FIGURE 6-1 At A, circuit X provides for treble loudness adjustment only. At B, circuit X allows adjustment of the treble loudness, and circuit Y allows adjustment of the bass loudness.
Hi-fi stereo, TV, and home theater systems can provide you with endless hours of entertainment. You can buy a simple appliance that you take out of the box, plug into a wall outlet or put batteries into it, and “just play it.” But sophisticated systems abound, and if you want good sound and video, you’ll have to opt for one of them. Let’s look at the basics of hi-fi stereo, TV, and Internet access. Then you’ll have plenty of ideas as to how you can combine them into a home entertainment system that’s ideal for you.
A true hi-fi lover usually assembles a complex set of audio devices into a big system over a period of time, not all at once. In that way, the design ends up best suited to the user’s unique needs. Don’t hurry as you gather together your “ultimate sound machine.” You, as well as the system, must evolve, a process that takes time!
The simplest type of home stereo arrangement, called a compact hi-fi system, resides in a single cabinet, with an AM/FM radio receiver called a tuner, along with a compact disk (CD) player or MP3 player, or both. The speakers can be either internal or external; if they’re external, the connecting cables are short. The assets of a compact system are small size, simplicity, and low cost.
More sophisticated hi-fi systems have separate, dedicated equipment cabinets containing components such as:
• An AM/FM tuner
• A CD player
• An MP3 player
• A tape player/recorder for old-fashioned audio tape
• A turntable for old-fashioned vinyl disks
• A satellite radio receiver
• One or more antennas
• An amplifier
• A graphic equalizer
• Large, complex speakers
• A headset
• A computer
The individual hardware units in this type of system, known as a component hi-fi system, should be interconnected with shielded coaxial cables. A component system costs more than a compact system, 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 as time goes by.
Some hi-fi manufacturers build all their equipment cabinets to a single, standardized width so that you can install them, one above the other, in a vertical rack. A so-called rack-mounted hi-fi system saves floor space and gives the system a certain professional look! The rack can be mounted on wheels so that you can easily move the whole system, except for external speakers, from place to place.
Each individual equipment chassis, on which all the electronic components are mounted, should be connected to a good electrical ground to minimize hum and noise, and to minimize susceptibility to interference from external sources. If your home has a good three-wire electrical system, the “third slot” in any wall outlet will serve this purpose.
In most home hi-fi tuners, the AM antenna is a small coil called a loopstick built into the cabinet or mounted on the rear panel. Usually, the FM antenna must be outside and some distance away from the radio. You’ll find a connector or pair of terminals for it on the back panel. An FM antenna can consist of a length of TV type twinlead, also known as 300-ohm ribbon, connected to the center of a four-to-six-foot length of wire to form a T-shaped configuration called a dipole. You can get ready-made FM dipoles at most good hi-fi stores for a few dollars. You can also use old-fashioned TV rabbit ears as the antenna for your FM tuner.
If you live in a fringe reception area and you want good FM radio reception, you’ll need an outdoor antenna equipped with lightning protection hardware. Radio Shack stores are a good place to shop for them. Large home appliance outlets often carry them too. For all intents and purposes, an FM outdoor antenna is the equivalent of an old-fashioned outdoor TV antenna. Some people who do not have access to cable TV use their outdoor TV antennas for FM radio reception as well.
As people rely on the Internet more and more for radio and television reception, using traditional receivers less and less, you should expect that antennas will eventually become rare in home entertainment systems, except for the outdoor dish antennas that go along with satellite TV and satellite Internet systems. Unless you’re an electronics technician, you’ll need to hire a professional to install any dish antenna because they must be precisely aligned with a specific satellite in order to function properly.
A typical tuner can receive signals in the standard AM broadcast band (535 to 1605 kHz) and/or the standard FM broadcast band (88 to 108 MHz). 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.
Modern hi-fi tuners employ frequency synthesizers and have digital displays. Most tuners have several programmable memory channels that allow you to select your favorite stations with a push of a single button, no matter where the stations happen to be in the frequency band. Some tuners also have seek and/or scan modes that allow the radio to automatically search the band for any station strong enough to come in clearly.
The balance control allows adjustment of the relative volume levels of the sounds coming from the left and right channels.
In a basic hi-fi system, the balance control comprises a single rotatable knob connected to a pair of potentiometers (variable resistors). When you turn the knob counterclockwise, the left-channel volume increases and the right-channel volume decreases. When you turn the knob clockwise, the right-channel volume increases and the left-channel volume decreases. In more sophisticated sound systems, you can adjust the balance using two independent volume controls, one for the left channel and the other for the right channel.
Proper balance is important in stereo hi-fi. A balance control can compensate for such factors as variations in speaker placement, relative loudness in the channels, and the acoustical characteristics of the room in which the equipment is installed.
The loudness-versus-frequency characteristics of a hi-fi sound system are adjusted by means of a tone control, although the term “tone” is technically a misnomer; a better term would be frequency-response control. In its simplest form, a tone control consists of a single rotatable knob or linear-motion sliding control. The counter–clockwise, 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. When you set the tone control to mid-position, the audio response of the amplifier is essentially flat, meaning that the bass, midrange, and treble loudness levels are in roughly the same proportions as they were in the original sound recording.
Figure 6-1A shows an arrangement in which a single-potentiometer tone control can be incorporated into the output circuit of an audio amplifier. The amplifier is designed so that its treble output is exaggerated in the absence of any tone control. Potentiometer X attenuates (makes weaker) the treble to a variable extent. When you set the potentiometer at zero resistance, the capacitor appears directly across the audio signal path, producing treble roll-off (decreasing volume with increasing frequency). As the resistance of the potentiometer increases, the treble roll-off becomes less pronounced. At the mid-point of the potentiometer setting, the treble roll-off caused by the resistance-capacitance (RC) circuit cancels out the effect of the exaggerated treble response in the amplifier, and you get a flat frequency response. When you set the potentiometer at its maximum resistance, there’s practically no capacitance across the audio signal path. Then the RC combination looks like an open circuit (as if neither the potentiometer nor the capacitor were there at all), and the treble response is exaggerated. This type of control causes a general increase in output volume as the resistance of the potentiometer increases; it interacts with the volume control.
FIGURE 6-1 At A, circuit X provides for treble loudness adjustment only. At B, circuit X allows adjustment of the treble loudness, and circuit Y allows adjustment of the bass loudness.
A more versatile tone control (Fig. 6-1B) has two capacitors and two potentiometers that you can adjust independently. The amplifier is designed so that it has a flat loudness-versus-frequency output characteristic in the absence of any tone control. The RC circuit labeled X produces adjustable treble roll-off, exactly as does the circuit shown at A. When you set potentiometer X at zero resistance, the capacitor appears across the audio signal, causing treble roll-off. As the resistance of the potentiometer increases, the roll-off becomes less pronounced. When you set potentiometer X at its maximum resistance, there’s practically no capacitance across the audio signal. Then the RC combination appears as an open circuit, and you get no treble roll-off at all. The RC circuit labeled Y attenuates the bass to a variable extent. When potentiometer Y is at its maximum resistance, the capacitor across it causes a bass roll-off (decreasing volume with decreasing frequency). As the resistance of the potentiometer decreases, the effect of the capacitor diminishes, and the roll-off becomes less pronounced. When you set potentiometer Y at zero resistance, you get essentially no bass roll-off.
In either of the arrangements shown in Fig. 6-1, the optimum values of the potentiometers and capacitors must be found by experimentation, a task normally done by the engineers who design the equipment. Of course, each audio channel needs its own dedicated tone control circuit, so a stereo amplifier will have two tone controls, one for the left-hand channel and the other for the right-hand channel.
Sophisticated tone controls, commonly found in most systems these days, make use of specialized integrated circuits (ICs) called operational amplifiers or op amps. These devices can be “tweaked” to have almost any desired loudness-versus-frequency characteristic.
If you connect two or more audio sources directly to the same input jack or terminals of an amplifier, you can’t expect good results. Different signal sources, such as a computer, a tuner, and a CD player will almost certainly have different AC resistances, called impedance values, for audio signals. When connected together, these impedances appear in parallel, that is, across each other like the rungs in a ladder. This sort of situation can hinder the performance of the sound-generating devices, as well as mess things up at the amplifier input terminals. You’ll end up with low system efficiency and poor overall performance. In some cases, one or more of the input devices will fail to produce any sound at all in your amplifier.
Another problem with direct interconnection of multiple sound sources arises from the fact that the signal levels from the devices usually differ. A microphone produces tiny audio-frequency currents, whereas a tuner produces enough to drive a headset or even a small speaker. Connecting the outputs of these devices directly across each other will cause the microphone signal to be obliterated by the signal from the tuner, and the tuner’s output audio current might physically damage the microphone.
An audio mixer eliminates the problems that you face when you want to connect the outputs of multiple audio devices to a single channel input for an amplifier. The mixer isolates the input impedances 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 or gain for each device without affecting the behavior of any other device. That way, you won’t be surprised by near silence from one device or a gigantic sound blast from another.
An equalizer allows for the adjustment of loudness of audio signals at various frequencies. You learned about this type of device in Chapter 5. Equalizers serve the same function in a home hi-fi system as they do in a mobile system. In general, however, equalizers for home systems are more sophisticated (and expensive) than those for automotive systems. You’ll find graphic and parametric equalizers commonly available for home audio systems. After all, you can “fool around with the controls” a lot more easily in a fixed system than you can do in a mobile system because you don’t have to worry about causing a motor-vehicle wreck if you get distracted!
In hi-fi systems, an amplifier delivers significant audio power to a set of speakers. An amplifier always has at least one input, but more often there are three or more: one for a CD player, another for a tuner, and still others for auxiliary devices, such as a tape player, turntable, or computer.
You don’t perceive the loudness of sound in direct proportion to the power contained in the acoustic waves. Instead, your ears and brain sense sound levels according to the logarithm of the actual intensity. Another variable is the phase with which waves arrive at your ears. Phase allows you to perceive the direction from which a sound is coming, and it also affects the apparent sound volume as you hear it.
Engineers express sound levels in units called decibels (dB). 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. In acoustic applications, decibels express relative, not absolute, sound power. If you adjust an amplifier’s volume control so as to double the actual sound power coming from a set of speakers, then you cause a volume change of +3 dB (3 dB of gain). Conversely, if you halve the sound power, you get a volume change of −3 dB (3 dB of loss). Increases in sound power go along with positive decibel values, and decreases in sound power go along with negative decibel values.
If you want decibels to mean anything, you need a reference volume level against which you can compare all other sounds. Have you been told that a large electric vacuum cleaner produces 80 dB as heard by the person operating it? This figure is determined with respect to the threshold of hearing, which represents the faintest sound that a person with “good ears” can detect in a quiet room specially designed to have a minimum of background noise.
Linearity is the extent to which an amplifier’s output waveform (the shape of the wave as it would look on the screen of a laboratory oscilloscope) represents a faithful, exact magnification of the input waveform. In hi-fi equipment, all amplifiers must be as linear as possible. You can think of audio amplifier linearity as the equivalent of optical precision in a microscope or telescope.
If you connect a dual-trace oscilloscope (one that lets you observe two waveforms at the same time) to the input and output terminals of a hi-fi audio amplifier that has good linearity, the output waveform will show up as a vertically magnified duplicate of the input waveform. If you apply the amplifier’s input signal to the horizontal scope input and the amplifier’s output signal to the vertical scope input, you’ll see a straight line on the screen. In an amplifier with poor linearity, the line on the screen will appear “bent” or “kinked,” indicating that the output waveform is not a faithful reproduction of the input. In that case, you know that the amplifier produces distortion. Sometimes you can’t notice distortion simply by listening to the sound, even if that distortion shows up clearly on an oscilloscope.
When engineers talk about dynamic range in a hi-fi audio system, they refer to the difference between the strongest and the weakest output audio signals that the system can produce without objectionable distortion taking place. Dynamic range is usually specified in decibels, by comparing the strongest and weakest signal levels in logarithmic terms. 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. You’ll want to compare this specification among different amplifiers when you’re shopping.
At low volume levels, the limiting factor in dynamic range is the background noise in the system. At high volume levels, the power-handling capability of an audio amplifier limits the dynamic range. If all other factors are equal, you can expect a 200-watt audio system to have greater dynamic range than a 100-watt system. The speaker size is also important. As speakers get physically larger, their ability to handle high power improves, resulting in increased dynamic range for the entire amplifier/speaker arrangement.
No amplifier can deliver sound that’s any better than the speakers will allow. Speakers are rated according to the audio power they can handle. It’s a good idea to purchase speakers that can tolerate at least twice the audio output power that the amplifier can deliver. Such “overengineering” will ensure that distortion will not occur in the speakers during loud, low-frequency sound bursts. Overengineering in this department will also minimize the risk of physical damage to the speakers that might otherwise result from accidentally overdriving them.
A dynamic speaker comprises a coil and magnet that translate electrical current into mechanical vibration, thereby producing sound waves in the air. Figure 6-2 is a functional (but not literal) illustration of a dynamic speaker. A diaphragm, which sometimes takes the form of a speaker cone, is attached to a coil that can move back and forth rapidly along its axis. If you apply an audio signal to the coil, the variable current in the coil generates a fluctuating magnetic field that produces forces on the coil as it interacts with the permanent magnet’s field. These forces cause the coil to move, pushing the diaphragm back and forth to create acoustic waves in the surrounding air.
FIGURE 6-2 Functional diagram of a dynamic speaker.
An electrostatic speaker takes advantage of the forces produced by electric fields rather than magnetic fields. Two large, flat metal plates, one flexible and thin and the other rigid and thick, are placed parallel and close together as shown in the functional diagram of Fig. 6-3. The blocking capacitor allows for the connection of a high DC voltage between the speaker plates, but keeps the DC from getting back into the amplifier system and disrupting its performance. (Capacitors block DC but allow AC, such as audio signals, to pass through.) The fluctuating, high AC audio voltage that comes out of the transformer, combined with the DC voltage between the plates, gives rise to a powerful, fluctuating electrostatic field between the plates. That field produces a variable force on the flexible plate with respect to the rigid plate, so that the flexible plate “bows in and out” and causes sound waves to arise in the air.
FIGURE 6-3 Functional diagram of an electrostatic speaker.
Good speakers contain two or three individual “signal-to-sound converters” (technically a form of electromechanical transducer) within a single cabinet. The woofer reproduces the bass (low-frequency) sound. The midrange speaker handles medium and, sometimes, treble (high-frequency) sound. A tweeter is designed especially for enhanced treble reproduction, and most good ones can turn signals at frequencies above the human hearing range into ultrasound. The design of the cabinet has a profound effect on the quality of the sound that comes out of the speakers.
Because a speaker cabinet is an enclosed chamber, it will have resonant frequencies at which it reinforces the sound waves inside itself, and also null frequencies at which it cancels out the sound waves inside itself. These resonant and null effects should be minimized to keep the speakers from producing artificially exaggerated loudness at the resonant frequencies and artificially muted sound at the null frequencies. Speaker manufacturers use a variety of techniques in order to achieve this goal. Foam padding and internal baffles (sound reflectors) are common.
The shape, as well as the frequency, of a sound wave affects the manner in which and the extent to which the acoustic disturbance reflects from various physical objects as it travels through the air from the speakers to your ears. Acoustics engineers must consider the waveform (wave shape) when designing sound systems and concert halls. The goal is to make sure that all the musical instruments sound realistic everywhere in the room—or at least, that they get close to that ideal. Computer models and simulations can help with this process, but in the end, trial-and-error experimentation is necessary. Judgment must be made subjectively by the listeners. No matter how well a system works in theory, if the listeners don’t like the way it “plays,” the finest mathematical models don’t mean a thing!
Suppose that you have set up a sound system in your living room, and that, for the particular placement of speakers with respect to your ears, sounds propagate well at 1, 3, and 5 kHz, but poorly at 2, 4, and 6 kHz. This situation will affect the way that the various musical instruments sound. You’ll end up with more distortion in the sounds from some instruments than in the sounds from other instruments. Unless all sounds, at all frequencies, reach your ears in the same proportions that they come from the speakers, you won’t hear the music as it originally came from the instruments.
Figure 6-4 shows a listener, a speaker, and three baffles as they might be arranged in a large room. The waves X, Y, and Z as they reflect from the baffles, along with the direct-path wave D, add up to something different at the listener’s ears for each frequency of sound. The way that the sound waves combine will change as the listener moves around the room. This phenomenon is impossible to prevent entirely; the best you can hope for is to minimize it. That’s why even the best engineers find it difficult to design an acoustical room, such as a concert auditorium, that will propagate sound in an optimum way at all frequencies for every listener.
FIGURE 6-4 Reflected-path sound waves X, Y, and Z combine with the direct-path sound wave D to produce what the listener hears.
A headset 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.
Two equally expensive headsets can exhibit huge differences in the quality of the sound that they put out, and people will always disagree about what constitutes good sound. A good hi-fi store will have several headsets on display, connected to a sound system so that you can “test listen” to each one and then choose the headset that you like the best.
Television (TV) grew popular in the United States during the 1950s, and became firmly established by the end of 1960 after the airing of the debates between John F. Kennedy and Richard M. Nixon in their contest for President of the United States. The first TV sets were built into cabinets that weighed well over 200 pounds and employed vacuum tubes at every stage. The “picture tube,” a primitive version of a cathode-ray-tube (CRT) display, produced a blurred, grayscale image with a diagonal measure of less than two feet. The signals employed amplitude modulation (AM) like the standard radio broadcasts of the same era, and used analog (continuously variable) methods to convey both the image and the sound.
Old-fashioned analog television is 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, chances are good that it was designed for analog TV and won’t work nowadays unless you get a digital-to-analog converter box.
In analog TV, the individual images, called frames, were transmitted at the rate of 30 per second. There were 525 lines of video information per frame. Color NTSC TV worked by sending three separate monochromatic signals, corresponding to the primary colors red, blue, and green. The signals, in effect, were “redscale,” “bluescale,” and “greenscale.” The receiver recombined these signals and displayed the resulting video as a fine, interwoven matrix of red, blue, and green dots.
When viewed from a distance, the image dots in an analog color TV display were too small to be individually discernible, but you could easily see them close-up. Various combinations of red, blue, and green intensities could yield any color that the human eye can perceive. In a good analog color TV set receiving a strong signal, the color quality was excellent, even by today’s standards, but the detail left something to be desired.
FIGURE 6-5 A single line in an old-fashioned analog TV video frame as it would appear on a lab oscilloscope.
The term high-definition television (HDTV) refers to any of several methods for getting more detail into a TV picture than could ever be done with NTSC TV. The HDTV mode also offers superior sound quality, making for a more satisfying home TV and home theater experience. High-definition TV is sent in a digital mode; this offers another advantage over analog TV. Digital signals propagate better than analog signals do, they’re easier to deal with when they are weak (if they’re not good enough, they just go away!), and they can be processed in ways that analog signals would not allow.
Television technology has evolved in ways that few people imagined in the 1950s. Digital modulation, which conveys both video and audio information in discrete data bits in the same way as computer data is transmitted, has replaced analog modulation. Solid-state components, based on semiconductor materials, such as silicon and gallium arsenide, have replaced electron tubes. Color images have supplanted grayscale images. Video detail, called image resolution, has improved immeasurably. Today you can enter a department store with a few hundred dollars and come back out with a flat-screen TV set that has a diagonal measure upwards of four feet and offers hi-fi sound that you can interconnect with your home stereo system. Some sets even provide for three-dimensional (3D) image viewing.
When you’re in the market for a new TV set, you’ll find several types of display. In recent years, display types have converged toward light-emitting diode (LED) technology. A few sets still use old-fashioned CRTs, but most video experts agree that they’re not long for this world. Plasma displays, of the sort that department stores sometimes put in prominent places for mass viewing by consumers, exist for use in home video systems, but they, like CRTs, are dated. That leaves LED screens and liquid-crystal-display (LCD) screens, which are equivalent for practical purposes. As you shop for a flat-screen TV, you should take the following factors into account:
• Screen size (diagonal measure in inches)
• Weight (in pounds or kilos)
• Resolution (amount of detail in the image)
• Screen surface type (shiny or matte)
• Internet capability (or not)
• Sound capability (hi-fi is standard but not universal)
• 3D capability (or not)
• Brand name (if you have a favorite)
• Cost (if you’re on a budget)
No matter how many things you ponder in theory, you should always get a look at your chosen TV set in action before you invest in it. Most stores that sell big-screen TVs have several of them mounted up on a wall, side by side, all showing the same program. You can get a good idea of which set has the brightest and truest colors, and which one produces the clearest image, within a couple of minutes.
The term pixel is a contraction of the words “picture element.” A pixel is the smallest unit of visible information in a video image. In a digital color 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. Any video display will carry a specification that tells you the number of pixels going vertically; some will tell you both the horizontal and vertical values.
For example, in a display that claims 1080p, there are 1080 individual picture elements in each vertical row on the screen. If a display’s specifications tell you that the screen measures 1600 × 900, then you know it has 1600 pixels going horizontally from left to right, and 900 pixels going vertically from top to bottom. (That’s 1.44 million individual video elements, by no means the largest number that you’ll ever see!) Even a modest digital TV set can display an image consisting of several hundred thousand pixels in total.
A contemporary digital TV set has a connector that goes directly to the coaxial cable through which the incoming video and audio signals arrive. You can recognize this connector by its finely threaded cylindrical form measuring about 1/4 of an inch (a little over 6 millimeters) in diameter. The center of this signal input port has a tiny hole into which the center conductor of the cable goes; the threaded exterior connects to the cable’s outer conductor or shield. To make the set play, you will normally connect the signal cable directly to this port, exactly as you would do with any other cable-ready TV set.
The best big-screen TVs have other input signal ports besides the one for conventional TV viewing. Always look for a set that has a High-Definition Multimedia Interface (HDMI) port. It will let you connect your big screen 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, camcorders, and Apple iPads. You might also want to have a set that includes a Video Graphics Array (VGA) port so that you can connect it to an older computer and use it as a display.
Until the early 1990s, a satellite television installation required a dish antenna roughly six to 10 feet (two or three meters) in diameter. A few such systems are still in use. The antennas are expensive, they attract attention (sometimes unwanted), and they’re subject to damage from ice storms, heavy snows, and high winds. Digitization has changed this situation. In any communications system, digital modes allow the use of smaller receiving antennas, smaller transmitting antennas, and/or lower transmitter power levels. Engineers have managed to get the diameter of the receiving dish down to about two feet or 2/3 of a meter.
The Radio Corporation of America (RCA) pioneered digital satellite TV with its so-called Digital Satellite System (DSS). The analog signal was changed into digital pulses at the transmitting station using A/D conversion. The digital signal was amplified and sent up to a satellite. The satellite had a transponder that received the signal, converted it to a different frequency, and retransmitted it back to the earth. A portable dish picked up the downcoming (or downlink) signal. A tuner selected the channel. The digital signal was changed back into analog form, suitable for viewing on a conventional FSTV set, by means of digital-to-analog (D/A) conversion. Although digital satellite TV technology has evolved since the initial days of the RCA DSS, today’s systems work in essentially the same way as the original one did.
Figure 6-6 shows two types of dish antennas that you’ll find in satellite TV systems. The design at A is by far more common. 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 the coaxial-cable feed line to the TV equipment inside your house. The whole assembly measures less than a meter wide and a meter long. The design at B, called a Cassegrain fed-dish because its geometry resembles that of a Schmidt-Cassegrain reflecting telescope, is sometimes found in more remote areas where a larger antenna is necessary. This type of dish may measure more than two meters in diameter. The signal arrives right 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.
FIGURE 6-6 At A, a dish antenna with conventional feed, commonly used today. At B, a dish antenna with Cassegrain feed, sometimes found in older satellite TV systems.
If you live in a place where cable TV service doesn’t exist, and if you don’t want to pay for a satellite TV system, you can do either of two things: go without TV entirely, or attempt to receive broadcast signals using an outdoor antenna. You can obtain outdoor TV antennas, technically known as log-periodic antennas (LPAs) or log-periodic dipole arrays (LPDAs), along with various other specialized antenna types that can work in either the VHF (very-high-frequency) or UHF (ultra-high-frequency) TV broadcast bands.
The log-periodic antenna receives signals best from a single direction, just as a dish antenna does, but its alignment is a lot less critical than that of a dish. Figure 6-7 shows a functional diagram of a log-periodic antenna. It’s designed for reception of signals in the VHF TV band, known as channels 2 through 13 and covering a frequency range of 54 to 216 MHz. You can also use an outdoor TV antenna of this type to receive standard FM broadcast signals in the range of 88 to 108 MHz. The balun (an acronym based on the words “balanced” and “unbalanced” is a transformer that you need if you want to use coaxial cable to feed the antenna.
FIGURE 6-7 A typical old-fashioned log-periodic antenna for receiving VHF TV. The term “balun” stands for “balanced-to-unbalanced” and refers to a transformer that’s needed if you want to feed the antenna with coaxial cable.
Lightning presents a hazard to anyone who has a large outdoor antenna installed. The antenna and its feed line can acquire a large electrostatic charge during a thundershower. That charge is like the “static” that accumulates on your body when you shuffle around on a carpeted floor on a dry day, but it is far larger. In the case of a nearby lightning strike, the electromagnetic pulse (EMP) caused by fast-moving electrons can produce a surge of current in an antenna. A direct lightning hit, should you suffer one, will cause a massive current surge that can start fires and electrocute people. Lightning can also induce dangerous surge currents on utility and telephone lines. Those little old ladies who run around unplugging everything before a heavy thunderstorm are not as stupid or paranoid as you might think! In fact, lightning is more dangerous, statistically, than hurricanes or tornadoes, perhaps because lightning strikes without any warning whatsoever.
A lightning “bolt,” technically called a stroke, lasts for only a small fraction of a second, but the extreme current and voltage produces a fantastic amount of power for that brief instant. Four types of lightning exist, as follows:
1. Lightning that occurs within a single cloud (intracloud), shown at A in Fig. 6-8
2. Lightning in which electrons flow from a cloud to the earth’s surface (cloud-to-ground), shown at B in Fig. 6-8
3. Lightning that occurs between two clouds (intercloud), shown at C in Fig. 6-8
4. Lightning in which the electrons flow from the earth’s surface to a cloud (ground-to-cloud), shown at D in Fig. 6-8
FIGURE 6-8 Four types of lightning stroke: intracloud (A), cloud-to-ground (B), intercloud (C), and ground-to-cloud (D).
Cloud-to-ground and ground-to-cloud lightning present the greatest danger to home electronics equipment. Intracloud or intercloud lightning can cause an EMP sufficient to damage sensitive apparatus, even though the lightning “bolt” itself never reaches the surface.
Warning! Whenever you install an outdoor antenna, especially a large one such as a log-periodic that has a considerable amount of exposed metal, you must take the lightning hazard seriously. You should install a lightning arrestor at the point where the antenna’s feed line enters the house. In addition, it’s a good idea to disconnect the feed line completely from the TV receiving equipment when you aren’t actually watching TV. Even then, you can’t completely eliminate the danger posed by an outdoor antenna system with regards to lightning. An EMP from a nearby lighting strike can induce a surge of current in your antenna and feed line that can damage your TV. If you suffer a direct hit, it might set your house on fire. For this reason, I don’t recommend outdoor TV antennas except for those stubborn few folks who absolutely insist on having one (small satellite dishes being the notable exception because they’re relatively safe). For detailed information about protecting your home appliances against the effects of lightning, consult a competent communications engineer. If you have any doubts about the fire safety of an electronic installation, consult your local fire inspector.
You can take the following precautions to minimize the hazard to yourself in and near thundershowers. These measures will not guarantee immunity, however. As an old saying goes, “Lightning has a mind of its own.” Sometimes, lightning defies logic and seems to operate outside the laws of physics, so beware!
• Remain indoors, or inside a metal enclosure, such as a car, bus, or train.
• Stay away from windows whether they’re open or closed, and whether they have coverings or not.
• If you can’t get indoors, find a low-lying spot on the ground, such as a ditch or ravine, and squat down with your feet close together and your head between your legs until the threat has passed.
• Avoid lone trees or other isolated, tall objects, such as utility poles or flagpoles.
• Avoid electric appliances, or electronic equipment that makes use of the utility power lines or that has an outdoor antenna.
• Stay out of the shower or bathtub.
• Avoid swimming pools, either indoors or outdoors.
• If you’re on a beach, get into a nearby building or shelter immediately. Do not stay out there on the sand!
• Don’t use hard-wired telephone sets. (Cordless sets or cell phones are okay.)
• Don’t use computers with external modems connected, or that operate from the AC utility lines. (Things like an iPad with a wireless Internet connection are okay.)
Precautions that minimize the risk of damage to electronic equipment (but can’t guarantee absolute immunity), particularly hardware such as TVs with outdoor antennas, include the following.
• Never operate any type of electronic device that has an outdoor antenna when a thundershower is taking place near your location.
• Disconnect all antennas, and ground all feed line conductors, to a good electrical ground other than the utility power-line ground. Leave the lines outside the building and connect them to an earth ground that’s at least a few feet away from the building.
• When you’re not using the equipment, unplug it from the utility outlet.
• When you’re not using the equipment, disconnect and ground all antenna rotator cables and other wiring that leads outdoors.
• Lightning arrestors provide some protection from electrostatic-charge buildup, but they can’t offer complete safety, and you shouldn’t rely on them for absolute protection.
• Lightning rods reduce (but don’t eliminate) the chance of a direct hit, and they can help protect your house from fire in case a direct hit does occur, but they should not be used as an excuse to neglect other precautions.
• Power line transient suppressors help to prevent computer “glitches” and can sometimes protect sensitive components in a power supply, but they should not be used as an excuse to neglect the other precautions.
• Connect antenna supporting masts or towers to an earth ground using heavy-gauge wire or braid.
• You’ll find other secondary protection devices advertised in electronics-related and radio-related magazines. You can also consult a competent electrician or your local fire inspector, or both.
If you live in a location that offers decent cable service, accessing the Internet (also called the Web) is as simple as running any other appliance. However, if you live in a rural area or a remote wilderness retreat, or if you haven’t used the Internet very much in the past but want to start now, you might want to gain a little bit of web-related wisdom so that you can get the most out of the experience.
If you want to get Internet access in your home and you happen to live in a large city, you have several choices, all of them good. Cable TV providers commonly bundle their services so that you can have Internet access (and sometimes landline telephone service as well). Usually, you’ll find that cable Internet connections offer the highest data speeds, measured in megabits per second (Mbit/s), where a megabit represents a million (1,000,000) individual digits of information. Wireless is a little slower than cable, followed by satellite service and finally dialup, which is excruciatingly slow for today’s Internet applications. If you live in a truly progressive town, you might be able to get fiber-optic service directly into your house; this mode is faster still, in some cases offering speeds in excess of a gigabit per second (Gbit/s) where a gigabit represents a billion (1,000,000,000) digits of data!
Wireless service can provide good connection speeds in large cities, but it’s rarely as fast as cable. In order to use a wireless Internet service, you’ll probably have to get it from a cell phone provider. Most cell phone providers these days offer bundle deals in which you can get a phone set along with wireless Internet service, but some of these plans are quite expensive, and some service providers limit the amount of data that you can upload and download per month. If you want to use the Internet only for electronic mail (e-mail) or casual Web browsing, this type of service might suffice for you. However, if you intend to download lots of movies or watch a lot of videos, or if you expect to use the Internet for online gaming, you’ll do better with cable (or ideally, fiber-optic) service.
In rural locations too far removed from cell phone towers to get good wireless Internet service (or if the local cell phone provider doesn’t include wireless service in any of their packages), you’ll probably want to opt for a satellite Internet connection. This mode works like satellite TV, and uses a dish antenna similar to the ones you see in satellite TV installations. The important difference is the fact that with a satellite Internet connection, your dish antenna doesn’t merely receive the signals. It transmits signals too, all the way up to a satellite that hovers thousands of miles above the earth! For that reason, you’ll need to have a professional technician install your system and align the dish because the antenna alignment is more critical for satellite Internet than it is for TV reception.
The mode of last resort is a dialup connection, in which you use a landline telephone system to access the Internet. It’s so slow that most people will find it useless for Web browsing these days; video and streaming audio are out of the question. However, if it’s all you can afford, it’s better than nothing. Be forewarned, however: Some telecommunications companies have begun to talk about getting rid of landline telephone service altogether. When and if that day comes, you won’t be able to get dialup Internet service at all.
The term modem is an acronym that derives from the first letters of the words “modulator” and “demodulator.” In technical terms, those words describe precisely what the thing does. It modulates (or encodes) signals going out from your computer into the wilds of the Web, and it demodulates (or decodes) signals coming in from the Web to your computer. Several different types of modems exist, and the type that you get will depend on how you want to connect to the Internet. A modem can link a computer to the same cable system as you get your TV service from. 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 modems work with a telephone landline to get you a dialup connection.
Most new notebook and tablet computers come equipped with internal wireless modems, so you don’t have to think about them at all in order to use them. In fact, with some computers, you have to actively disable the internal wireless modem if you want to make sure that your computer doesn’t automatically connect to the Internet without your knowledge! To take advantage of the Internet with a wireless-equipped computer or tablet device, you can go to a so-called wireless hotspot, follow the instructions provided with your device, and get online. Most public libraries, and a lot of restaurants and bars, provide wireless hotspots. So do hotels, airports, bus terminals, and some retail establishments.
If you want to use the Internet with a cable or satellite system, you’ll need an external modem. Your cable provider will probably be willing to supply you with one as part of your monthly TV-and-Internet subscription. They’ll sell or rent you a cable modem. It’s a box roughly the size and shape of a paperback novel, and it sits or stands on your desk next to your computer. Figure 6-9 shows a cable modem on the author’s desk, sitting right underneath the base unit for a cordless phone set. (The upright box to the left of the phone and modem is a wireless router, which we’ll talk about in a moment.)
FIGURE 6-9 A cable modem, a cell-phone base unit, and a wireless router. Note the cup with the writing instruments for size comparison.
Ever since the birth of the Internet, modems have done the same thing: convert signals from a form that travels over a communications medium to a form that your computer can “understand,” and vice-versa. They do it faster now than they did in the early years; that’s all. Your computer works with binary digital signals that occur in bits (technically binary digits) that can represent either the number 1 or the number 0, but nothing else. These signals are rapidly fluctuating direct currents. In order for binary (two-state) digital information to go over a communications system, the data must be converted to some form of AC signal. That signal can be an electric current in a cable made out of ordinary copper wire, a light beam or infrared beam in an optical fiber, or a radio wave through the atmosphere or outer space.
A router is a device that allows you to access a single Internet connection with more than one computer, although you can use a router 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 computers through the router and the modem combined. Routers will work with cable or satellite Internet connections. You can use a router with a wireless Internet service, too, although there’s little reason to do that unless you want the router to act as a firewall between your computers and the Internet.
With a hard-wired router, you’ll need to connect every computer to it using a cord called an Ethernet cable, which looks like a telephone landline cord but has more wires. You’ll also need an Ethernet cable to hook your router up to your modem. Hard-wired routers aren’t convenient if you want to use computers all over the house, and especially if you want to move them around freely. Hard-wired routers are out of the question if you want to use wireless-equipped tablet devices or e-book readers, such as the iPad, Kindle Fire, or Nook Tablet. These devices lack Ethernet ports (jacks for Ethernet cables), but an increasing number of them do have tiny wireless modems that you can use with any wireless router in a home or business.
Fact or Myth?
If anyone tells you that all e-book readers will work with wireless routers or wireless Internet connections, don’t believe it! Some of them require you to use a computer to download your e-books, and then transfer them to the reader itself, using a special connecting cable. If you are interested in buying an e-book reader and you want it to have wireless capability, make sure that you read the specifications carefully to avoid disappointment.
Because of their convenience and ease of installation, most people use wireless routers when they want to assemble and use in-home local area networks (called LANs by techies). That way, they can have multiple computers and tablet devices accessing the Internet all over the house. Figure 6-10 is a block diagram of a wireless LAN serving two computers and two tablet devices. (You can add more devices simply by bringing them within range of the router and switching them on.) The little triangle symbols represent antennas, which are usually inside the devices so you can’t see them. The dotted gray lines represent radio waves that travel between your wireless router and the individual devices. Most wireless routers have a maximum range of 100 feet or so, and although that might seem like a limitation, it’s actually a good thing. If wireless routers had a much greater range than that, it would increase the risk that unauthorized people might get into your home LAN, especially if you live in a large city or in an apartment or condominium building. Wireless routers require passwords for access, but that security provision can’t guarantee that some smart kid won’t hack into your LAN anyway.
FIGURE 6-10 A home computer network with a modem, wireless router, two computers, and two tablet devices. The little triangle symbols represent the internal antennas in the router, computers, and tablets.
If you enjoy exotic electronics, and if you live in a remote area where neither cable nor wireless services exist, then you’ll doubtless consider having a satellite Internet system installed. Several vendors offer Internet access along with satellite TV service. In the United States, DirecTV and Dish Network are both popular. You can also get a stand-alone satellite Internet connection through a service, such as Starband, Wild Blue, or Hughesnet. Although a good satellite Internet connection can save you from the drudgery of dialup, you will have to contend with certain technical anomalies. Once in awhile, a disgruntled satellite Internet subscriber lets their service contract expire and goes back to dialup because they could not deal with the inherent limitations of satellite Internet service.
A dedicated satellite Internet dish antenna resembles the “hybrid” TV-and-Internet antenna shown in Fig. 6-11. You’ll need to have a professional installer mount and align any satellite Internet dish, whether or not it includes other services, such as TV (or even satellite telephone, which some people rely on in extremely remote places), so that it points exactly at the “bird” that it’s meant to reach, and so that it’ll stay pointed the right way in case of a windstorm, heavy snowstorm, or other disturbance. Even if you get a perfect installation done, however, you should not expect your satellite Internet connection to perform as well as a good cable or wireless system does.
FIGURE 6-11 A typical dish antenna equipped for satellite TV reception and satellite Internet access. It measures about two feet (60 to 70 centimeters) in diameter.
Satellites can contain only a limited amount of electronic memory, processing power, and other resources to give users a fast connection. All the signals from all the subscribers within range must pass through that single satellite. Some services have two or three different satellites, but that’s still quite a limitation compared with the hundreds of nodes (branch points) in the terrestrial communications network. It’s a bottleneck that can get jammed up if every subscriber tries to use the service at once. The provider makes a “deal with fate” in the hope that a situation of that sort won’t happen, but if more subscribers sign up and use the service than the vendor originally expected to have, slowdowns and shutdowns can occur in the event of an extreme demand for the service, such as can happen during a natural disaster or national emergency.
The satellite to which your system is assigned will probably follow a geostationary orbit, also called a parking orbit because the satellite remains fixed in the sky, as “seen” from any point on the surface, for 24 hours a day and seven days a week. In order for the satellite to stay in that special type of orbit, it must fly directly over the earth’s equator, going from west to east at an altitude of about 22,500 miles (36,000 kilometers). That way, it revolves around the earth at exactly the same speed, and in the same direction, as the earth rotates on its axis, and always stays directly above the same point on the earth’s equator.
When you make a request for a Web page by clicking on a link, tapping on a touch screen, or making whatever other maneuver is required, a signal travels from your dish up to the satellite, then back down to the earth’s Internet system to find the server (computer) where the content resides. That server then sends the data back up to the satellite, which, in turn, sends the final bits of digital information to your system. All in all, the signals make two complete round trips between the earth and the satellite for a total of more than 90,000 miles (145,000 kilometers). The radio waves alone take half a second to go that far, so the best possible return time you can expect is half a second. In real life, it’s usually more like a full second because systems on the ground impose an additional delay. That long delay, called latency, will make it impossible for you to use VoIP (technically known as Voice over Internet Protocol, but often called Internet telephone) with the ease and convenience you’ll have come to expect if you’ve done it over a cable connection. Internet gaming will also suffer because of the latency.
As if the limitations imposed by the laws of physics weren’t enough, you’ll also have to deal with the rules and regulations imposed by the provider. In order to guarantee reliable service for all users, they put a limit on the amount of data that each individual user can receive from (download) or transmit to (upload) the satellite per 24-hour period. If you use the Internet only for e-mail and text-article viewing, you might not bump up against that limit. But if you download a lot of movies or watch long videos online, you should expect to hit the so-called fair access policy (FAP) limit. In that case, the service provider will slow your connection down for awhile, in order to keep you from “hogging the bandwidth” and compromising the performance of all the other users.
Other technical glitches can occasionally get into a satellite Internet system. One of the more interesting effects occurs during the short and infrequent time intervals when the sun passes behind the satellite. These periods last only a few minutes, and they occur only during the middle of March and the end of September; but when the satellite and the sun align as your dish “sees” them, the sun’s radio noise can overcome the satellite’s signal and wipe out your Internet access momentarily. Snow or ice on your dish, extreme temperatures (over 100°F or 38°C), exceptionally heavy rain or snow showers, sandstorms, and dust storms can also disrupt a satellite Internet connection.
