lamp.
Charge controller—In an alternative electric power system with batteries, an essential component that makes sure the battery bank receives the optimum amount of charging current at all times from the solar panel, wind turbine, water turbine, or other energy-producing device. Also prevents overcharging, which can shorten the life of a deep-cycle battery.
Charge polarity—The “sense” of electricity, either negative (an excess of electrons) or positive (a shortage of electrons). Sometimes negative is called “minus” and positive is called “plus.” In electric circuits, electrons flow from regions having relatively more negative polarity to regions having relatively more positive polarity. Physicists consider the current to flow from positive to negative in theory, but that’s an old convention that scientists invented before they knew that electrons, which carry negative charge, existed.
Chip—See Integrated circuit.
Circuit breaker—A current-actuated switch that performs the same basic functions as a fuse, but that can be reset, and does not need to be replaced every time it “trips.” Most homes in the United States use circuit breakers in their electrical systems. Some individual appliances, such as electric space heaters and transient suppressors, also contain circuit breakers, typically rated at 15 A in the United States (for 117-V circuits).
Clip lead—A short length of flexible wire, equipped at one or both ends with a simple, temporary connector.
Coaxial cable—A single-conductor shielded cable in which a length of wire, called the center conductor, is surrounded by a cylinder of solid metal, a cylindrical wire braid, or a layer of metal foil called the outer conductor or shield. The center conductor is separated from the shield by a layer of dielectric (insulating) material such as polyethylene. Commonly used in radio and television communications systems, as well as for high-speed Internet connections.
Coefficient of performance—An expression of how well a heat pump works. Sometimes mistakenly called “heat-pump efficiency.” Mathematically, the COP equals the ratio of thermal energy that the system transfers to the amount of energy that the system consumes in order to do its job.
Combustion generator—An independent source of electricity that uses an internal combustion engine. Most small generator engines burn gasoline. Larger ones burn diesel fuel, propane, or methane.
Compact fluorescent lamp—Abbreviation, CFL. A lamp or bulb comprising a coiled-up, miniaturized fluorescent tube with electronic circuits that allow it to function much more efficiently than traditional incandescent lamps. You can expect a CFL to last far longer than an incandescent lamp in the same application. Some concerns have arisen about CFLs because they contain mercury, a known environmental toxin. Nevertheless, CFLs have attained popularity as direct replacements for incandescent lamps.
Compact hi-fi system—The simplest type of home audio arrangement. It resides in a single cabinet. The speakers can be either internal or external; if they’re external, the connecting cables are short. The assets of a compact system include small size, simplicity, and low cost.
Component hi-fi system—A home audio arrangement with dedicated equipment cabinets containing components that perform specific functions. The individual units are interconnected with cables, ideally of the shielded coaxial type. A component system costs more than a compact system does, but you get better sound fidelity, more audio power, the ability to do more tasks, and the opportunity to tailor the system to your preferences.
Conductance—The ease with which an electrical current can flow through a substance.
Conductor—A substance in which electrical current can flow easily. Examples include most metals, particularly copper and aluminum, which are used for making wire and in the construction of wireless antennas.
Continuity test—In an electrical circuit or system, a test that you can conduct with a multimeter to find out whether two points are directly connected or not. If they are, then you will observe no DC or AC voltage between them, and the resistance between them will equal zero.
Conventional dish—A satellite TV or satellite Internet dish in which the signal arrives at a slight angle with respect to the dish axis, reflects from the spherical or paraboloidal metal surface of the dish, and then enters a device called a feed horn, which acts like an “ear for microwaves.” The feed horn is connected to a converter that changes the frequency of the signal so that it can travel along a coaxial cable to the TV equipment inside your house. The whole assembly measures less than 1 meter wide, 1 meter long, and 1 meter deep.
Conversion efficiency—For a photovoltaic cell, the ratio of the available electrical output power to the total radiant power striking the cell (with both quantities expressed in the same units, such as watts). Can be multiplied by 100 to obtain the figure as a percentage.
Corona—A visible glow that commonly occurs when extreme voltages on electrical conductors ionize the surrounding air. A corona can appear at the ends of a radio-transmitting antenna element. It is also seen in high-tension power lines. A corona occurs increasingly often as the relative humidity rises because it takes less voltage to ionize moist air than it takes to ionize dry air. A corona is normally not visible in daylight, but it shows up clearly at night, when it is sometimes called “Saint Elmo’s fire.”
Current—The movement of particles that carry an electrostatic charge from one point to another. Usually these particles are electrons.
Decibel—Abbreviation, dB. A real-world unit of relative sound loudness, based on the way people perceive it. If you change the volume control on a hi-fi set so that you can just barely tell the difference in the loudness when you anticipate the change, then that change equals approximately 1 dB. Decibels are worked out by engineers with respect to the threshold of hearing, which represents the faintest sound that you can detect in an otherwise silent place, assuming that you have good hearing.
Degree of phase—See Phase.
Deep-cycle battery—A rechargeable battery that can store a lot of energy, and that you can repeatedly charge and discharge to run electrical devices. Often used with alternative electric power systems so that they get their original energy from renewable, natural sources, such as the sun, the wind, or moving water.
Digital logic—A form of “reasoning” used by electronic machines, particularly devices and systems controlled by computer chips. Works on the basis of two conditions, called high (usually logic 1) and low (usually logic 0). These conditions are like “truth” and “falsity” in mathematical logic.
Digital spread spectrum—Abbreviation, DSS. A communications mode in which the signal frequency hops or sweeps over a defined range. The transmitter frequency varies according to a specific, encoded, repeating pattern. No receiver can hear the signal unless it “knows the code” and acts on it correctly.
Dip—A momentary decrease in the power-line voltage that can occur when a large appliance first comes on. You’ve probably noticed these fluctuations as momentary “blinks” in old-fashioned incandescent bulbs when some heavy appliance, such as a washing machine or refrigerator, starts up.
Direct current—Abbreviation, DC. Electrical current that always flows in the same direction. The intensity (or strength) of the current can vary, but in true DC, the polarity (direction) never changes. Nearly all electronic equipment needs DC in order to function properly. That’s why, unless they operate from batteries, your gadgets and systems usually have specialized power supplies.
Dirty electricity—A term that describes the fact that ordinary household utility electricity contains energy at many frequencies other than the 60 Hz “main” AC frequency (or 50 Hz in much of the world outside the United States). All of the frequency components produce electromagnetic fields that can sometimes interfere with wireless electronic devices.
D-shell connector—A specialized, multiconductor plug and jack combination with trapezoidal (D-shaped) shells that force you to insert the plug correctly into the jack.
Dynamic range—The difference in decibels between the strongest and the weakest output audio signals that the system can produce without objectionable distortion. It’s a prime consideration in hi-fi recording and reproduction. As the dynamic range specification of an amplifier increases, the sound quality improves for music or programming having a wide range of volume levels.
Dynamic speaker—A coil-and-magnet combination that translates alternating electrical current into mechanical vibration, thereby producing sound waves in the air. Used in most hi-fi sound systems.
Electric eye—An intrusion-detection system with a visible-light or infrared (IR) source, usually a laser diode, and a sensor, such as a photoelectric or photovoltaic cell. These devices are connected into an actuating circuit. When something interrupts the light or IR beam, the current or voltage passing through, or generated by, the sensor changes. An electronic circuit detects this change and sends a signal to an alarm or other alerting device.
Electric field—A “region of influence” that occurs in space around all electrically charged particles and objects. Electric fields are responsible for the attraction and repulsion that we observe between charged objects.
Electric flux lines—Imaginary contours in space that define the orientation, direction, and intensity of an electric field.
Electrical ground—A connection in the wiring of a home or business that remains at zero voltage with respect to the earth. In any good home or business electrical system, the electrical ground connection is established at the point where the utility lines enter the building, usually in the form of a ground rod at or near the distribution panel (fuse or breaker box). In a well-engineered electrical system, the “third prong” in every wall outlet should be connected directly to the building’s electrical ground.
Electrolyte—In an electrochemical cell or battery (such as the zinc-carbon, alkaline, lead-acid, or lithium type), the solution or paste inside the component. This solution or paste contains energy in chemical form, which converts to electrical energy when you connect a lamp, radio, tablet computer, or other electronic device to the cell or battery.
Electromagnet—A magnet constructed with a coil of wire around a “magnetizable” rod of metal, such as iron or steel. When current flows through the coil, the rod becomes a magnet. When current stops flowing through the coil, the rod loses its magnetism.
Electromagnetic (EM) field—A complex energy field comprising an alternating or fluctuating electric field and an alternating or fluctuating magnetic field working together, arising from alternating current in a wire or from certain physical phenomena. Radio waves, infrared, visible light, ultraviolet, x rays, and gamma rays all manifest themselves as EM fields.
Electromagnetic (EM) spectrum—The range of all electromagnetic field (EM field) frequencies or wavelengths commonly encountered in the real world. Frequencies range from a few hertz to millions of terahertz; wavelengths range from many kilometers down to a tiny fraction of a millimeter.
Electrostatic charge—An excess or shortage of electrons that tends to persist, so that an object maintains a positive or negative charge polarity with respect to its surroundings. Sometimes lay people call this condition “static electricity.”
Electrostatic speaker—A pair of large, flat, closely spaced metal plates that translates electrical voltage into mechanical vibration, thereby producing sound waves in the air. Used in some high-end hi-fi audio systems.
Ethernet cable—A cable that connects a modem or a hard-wired router to your computer for Internet use. It looks like a telephone landline cord with similar plugs on the ends, but the Ethernet cable has more wires than an old-fashioned phone cord does.
Female connector—A receptacle, such as a wall outlet, into which a male connector fits.
Firewall—A computer program or hardware device that helps to keep rogue computer wizards (known as hackers in technical jargon) from taking control of your computer when it’s connected to the Internet. No firewall is perfect, however; the best hackers can get through them all.
Frequency—The number of complete cycles that occur every second in alternating current (AC) or pulsating direct current (DC).
Fuel cell—A device that converts combustible gaseous or liquid fuel into electricity at a lower temperature than normal combustion does. Hydrogen is a common energy source for these devices. The hydrogen oxidizes to form energy and water (along with a small amount of nitrous oxide if air serves as the oxidizer). The proton exchange membrane (PEM) fuel cell represents one of the most widely used technologies. A single PEM hydrogen fuel cell generates approximately 0.7 V DC. When two or more fuel cells are connected in series to get higher voltage, the combination is called a stack.
Fuse—An electrical component that protects circuits and devices from overload. Found in older houses, and in most motor vehicles. Also found in some individual electrical appliances. In a motor vehicle, the fuses protect the battery and the alternator in case of a short circuit. Fuses also minimize the risk of electrical overheating that can cause fires. Vehicle headlights, brake lights, turn signals, backup lights, interior lights, climate-control fans, radios, and other electrical devices all have fuses in their lines. If a fuse blows, the affected device or circuit won’t get the electricity it needs, so it can’t work.
Generator efficiency—In an electric generator, the ratio of the electrical power output to the mechanical driving power, both measured in the same units, such as watts (W) or kilowatts (kW), and multiplied by 100 to get a percentage.
Global Positioning System—Abbreviation, GPS. A network of radiolocation and radionavigation devices that operates on a worldwide basis. The GPS employs numerous satellites, and allows you to determine your location on the earth’s surface, and in some cases, your altitude above the surface as well.
Graphic equalizer—A device that lets you adjust the relative loudness of audio signals at various frequencies. It allows for meticulous tailoring of the sound quality in hi-fi equipment. The circuit contains several independent gain controls, each one affecting a different part of the audible spectrum. Acts as a sophisticated tone control.
Grid-intertie system—See Interactive system.
Hacker—A smart computer user who likes to break into other people’s systems, usually over the Internet. Some hackers simply enjoy the challenge and the intrigue of snooping around in other people’s business, and the technical process can be fascinating. More nefarious hackers break into systems for the purpose of stealing people’s money, identity, or other information. Still others do it to make a political statement.
Ham radio—Common slang for amateur radio.
Harmonic—A signal or wave that exists at a whole-number multiple of the main or fundamental frequency. For example, if 60 Hz is the fundamental frequency, then harmonics can exist at 120 Hz, 180 Hz, 240 Hz, and so on. The 120 Hz wave forms the second harmonic (twice the fundamental frequency), the 180 Hz wave forms the third harmonic (three times the fundamental frequency), the 240 Hz wave forms the fourth harmonic (four times the fundamental frequency), and so on.
Head unit—In a mobile sound system, the component that gathers signals from the radio, and/or converts data from media, such as compact-disc (CD) players, MP3 players, or tape cassettes, into audio signals. When you buy a vehicle, it will have a factory-installed head unit in the dashboard, where both the driver and the front-seat passenger can reach it.
Headset—Also known as a pair of headphones. A hi-fi component that offers listening privacy, keeps your “big sound” experience from disturbing people around you, and gets rid of sound-wave reflection problems inherent in all systems that use speakers. In effect, a headset comprises two small dynamic speakers, one placed directly against (or very close to) each ear.
Heat pump—An appliance that transfers thermal energy from one place to another to warm up or cool down the indoor environment. The term “pump” comes from the fact that the system uses a common external source of power, usually electricity, to move thermal energy rather than generating it directly.
Hermaphroditic connector—An electrical plug/jack pair with two or more contacts, some of them male and some of them female. In some cases, hermaphroditic connectors at opposite ends of a single length of cable look identical when viewed “face-on.” However, the pins and holes have a special geometry, so you can join the two connectors in the correct way only.
High-Definition Multimedia Interface—Abbreviation, HDMI. On a big-screen display or computer monitor, a port and cable that will let you connect your set to an up-to-date computer so that you can view programs on the Internet, and also look at homemade videos that you can create using popular devices, such as webcams and camcorders.
High-definition television—Abbreviation, HDTV. Any of several methods for getting more detail into a TV picture than could ever be done with analog television. The HDTV mode also offers superior sound quality, making for a more satisfying home TV and home theater experience. High-definition TV is transmitted in a digital mode. Digital signals propagate better than analog signals do, they’re easier to deal with when they are weak, and they can be processed in ways that analog signals would not allow.
High frequencie s—Abbreviation, HF. The range of radio frequencies from 3 MHz up to 30 MHz, corresponding to wavelengths from 100 meters down to 10 meters. Also called the shortwave band.
Hydrogen fuel cell—See Fuel cell.
Ignition noise—Interference to radio reception caused by internal combustion engines. Typically sounds like a rapid sequence of “pops” or a steady “buzz.” A special form of impulse noise.
Impulse noise—Interference to radio reception caused by a sudden, high-amplitude voltage pulse or regular sequence of pulses. This noise can come from all kinds of household appliances, such as vacuum cleaners, hair dryers, electric blankets, thermostats, and fluorescent-light starters. Impulse noise tends to get worse as the frequency goes down, and can plague AM broadcast receivers to the consternation of their users.
Incandescent lamp—A lamp (or bulb) that works by allowing an electric current to flow through a piece of wire that has a precisely tailored resistance and current-carrying capacity. As a result, the wire, called the filament, glows white hot.
Infrared—The portion of the electromagnetic spectrum with wavelengths longer than those of visible light but shorter than those of radio microwaves.
Infrared motion detector—An intrusion alarm system that uses infrared (IR) devices. Two or three wide-angle IR pulses are transmitted at regular intervals; these pulses cover most of the room in which the device is installed. A sensor picks up the returned IR energy, normally reflected from the walls, the floor, the ceiling, and the furniture. The intensity of the received pulses is measured and recorded by a microprocessor. If anything in the room changes position, the intensity of the received energy will vary, and the resulting signal will set off an alarm.
Infrared presence detector—An intrusion alarm system that employs a simple IR sensor, in conjunction with a microprocessor, to detect sudden increases in the amount of IR (or “radiant heat”) present in a particular place. The time threshold can be set so that gradual changes, such as might be caused by the sun warming a room, do not trigger the alarm, while rapid changes, such as a person entering the room, will set it off.
Insulator—A substance in which electric current cannot flow under normal circumstances. Examples include most plastics, glass, dry wood, paper, and dry air.
Integrated circuit—Abbreviation, IC. A “wafer” of semiconductor material with many components etched onto it to create a device that performs a specific function in an electronic system. Computers are built largely with these devices. Also called a chip.
Interactive system—In solar, wind, and hydroelectric alternative energy use, a system that connects with your commercial electric utility provider’s circuits to reduce or offset your electric bill. Compare Stand-alone system.
Inverter—See Power inverter.
Kilowatt hou r—Abbreviation, kWh. The amount of electrical energy that a 1000-watt (1-kilowatt) appliance consumes in an hour, or the equivalent of it.
Knowledge-based access contro l—A property-protection technology in which people are issued numerical codes. The entrances to your property have locks that disengage when the proper sequence of numbers is punched into a keypad. This keypad can be hard-wired into the system, or it can be housed in a box about the size of a cell phone. It works like a bank automatic-teller machine (ATM) personal identification code.
Lamp cord—Also known as “zip cord” and consisting of two stranded wires embedded in rubber or plastic insulation. Commonly used with small appliances, such as table lamps, portable battery chargers, and clock radios.
Lead-acid cell—A common type of rechargeable electrochemical cell, used in automotive and power-backup applications. When the cell has a full charge, the negative electrode consists of pure lead, and the positive electrode consists of lead dioxide. The electrolyte, which contains all the battery’s energy in chemical form (and which converts to electrical energy when something demands current), is sulfuric acid diluted with water.
LED—See Light-emitting diode.
Light-emitting diode—Abbreviation, LED. A semiconductor device in the form of a lamp (or bulb) that is specially designed to emit visible light when current passes through it. These lamps produce a reasonable amount of light but consume only a small amount of electrical power. As a result, LEDs cost less to operate, once you buy them, than any other type of lamp known as of this writing.
Logic—See Digital logic.
Logic gate—A device, usually etched onto an integrated circuit, that performs a specific function in digital logic.
Log-periodic antenna—Also called a log-periodic dipole array (LPDA). For TV and FM broadcast reception in remote areas where cable service is not available and satellite service is not desired, an antenna that consists of several straight, parallel metal elements called dipoles, all of which are connected together with a pair of wires. The shortest dipole is closest to the feed point that connects to the ribbon or cable going down to your receiver. The longest element resides at the back of the antenna, farthest from the feed point.
Magnetic field—A “region of influence” that occurs in space whenever charged particles, such as electrons, move, or when the atoms in certain substances align with each other. All magnets are surrounded by these “regions of influence.” Magnetic fields are responsible for the attraction and repulsion that we observe between magnets in close proximity.
Magnetic flux lines—Imaginary contours or “threads” in space that define the orientation, direction, and intensity of a magnetic field.
Male connector—A connector with exposed prongs or pins, such as the plug on the end of a lamp cord, that fits into a receptacle called a female connector.
Memory drain—A phenomenon that can occur with nickel-based rechargeable cells and batteries, especially the older nickel-cadmium (NICAD) types. The device loses its ability to deliver current after only a partial discharge, so that the useful life between recharging sessions is greatly reduced. In some cases, this problem can be overcome by discharging and recharging the device several times. Memory drain does not occur with lithium-based rechargeable cells and batteries, which have largely replaced the nickel-based ones in recent years.
Microwave frequencies—Also called simply microwaves. In its broadest context, the range of radio frequencies above 300 MHz, corresponding to wavelengths shorter than 1 meter. The literature disagrees about the exact upper and lower limits of the microwave band: some texts put the lower limit at 1 GHz (a wavelength of 30 centimeters) and others put it at 3 GHz (a wavelength of 10 centimeters). In no case, however, does this range extend into the infrared (IR) portion of the spectrum, which begins at frequencies of around 1 THz (a wavelength of 0.3 millimeter or 300 micrometers) and ends at the lower limit of the visible-light range.
Midrange speaker—A speaker that handles sound at frequencies near the middle of the audio range. Commonly combined with a tweeter and a woofer in high-end hi-fi sound systems.
Modem—A device that encodes signals going out from your computer into the Internet, and decodes signals coming in from the Internet to your computer. A modem can link a computer to the same cable system that provides your TV service. Some modems are designed to connect directly to a network of optical fibers. Still others contain a small radio transceiver for wireless or satellite access. The most primitive work with a telephone landline to get you a dial-up connection.
Multimeter—A simple laboratory instrument designed to measure current, voltage, and resistance in electrical circuits. Also called a volt-ohm-milliammeter (VOM).
Negative-ground vehicle—A motor vehicle in which the negative battery terminal goes directly to the metal frame or chassis, which represents the reference voltage level, called “common” or “ground.” This arrangement is found in the vast majority of cars and trucks in the United States.
Ohm—The standard unit of electrical resistance. Mathematically it can be considered the equivalent of a volt per ampere in a simple DC circuit.
Ohmic loss—The loss of power or energy that occurs in a long span of electrical transmission line, as a result of resistance in the wires.
Ohmmeter—A meter designed to measure electrical resistance.
Parallel connection—A method of combining two or more electrical components by joining all their left-hand ends together and all their right-hand ends together, getting an arrangement in which the components resemble the rungs in a ladder, and the interconnecting wires resemble the two vertical supports in the ladder. In a parallel circuit, all the components receive the same voltage, but the currents through them might differ. Compare Series connection.
Parametric equalizer—A hi-fi audio graphic equalizer in which the gain (volume), center frequency, bandwidth, and skirt slopes are independently adjustable. In addition to several bandpass filters for each channel, a parametric equalizer can incorporate a low-frequency shelf filter and a high-frequency shelf filter, both of which have adjustable gain, shelf frequency, and skirt slope. It’s the most sophisticated form of tone control commonly available.
Passive transponder—A wireless possession-based access control system. It’s a magnetic tag that authorized people can wear or carry. They’re the same little things that department stores employ to deter petty thieves. The transponder can be read from several feet away.
Phase—A technical term that refers to points along an AC wave cycle. Phase can also express the extent of the timing difference between two AC waves that have the same frequency. Often expressed in degrees, where one degree of phase equals 1/360 of a cycle.
Phone jack—A female connector with recessed contacts that mate with phone plug contacts. The contacts have built-in spring action that holds the phone plug in place after insertion. The most common diameters are 1/4 inch (6.35 millimeters) and 1/8 inch (3.175 millimeters).
Phone plug—A male connector with a rod-shaped metal sleeve and one or two other contacts. A ring of hard-plastic insulation separates the contacts. The most common diameters are 1/4 inch (6.35 millimeters) and 1/8 inch (3.175 millimeters).
Phono connector—A simple plug or jack designed for coaxial cable at low voltages and low current levels. You simply push the plug onto the jack, or pull it off. Also known as an RCA connector. Commonly used with audio equipment.
Photovoltaic cell—Abbreviation, PV cell. An electronic component that converts visible light, infrared, or ultraviolet rays directly into DC electricity. When used to obtain electricity from sunlight, this type of device is known as a solar cell. A silicon PV cell produces approximately 0.5 V DC in sunlight. Multiple PV cells can be connected together to get higher voltages in so-called PV panels, PV batteries, PV modules, and PV arrays.
PIN lock—Acronym for “personal identification number lock.” A setting that makes it practically impossible for anyone to use your cell-phone set if you lose it. You should activate the PIN lock if you want to keep your account, and any personal information that you might have stored on the phone, secure. Experts recommend that everybody who has a cell phone “lock it down” with a PIN code right away after buying it.
Pixel—A contraction of the words “picture element.” It’s the smallest unit of visible information in a video image or display. Each pixel can have any of numerous hues (color tints), saturation (color richness) levels, and brightness (actual brilliance) levels, independently of all the other pixels. A video display will carry a specification that tells you the number of pixels going horizontally. Some will tell you both the horizontal and vertical values.
Possession-based access control—A property-protection method that requires authorized people to possess a physical object that unlocks the entry to your property. Magnetic cards are a popular form of possession-based security devices. You insert the card into a slot, and a microcomputer reads data encoded on a magnetic strip. This data can be as simple as an access code, of the sort you punch on a keypad.
Power inverter—An electronic device that produces utility AC, usually 117 V at 60 Hz (in the United States), from low-voltage DC, usually 12 to 24 V. The best power inverters synthesize a sine wave resembling the output at a typical household utility outlet.
Power supply—A circuit that converts utility AC into pure DC suitable for use with electronic devices. Many devices have their power supplies built in. Each particular electronic device requires DC at a specific voltage, and also needs a certain amount of current.
Precipitation noise—Also called precipitation static. Radio interference caused by electrically charged water droplets or ice crystals as they strike metallic objects, especially antennas. The resulting discharge produces wideband noise that sounds similar to the noise generated by electric motors, fluorescent lights, or other appliances.
Proton exchange membrane—Abbreviation, PEM. See Fuel cell.
Rack-mounted hi-fi system—A home audio ensemble with multiple hardware units, similar to a component hi-fi system, but with all the units built to a single, standardized width for installation in a vertical rack. The rack can be mounted on wheels so that you can easily move the whole system, except for external speakers, from place to place.
RCA connector—See Phono connector.
Rectifier—A device or circuit that converts AC to pulsating DC. Usually comprises one, two, or four semiconductor diodes.
Relay—An electromechanical device that allows for remote switching of large appliances. A small electromagnet causes a lever to open and close the circuit.
Resistance—The extent to which a substance opposes the flow of current.
RMS voltage—An expression of the effective or DC-equivalent voltage in an AC circuit. The abbreviation RMS stands for “root mean square,” a mathematical process that engineers use to define the effective or DC-equivalent voltage. In most countries, the RMS voltage of standard utility AC electricity is either 117 V or 234 V, give or take a few percent.
Quick charger—A device that replenishes the charge in an electrochemical cell or battery by driving a relatively large current through it for a relatively short period of time. Not recommended. Compare Trickle charger.
Router—A device that allows you to access a single Internet connection with more than one computer (although you can use a router even if you have only one computer). Routers come in two types: hard-wired and wireless. To use a router, you plug it into your modem in place of a computer, activate the router according to the instruction manual, and then access the Internet from your computer(s) through the router and the modem combined.
Semiconductor—A substance in which electric current can flow easily under certain conditions, and with difficulty (or not at all) under other conditions. Examples include certain solid elements and compounds including silicon, selenium, germanium, gallium arsenide, and the oxides of some metals. The conductance can be controlled to generate, amplify, modify, mix, rectify, and switch electrical currents or electronic signals.
Series connection—A method of combining two or more electrical components by joining them end-to-end, getting an arrangement that geometrically resembles the links in a chain. In a series circuit, all the components carry the same current, but the voltages across them might differ. Compare Parallel connection.
Sferics—Radio-frequency noise generated in the atmosphere of our planet, mostly by lightning discharges in thundershowers. In a radio receiver, sferics cause a faint background hiss or roar, punctuated by bursts of sound called “static.” You can hear sferics on an AM broadcast receiver during the summer in regions where thundershowers commonly occur.
Shelf filter—A device that allows you to adjust the volume of an audio amplifier circuit as a function of frequency. A low-frequency shelf filter keeps the volume constant above a certain critical frequency; below that frequency, the volume is adjustable. A high-frequency shelf filter keeps the volume constant below a certain critical frequency; above that frequency, the volume is adjustable. Shelf filters act like sophisticated tone controls. However, they’re not as sophisticated as graphic equalizers.
Shielded cable—An electrical or electronic cable surrounded by a cylindrical wire braid, solid metal cylinder, or layer of metal foil that’s connected to ground. The shield keeps electromagnetic (EM) fields from getting into or out of the cable.
Shortwave band—The range of radio frequencies from 3 to 30 MHz. Technically known as high frequencies. The waves are actually long, as they travel through space, compared to the waves in most wireless communications. But they’re short compared to the wavelengths that were most commonly used when the term was coined in the early 1900s.
Shortwave listening—Abbreviation, SWLing. A popular electronics hobby in which people listen to signals from all around the world on the shortwave band. In the United States, the proliferation of computers and online communications has largely overshadowed SWLing since the 1980s, and many young people grow up today ignorant of a realm of broadcasting and communications that still predominates in much of the world.
Sine wave—An electrical waveform in alternating current (AC), in which all of the energy exists at a single frequency. This type of wave gets its name because, if viewed on a laboratory oscilloscope, it looks like a graph of the mathematical sine function. Also called a sinusoid.
Single-phase AC—Utility electricity that consists of a single, pure AC sine wave. You’ll find it at standard wall outlets intended for small appliances, such as lamps, TV sets, and computers.
Smart electric meter—A sophisticated electric utility meter that has no moving parts. This type of meter can record various details about your electric energy consumption, such as peak power demand and changes in usage patterns. It can also interconnect with supplemental systems, such as solar panels and wind turbines, allowing you to reduce your monthly electric bill and, in some cases, actually profit by selling surplus power to the electric company.
Solar cell—See Photovoltaic cell.
Split-phase AC—Utility electricity that consists of two AC sine waves that travel along their own dedicated wires, with a third wire connected to electrical ground. The two waves directly oppose each other in phase.
Stack—See Fuel cell.
Stand-alone system—In solar, wind, and hydroelectric alternative energy use, a system that works all by itself, independent from commercial electric utility providers. Compare Interactive system.
Surge—The initial high current drawn by a poorly designed power supply when it’s first switched on with a load connected, or a momentary increase in power-line voltage that lasts longer than a transient but is less intense. Don’t confuse this term with transient.
Surge protector—See Transient suppressor.
Three-phase AC—Utility electricity in the form of three sine waves, each having the same voltage, but differing in relative phase by 120° (1/3 of a cycle). Each wave travels along its own wire, so the transmission line has three wires.
Three-wire electrical system—In most homes and buildings, an electrical wiring scheme that includes three wires: “live,” “neutral,” and “ground.” This type of system requires the installation of three-slot wall outlets. In order to work effectively, the “third slot” (usually D-shaped and situated below the two vertical slots) in each outlet must go directly to the building’s electrical ground.
Tone control—A control found in most audio amplifiers and also in many radios, CD players, and MP3 players. Allows the listener to adjust the relative bass (low-frequency) and treble (high-frequency) sound to get the best audio quality. In its simplest form, a tone control consists of a single rotatable knob or linear-motion sliding control. The counterclockwise, lower, or left-hand settings of this control result in strong bass and weak treble audio output. The clockwise, upper, or right-hand settings result in weak bass and strong treble.
Transceiver—A wireless transmitter and receiver contained in a single package. Examples include all cell phone sets, most ham radios, and all CB radios.
Transformer—A device that increases or decreases the AC voltage in an electrical system. A step-up transformer increases the voltage; a step-down transformer decreases the voltage.
Transient—A voltage “spike” on the AC utility line that can greatly exceed the positive or negative peak AC voltage. It usually lasts only a few millionths of a second, but if it’s extreme, it can cause damage to sensitive electronic equipment. Don’t confuse this term with surge.
Transient suppressor—A device that eliminates transients on an AC power line. Most such devices can be plugged into a standard wall outlet, and the protected equipment plugged into the suppressor box, which might contain up to half a dozen individual outlets. Sometimes inaccurately called a “surge protector.”
Trickle charger—A device that replenishes the charge in an electrochemical cell or battery by driving a small current through it for a long time. This type of charger works better than a so-called quick charger.
Tuner—A home hi-fi stereo system component that contains a radio receiver. A typical tuner can receive signals in the standard AM broadcast band and/or the standard FM broadcast band. Some tuners can also receive satellite radio signals if you have a subscription to a service of that sort. Tuners don’t have built-in amplifiers. A tuner can provide enough power to drive a headset, but you’ll probably want to add an “outboard” amplifier to provide sufficient power for a pair of speakers.
Tweeter—A speaker designed especially for enhanced treble reproduction, and found in most high-end audio systems. Commonly used in conjunction with a midrange speaker and a woofer.
Twist splice—A simple, temporary wire splice, made by twisting the ends of two wires together and then putting electrical tape over the connection.
Two-wire electrical system—In older homes and buildings, an electrical wiring scheme that includes only two wires, one “neutral” and the other “live.” You can recognize this type of system by the presence of two-slot outlets in the walls.
Ultra high frequencies—Abbreviation, UHF. The range of radio frequencies from 300 MHz up to 3 GHz, corresponding to wavelengths from 1 meter down to 10 centimeters.
Ultrasonic motion detector—An intrusion alarm system that detects motion by sensing changes in ultrasonic waves, which are acoustic waves at frequencies above the range of human hearing. A set of transducers sends out ultrasonic waves. Another set of transducers picks up the waves reflected from objects in the room. If anything shifts position, the relative phase of the waves will change. This data goes to a microprocessor, which can trigger an alarm.
Uninterruptible power supply—Abbreviation, UPS. A temporary backup power source with a battery that charges from the AC utility under normal conditions, but provides a few minutes of emergency AC if the utility power fails. That time allows you to deploy a backup generator without having to shut any of the connected devices down, or else shut down your computers and other devices properly before removing power altogether.
Vacuum tube—An amplifying device found in older electronic systems (mainly before 1970). Largely obsolete, these components needed high voltages in order to function, and they consumed power vastly out of proportion to the actual work that they did. Vacuum tubes are still used today in some high-power radio transmitters and high-fidelity audio amplifiers.
Valve—British expression for vacuum tube.
Very high frequencies—Abbreviation, VHF. The range of radio frequencies from 30 MHz up to 300 MHz, corresponding to wavelengths from 10 meters down to 1 meter.
Video Graphics Array—Abbreviation, VGA. On a big-screen display or computer monitor, a port and cable that will let you connect your set to a computer (even an old one) for viewing images.
Volt—The standard unit of electrical voltage. Mathematically, volts equal amperes times ohms in a simple DC circuit.
Voltage—Also called potential difference or electromotive force. An expression of the “pressure” caused by a charge difference between two points in a circuit, causing current to flow.
Volt-ohm-milliammeter—See Multimeter.
Volume-unit meter—Abbreviation, VU meter. Also called a distortion meter; used in high-end audio amplifier systems. Excessive input causes the meter needles or bars to “kick up” into the red range of the scales during audio peaks. You should operate your amplifiers so that the VU meter readings stay below the red range.
Waveform—The shape of a sound wave, radio wave, AC wave, or other signal wave as it would look on the screen of a laboratory oscilloscope. With this instrument, you get a graph of voltage versus time, with time on a horizontal axis going from left to right, and voltage on a vertical axis where downward represents negative and upward represents positive.
Western Union splice—A method of wire splicing that involves twisting the ends of two wires together from opposite directions, and then covering the entire splice with electrical tape. Solder can be applied before covering the splice to get the best possible electrical and mechanical bond.
Wi-Fi hotspot—The zone near a wireless router connected to an Internet modem, such as the one you get as part of a cable or satellite installation. You’ll find Wi-Fi hotspots in public libraries, hotels, motels, restaurants, bars, and airports. Even a few fast-food places and department stores have them. You can bring your notebook computer or Wi-Fi-equipped tablet device into such a place, obtain the password from one of the employees, and get on the Internet.
Wind turbine—An electromechanical system that converts wind energy to electric energy. The most common type has a large propeller, resembling the ones in old-fashioned aircraft, attached to an electric generator with a rotatable shaft. However, other geometries exist, and new ones are constantly being developed.
Woofer—A speaker designed especially to reproduce low-frequency sound. Commonly found along with a midrange speaker and a tweeter in a single cabinet.