Gibilisco S. Teach Yourself Electricity and Electronics

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Digital images can be compressed in either of two ways. In lossless image compression, detail is

not sacrificed; only the redundant bits are eliminated. In lossy image compression, some detail is lost,

although the loss is usually not significant.

Packet Wireless

In packet wireless, a computer is connected to a radio transceiver using a terminal node controller

(TNC), which is similar to a modem. An example is shown in Fig. 26-6A. The computer has a tele-

Binary Digital Communications 451

26-5 A communications

circuit employing

parallel-to-serial (P/S)

conversion at the

source, and serial-

to-parallel (S/P)

conversion at the

destination.

phone modem as well as a TNC, so messages can be sent and received using conventional online

services as well as radio.

Figure 26-6B shows how a packet wireless message is routed. Black dots represent subscribers. Rec-

tangles represent local nodes, each of which serves subscribers by means of short-range links at very

high, ultra high, or microwave radio frequencies. The nodes are interconnected by terrestrial radio

links if they are relatively near each other. If the nodes are widely separated, satellite links are used.

452 Digital Basics

26-6 At A, a packet-wireless station. At B, passage of a packet through nodes in a

wireless communications circuit.

The RGB Color Model

All visible colors can be obtained by combining red, green, and blue light. The red/green/blue (RGB)

color model takes advantage of this fact.

Hue, Saturation, and Brightness

Color, as perceived by the human eye, is a function of the wavelength of optical EM energy. When

most of the energy is concentrated near a single wavelength, you see an intense hue. The vividness

of a hue is called the saturation. The brightness of a color is a function of how much total energy

the light contains. In most video displays, there is a control for adjusting the brightness, also called

brilliance.

3D Color

A color palette is obtained by combining pure red, green, and blue in various ratios. Assign each pri-

mary color an axis in Cartesian three-dimensional (3D) space as shown in Fig. 26-7. Call the axes R

(for red), G (for green), and B (for blue). Color brightness can range from 0 to 255, or binary

The RGB Color Model 453

26-7 The RGB color model, depicted as a cube in Cartesian three-dimensional (3D) space.

00000000 to 11111111. The result is 16,777,216 (256

) possible colors. Any point within the cube

represents a unique color.

Colors in the RGB model can also be represented by six-digit hexadecimal numbers, such as

005CFF. In this scheme, the first two digits represent the red (R) intensity in 256 levels ranging

from 00 to FF. The middle two digits represent the green (G) intensity, and the last two digits rep-

resent the blue (B) intensity.

Some RGB systems use only 16 levels for each primary color (binary 0000 through 1111). This

results in 4096 possible colors.

Quiz

Refer to the text in this chapter if necessary. A good score is at least 18 correct. Answers are in the

back of the book.

1. Suppose inverters are placed in series with both inputs of an AND gate. Under what

conditions is the output of the resulting black box high?

(a) If and only if both inverter inputs are high

(b) If and only if both inverter inputs are low

(d) Under no conditions (the output is always low)

2. Suppose an AND gate is followed by an inverter. Under what conditions is the output of the

resulting black box low?

(a) If and only if both inputs are high

(b) If and only if both inputs are low

(d) Under no conditions (the output is always high)

3. What is the binary equivalent of decimal 29?

(a) 10101

(b) 11101

(d) 11011

4. In Boolean algebra, addition represents

(a) the logical NOT operation.

(b) the logical AND operation.

(d) the logical NAND operation.

5. If the output to a logical inverter is low, it means that

(a) both of the two inputs are high.

(b) both of the two inputs are low.

454 Digital Basics

(d) the single input is low.

6. What is the decimal equivalent of binary 1111?

(a) 15

(b) 31

(d) 127

7. The output of an AND gate is high if and only if

(a) one input is high and the others are low.

(b) one input is low and the others are high.

(d) all inputs are high.

8. DeMorgan’s Theorem states that, for all logical statements X and Y,

(a) −(X*Y) is equivalent to X+Y.

(b) X*Y is equivalent to −(X+Y).

(d) (−X)+(−Y) is equivalent to −(X*Y).

9. If you see a number represented by FF in the documentation for an electronic circuit or

system, you can be certain that the number is

(a) radix 16.

(b) radix 10.

(d) radix 2.

10. Which of the following codes is digital?

(a) Morse

(b) Baudot

(d) All of the above

11. Which of the following voltages could normally represent a 1 in positive logic?

(a) 0.0 V

(b) +0.5 V

(d) +50 V

12. Which of the following voltages might normally represent a 1 in negative logic?

(a) 0.0 V

(b) +12 V

Quiz 455

(d) +50 V

13. Fill in the blank to make the following sentence true: “

data transmission refers to digital

bits sent along a single line, one bit after another.”

(a) Serial

(b) Synchronous

(d) Analog

14. The inputs of an R-S flip-flop are known as

(a) low and high.

(b) octal and binary.

(d) reset and set.

15. When both inputs of an R-S flip-flop are 0,

(a) the outputs stay as they are.

(b) Q = 0 and −Q = 1.

(d) the resulting outputs can be absurd.

16. The fifth digit from the right in a binary number carries which decimal value?

(a) 64

(b) 32

(d) 16

17. What is the octal equivalent of binary 1010?

(a) 4

(b) 10

(d) There is no way to tell without more information.

18. What is the largest possible radix 10 number that can be represented as a six-digit binary

number?

(a) Decimal 256

(b) Decimal 128

(d) Decimal 63

19. If one of the inputs to a two-input NOR gate is high, what is the output state?

(a) There is not enough information to tell.

(b) Low

456 Digital Basics

(d) It depends on the state of the other input.

20. Suppose a logic circuit has four inputs W, X, Y, and Z. How many possible input

combinations are there?

(a) 4

(b) 8

(d) 32

Quiz 457

DO NOT REFER TO THE TEXT WHEN TAKING THIS TEST. A GOOD SCORE IS AT LEAST 37 CORRECT.

Answers are in the back of the book. It’s best to have a friend check your score the first time, so you

won’t memorize the answers if you want to take the test again.

1. In a JFET, the control electrode is usually the

(a) source.

(b) emitter.

(d) base.

(e) gate.

2. A diode can be used as a frequency multiplier because of its

(a) junction capacitance.

(b) nonlinearity.

(d) forward breakover.

(e) charge carrier concentration.

3. Which of the following is not a common form of data transmission?

(a) Polarization modulation

(b) Frequency modulation

(d) Phase modulation

(e) Pulse modulation

4. A very brief, high-voltage spike on an ac power line is called

(a) a bleeder.

(b) an arc.

458

Test: Part 3

(d) an avalanche.

(e) a clipped peak.

5. Which of the following is not characteristic of an oscillator?

(a) Negative feedback

(b) Good output-to-input coupling

(d) Alternating current signal output

(e) Usefulness as a signal generator

6. Which layer of the ionosphere exists at the lowest altitude?

(a) The F layer

(b) The E layer

(d) The C layer

(e) The B layer

7. The beta of a bipolar transistor is another name for its

(a) current amplification factor.

(b) voltage amplification factor.

(d) maximum amplification frequency.

(e) optimum amplification frequency.

8. In a schematic diagram, the symbol for a PNP bipolar transistor can be recognized by

(a) a broken vertical line inside the symbol circle.

(b) an arrow inside the symbol circle, pointing from the base toward the emitter.

(d) a collector biased at a positive voltage with respect to the emitter.

(e) an arrow inside the symbol circle, pointing from the emitter toward the base.

9. Fill in the blank in the following sentence to make it true: “In an oscillator,

is an

expression of the extent to which the circuit maintains constant signal frequency output under

variable operating conditions, and is also an expression of its overall reliability.”

(a) sensitivity

(b) drift ratio

(d) selectivity

(e) stability

10. A Zener diode would most likely be found in

(a) the mixer in a superheterodyne receiver.

(b) the PLL in a circuit for detecting FM.

Test: Part 3 459

(d) the voltage regulator in a power supply.

(e) the AF oscillator in an AFSK transmitter.

11. When the bias in an FET stops the flow of current, the condition is called

(a) forward breakover.

(b) cutoff.

(d) pinchoff.

(e) avalanche.

12. The VA rating of a transformer is an expression of

(a) the maximum frequency at which it can function.

(b) the type of core material it has.

(d) the impedance transfer ratio.

(e) none of the above.

13. In an N-type semiconductor, the minority carriers are

(a) electrons.

(b) protons.

(d) neutrons.

(e) positrons.

14. A disadvantage of a half-wave rectifier is the fact that

(a) the output voltage is excessive compared to that of a full-wave rectifier.

(b) the output current is excessive compared to that of a full-wave rectifier.

(d) it requires several expensive diodes, whereas a full-wave rectifier requires only a single

cheap diode.

(e) it requires an expensive center-tapped transformer, whereas a full-wave rectifier does not

need a transformer at all.

15. A power gain of 30 dB is equivalent to which amplification factor?

(a) 0.001

(b)

⁄30

(d) 1000

(e) None of the above

460 Test: Part 3