ROY BLAKE Multiple Choice Questions for ECE BOARD TAKERS

Chapter 1: Introduction to Communication Systems MULTIPLE CHOICE 1. The theory of radio waves was originated by: a. Marconi b. Bell

c. Maxwell d. Hertz

ANS: C 2. The person who sent the first radio signal across the Atlantic ocean was: a. Marconi c. Maxwell b. Bell d. Hertz ANS: A 3. The transmission of radio waves was first done by: a. Marconi c. Maxwell b. Bell d. Hertz ANS: D 4. A complete communication system must include: a. a transmitter and receiver b. a transmitter, a receiver, and a channel c. a transmitter, a receiver, and a spectrum analyzer d. a multiplexer, a demultiplexer, and a channel ANS: B 5. Radians per second is equal to: a. 2π × f b. f ÷ 2π

c. the phase angle d. none of the above

ANS: A 6. The bandwidth required for a modulated carrier depends on: a. the carrier frequency c. the signal-plus-noise to noise ratio b. the signal-to-noise ratio d. the baseband frequency range ANS: D 7. When two or more signals share a common channel, it is called: a. sub-channeling c. SINAD b. signal switching d. multiplexing ANS: D 8. TDM stands for: a. Time-Division Multiplexing b. Two-level Digital Modulation

c. Time Domain Measurement d. none of the above

ANS: A 9. FDM stands for: a. Fast Digital Modulation b. Frequency Domain Measurement

c. Frequency-Division Multiplexing d. none of the above

ANS: C 10. The wavelength of a radio signal is: a. equal to f ÷ c b. equal to c ÷ λ c. the distance a wave travels in one period d. how far the signal can travel without distortion ANS: C 11. Distortion is caused by: a. creation of harmonics of baseband frequencies b. baseband frequencies "mixing" with each other c. shift in phase relationships between baseband frequencies d. all of the above ANS: D 12. The collection of sinusoidal frequencies present in a modulated carrier is called its: a. frequency-domain representation c. spectrum b. Fourier series d. all of the above ANS: D 13. The baseband bandwidth for a voice-grade (telephone) signal is: a. approximately 3 kHz c. at least 5 kHz b. 20 Hz to 15,000 Hz d. none of the above ANS: A 14. Noise in a communication system originates in: a. the sender c. the channel b. the receiver d. all of the above ANS: D 15. "Man-made" noise can come from: a. equipment that sparks b. temperature

c. static d. all of the above

ANS: A 16. Thermal noise is generated in: a. transistors and diodes b. resistors ANS: D

c. copper wire d. all of the above

17. Shot noise is generated in: a. transistors and diodes b. resistors

c. copper wire d. none of the above

ANS: A 18. The power density of "flicker" noise is: a. the same at all frequencies b. greater at high frequencies

c. greater at low frequencies d. the same as "white" noise

ANS: C 19. So called "1/f" noise is also called: a. random noise b. pink noise

c. white noise d. partition noise

ANS: B 20. "Pink" noise has: a. equal power per Hertz b. equal power per octave

c. constant power d. none of the above

ANS: B 21. When two noise voltages, V1 and V2, are combined, the total voltage VT is: a. VT = sqrt(V1 × V1 + V2 × V2) c. VT = sqrt(V1 × V2) d. VT = V1 + V2 b. VT = (V1 + V2)/2 ANS: A 22. Signal-to-Noise ratio is calculated as: a. signal voltage divided by noise voltage b. signal power divided by noise power c. first add the signal power to the noise power, then divide by noise power d. none of the above ANS: B 23. SINAD is calculated as: a. signal voltage divided by noise voltage b. signal power divided by noise power c. first add the signal power to the noise power, then divide by noise power d. none of the above ANS: D 24. Noise Figure is a measure of: a. how much noise is in a communications system b. how much noise is in the channel c. how much noise an amplifier adds to a signal d. signal-to-noise ratio in dB ANS: C

25. The part, or parts, of a sinusoidal carrier that can be modulated are: a. its amplitude c. its amplitude, frequency, and direction b. its amplitude and frequency d. its amplitude, frequency, and phase angle ANS: D COMPLETION 1. The telephone was invented in the year

.

ANS: 1863 2. Radio signals first were sent across the Atlantic in the year

.

ANS: 1901 3. The frequency band used to modulate the carrier is called the

band.

ANS: base 4. The job of the carrier is to get the information through the

.

ANS: channel 5. The bandwidth of an unmodulated carrier is

.

ANS: zero 6. The 'B' in Hartley's Law stands for

.

ANS: bandwidth 7. The more information per second you send, the

the bandwidth required.

ANS: greater larger wider 8. In multiple signals.

, you split the bandwidth of a channel into sub-channels to carry

ANS: FDM 9. In

, multiple signal streams take turns using the channel.

ANS: TDM 10. VHF stands for the

frequency band.

ANS: very high 11. The VHF band starts at

MHz.

ANS: 30 12. The UHF band starts at

MHz.

ANS: 300 13. A radio signal's

is the distance it travels in one cycle of the carrier.

ANS: wavelength 14. In free space, radio signals travel at approximately

meters per second.

ANS: 300 million 15. The equipment used to show signals in the frequency domain is the

.

ANS: spectrum analyzer 16. Mathematically, a spectrum is represented by a

series.

ANS: Fourier 17. Disabling a receiver during a burst of atmospheric noise is called

.

ANS: noise blanking blanking 18. For satellite communications,

noise can be a serious problem.

ANS: solar 19. Thermal noise is caused by the random motions of ANS: electrons SHORT ANSWER 1. Name the five elements in a block diagram of a communications system. ANS: Source, Transmitter, Channel, Receiver, Destination 2. Name five types of internal noise.

in a conductor.

ANS: Thermal, Shot, Partition, 1/f, transit-time 3. Why is thermal noise called "white noise"? ANS: White light is composed of equal amounts of light at all visible frequencies. Likewise, thermal noise has equal power density over a wide range of frequencies. 4. What is "pink noise"? ANS: Light is pink when it contains more red than it does other colors, and red is at the low end of the visible spectrum. Likewise, pink noise has higher power density at lower frequencies. 5. Suppose there is 30 µV from one noise source that is combined with 40 µV from another noise source. Calculate the total noise voltage. ANS: 50 µV 6. If you have 100 mV of signal and 10 mV of noise, both across the same 100-ohm load, what is the signal- to-noise ratio in dB? ANS: 20 dB 7. The input to an amplifier has a signal-to-noise ratio of 100 dB and an output signal-to-noise ratio of 80 dB. Find NF, both in dB and as a ratio. ANS: 20 dB, NF = 100 8. A microwave receiver has a noise temperature of 145 K. Find its noise figure. ANS: 1.5 9. Two cascaded amplifiers each have a noise figure of 5 and a gain of 10. Find the total NF for the pair. ANS: 5.4 10. Explain why you could use a diode as a noise source with a spectrum close to that of pure thermal noise. How would you control the amount of noise generated? ANS: When current flows through a diode, it generates shot noise that can be represented as a current source, the output of which is a noise current. The equation for the noise current is very similar to the equation for thermal noise voltage. Since the power in the shot noise is proportional to the diode current, controlling the diode current controls the noise power.

Chapter 2: Radio-Frequency Circuits MULTIPLE CHOICE 1. The time it takes a charge carrier to cross from the emitter to the collector is called: a. base time c. charge time b. transit time d. Miller time ANS: B 2. A real capacitor actually contains: a. capacitance and resistance only b. capacitance and inductance only

c. capacitance, inductance, and resistance d. reactance only

ANS: C 3. Bypass capacitors are used to: a. remove RF from non-RF circuits b. couple RF around an amplifier

c. neutralize amplifiers d. reduce the Miller effect

ANS: A 4. A resonant circuit is: a. a simple form of bandpass filter b. used in narrowband RF amplifiers

c. both a and b d. none of the above

ANS: C 5. Loading down a tuned-circuit amplifier will: a. raise the Q of the tuned circuit b. lower the Q of the tuned circuit

c. "multiply" the Q d. have no effect on Q

ANS: B 6. The "Miller Effect" can: a. cause an amplifier to oscillate b. cause an amplifier to lose gain

c. reduce the bandwidth of an amplifier d. all of the above

ANS: D 7. The Miller Effect can be avoided by: a. using a common-emitter amplifier b. using a common-base amplifier

c. increasing the Q of the tuned circuit d. it cannot be avoided

ANS: B 8. In a BJT, the Miller Effect is due to: a. inductance of collector lead b. collector-to-emitter capacitance ANS: D

c. base-to-emitter capacitance d. base-to-collector capacitance

9. In RF amplifiers, impedance matching is usually done with: a. RC coupling c. direct coupling b. transformer coupling d. lumped reactance ANS: B 10. Neutralization cancels unwanted feedback by: a. adding feedback out of phase with the unwanted feedback b. bypassing the feedback to the "neutral" or ground plane c. decoupling it d. none of the above ANS: A 11. For a "frequency multiplier" to work, it requires: a. a nonlinear circuit b. a linear amplifier c. a signal containing harmonics d. an input signal that is an integer multiple of the desired frequency ANS: A 12. A sinusoidal oscillation from an amplifier requires: a. loop gain equal to unity b. phase shift around loop equal to 0 degrees c. both a and b, but at just one frequency d. none of the above ANS: C 13. The conditions for sinusoidal oscillation from an amplifier are called: a. the loop-gain criteria c. the Bode criteria b. the Hartley criteria d. the Barkhausen criteria ANS: D 14. The Hartley oscillator uses: a. a tapped inductor b. a two-capacitor divider

c. an RC time constant d. a piezoelectric crystal

ANS: A 15. The Colpitts VFO uses: a. a tapped inductor b. a two-capacitor divider

c. an RC time constant d. a piezoelectric crystal

ANS: B 16. The Clapp oscillator is: a. a modified Hartley oscillator b. a modified Colpitts oscillator ANS: B

c. a type of crystal-controlled oscillator d. only built with FETs

17. A varactor is: a. a voltage-controlled capacitor b. a diode

c. used in tuner circuits d. all of the above

ANS: D 18. Crystal-Controlled oscillators are: a. used for a precise frequency b. used for very low frequency drift (parts per million) c. made by grinding quartz to exact dimensions d. all of the above ANS: D 19. If two signals, Va = sin(ωat) and Vb = sin(ωbt), are fed to a mixer, the output: a. will contain ω1 = ωa + ωb and ω2 = ωa – ωb b. will contain ω1 = ωa / ωb and ω2 = ωb / ωa c. will contain ω = (ωa + ωb ) / 2 d. none of the above ANS: A 20. In a balanced mixer, the output: a. contains equal (balanced) amounts of all input frequencies b. contains the input frequencies c. does not contain the input frequencies d. is a linear mixture of the input signals ANS: C 21. "VFO" stands for: a. Voltage-Fed Oscillator b. Variable-Frequency Oscillator

c. Varactor-Frequency Oscillator d. Voltage-Feedback Oscillator

ANS: B 22. A "frequency synthesizer" is: a. a VCO phase-locked to a reference frequency b. a VFO with selectable crystals to change frequency c. a fixed-frequency RF generator d. same as a mixer ANS: A COMPLETION 1. Generally, conductor lengths in RF circuits should be

.

ANS: short 2. At UHF frequencies and above, elements must be considered as being "lumped".

instead of as

ANS: distributed 3. When one side of a double-sided pc board is used for ground, it is called a

.

ANS: ground-plane 4. Interactions between parts of an RF circuit can be reduced by using them.

between

ANS: shielding 5. In high-frequency RF circuits, the placement of wires and

can be critical.

ANS: components 6. A

circuit is used to remove RF from the DC voltage bus.

ANS: decoupling 7. A

capacitor is used to short unwanted RF to ground.

ANS: bypass 8. The bandwidth of a tuned-circuit amplifier depends on the

of the tuned circuit.

ANS: Q 9. A value of to be valid.

or more for Q is required for the approximate tuned circuit equations

ANS: 10 10. In a class C RF amplifier, the extracts one frequency from all the harmonics contained in the device current (e.g. collector current). ANS: tuned circuit 11. Using additional feedback to compensate for "stray" feedback is called

.

ANS: neutralization 12. A Colpitts oscillator uses a

voltage divider to provide feedback.

ANS: capacitive 13. Electrically, a piezoelectric crystal has both a resonant frequency. ANS: series, parallel

and a

14. To produce sum and difference frequencies, a mixer must be a non-

circuit.

ANS: linear 15. At some bias point, a diode or a transistor can act as a

-law mixer.

ANS: square SHORT ANSWER 1. What inductance would you use with a 47-pF capacitor to make a tuned circuit for 10 MHz? ANS: 5.4 µH 2. What value of Q is required for a 10-MHz tuned circuit to have a bandwidth of 100 kHz? ANS: 100 3. A tuned-circuit amplifier with a gain of 10 is being used to make an oscillator. What should be the value of the feedback ratio to satisfy the Barkhausen criteria? ANS: 0.1 4. What is the advantage of a Clapp oscillator compared to a Colpitts oscillator? ANS: It is more stable because it "swamps" the device capacitance with large value capacitors in the feedback divider. 5. If a varactor has a capacitance of 90 pF at zero volts, what will be the capacitance at 4 volts? ANS: 30 pF 6. An oscillator has a frequency of 100 MHz at 20°C, and a tempco of +10 ppm per degree Celsius. What will be the shift in frequency at 70°C? What percentage is that? ANS: 50 kHz, 0.05% 7. Two sinusoidal signals, V1 and V2, are fed into an ideal balanced mixer. V1 is a 20-MHz signal; V2 is a 5MHz signal. What frequencies would you expect at the output of the mixer? ANS: 15 MHz and 25 MHz

8. Suppose the phase-locked-loop frequency synthesizer of Figure 2.39 has a reference frequency of 1 MHz and a fixed-modulus divider of 10. What should be the value of the programmable divider to get an output frequency of 120 MHz? ANS: 12

Chapter 3: Amplitude Modulation

MULTIPLE CHOICE 1. AM stands for: a. Audio Modulation b. Amplitude Modulation

c. Angle Modulation d. Antenna Modulation

ANS: B 2. The "envelope" of an AM signal is due to: a. the baseband signal b. the carrier signal

c. the amplitude signal d. none of the above

ANS: A 3. If the audio Va sin(ωat) modulates the carrier Vc sin(ωct), then the modulation index, m, is: 2 a. m = ωa / ωc c. m = (Va / Vc) b. m = Va / Vc d. m = Va / ωa ANS: B 4. The equation for full-carrier AM is: a. v(t) = (Ec + Em) × sin(ωct) b. v(t) = (Ec + Em) × sin(ωmt) + sin(ωct)

c. v(t) = (Ec × Em) × sin(ωmt) × sin(ωct) d. v(t) = (Ec + Em sin(ωmt)) × sin(ωct)

ANS: D 5. Overmodulation causes: a. distortion b. splatter

c. both a and b d. none of the above

ANS: C 6. The peak voltage of an AM signal goes from Emax to Emin. The modulation index, m, is: a. m = Emin / Emax c. m = (Emax – Emin) / (Emax + Emin) b. m = Emax / Emin d. m = (Emax + Emin) / (Emax – Emin) ANS: C 7. If Va sin(ωat) amplitude modulates the carrier Vc sin(ωct), it will produce the frequencies: a. ωc + ωa and ωc – ωa c. ωc + ωa and 2ωc + 2ωa b. (ωc + ωa)/2 and (ωc – ωa)/2 d. none of the above ANS: A 8. At 100% modulation, the total sideband power is: a. equal to the carrier power c. half the carrier power b. twice the carrier power d. 1.414 × carrier power

ANS: C 9. If a 5-kHz signal modulates a 1-MHz carrier, the bandwidth of the AM signal will be: a. 5 kHz c. 1.005 MHz b. 10 kHz d. none of the above ANS: B 10. If an AM radio station increases its modulation index, you would expect: a. the audio to get louder at the receiver c. the signal-to-noise ratio to increase b. the received RF signal to increase d. all of the above ANS: D 11. The modulation index can be derived from: a. the time-domain signal b. the frequency-domain signal

c. both a and b d. none of the above

ANS: C 12. The main problem in using quadrature AM would be: a. requires too much bandwidth c. incompatibility with ordinary AM radios b. requires too much power d. all of the above ANS: C 13. As compared to plain AM, SSB AM: a. is more efficient b. requires a more complex demodulator circuit c. requires less bandwidth d. all of the above ANS: D 14. The SC in SSB SC stands for: a. single-carrier b. suppressed-carrier

c. sideband-carrier d. none of the above

ANS: B 15. PEP stands for: a. Peak Envelope Power b. Peak Efficiency Power

c. Peak Envelope Product d. none of the above

ANS: A 16. If an SSB transmitter radiates 1000 watts at peak modulation, what will it radiate with no modulation? a. 1000 watts c. 250 watts b. 500 watts d. 0 watts ANS: D 17. Music on AM radio stations is "low-fidelity" because: a. AM is susceptible to noise

b. commercial AM stations use low power c. commercial AM stations have a narrow bandwidth d. all of the above ANS: C 18. The type of information that can be sent using AM is: a. audio c. digital data b. video d. all of the above ANS: D 19. Two tones modulate an AM carrier. One tone causes a modulation index of m1 and the other tone causes a modulation index of m2. The total modulation index is: a. m1 + m2 c. sqrt(m1 × m2 + m2 × m1) b. (m1 + m2) / 2 d. sqrt(m1 × m1 + m2 × m2) ANS: D 20. To demodulate a USB SSB signal, the receiver must: a. be set to USB mode c. both a and b b. reinsert the carrier d. none of the above ANS: C COMPLETION 1. An advantage of AM is that the receiver can be very

.

ANS: simple 2. A disadvantage of AM is its

use of power.

ANS: inefficient 3. The

of an AM signal resembles the shape of the baseband signal.

ANS: envelope 4. In AM, modulating with a single audio tone produces

sidebands.

ANS: two 5. Compared to the USB, the information in the LSB is

.

ANS: the same 6. Compared to the USB, the power in the LSB is ANS: the same

.

7. In AM, total sideband power is always

than the carrier power.

ANS: less 8. In AM, as the modulation index increases, the carrier power

.

ANS: remains constant 9. The power in an AM signal is maximum when the modulation index is

.

ANS: one 10. In AM, a voice-band signal of 300 Hz to 3000 Hz will require a bandwidth of

.

ANS: 6000 Hz 11. With a 1-MHz carrier, if the LSB extends down to 990 kHz, then the USB will extend up to . ANS: 1010 kHz 12. If an AM transmitter puts out 100 watts with no modulation, it will put out with 100% modulation.

watts

ANS: 150 SHORT ANSWER 1. An AM transmitter generates 100 watts with 0% modulation. How much power will it generate with 20% modulation? ANS: 102 watts 2. If the carrier power is 1000 watts, what is the power in the USB at 70.7% modulation? ANS: 125 watts 3. A carrier is modulated by three audio tones. If the modulation indexes for the tones are 0.3, 0.4, and 0.5, then what is the total modulation index? ANS: 0.707 4. You look at an AM signal with an oscilloscope and see that the maximum Vpp is 100 volts and the minimum Vpp is 25 volts. What is the modulation index? ANS: 0.6

5. A SSB transmitter is connected to a 50-ohm antenna. If the peak output voltage of the transmitter is 20 volts, what is the PEP? ANS: 4 watts

Chapter 4: Angle Modulation MULTIPLE CHOICE 1. The FM modulation index: a. increases with both deviation and modulation frequency b. increases with deviation and decreases with modulation frequency c. decreases with deviation and increases with modulation frequency d. is equal to twice the deviation ANS: B 2. One way to derive FM from PM is: a. integrate the modulating signal before applying to the PM oscillator b. integrate the signal out of the PM oscillator c. differentiate the modulating signal before applying to the PM oscillator d. differentiate the signal out of the PM oscillator ANS: A 3. The bandwidth of an FM signal is considered to be limited because: a. there can only be a finite number of sidebands b. it is equal to the frequency deviation c. it is band-limited at the receiver d. the power in the outer sidebands is negligible ANS: D 4. Mathematically, the calculation of FM bandwidth requires the use of: a. ordinary trigonometry and algebra c. Taylor series b. Bessel functions d. fractals ANS: B 5. FM bandwidth can be approximated by: a. Armstrong's Rule b. Bessel's Rule

c. Carson's Rule d. none of the above

ANS: C 6. NBFM stands for: a. National Broadcast FM b. Non-Broadcast FM

c. Near Band FM d. Narrowband FM

ANS: D 7. When FM reception deteriorates abruptly due to noise, it is called: a. the capture effect c. the noise effect b. the threshold effect d. the limit effect ANS: B

8. An FM receiver switching suddenly between two stations on nearby frequencies is called: a. the capture effect c. the "two-station" effect b. the threshold effect d. none of the above ANS: A 9. Pre-emphasis is used to: a. increase the signal to noise ratio for higher audio frequencies b. increase the signal to noise ratio for lower audio frequencies c. increase the signal to noise ratio for all audio frequencies d. allow stereo audio to be carried by FM stations ANS: A 10. A pre-emphasis of 75 µs refers to: a. the time it takes for the circuit to work b. the "dead time" before de-emphasis occurs c. the time delay between the L and R channels d. the time-constant of the filter circuits used ANS: D 11. FM stereo: a. uses DSBSC AM modulation b. is implemented using an SCA signal

c. has a higher S/N than mono FM d. is not compatible with mono FM

ANS: A 12. An SCA signal: a. can use amplitude modulation b. can use FM modulation

c. is monaural d. all of the above

ANS: D 13. The modulation index of an FM signal can be determined readily: a. using measurements at points where J0 equals one b. using measurements at points where J0 equals zero c. using measurements at points where the deviation equals zero d. only by using Bessel functions ANS: B COMPLETION 1. FM and PM are two forms of

modulation.

ANS: angle 2. PM is extensively used in ANS: data

communication.

3. Compared to AM, the signal-to-noise ratio of FM is usually

.

ANS: better 4. Compared to AM, the bandwidth of FM is usually

.

ANS: wider greater 5. FM transmitters can use Class important.

amplifiers since amplitude linearity is not

ANS: C 6. Both the power and amplitude of an FM signal

as modulation is applied.

ANS: stay constant 7. In FM, the frequency deviation is proportional to the instantaneous modulating signal.

of the

ANS: amplitude 8. The frequency deviation of an FM signal occurs at a rate equal to the modulating signal.

of the

ANS: frequency 9. Mathematically, the number of sidebands in an FM signal is

.

ANS: infinite 10. As FM sidebands get farther from the center frequency, their power

.

ANS: decreases 11. Mathematically, the value of an FM modulation index can be as high as

.

ANS: any number 12. In FM, as the modulating frequency decreases, the modulation index

.

ANS: increases 13. In FM, as the frequency deviation decreases, the modulation index

.

ANS: decreases 14. As the FM modulation index increases, the number of significant sidebands

.

ANS: increases 15. For certain values of mf, such as 2.4, the amplitude of the carrier frequency

.

ANS: disappears goes to zero 16. The bandwidth of an FM signal can be approximated using

rule.

ANS: Carson's 17. FM bandwidth can be calculated precisely using

functions.

ANS: Bessel 18. The

effect is characteristic of FM reception in a noisy environment.

ANS: threshold 19. The effect is seen when an FM receiver is exposed to two FM signals that are close to each other in frequency. ANS: capture 20. Rest frequency is another name for an FM

frequency.

ANS: carrier SHORT ANSWER 1. If a 2-volt instantaneous value of modulating signal amplitude causes a 10-kHz deviation in carrier frequency, what is the deviation sensitivity of the modulator? ANS: 5 kHz / volt 2. If a 2-kHz audio tone causes a frequency deviation of 4 kHz, what is the modulation index? ANS: 2 3. What will be the deviation caused by a 3-kHz tone if the modulation index is 3? ANS: 9 kHz 4. If the deviation sensitivity of an FM modulator is 2 kHz /V, what will be the modulation index caused by a 1-volt, 1-kHz audio signal?

ANS: 2 5. At a modulation index of 2, how much power is in the carrier of a 1000-watt FM transmitter? ANS: 48.4 watts 6. At a modulation index of 2, how much power is in the first pair of sidebands of a 1000-watt FM transmitter? ANS: 673 watts 7. At a modulation index of 2, how much power is in the fifth pair of sidebands of a 1000-watt FM transmitter? ANS: 200 mW (0.2 watt) 8. Using Carson's rule, what is the approximate bandwidth of an FM signal with a modulation index of 2 being modulated by a 5-kHz signal? ANS: 30 kHz 9. Using the Bessel chart of Figure 4.1, what is the bandwidth of an FM signal with a modulation index of 2 being modulated by a 5-kHz signal if we ignore sidebands containing less than 1% of the total power? ANS: 30 kHz 10. How would you use the fact that J0 is zero for certain known values of mf (2.4, 5.5, etc) to measure the frequency deviation of an FM modulator? ANS: Use an audio frequency generator to modulate the FM carrier. Using a spectrum analyzer, adjust the audio frequency until the carrier amplitude vanishes. Record the audio frequency. Then do the calculation: δ = fm × mf where mf will have one of the known values. For example, if fm is measured to be 2 kHz when mf is 5.5, then δ is 11 kHz.

Chapter 5: Transmitters MULTIPLE CHOICE 1. The ability to change operating frequency rapidly without a lot of retuning is called: a. agility c. VFO b. expansion d. spread-spectrum ANS: A 2. The difference between the DC power into a transmitter and the RF power coming out: a. is a measure of efficiency c. may require water cooling b. heats the transmitter d. all of the above ANS: D 3. Baseband compression produces: a. a smaller range of frequencies from low to high b. a smaller range of amplitude from soft to loud c. a smaller number of signals d. none of the above ANS: B 4. ALC stands for: a. Amplitude Level Control b. Automatic Level Control

c. Accurate Level Control d. none of the above

ANS: B 5. In an AM transmitter, ALC is used to: a. keep the modulation close to 100% b. keep the modulation below 100%

c. maximize transmitted power d. all of the above

ANS: D 6. With high-level AM: a. all RF amplifiers can be nonlinear b. minimum modulation power is required

c. minimum RF power is required d. all of the above

ANS: A 7. With high-level AM: a. the RF amplifiers are typically Class A b. the RF amplifiers are typically Class B

c. the RF amplifiers are typically Class C d. the RF amplifiers are typically Class AB

ANS: C 8. With low-level AM: a. the RF amplifiers must be Class A b. the RF amplifiers must be Class B

c. the RF amplifiers must be linear d. the RF amplifiers must be low-power

ANS: C 9. Power amplifiers must be linear for any signal that: a. is complex c. has variable frequency b. has variable amplitude d. all of the above ANS: B 10. In high-level AM, "high-level" refers to: a. the power level of the carrier b. the power level of the modulation

c. the power level of the final RF amplifier d. none of the above

ANS: D 11. In high-level AM, the power in the sidebands comes from: a. the modulating amplifier c. the driver stage b. the RF amplifier d. the carrier ANS: A 12. In an AM transmitter with 100% modulation, the voltage of the final RF stage will be: a. approximately half the DC supply voltage b. approximately twice the DC supply voltage c. approximately four times the DC supply voltage d. none of the above ANS: C 13. Practical transmitters are usually designed to drive a load impedance of: a. 50 ohms resistive c. 300 ohms resistive b. 75 ohms resistive d. 600 ohms resistive ANS: A 14. Which of the following can be used for impedance matching? a. pi network c. both a and b b. T network d. a bridge circuit ANS: C 15. When a transmitter is connected to a resistor instead of an antenna, the resistor is called: a. a heavy load c. a temporary load b. a dummy load d. a test load ANS: B 16. When a transmitter is connected to a resistor instead of an antenna, the resistor must be: a. wire-wound c. 1% tolerance or better b. noninductive d. all of the above ANS: B 17. A Class D amplifier is: a. very efficient

c. essentially pulse-duration modulation

b. essentially pulse-width modulation

d. all of the above

ANS: D 18. To generate a SSB signal: a. start with full-carrier AM b. start with DSBSC

c. start with a quadrature signal d. all of the above

ANS: B 19. The carrier is suppressed in: a. a balanced modulator b. a mixer

c. a frequency multiplier d. none of the above

ANS: A 20. To remove one AM sideband and leave the other you could use: a. a mechanical filter c. both a and b b. a crystal filter d. none of the above ANS: C 21. A direct FM modulator: a. varies the frequency of the carrier oscillator b. integrates the modulating signal c. both a and b d. none of the above ANS: A 22. An indirect FM modulator: a. requires a varactor in the carrier oscillator b. varies the phase of the carrier oscillator c. both a and b d. none of the above ANS: B 23. AFC stands for: a. Amplitude to Frequency Conversion b. Automatic Frequency Centering

c. Automatic Frequency Control d. Audio Frequency Control

ANS: C 24. Frequency multipliers are: a. essentially balanced modulators b. essentially Class C amplifiers

c. essentially mixers d. none of the above

ANS: B 25. With mixing: a. the carrier frequency can be raised b. the carrier frequency can be lowered c. the carrier frequency can be changed to any required value

d. the deviation is altered ANS: C COMPLETION 1. The accuracy and stability of a transmitter frequency is fixed by the

oscillator.

ANS: carrier 2. In the USA, the frequency.

sets requirements for accuracy and stability of a transmitter's

ANS: FCC 3. In Canada, transmitter's frequency.

sets requirements for accuracy and stability of a

ANS: Industry Canada 4. Frequency retuning.

is the ability of a transmitter to change frequency without a lot of

ANS: agility 5. Power output of SSB transmitters is rated by

.

ANS: PEP 6. Reducing the dynamic range of a modulating signal is called

.

ANS: compression 7. The opposite of compression is called

.

ANS: expansion 8. ALC is a form of

.

ANS: compression 9. High-level modulation allows the RF amplifiers to operate more

.

ANS: efficiently 10. Low-level modulation requires the RF amplifiers to be

.

ANS: linear 11. To isolate the oscillator from load changes, a

stage is used.

ANS: buffer 12. The peak collector voltage in a Class C RF amplifier is voltage.

than the DC supply

ANS: higher 13. Most practical transmitters are designed to operate into a

-ohm load.

ANS: 50 14. Transmitters built with transistor RF amplifiers often use a impedance matching.

network for

ANS: T 15. Matching networks also act as filters to help reduce

levels.

ANS: harmonic 16. Severe impedance

can destroy a transmitter's output stage.

ANS: mismatch 17. Transceivers combine a transmitter and a

into one "box".

ANS: receiver 18. To allow a high modulation percentage, it is common to modulate the the power amplifier in transistor modulators.

as well as

ANS: driver 19. Pulse-width modulation is the same as pulse-

modulation.

ANS: duration 20. Switching amplifiers are sometimes called Class

amplifiers.

ANS: D 21. Because the sideband filter in a SSB transmitter is fixed, more than one frequency.

is used to operate at

ANS: mixing 22. To generate a SSB signal, it is common to start with a ANS: DSBSC

signal.

23. Indirect FM is derived from

modulation.

ANS: phase 24. Using a varactor to generate FM is an example of a

modulator.

ANS: reactance 25. The modern way to make a stable VFO is to make it part of a

loop.

ANS: phase-locked SHORT ANSWER 1. If a 50-MHz oscillator is accurate to within 0.001%, what is the range of possible frequencies? ANS: 50 MHz ± 500 hertz 2. What is the efficiency of a 100-watt mobile transmitter if it draws 11 amps from a 12-volt car battery? ANS: 75.8% 3. The power amplifier of an AM transmitter draws 100 watts from the power supply with no modulation. Assuming high-level modulation, how much power does the modulation amplifier deliver for 100% modulation? ANS: 50 watts 4. If the final RF amplifier of an AM transmitter is powered by 100 volts DC, what is the maximum collector voltage at 100% modulation? ANS: 400 volts 5. Suppose the output of a balanced modulator has a center frequency of 10 MHz. The audio modulation frequency range is 1 kHz to 10 kHz. To pass the USB, what should be the center frequency of an ideal crystal filter? ANS: 10.005 MHz 6. Suppose you have generated a USB SSB signal with a nominal carrier frequency of 10 MHz. What is the minimum frequency the SSB signal can be mixed with so that the output signal has a nominal carrier frequency of 50 MHz? ANS: 40 MHz

7. Suppose you have an FM modulator that puts out 1 MHz carrier with a 100-hertz deviation. If frequency multiplication is used to increase the deviation to 400 hertz, what will be the new carrier frequency? ANS: 4 MHz 8. Suppose you had an FM signal with a carrier of 10 MHz and a deviation of 10 kHz. Explain how you could use it to get an FM signal at 100 MHz with a deviation of 20 kHz. ANS: First, put the signal through a frequency doubler to get a 20-MHz carrier with a 20-kHz deviation. Then mix that signal with an 80-MHz carrier to generate a 100-MHz carrier with 20-kHz deviation.

Chapter 6: Receivers MULTIPLE CHOICE 1. The two basic specifications for a receiver are: a. the sensitivity and the selectivity b. the number of converters and the number of IFs c. the spurious response and the tracking d. the signal and the noise ANS: A 2. The superheterodyne receiver was invented by: a. Foster c. Armstrong b. Seeley d. Hertz ANS: C 3. Trimmers and padders are: a. two types of adjusting tools b. small adjustable resistors

c. small adjustable inductors d. small adjustable capacitors

ANS: D 4. "Skin effect" refers to: a. the way radio signals travel across a flat surface b. the tissue-burning effect of a strong RF signal c. the increase of wire resistance with frequency d. none of the above ANS: C 5. The "front end" of a receiver can include: a. the tuner b. the RF amplifier

c. the mixer d. all of the above

ANS: D 6. "IF" stands for: a. intermediate frequency b. intermodulation frequency

c. indeterminate frequency d. image frequency

ANS: A 7. AGC stands for: a. Audio Gain Control b. Automatic Gain Control ANS: B 8. The frequency of the local oscillator: a. is above the RF frequency

c. Active Gain Control d. Active Gain Conversion

b. is below the RF frequency c. can be either above of below the RF frequency d. is fixed, typically at 455 kHz. ANS: C 9. The local oscillator and mixer are combined in one device because: a. it gives a greater reduction of spurious responses b. it increases sensitivity c. it increases selectivity d. it is cheaper ANS: D 10. Basically, sensitivity measures: a. the weakest signal that can be usefully received b. the highest-frequency signal that can be usefully received c. the dynamic range of the audio amplifier d. none of the above ANS: A 11. Basically, selectivity measures: a. the range of frequencies that the receiver can select b. with two signals close in frequency, the ability to receive one and reject the other c. how well adjacent frequencies are separated by the demodulator d. how well the adjacent frequencies are separated in the mixer ANS: B 12. When comparing values for shape factor: a. a value of 1.414 dB is ideal b. a value of 0.707 is ideal

c. a value of 1.0 is ideal d. there is no ideal value

ANS: C 13. When comparing values for shape factor: a. a value of 2 is better than a value of 4 b. a value of 4 is better than a value of 2

c. both values are basically equivalent d. none of the above

ANS: A 14. Distortion in a receiver can occur in: a. the mixer b. the detector

c. the IF amplifiers d. all of the above

ANS: D 15. Phase distortion is important in: a. voice communications systems b. color video receivers ANS: B

c. monochrome video receivers d. all of the above

16. The response of a receiver to weak signals is usually limited by: a. the AGC c. the dynamic range of the receiver b. noise generated in the receiver d. the type of detector circuit being used ANS: B 17. Image frequencies occur when two signals: a. are transmitted on the same frequency b. enter the mixer, with one being a reflected signal equal to the IF frequency c. enter the mixer, one below and one above the local oscillator by a difference equal to the IF d. enter the mixer, and the difference between the two signals is equal to twice the IF ANS: C 18. An image must be rejected: a. prior to mixing b. prior to IF amplification

c. prior to detection d. images cannot be rejected

ANS: A 19. Image frequency problems would be reduced by: a. having an IF amplifier with the proper shape factor b. having a wideband RF amplifier after the mixer c. having a narrowband RF amplifier before the mixer d. none of the above ANS: C 20. A common AM detector is the: a. PLL b. envelope detector

c. ratio detector d. all of the above

ANS: B 21. An FM detector is the: a. PLL b. ratio detector

c. quadrature detector d. all of the above

ANS: D 22. Germanium diodes are used in AM detectors because: a. they are faster than silicon diodes b. they are cheaper than silicon diodes c. they minimize distortion from nonlinearity d. all of the above ANS: C 23. A common SSB detector is: a. a PLL b. a diode ANS: D

c. a BFO d. a product detector

24. BFO stands for: a. Beat Frequency Oscillator b. Barrier Frequency Oscillator

c. Bipolar Frequency Oscillator d. Bistable Frequency Oscillator

ANS: A 25. To demodulate both SSB and DSBSC, you need to: a. use a Foster-Seeley discriminator b. reinject the carrier c. use double conversion d. use one diode for SSB and two diodes for DSBSC ANS: B 26. Which would be best for DSBSC: a. carrier detection b. coherent detection

c. envelope detection d. ratio detection

ANS: B 27. An FM detector that is not sensitive to amplitude variations is: a. Foster-Seeley detector c. a PLL detector b. a quadrature detector d. all of the above ANS: C 28. The function of a limiter is: a. to remove amplitude variations b. to limit spurious responses

c. to limit dynamic range d. to limit noise response

ANS: A 29. Suppressing the audio when no signal is present is called: a. AGC c. AFC b. squelch d. limiting ANS: B 30. LNA stands for: a. Limited-Noise Amplifier b. Low-Noise Amplifier

c. Low-Noise Audio d. Logarithmic Noise Amplification

ANS: B 31. AFC stands for: a. Audio Frequency Compensator b. Autodyne Frequency Compensation

c. Automatic Frequency Control d. Autonomous Frequency Control

ANS: C 32. The function of AFC is: a. maintain a constant IF frequency b. match the local oscillator to the received signal

c. lock the discriminator to the IF frequency d. none of the above ANS: B 33. SAW stands for: a. Symmetrical Audio Wave b. Surface Acoustic Wave

c. Silicon-Activated Wafer d. Software-Activated Wave

ANS: B 34. The important property of a SAW is: a. it stabilizes the audio in a receiver b. it allows software radios to be built

c. it is a stable bandpass filter d. none of the above

ANS: C 35. The main function of the AGC is to: a. keep the gain of the receiver constant b. keep the gain of the IF amplifiers constant c. keep the input to the detector at a constant amplitude d. all of the above ANS: C 36. DSP stands for: a. Dynamic Signal Properties b. Direct Signal Phase

c. Distorted Signal Packet d. Digital Signal Processor

ANS: D 37. SINAD stands for: a. Sinusoidal Amplitude Distortion b. Signal and Noise Amplitude Distortion c. Signal-plus-Noise-to-Noise Ratio d. Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio ANS: D 38. TRF stands for: a. Tuned Radio Frequency b. Tracking Radio Frequency

c. Transmitted Radio Frequency d. Tuned Receiver Function

ANS: A COMPLETION 1. Almost all modern receivers use the

principle.

ANS: superheterodyne 2. The first radio receiver of any kind was built in the year

.

ANS: 1887 3. When two tuned circuits adjusted, the other changes with it.

each other, it means that when the frequency of one is

ANS: track 4. The

effect causes the resistance of wire to increase with frequency.

ANS: skin 5. The superhet was invented in the year

.

ANS: 1918 6. In a receiver, the

refers to the input filter and RF stage.

ANS: front end 7. In a superhet, the output of the

goes to the IF amplifiers.

ANS: mixer 8. In a superhet, the frequency is the difference between the local oscillator frequency and the received signal frequency. ANS: intermediate IF 9. The

circuit adjusts the gain of the IF amplifiers in response to signal strength.

ANS: AGC 10. An

converter uses the same transistor for both the local oscillator and the mixer.

ANS: autodyne 11. In low-side injection, the local oscillator is

than the received signal frequency.

ANS: lower 12.

is the ability of a receiver to separate two signals that are close to each other in frequency. ANS: Selectivity

13.

is the ability of a receiver to receive and successfully demodulate a very weak signal. ANS: Sensitivity

14. A receiver with two different IF frequencies is called a double-

receiver.

ANS: conversion 15. A multiple-conversion receiver will have better rejection of

frequencies.

ANS: image 16. A demodulator is also called a

.

ANS: detector 17. An

detector uses a diode to half-wave rectify an AM signal.

ANS: envelope 18. A

detector is used for SSB signals.

ANS: product 19. A BFO produces a locally generated

.

ANS: carrier 20. A DSBSC signal requires a

detection circuit.

ANS: coherent 21. FM detectors have a characteristic

-shaped curve.

ANS: S 22. While still commonly found, the Foster-Seeley and ratio detectors are

.

ANS: obsolescent 23. Unlike the PLL detector, the quadrature detector is sensitive to changes in input signal.

of the

ANS: amplitude 24. A dual-

MOSFET is useful for AGC.

ANS: gate 25. Diode mixers are too

to be practical in most applications.

ANS: noisy 26. The IF amplifiers in an AM receiver must be Class

.

ANS: A 27. A double-tuned IF transformer is usually top and steep sides.

coupled for the response to have a flat

ANS: over 28. Multiple IF stages can be

-tuned to increase the bandwidth.

ANS: stagger 29. Compared to tuned circuits, ceramic and crystal IF filters do not require

.

ANS: adjustment 30. Up-conversion is when the output of the mixer is a signal.

frequency than the incoming

ANS: higher 31. In a block converter, the frequency of the first local oscillator is

.

ANS: fixed constant 32. Typically, AGC reduces the gain of the

amplifiers.

ANS: IF 33. An receivers.

-meter is designed to indicate signal strength in many communications

ANS: S 34. The effectiveness of FM

is measured by a receiver’s quieting sensitivity.

ANS: limiting 35. A

refers to any kind of FM or PM detector.

ANS: discriminator SHORT ANSWER 1. Suppose the bandwidth of a tuned circuit is 10 kHz at 1 MHz. Approximately what bandwidth would you expect it to have at 4 MHz? ANS:

20 kHz 2. Using high-side injection for a 1-MHz IF, what is the frequency of the local oscillator when the receiver is tuned to 5 MHz? ANS: 6 MHz 3. An IF filter has a –60 dB bandwidth of 25 kHz and a –6 dB bandwidth of 20 kHz. What is the shape factor value? ANS: 1.25 4. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what would be the image frequency if the receiver was tuned to 50 MHz? ANS: 60 MHz 5. Suppose a SSB receiver requires an injected frequency of 1.5 MHz. What would be the acceptable frequency range of the BFO if the maximum acceptable baseband shift is 100 hertz? ANS: 1.5 MHz ± 100 hertz 6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary and secondary. What value of kc do you need to achieve optimal coupling? ANS: 0.06 7. What value of transformer coupling would a double-tuned 10-MHz IF amplifier with optimal coupling need to get a bandwidth of 100 kHz? ANS: 0.01

Chapter 7: Digital Communications MULTIPLE CHOICE 1. The first digital code was the: a. ASCII code b. Baudot code

c. Morse code d. none of the above

ANS: C 2. In digital transmission, signal degradation can be removed using: a. an amplifier c. a regenerative repeater b. a filter d. all of the above ANS: C 3. TDM stands for: a. Time-Division Multiplexing b. Time-Domain Multiplexing

c. Ten-Digital Manchester d. Ten Dual-Manchester

ANS: A 4. Hartley's Law is: a. I = ktB b. C = 2B log2M

c. C = B log2(1 + S/N) d. SR = 2fmax

ANS: A 5. The Shannon-Hartley theorem is: a. I = ktB b. C = 2B log2M

c. C = B log2(1 + S/N) d. SR = 2fmax

ANS: B 6. The Shannon Limit is given by: a. I = ktB b. C = 2B log2M

c. C = B log2(1 + S/N) d. SR = 2fmax

ANS: C 7. The Nyquist Rate can be expressed as: a. I = ktB b. C = 2B log2M

c. C = B log2(1 + S/N) d. SR = 2fmax

ANS: D 8. Natural Sampling does not use: a. a sample-and-hold circuit b. true binary numbers ANS: A

c. a fixed sample rate d. an analog-to-digital converter

9. Which is true about aliasing and foldover distortion? a. They are two types of sampling error. b. You can have one or the other, but not both. c. Aliasing is a technique to prevent foldover distortion. d. They are the same thing. ANS: D 10. Foldover distortion is caused by: a. noise b. too many samples per second

c. too few samples per second d. all of the above

ANS: C 11. The immediate result of sampling is: a. a sample alias b. PAM

c. PCM d. PDM

ANS: B 12. Which of these is not a pulse-modulation technique: a. PDM c. PPM b. PWM d. PPS ANS: D 13. Quantizing noise (quantization noise): a. decreases as the sample rate increases b. decreases as the sample rate decreases c. decreases as the bits per sample increases d. decreases as the bits per sample decreases ANS: C 14. The dynamic range of a system is the ratio of: a. the strongest transmittable signal to the weakest discernible signal b. the maximum rate of conversion to the minimum rate of conversion c. the maximum bits per sample to the minimum bits per sample d. none of the above ANS: A 15. Companding is used to: a. compress the range of base-band frequencies b. reduce dynamic range at higher bit-rates c. preserve dynamic range while keeping bit-rate low d. maximize the useable bandwidth in digital transmission ANS: C 16. In North America, companding uses: a. the Logarithmic Law b. the A Law

c. the α Law (alpha law) d. the µ Law (mu law)

ANS: D 17. In Europe, companding uses: a. the Logarithmic Law b. the A Law

c. the α Law (alpha law) d. the µ Law (mu law)

ANS: B 18. Codec stands for: a. Coder-Decoder b. Coded-Carrier

c. Code-Compression d. none of the above

ANS: A 19. A typical codec in a telephone system sends and receives: a. 4-bit numbers c. 12-bit numbers b. 8-bit numbers d. 16-bit numbers ANS: B 20. Compared to PCM, delta modulation: a. transmits fewer bits per sample b. requires a much higher sampling rate

c. can suffer slope overload d. all of the above

ANS: D 21. In delta modulation, "granular noise" is produced when: a. the signal changes too rapidly c. the bit rate is too high b. the signal does not change d. the sample is too large ANS: B 22. Compared to PCM, adaptive delta modulation can transmit voice: a. with a lower bit rate but reduced quality c. only over shorter distances b. with a lower bit rate but the same quality d. only if the voice is band-limited ANS: B 23. Which coding scheme requires DC continuity: a. AMI c. unipolar NRZ b. Manchester d. bipolar RZ ANS: C 24. Manchester coding: a. is a biphase code b. has a level transition in the middle of every bit period c. provides strong timing information d. all of the above ANS: D 25. The number of framing bits in DS-1 is:

a. 1 b. 2

c. 4 d. 8

ANS: A 26. Framing bits in DS-1 are used to: a. detect errors b. carry signaling

c. synchronize the transmitter and receiver d. all of the above

ANS: C 27. So-called "stolen" bits in DS-1 are used to: a. detect errors b. carry signaling

c. synchronize the transmitter and receiver d. all of the above

ANS: B 28. The number of bits per sample in DS-1 is: a. 1 b. 2

c. 4 d. 8

ANS: D 29. The number of samples per second in DS-1 is: a. 8 k c. 64 k b. 56 k d. 1.544 × 106 ANS: A 30. The bit rate for each channel in DS-1 is: a. 1.544 Mb/s b. 64 kb/s

c. 56 kb/s d. 8 kb/s

ANS: B 31. In DS-1, bits are transmitted over a T-1 cable at: a. 1.544 MB/s c. 56 kb/s b. 64 kb/s d. 8 kb/s ANS: A 32. A T-1 cable uses: a. Manchester coding b. bipolar RZ AMI coding

c. NRZ coding d. pulse-width coding

ANS: B 33. The number of frames in a superframe is: a. 6 b. 12 ANS: B 34. A typical T-1 line uses:

c. 24 d. 48

a. twisted-pair wire b. coaxial cable

c. fiber-optic cable d. microwave

ANS: A 35. "Signaling" is used to indicate: a. on-hook/off-hook condition b. busy signal

c. ringing d. all of the above

ANS: D 36. A vocoder implements compression by: a. constructing a model of the transmission medium b. constructing a model of the human vocal system c. finding redundancies in the digitized data d. using lossless techniques ANS: B 37. Compared to standard PCM systems, the quality of the output of a vocoder is: a. much better c. about the same b. somewhat better d. not as good ANS: D COMPLETION 1. Digitizing a signal often results in

transmission quality.

ANS: improved better 2. To send it over an analog channel, a digital signal must be

onto a carrier.

ANS: modulated 3. To send it over a digital channel, an analog signal must first be

.

ANS: digitized 4. In analog channels, the signal-to-noise ratio of an analog signal gradually length of the channel increases. ANS: decreases gets worse 5. The ANS: binary

value of a pulse is the only information it carries on a digital channel.

as the

6. A

repeater is used to restore the shape of pulses on a digital cable.

ANS: regenerative 7. There are techniques to detect and

some errors in digital transmission.

ANS: correct 8. Converting an analog signal to digital form is another source of transmission systems.

in digital

ANS: error noise 9.

-division multiplexing is easily done in digital transmission. ANS: Time

10. All practical communications channels are band-

.

ANS: limited 11.

Law gives the relationship between time, information capacity, and bandwidth. ANS: Hartley's

12. Ignoring noise, the for a given bandwidth.

theorem gives the maximum rate of data transmission

ANS: Shannon-Hartley 13. The limit gives the maximum rate of data transmission for a given bandwidth and a given signal-to-noise ratio. ANS: Shannon 14.

sampling is done without a sample-and-hold circuit. ANS: Natural

15. The format.

Rate is the minimum sampling rate for converting analog signals to digital

ANS: Nyquist 16.

distortion occurs when an analog signal is sampled at too slow a rate. ANS: Foldover

17.

means that higher frequency baseband signals from the transmitter "assume the identity" of low-frequency baseband signals at the receiver when sent digitally. ANS: Aliasing

18. The output of a sample-and-hold circuit is a pulse-

modulated signal.

ANS: amplitude 19.

modulation is the most commonly used digital modulation scheme. ANS: Pulse-code

20.

noise results from the process of converting an analog signal into digital format. ANS: Quantizing

21.

is used to preserve dynamic range using a reasonable bandwidth. ANS: Companding

22. In North America, compression is done using the

-law equation.

ANS: µ mu 23. In Europe, compression is done using the

-law equation.

ANS: A 24. A

is an IC that converts a voice signal to PCM and vice versa.

ANS: codec 25. In a PCM system, the samples of the analog signal are first converted to before being compressed to 8 bits.

bits

ANS: 12 26. The number of bits per sample transmitted in delta modulation is

.

ANS: 1 one 27. Delta modulation requires a reproduction. ANS: higher

sampling rate than PCM for the same quality of

28.

noise is produced by a delta modulator if the analog signal doesn't change. ANS: Granular

29. In delta modulation,

overload can occur if the analog signal changes too fast.

ANS: slope 30. The

size varies in adaptive delta modulation.

ANS: step 31. Adaptive delta modulation can transmit PCM-quality voice at about of PCM.

the bit rate

ANS: half 32. Unipolar NRZ is not practical because most channels do not have

continuity.

ANS: DC 33. In AMI, binary ones are represented by a voltage that alternates in

.

ANS: polarity 34. Long strings of

should be avoided in AMI.

ANS: zeros 35. Manchester code has a level

in the center of each bit period.

ANS: transition 36. Manchester coding provides zeros.

information regardless of the pattern of ones and

ANS: timing 37. There are

channels in a DS-1 frame.

ANS: 24 38. DS-1 uses a

bit to synchronize the transmitter and receiver.

ANS: framing 39. In DS-1, each channel is sampled

times per second.

ANS: 8000 40. Data is carried over a T-1 line at a rate of

bits per second.

6

ANS: 1.544 × 10

41. A group of 12 DS-1 frames is called a

.

ANS: superframe 42. From a group of twelve frames, signaling bits are "stolen" from every

frame.

ANS: sixth 43.

compression transmits all the data in the original signal but uses fewer bits to do it. ANS: Lossless

SHORT ANSWER 1. Use Hartley's Law to find how much time it would take to send 100,000 bits over a channel with a bandwidth of 2,000 hertz and a channel constant of k = 10. ANS: 5 seconds 2. Use the Shannon-Hartley theorem to find the bandwidth required to send 12,000 bits per second if the number of levels transmitted is 8. ANS: 2000 hertz 3. What is the Shannon Limit of a channel that has a bandwidth of 4000 hertz and a signal-to-noise ratio of 15? ANS: 16 kbps 4. What is the minimum required number of samples per second to digitize an analog signal with frequency components ranging from 300 hertz to 3300 hertz? ANS: 6600 samples/second 5. What is the approximate dynamic range, in dB, of a linear PCM system that uses 12 bits per sample? ANS: 74 dB 6. What is the approximate data rate for a system using 8 bits per sample and running at 8000 samples per second?

ANS: 64 kbps 7. If bits were "stolen" from every DS-1 frame, what would the useable data-rate be for each channel in the frame? ANS: 56 kbps 8. Assuming maximum input and output voltages of 1 volt, what is the output voltage of a µ-law compressor if the input voltage is 0.388 volt? ANS: 0.833 volt

Chapter 8: The Telephone System MULTIPLE CHOICE 1. DTMF stands for: a. Digital Telephony Multiple Frequency b. Dial Tone Master Frequency

c. Dual-Tone Multifrequency d. Digital Trunk Master Frequency

ANS: C 2. PSTN stands for: a. Public Switched Telephone Network b. Private Switched Telephone Network

c. Primary Service Telephone Network d. Primary Service Telephone Numbers

ANS: A 3. POTS stands for: a. Private Office Telephone System b. Primary Office Telephone Service

c. Primary Operational Test System d. Plain Old Telephone Service

ANS: D 4. LATA stands for: a. Local Access and Transport Area b. Local Access Telephone Area

c. Local Area Telephone Access d. Local Area Transport Access

ANS: A 5. A LATA is a: a. a local calling area b. a type of digital local network

c. a way of accessing a tandem office d. a way of accessing a central office

ANS: A 6. Central offices are connected by: a. local loops b. trunk lines

c. both a and b d. none of the above

ANS: B 7. Local loops terminate at: a. a tandem office b. a toll station

c. a central office d. an interexchange office

ANS: C 8. Call blocking: a. cannot occur in the public telephone network b. occurs on the local loop when there is an electrical power failure c. occurs only on long-distance cables d. occurs when the central office capacity is exceeded

ANS: D 9. In telephony, POP stands for: a. Post Office Protocol b. Point Of Presence

c. Power-On Protocol d. none of the above

ANS: B 10. The cable used for local loops is mainly: a. twisted-pair copper wire b. shielded twisted-pair copper wire

c. coaxial cable d. fiber-optic

ANS: A 11. FITL stands for: a. Framing Information for Toll Loops b. Fiber In the Toll Loop

c. Framing In The Loop d. Fiber-In-The-Loop

ANS: D 12. Loading coils were used to: a. increase the speed of the local loop for digital data b. reduce the attenuation of voice signals c. reduce crosstalk d. provide C-type conditioning to a local loop ANS: B 13. DC current flows through a telephone: a. when it is on hook b. when it is off hook

c. as long as it is attached to a local loop d. only when it is ringing

ANS: B 14. The range of DC current that flows through a telephone is: a. 20 µA to 80 µA c. 2 mA to 8 mA b. 200 µA to 800 µA d. 20 mA to 80 mA ANS: D 15. The separation of control functions from signal switching is known as: a. step-by-step switching control c. common control b. crossbar control d. ESS ANS: C 16. The typical voltage across a telephone when on-hook is: a. 48 volts DC c. 90 volts DC b. 48 volts, 20 hertz AC d. 90 volts, 20 hertz AC ANS: A 17. The typical voltage needed to "ring" a telephone is:

a. 48 volts DC b. 48 volts, 20 hertz AC

c. 90 volts DC d. 90 volts, 20 hertz AC

ANS: D 18. The bandwidth of voice-grade signals on a telephone system is restricted in order to: a. allow lines to be "conditioned" c. allow signals to be multiplexed b. prevent "singing" d. all of the above ANS: C 19. VNL stands for: a. voltage net loss b. volume net loss

c. via net loss d. voice noise level

ANS: C 20. Signal loss is designed into a telephone system to: a. eliminate reflections c. improve signal-to-noise ratio b. prevent oscillation d. reduce power consumption ANS: B 21. The reference noise level for telephony is: a. 1 mW b. 0 dBm

c. 1 pW d. 0 dBr

ANS: C 22. The number of voice channels in a basic FDM group is: a. 6 c. 24 b. 12 d. 60 ANS: B 23. Basic FDM groups can be combined into: a. supergroups b. mastergroups

c. jumbogroups d. all of the above

ANS: D 24. In telephone system FDM, voice is put on a carrier using: a. SSB c. PDM b. DSBSC d. PCM ANS: A 25. PABX stands for: a. Power Amplification Before Transmission b. Private Automatic Branch Exchange c. Public Automated Branch Exchange d. Public Access Branch Exchange ANS: B

26. SLIC stands for: a. Single-Line Interface Circuit b. Standard Line Interface Card

c. Subscriber Line Interface Card d. Standard Local Interface Circuit

ANS: C 27. In DS-1, bits are "robbed" in order to: a. provide synchronization b. carry signaling

c. cancel echoes d. check for errors

ANS: B 28. "Bit-stuffing" is more formally called: a. compensation b. rectification

c. justification d. frame alignment

ANS: C 29. ISDN stands for: a. Integrated Services Digital Network b. Information Services Digital Network

c. Integrated Services Data Network d. Information Systems Digital Network

ANS: A 30. Basic ISDN has not been widely adopted because: a. it took to long to develop b. it is too slow c. it has been surpassed by newer technologies d. all of the above ANS: D 31. ADSL stands for: a. All-Digital Subscriber Line b. Asymmetrical Digital Subscriber Line

c. Allocated Digital Service Line d. Access to Data Services Line

ANS: B 32. Compared to ISDN, internet access using ADSL is typically: a. much faster c. much more expensive b. about the same speed d. none of the above ANS: A COMPLETION 1. A

is a local calling area.

ANS: LATA 2. Central offices are connected together by

lines.

ANS: trunk 3. One central office can be connected to another through a

office.

ANS: tandem 4. With 7-digit phone numbers, office.

thousand telephones can connect to a central

ANS: ten 5. Call is when it becomes impossible for a subscriber to place a call due to an overload of lines being used. ANS: blocking 6. New

switching equipment uses TDM to combine signals.

ANS: digital 7. Most local loops still use

copper wire.

ANS: twisted-pair 8. As compared to a hierarchical network, a intermediate switch.

network never needs more than one

ANS: flat 9.

coils were used to reduce the attenuation of voice frequencies. ANS: Loading

10. In a twisted-pair telephone cable, the red wire is called

.

ANS: ring 11. In a twisted-pair telephone cable, the green wire is called

.

ANS: tip 12. Of the red and green 'phone wires, the

wire is positive with respect to the other.

ANS: green 13. A telephone is said to have

the line when the central office sends it dial tone.

ANS: seized 14. The

functions are provided by a SLIC.

ANS: BORSCHT 15. A coil prevents loss of signal energy within a telephone while allowing fullduplex operation over a single pair of wires. ANS: hybrid 16. In a crosspoint switch, not all

can be in use at the same time.

ANS: lines 17. The old carbon transmitters generated a relatively

signal voltage.

ANS: large ®

18. The generic term for Touch-Tone signaling is

.

ANS: DTMF 19. A

line provides more bandwidth than a standard line.

ANS: conditioned 20. In the telephone system, amplifiers are called

.

ANS: repeaters 21. An echo

converts a long-distance line from full-duplex to half-duplex operation.

ANS: suppressor 22.

weighting is an attempt to adjust the noise or signal level to the response of a typical telephone receiver. ANS: C-message

23. In FDM telephony, the modulation is usually

.

ANS: SSB SSBSC 24. In FDM telephony,

bands separate the channels in a group.

ANS: guard 25. Because of "bit robbing", a channel in a DS-1 frame allows only used to send digital data. ANS: 56

kbps when

26. A twelfth frames.

is a group of 12 DS-1 frames with signaling information in the sixth and

ANS: superframe 27. In DS-1C,

bits are used to compensate for differences between clock rates.

ANS: stuff 28. Busy and dial tone are referred to as wires as the voice signal.

signals because they use the same pair of

ANS: in-channel 29. SS7 is the current version of

signaling.

ANS: common-channel 30. SS7 is a

-switched data network.

ANS: packet 31. In ISDN, the

channel is used for common-channel signaling.

ANS: D 32. In ISDN, the

channels are used for voice or data.

ANS: B 33. Terminal equipment especially designed for ISDN is designated

equipment.

ANS: TE1 34. The A in ADSL stands for

.

ANS: asymmetrical 35. In ADSL, the speed from the network to the subscriber is opposite direction.

than the speed in the

ANS: greater faster SHORT ANSWER 1. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If the loop current is 40 mA, what is the DC resistance of the local loop?

ANS: 1000 ohms 2. For a certain telephone, the DC loop voltage is 48 V on hook and 8 V off hook. If the loop current is 40 mA, what is the DC resistance of the telephone? ANS: 200 ohms 3. Which two DTMF tones correspond to the digit "1"? (Use the table in the text.) ANS: 697 Hz and 1209 Hz 4. Calculate the dB of VNL required for a channel with a 3 ms delay. ANS: 1 dB 5. If a telephone voice signal has a level of 0 dBm, what is its level in dBrn? ANS: 90 dBrn 6. A telephone test-tone has a level of 80 dBrn at a point where the level is +5dB TLP. If C-weighting produces a 10-dB loss, what would the signal level be in dBrnc0? ANS: 65 dBrnc TLP

Chapter 9: Data Transmission

MULTIPLE CHOICE 1. In practical terms, parallel data transmission is sent: a. over short distances only c. over any distance b. usually over long distances d. usually over a coaxial cable ANS: A 2. The five-level teletype code was invented by: a. the Morkum Company c. Western Union b. the Teletype Company d. Emile Baudot ANS: D 3. Data codes are also called: a. character codes b. character sets

c. they do not have any other name d. both a and b

ANS: C 4. Digital data that is not being used to carry characters is called: a. FIGS data c. numerical data b. binary data d. all of the above ANS: B 5. Character codes include: a. alphanumeric characters b. data link control characters

c. graphic control characters d. all of the above

ANS: D 6. ASCII stands for: a. American Standard Character-set 2 b. American Standard Code for Information Interchange c. American Standard Code 2 d. Alphanumeric Standard Code for Information Interchange ANS: B 7. BS, FF, and CR are examples of: a. nonstandard character codes b. escape characters

c. control characters d. none of the above

ANS: C 8. LF stands for: a. Line Feed

c. Line Forward

b. Link Feed

d. Link Forward

ANS: A 9. UART stands for: a. Universal Asynchronous Receiver-Transmitter b. Unidirectional Asynchronous Receiver-Transmitter c. Unaltered Received Text d. Universal Automatic Receiver for Text ANS: A 10. In asynchronous transmission, the transmitter and receiver are: a. frame-by-frame synchronized using the data bits b. frame-by-frame synchronized using a common clock c. frame-by-frame synchronized using the start and stop bits d. not synchronized at all, hence the name "asynchronous" ANS: C 11. In asynchronous transmission, the time between consecutive frames is: a. equal to zero c. equal to the start and stop bit-times b. equal to one bit-time d. not a set length ANS: D 12. In synchronous transmission, the frames are: a. about the same length as ten asynchronous frames b. much longer than asynchronous frames c. 128 bytes long d. 1024 bytes long ANS: B 13. Synchronous transmission is used because: a. no start and stop bits means higher efficiency b. it is cheaper than asynchronous since no UARTS are required c. it is easier to implement than asynchronous d. all of the above ANS: A 14. In synchronous transmission, the receiver "syncs-up" with the transmitter by using: a. the clock bits c. the CRC bits b. the data bits d. a separate clock line ANS: B 15. To maintain synchronization in synchronous transmission: a. long strings of 1s and 0s must not be allowed b. transmission must stop periodically for resynchronization c. the clock circuits must be precisely adjusted d. the channel must be noise-free

ANS: A 16. BISYNC: a. is an IBM product b. is a character-oriented protocol

c. requires the use of DLE d. all of the above

ANS: D 17. HDLC: a. is an IBM product b. is a bit-oriented protocol

c. is identical to SDLC d. all of the above

ANS: B 18. The use of flags in SDLC requires: a. "bit-stuffing" b. different flags at either end of a frame

c. FEC d. ARQ

ANS: A 19. The initials ARQ are used to designate: a. automatic request for resynchronization b. automatic request for retransmission

c. automatic receiver queue d. automatic request for queue

ANS: B 20. ARQ is used to: a. correct bit errors b. correct synchronization problems

c. put data into a temporary buffer d. none of the above

ANS: A 21. FEC stands for: a. Fixed Error Control b. Forward Error Control

c. Forward Error Correction d. False Error Condition

ANS: C 22. VRC is another name for: a. FEC b. ARQ

c. LRC d. parity

ANS: D 23. CRC stands for: a. Control Receiver Code b. Correct Received Character

c. Cyclic Redundancy Check d. Cycle Repeat Character

ANS: C 24. Huffman codes: a. allow errors to be detected but not corrected b. allow errors to be detected and corrected c. allow alphanumeric data to be corrected

d. allow alphanumeric data to be compressed ANS: D 25. Run-length encoding is used to: a. encrypt data b. compress data

c. correct data d. none of the above

ANS: B 26. Public-key encryption: a. allows the use of digital signatures b. is used to convey symmetric keys

c. avoids the "password problem" d. all of the above

ANS: D 27. SDLC stands for: a. Synchronous Data Link Control b. Synchronous Data Line Control

c. Synchronous Data Link Character d. Synchronous Data Line Character

ANS: A 28. HDLC is: a. a bit-oriented protocol b. based on SDLC

c. an ISO standard d. all of the above

ANS: D COMPLETION 1. Parallel transmission can be used only for

distances.

ANS: short 2. The term "baud" was named after Emil

.

ANS: Baudot 3. Data codes are also called

codes.

ANS: character 4. The computers.

code is a 7-bit code commonly used in communication between personal

ANS: ASCII 5. The two letters page. ANS: FF

designate the code character used to advance a printer to the next

6. An asynchronous frame begins with the

bit.

ANS: start 7. An asynchronous frame ends with the

bit.

ANS: stop 8. At the end of an asynchronous frame, the line will be at the

level.

ANS: mark binary 1 9. An integrated circuit called a to convert between parallel and serial data.

is used in an asynchronous communication system

ANS: UART 10. When receiving digital data,

are used to hold data until they can be read.

ANS: buffers 11. Synchronous communication is more "overhead" bits.

than asynchronous since there are fewer

ANS: efficient 12. There must be sufficient 1-to-0 transmission.

to maintain synchronization in synchronous

ANS: transitions 13. Clock sync is derived from the stream of

bits in synchronous transmission.

ANS: data 14. In the

protocol, each frame begins with at least two SYN characters.

ANS: BISYNC 15. In HDLC, each frame starts with an 8-bit

.

ANS: flag 16. The first eight bits of an SDLC frame are

.

ANS: 01111110 17. BCC stands for

check character.

ANS: block 18. DLE stands for data link

.

ANS: escape 19. HDLC uses bit-

to prevent accidental flags.

ANS: stuffing 20.

errors cause many consecutive bits to be bad. ANS: Burst

21. FEC stands for

error correction.

ANS: forward 22. An

scheme corrects errors by requiring the retransmission of bad blocks.

ANS: ARQ 23. Parity fails when an

number of bits are in error.

ANS: even 24. CRC codes are particularly good at detecting

errors.

ANS: burst 25. Huffman coding and run-length encoding are examples of data

.

ANS: compression 26. A

is an encoding scheme that is not public in order to protect data.

ANS: cipher 27. A

is often used to generate an encryption key because it is easier to remember.

ANS: password 28. If the key is

enough, private-key encryption can be quite secure.

ANS: long 29. Messages cannot be

using a public key.

ANS: decrypted 30. Because it is

-intensive, public-key encryption can be slow.

ANS: computation SHORT ANSWER 1. How many different characters could be encoded using a six-bit code? ANS: 64 2. What is the numerical difference between ASCII 'a' and ASCII 'A' if you treat them as hexadecimal (hex) numbers? ANS: 20 hex (32 decimal) 3. The ASCII codes for the characters '0' through '9' are what hex numbers? ANS: 30H to 39H 4. If an asynchronous frame is used to send ASCII characters in the form of bytes (8 bits), what is the shortest time it could take to send 1000 characters if each bit in a frame is 1 msec long? ANS: 10 seconds 5. Suppose an asynchronous frame holds 8 bits of data, a parity bit, and two stop bits (it could happen). Calculate the efficiency of the communication system. ANS: 66.7% 6. Suppose a synchronous frame has 16 bits of non-data in the front and a 16-bit BCC at the end. The frame carries 1024 bytes of actual data. Calculate the efficiency of the communication system. ANS: 97.0%

Chapter 10: Local Area Networks MULTIPLE CHOICE 1. CSMA stands for: a. Client-Server Multi-Access b. Carrier Sense Multiple Access

c. Carrier Server Master Application d. none of the above

ANS: B 2. The CD in CSMA/CD stands for: a. Carrier Detection b. Carrier Delay

c. Collision Detection d. Collision Delay

ANS: C 3. The Internet is: a. a network of networks b. a very large client-server network

c. a very large CSMA/CD network d. not really a network at all

ANS: A 4. Most LANs: a. are based on Ethernet b. use CSMA/CD

c. use UTP cable d. all of the above

ANS: D 5. Dumb terminals are still used: a. in token-passing networks b. in networks requiring central monitoring c. in networks that cannot provide central monitoring d. none of the above ANS: B 6. In a circuit-switched network: a. communication is half-duplex only b. each channel carries only one data stream c. connection is usually done using a bus topology d. all of the above ANS: B 7. Each computer on a network is called a: a. hub b. token

c. node d. circuit

ANS: C 8. Compared to CSMA/CD systems, token-passing rings are: a. slower c. not as widely used

b. more expensive

d. all of the above

ANS: D 9. The key feature of a star network is that individual workstations are connected to: a. a central ring c. a node b. a central bus d. none of the above ANS: D 10. On networks, long messages are divided into "chunks" called: a. packets c. carriers b. nodes d. tokens ANS: A 11. When two or more PCs try to access a baseband network cable at the same time, it is called: a. a collision c. excess traffic b. contention d. multiple access ANS: B 12. When two PCs send data over a baseband network cable at the same time, it is called: a. a collision c. excess traffic b. contention d. multiple access ANS: A 13. One type of network that never has a collision is: a. CSMA c. token-passing b. Ethernet d. all networks have collisions ANS: C 14. In an Ethernet-based network, a switch can be used to reduce the number of: a. nodes c. packets b. users d. collisions ANS: D 15. The effect of too many collisions is: a. the network goes down b. the network slows down

c. the cable overheats d. data is lost

ANS: B 16. MAU stands for: a. Multistation Access Unit b. Multiple Access Unit

c. Multiple Auxiliary Units d. none of the above

ANS: A 17. The standard that describes Ethernet-type networks is: a. EIA 232 c. IEEE 802.3

b. IEEE 488.1

d. CCITT ITU-E

ANS: C 18. Ethernet was invented by: a. IBM b. INTEL

c. Xerox d. Digital Equipment Corporation

ANS: C 19. An Ethernet running at 10 Mbits / second uses: a. Manchester encoding c. NRZ encoding b. Three-Level encoding d. AMI encoding ANS: A 20. A 100BaseT cable uses: a. fiber-optic cable b. twisted-pair copper wires

c. RG-58U coaxial cable d. 50-ohm coaxial cable

ANS: B 21. The word "Base" in 10BaseT means: a. the cable carries baseband signals b. the cable has a base speed of 10 Mbps c. it can be used as the base for a backbone cable system d. none of the above ANS: A 22. The reason a CSMA/CD network has a minimum length for packets is: a. to increase the data rate b. to prevent packets from reaching all other nodes during transmission c. to make sure all other nodes hear a collision in progress d. all of the above ANS: C 23. The reason a CSMA/CD network has a maximum length for cables is: a. to increase the data rate b. to prevent packets from reaching all other nodes during transmission c. to make sure all other nodes hear a collision in progress d. all of the above ANS: C 24. NIC stands for: a. Network Interface Card b. Network Interface Cable

c. Network Interface Code d. Network Internal Code

ANS: A 25. 10BaseT cable typically uses: a. a BNC connector

c. an RJ45 connector

b. a T connector

d. an RS11 connector

ANS: C 26. UTP stands for: a. Untwisted-Pair copper wire b. Unshielded Twisted-Pair copper wire

c. Uninterruptible Terminal Packet d. Unicode Text Packet

ANS: B 27. Compared to twisted-pair telephone cables, CAT-5 cables: a. are cheaper c. allow faster bit rates b. are easier to crimp connectors onto d. all of the above ANS: C 28. A hub: a. sends incoming packets out to all other terminals connected to it b. sends incoming packets out to specific ports c. cannot be used in an Ethernet-type network d. are more common in token-passing networks ANS: A 29. A switch: a. sends incoming packets out to all other terminals connected to it b. sends incoming packets out to specific ports c. cannot be used in an Ethernet-type network d. are more common in token-passing networks ANS: B 30. An advantage of using a switch instead of a hub is: a. it is cheaper when used in large networks b. it is faster when used in large networks c. it reduces the number of collisions in large networks d. all of the above ANS: C 31. Broadband LANs: a. modulate the data onto a carrier b. use coaxial cables c. are provided by cable TV companies for Internet access d. all of the above ANS: D 32. Using one node in the network to hold all the application software is done in: a. peer-to-peer networks c. both a and b b. client-server networks d. none of the above ANS: B

33. Record locking is used to: a. store records securely on a server b. prevent multiple users from looking at a document simultaneously c. prevent one user from reading a record that another user is writing to d. none of the above ANS: C 34. The software that runs a client-server network must be: a. UNIX-based c. multitasking b. WINDOWS-based d. Novell certified ANS: C 35. A "thin" client is: a. basically, a PC with no disk drives b. a node that rarely sends data

c. same as a "dumb" terminal d. all of the above

ANS: A COMPLETION 1. A LAN is a

Area Network.

ANS: Local 2. The Internet is a network of

.

ANS: networks 3. In a

network, all nodes are connected to a central computer.

ANS: star 4. In a of communications.

-switched network, users have a dedicated channel for the duration

ANS: circuit 5. The

of a network describes how it is physically connected together.

ANS: topology 6. Ring networks often use

-passing.

ANS: token 7. A ANS: packet

is a short section of a message in digital form.

8.

is when two nodes try to seize the same cable at the same time. ANS: Contention

9. A

occurs when two nodes transmit simultaneously on the same baseband cable.

ANS: collision 10. In CSMA/CD networks, all collisions must be

.

ANS: detected 11. Carrier-Sense means that a node "listens" for the cable to be

before using it.

ANS: quiet free unused available 12. A "

" cable links clusters of computers together.

ANS: backbone 13. 100BaseT cables can reliably carry up to

bits per second.

ANS: 100 mega 14. In CSMA/CD, packets must have a

length to ensure that collisions are detected.

ANS: minimum 15. In CSMA/CD, the

of a cable is limited to ensure that collisions are detected.

ANS: length 16. A unique numerical address is provided to a node by its ANS: NIC 17. A 100BaseTX cable is a

cable.

ANS: fiber-optic 18. Hubs can be

to form, in effect, one big hub.

ANS: stacked 19. A switch looks at the ANS: address

of each incoming packet.

.

20. The effect of a switch is to greatly reduce

.

ANS: contention SHORT ANSWER 1. Explain how a network can be a physical bus but a logical ring. ANS: A token-passing network sends the token from node to node in a prescribed order. So it doesn't matter how the physical connection is made. It still works like a token-passing ring. 2. What is the key difference between a hub and a switch? ANS: A hub sends incoming packets out to all other ports on the hub. A switch sends a packet to a specific port based on the address in the packet. 3. What is the advantage of a CSMA/CD network over a basic star network? ANS: If the central computer in a star network fails, the entire network is inoperative. If a node fails in a CSMA/CD network, it can be disconnected and the network still functions. 4. Why do CSMA/CD packets have a minimum size limit? ANS: If a packet is too short, nodes at either end of a cable could get on, send a packet, and get off before the packets travel far enough to collide. The collision would not be detected. 5. What is a NIC address, and why is it unique? ANS: The address is a long binary number "burned" into a NIC's memory chip at the factory. Each factory uses a different sequence of numbers, so the chances of two NICs on the same network having the same address is extremely small.

Chapter 11: Wide-Area Networks and the Internet MULTIPLE CHOICE 1. MAN stands for: a. Manchester Access Network b. Multiple-Area Network

c. Metropolitan-Area Network d. Multiple Access Network

ANS: C 2. Packet switching is based on: a. store-and-forward b. switched circuits

c. real-time delivery d. all of the above

ANS: A 3. SNA stands for: a. Standard Network Access b. Small Network Access

c. Standard Network Architecture d. Systems Network Architecture

ANS: D 4. The number of layers in ISO OSI is: a. 3 b. 5

c. 7 d. 8

ANS: C 5. The lowest-level layer in ISO OSI is called the: a. physical layer c. cable layer b. link layer d. transport layer ANS: A 6. Bad frames are usually detected by the: a. frame layer b. physical layer

c. error-check layer d. link layer

ANS: D 7. A virtual circuit is set up by the: a. user b. link layer

c. network d. frame

ANS: C 8. Frame Relay: a. is faster than X.25 b. does less error checking than X.25 ANS: D

c. allows for variable length packets d. all of the above

9. ATM stands for: a. Asynchronous Transfer Mode b. Asynchronous Transmission Mode

c. Asynchronous Transmission Model d. Automatic Test Mode

ANS: A 10. A bridge: a. separates a network into "collision domains" b. looks at the address of each packet c. operate at the data-link level d. all of the above ANS: D 11. IP stands for: a. Internet Process b. Internet Protocol

c. Interconnect Protocol d. Interconnect Procedure

ANS: B 12. TCP stands for: a. Transmission Control Process b. Transmission Control Protocol

c. Transfer Connection Protocol d. none of the above

ANS: B 13. Together, TCP/IP consists of: a. 5 layers b. 7 layers

c. an application and a process d. datagrams

ANS: A 14. IP is a: a. connection-oriented protocol b. virtual circuit

c. connectionless protocol d. non-robust protocol

ANS: C 15. The "lifetime" of a packet in an IP network: a. is essentially forever b. depends on elapsed time since transmission c. depends on number of "hops" between nodes d. is approximately 200 milliseconds ANS: C 16. UDP stands for: a. User Datagram Protocol b. User Data Protocol ANS: A 17. HTTP stands for: a. High-speed Transmission Test Procedure

c. User Data Packet d. Universal Data Packet

b. High-Level Transfer Test Procedure c. Hypertext Transmission and Transport Procedure d. Hypertext Transport Protocol ANS: D 18. HTTP allows the use of: a. dumb terminals b. file transport

c. browsers d. none of the above

ANS: C 19. HTML stands for: a. Hypertext Markup Language b. Hypertext Transfer-Mode Level

c. Hypertext Transfer-Mode Layer d. High-speed Transfer-Mode Language

ANS: A 20. HTML allows: a. telneting b. high-speed file transfer

c. web page layout d. all of the above

ANS: C 21. FTP stands for: a. File Transfer Protocol b. File Transport Protocol

c. File Test Procedure d. Fast Transport Packet

ANS: A 22. FTP is used to: a. transfer files between a server on the network and a user b. test files to see if their data has been "corrupted" c. transport packets at maximum speed through the network d. none of the above ANS: A 23. SMTP stands for: a. Short Message Transport Protocol b. Simple Message Transport Protocol

c. Simple Mail Transport Protocol d. Secondary Mail Transfer Procedure

ANS: C 24. ISP stands for: a. Internet Service Protocol b. Internet Service Provider

c. Internet Service Procedure d. none of the above

ANS: B 25. The standard Internet address (or URL) is: a. a 32-bit binary number b. four groups of base-ten numbers

c. running out of available values d. all of the above

ANS: D 26. DNS stands for: a. Domain Name Server b. Domain Name System

c. Domain Numbering System d. Domain Naming System

ANS: A 27. A DNS: a. has become obsolete on the Internet b. translates words to numbers c. stores all domain addresses d. describes the Internet address-naming procedure ANS: B 28. An intranet connected to the Internet is often protected by: a. a DNS c. a "firewall" b. a "brick wall" d. the use of "spoofing" protocols ANS: C 29. OSI stands for: a. Open Systems Interconnection b. Open Standard Interconnection

c. Open Systems Internet d. none of the above

ANS: A COMPLETION 1. A

-Area Network would extend typically across a city.

ANS: Metropolitan 2. A

-Area Network could extend across a nation.

ANS: Wide 3. A dedicated telephone line can be

on a monthly basis.

ANS: leased 4. The use of digital circuit-

lines is cheaper than dedicated lines.

ANS: switched 5. Packet switching is done on a store-and-

network.

ANS: forward 6. A

is a hierarchy of procedures for implementing digital communications.

ANS: protocol 7. Voltage levels on a cable are specified at the

layer.

ANS: physical 8. Bad frames are usually detected at the

layer.

ANS: data-link 9. Setting up a path through the network is done by the

layer.

ANS: network 10. The X.25 protocol was developed by the

.

ANS: CCITT 11. In X.25, the data-link layer is called the

layer.

ANS: frame 12. In X.25, the network layer is called the

layer.

ANS: packet 13. The physical route of a

circuit changes each time it is used.

ANS: virtual 14. Frame Relay requires channels with low

rates.

ANS: bit-error 15. Compared to X.25, Frame Relay does

error checking.

ANS: less 16. All ATM frames contain just

bytes.

ANS: 53 17. Small frame size and a high-speed channel allow

-time communications.

ANS: real 18.

simply regenerate and retransmit packets in a network. ANS: Repeaters

19.

look at the address inside a packet to decide whether or not to retransmit it. ANS: Bridges

20.

decide the best network path on which to forward a packet. ANS: Routers

21. TCP/IP goes back to the

of the 1970s.

ANS: ARPANET DARPANET 22. Between ISO OSI and TCP/IP,

was used first.

ANS: TCP/IP 23. A

protocol does not track packets after they are sent.

ANS: connectionless 24. HTTP allows the use of

that jump to other pages on the web.

ANS: hyperlinks 25. The Internet "backbone" mostly uses high-speed

cables.

ANS: fiber-optic 26. A

translates words in an Internet address to numbers.

ANS: DNS 27. Intranets usually connect to the Internet through a

for security.

ANS: firewall 28. Voice over

is telephony done over the Internet.

ANS: IP 29. "

" is another term for real-time transmission over the Internet.

ANS: Streaming 30. Most people gain access to the Internet by subscribing to an ANS: ISP

.

SHORT ANSWER 1. Name the three parts of an IP address as used on the Internet. ANS: Network number, Subnet number, Host number 2. Why is a logical channel called a "virtual" circuit? ANS: A logical channel is a way of keeping track of which two nodes on the network have messages for each other. The actual physical path can change while packets are being sent. Virtual means it behaves like direct circuit between 'A' and 'B', but it is not a direct circuit. 3. Why is it faster to send packets of a fixed size compared to packets of variable size? ANS: The processing required to store and forward packets of different lengths is greater than that required for packets of a fixed length. More processing implies more time per packet, which implies fewer packets per second through the network. 4. Why are the tasks involved in digital communications divided into layers in a protocol stack? Why not just have one layer that does it all? ANS: Divide and conquer: it reduces complexity to a manageable job. One big layer could not be adapted to newer media etc as easily as a system of independent layers. Think of subroutines in a computer program. 5. What is a "hop"? ANS: Every time a packet is forwarded on to the next store-and-forward node in the network, it is considered to be one "hop". 6. What does it mean to say a packet has a lifetime measured in hops? ANS: Each packet contains a number representing the maximum number of allowed hops. At each hop, this number is reduced by one. When it gets to zero, the packet is deleted from the network. 7. Why should packets have a lifetime? ANS: If they didn't, then the number of "lost" packets traveling around the network would continuously increase. At some point, there would be no bandwidth left to carry real traffic.

Chapter 12: Digital Modulation and Modems MULTIPLE CHOICE 1. FSK stands for: a. Full-Shift Keying b. Frequency-Shift Keying

c. Full-Signal Keying d. none of the above

ANS: B 2. PSK stands for: a. Pulse-Signal Keying b. Pulse-Shift Keying

c. Phase-Signal Keying d. Phase-Shift Keying

ANS: D 3. QAM stands for: a. Quadrature Amplitude Modulation b. Quadrature Amplitude Masking

c. Quadrature Amplitude Marking d. none of the above

ANS: A 4. In the equation I = ktB, I is measured in: a. amperes b. amperes per second

c. bits d. bits per second

ANS: C 5. In the equation C = 2Blog2M, M is the: a. margin of noise b. modulation index

c. number of possible states per symbol d. maximum number of symbols per second

ANS: C 6. An "eye pattern" shows a good channel when: a. the eye is maximally open c. the eye is half open b. the eye is maximally closed d. the eye alternately opens and closes ANS: A 7. What you see in an eye pattern is the effect of: a. too many bits high c. intermodulation distortion b. too many bits low d. intersymbol interference ANS: D 8. High-frequency radioteletype systems commonly use: a. FSK c. PSK b. AFSK d. QAM ANS: A

9. Instead of a single bit, a QPSK symbol contains: a. a byte c. a dibit b. 4 bits d. a Q-bit ANS: C 10. To reduce the need for linearity, π/4 DQPSK uses: a. angles of 0, 90, 180, and 270 degrees c. angles of π/4, 2π/4, 3π/4, and 4π/4 b. angles of 45, 135, 225, and 315 degrees d. double phase-shift angles ANS: B 11. For QAM, a "constellation diagram" shows: a. location of symbols in "symbol space" b. separation of symbols in "symbol space"

c. effects of noise on symbols d. all of the above

ANS: D 12. For QAM, the two dimensions of its symbol space are: a. amplitude and frequency c. frequency and phase angle b. amplitude and phase angle d. I-bits and Q-bits ANS: B 13. The specs of the old Bell type 103 modem were: a. 300 bps, full-duplex, FSK c. 1200 bps, full-duplex, FSK b. 600 bps, full-duplex, FSK d. 1200 bps, half-duplex, FSK ANS: A 14. ITU is an abbreviation for: a. International Telephony Unit b. International Telephony Union

c. International Telecommunications Union d. International Telecommunications Units

ANS: C 15. The ITU is under the auspices of: a. CCITT b. the U.N.

c. IEEE d. ANSI

ANS: B 16. High-speed modems equalize the line to compensate for: a. noise and interference b. uneven phase and frequency response c. low SNR d. inconsistent bit rates at either end of channel ANS: B 17. The bits sent to allow equalization are called: a. Gaussian bits b. random bits

c. a training sequence d. a random sequence

ANS: C 18. The V.90 standard is issued by: a. the EIA b. the TIA

c. the ITU d. the ISO

ANS: C 19. MNP2, MNP3, MNP4, and MNP10 are all: a. data-compression schemes b. error-correction protocols

c. both a and b d. none of the above

ANS: B 20. MNP5 and V.42 bis are both: a. data-compression schemes b. error-correction protocols

c. both a and b d. none of the above

ANS: A 21. In RS-232, flow control is done using: a. RTS/CTS handshake b. XON/XOFF characters

c. both a and b d. none of the above

ANS: C 22. The official name for RS-232C is: a. RS-232C b. EIA-232D

c. ISO-232C/D d. ANSI-232C

ANS: B 23. In RS-232, a modem would be: a. a DTR b. a DSR

c. a DCE d. a DTE

ANS: C 24. In RS-232, a personal computer would be: a. a DTR b. a DSR

c. a DCE d. a DTE

ANS: D 25. On a DB-9 RS-232 connector, signal ground is pin: a. 1 c. 5 b. 3 d. 7 ANS: C 26. On a DB-25 RS-232 connector, signal ground is pin: a. 1 c. 5 b. 3 d. 7

ANS: D 27. The minimum lines required for RS-232 are: a. TD and RD b. TD, RD, and signal ground

c. TD, RD, DSR, and signal ground d. TD, RD, RTS, CTS, and signal ground

ANS: B 28. Hardware flow control uses: a. XON and XOFF b. TD and RD

c. RTS and CTS d. DSR and DCD

ANS: C 29. Software flow control uses: a. XON and XOFF b. TD and RD

c. RTS and CTS d. DSR and DCD

ANS: A 30. Which voltage represents a binary zero on an RS-232 data pin: a. +15 volts c. +9 volts b. +12 volts d. all of the above ANS: D 31. DSL stands for: a. Data Signal Line b. Digital Signal Line

c. Digital Subscriber Line d. Double-Speed Loop

ANS: C 32. ADSL stands for: a. Asynchronous DSL b. Asymmetrical DSL

c. Analog DSL d. All DSL

ANS: B 33. In a CATV system, HFC stands for: a. Head Frequency Control b. Hybrid Frequency Control

c. Hybrid Fiber-Coax d. Hybrid Fiber Control

ANS: C 34. In a CATV system, CMTS stands for: a. Cable Modem Terminal Server b. Cable Modem Transmission System

c. Cable Modem Terminal System d. Cable Modem Transmission Server

ANS: A 35. A "splitter" at the subscriber end is not required for: a. Any DSL scheme c. ADSL Lite b. ADSL d. none of the above

ANS: C COMPLETION 1. RTS means Request To

.

ANS: Send 2. The response to RTS is

.

ANS: CTS 3. FSK stands for Frequency-Shift

.

ANS: Keying 4. DSR stands for

Set Ready.

ANS: Data 5. QAM stands for

Amplitude Modulation.

ANS: Quadrature 6. The number of symbols per second is called the

rate.

ANS: baud 7. The 2 bits of information in a QPSK symbol is called a

.

ANS: dibit 8. QPSK uses

different phase angles.

ANS: four 9. DPSK stands for

PSK.

ANS: Delta 10. The QAM amplitude-phase combinations are shown with a

diagram.

ANS: constellation 11. ITU stands for International

Union.

ANS: Telecommunications 12. In QAM modems, line.

coding adds extra bits to improve performance on a noisy

ANS: Trellis 13.

is used in a high-speed modem to compensate for uneven frequency and phase response on a line. ANS: Equalization

14. The maximum allowed speed for a modem on a dial-up line is about

bps.

ANS: 54k 15. The nominal maximum speed on an RS-232 cable is

bps.

ANS: 20k 16. In RS-232, the being received.

line is asserted when the analog carrier from another modem is

ANS: CD DCD RLSD 17. Between hardware flow control and software flow control, preferred.

flow control is

ANS: hardware 18. A voltage higher than

volts should be considered a high on an RS-232 receiver.

ANS: 3 19. A

modem cable is used to connect two DTEs via their serial ports.

ANS: null 20. ADSL stands for

DSL.

ANS: Asymmetrical 21. A typical CATV system is organized as a

network.

ANS: tree 22. In a CATV system using cable modems, a onto a fiber-optic backbone.

is used to put several channels of data

ANS: CMTS 23.

is the process of synchronizing transmitted data from cable modems to a CMTS.

ANS: Ranging 24.

systems send high-speed data over a POTS line while sharing the line with dialup service. ANS: ADSL

25. The

version of ADSL does not require a splitter at the subscriber end.

ANS: lite 26.

modulation divides the line bandwidth into many narrow bands called tones or bins for ADSL. ANS: DMT

27. A DSLAM is a DSL Access

.

ANS: Multiplexer SHORT ANSWER 1. Calculate the bits per second capacity of a system sending 1000 symbols per second with 16 possible states per symbol. ANS: 4000 2. How many points will be on the constellation diagram of a QAM system using 8 phase angles and 2 amplitude levels? ANS: 16 3. A CATV system has 100 cable-modem customers sharing a single channel with a data rate of 36 Mbps. If half the modems are active at any given time, what bit rate can a customer expect? ANS: 720 kbps 4. A DMT system uses 4.3-kHz bins on a 1-MHz cable. Approximately how many bins are there? ANS: 230 5. Assuming a maximum symbol rate of 400 per second, how many possible states must a symbol have to achieve a data rate of 1200 bps? ANS:

8

Chapter 13: Multiplexing and Multiple-Access Techniques MULTIPLE CHOICE 1. TDMA stands for: a. Time Domain Multiple Access b. Time-Division Multiple Access

c. Tone Division Multiple Access d. none of the above

ANS: B 2. CDMA stands for: a. Code-Division Multiple Access b. Carrier Division Multiple Access

c. Compact Digital Multiplex Arrangement d. none of the above

ANS: A 3. TDMA is used instead of TDM when: a. all the signals come from the same source b. the signals come from different sources c. TDM is used in RF communications d. they mean the same thing ANS: B 4. When calculating the maximum number of users, a limiting factor in FDM is: a. the type of media used c. the bandwidth of each signal b. the length of the channel d. all of the above ANS: C 5. A DS-1 signal contains: a. 12 channels b. 24 channels

c. 32 channels d. 64 channels

ANS: B 6. The bit-rate of a DS-1 signal over a T-1 line is: a. 64 kbps c. 1.536 Mbps b. 256 kbps d. 1.544 Mbps ANS: D 7. Besides data bits, a DS-1 frame contains a: a. timing bit b. T-bit

c. signaling bit d. framing bit

ANS: D 8. In DS-1, a bit is "stolen" out of each channel: a. every frame b. every other frame

c. every sixth frame d. every twelfth frame

ANS: C 9. Moving signals from one line to another is called: a. time switching c. line switching b. space switching d. cross-point switching ANS: B 10. Moving PCM samples from one time-slot to another is called: a. time switching c. signal switching b. space switching d. crosspoint switching ANS: A 11. A digital space switch is a: a. multiplexer b. TDM switch

c. computerized Strowger switch d. crosspoint switch

ANS: D 12. Spread-spectrum can be done by using: a. computer-controlled frequency reuse b. frequency-hopping

c. direct-sequence method d. all of the above

ANS: D 13. The term "chip rate" is used in describing: a. computer-controlled frequency reuse b. frequency-hopping

c. direct-sequence method d. all of the above

ANS: C 14. For a given data rate, direct-sequence systems, compared to standard RF systems, use: a. about the same bandwidth c. much less bandwidth b. much more bandwidth d. approximately double the bandwidth ANS: B 15. "Processing gain" is another term for: a. RF gain b. computer speed

c. spreading gain d. improved signal-to-noise ratio

ANS: C 16. To calculate processing gain, divide the transmitted RF bandwidth by: a. the digital data bit rate c. the S/N ratio b. bandwidth of original baseband d. the chip size ANS: B 17. A receiver for frequency-hopping spread-spectrum would be: a. a narrowband receiver c. a direct-conversion receiver b. a wideband receiver d. a CDMA receiver

ANS: A 18. A receiver for direct-sequence spread-spectrum would be: a. a narrowband receiver c. a direct-conversion receiver b. a wideband receiver d. a "chip-rate" receiver ANS: B 19. CDMA: a. cannot be used with frequency-hopping spread-spectrum b. cannot be used with direct-sequence spread-spectrum c. cannot be used on an RF channel d. allows many transmitters to use a band simultaneously ANS: D 20. For optimal performance, CDMA requires the use of: a. orthogonal PN sequences c. true-random PN sequences b. non-orthogonal PN sequences d. none of the above ANS: A COMPLETION 1. Multiplexing allows many signals to

a channel.

ANS: share 2. Three methods of multiple access are FDMA, TDMA, and

.

ANS: CDMA 3. In FDM, each signal uses part of the bandwidth

of the time.

ANS: all 4. In TDM, each signal uses all of the bandwidth

of the time.

ANS: part 5. Using CDMA on a radio channel, all signals can transmit

of the time.

ANS: all 6. DS-1 is an example of

-division multiplexing.

ANS: time 7. The AM radio band is an example of ANS: frequency

-division multiplexing.

8. A DS-1 frame contains one sample from each of

channels.

ANS: 24 9. T1 uses the

line code.

ANS: AMI 10. Each DS-1 frame contains a total of

bits.

ANS: 193 11. A DS-1 frame is transmitted at a rate of

bits per second.

ANS: 1.544 Meg 12. Each sample in a DS-1 frame contains

bits.

ANS: 8 13. A group of twelve DS-1 frames is called a

.

ANS: superframe 14. Switching signals from one line to another is called

switching.

ANS: space 15. Moving PCM samples from one time slot to another is called

switching.

ANS: time 16. The deep fades caused by signal-cancellation due to reflection are called ANS: Rayleigh 17. A PN sequence is a

-random noise sequence.

ANS: pseudo 18. One method of spread-spectrum is frequency

.

ANS: hopping 19. It is

to jam a spread-spectrum signal.

ANS: difficult 20. It is

to eavesdrop on a spread-spectrum signal.

fading.

ANS: difficult 21. The extra bits added to the data in direct-sequence spread-spectrum are called

.

ANS: chips 22. A chipping-rate of at least

times the bit rate of the data is common.

ANS: ten 23. The 'C' in CDMA stands for

.

ANS: code 24. In a frequency-hopping CDMA system, when no two transmitters use the same frequency at the same time the PN sequences are said to be . ANS: orthogonal SHORT ANSWER 1. What does Hartley's Law tell us about the relationship between time and bandwidth for digital transmission? ANS: The more bandwidth, the less time it takes to send a given amount of information. So the more bandwidth available, the higher the possible bit rate. 2. How many signals could fit into 1 MHz of bandwidth if each signal required 100 kHz of bandwidth and the separation between adjacent channels was 10 kHz? ANS: 9 3. Why is it difficult to jam a spread-spectrum signal? ANS: Jamming requires an interference signal of sufficient power in the same part of the spectrum the information signal occupies. Because a spread-spectrum signal is, by definition, spread out over a very wide bandwidth, jamming can interfere with only a small fraction of the total signal. 4. Why is it difficult to eavesdrop on a spread-spectrum signal? ANS: In a spread-spectrum transmission, the signal power at any given frequency in its band is so low that it is virtually indistinguishable from noise. An eavesdropper would not know a signal was being sent. And without knowing the exact sequence being used, it is virtually impossible to "de-spread" the signal. 5. Why is autocorrelation used to receive direct-sequence spread-spectrum signals?

ANS: Autocorrelation allows a signal to be "pulled out of" the noise even when the signal-to-noise ratio is less than one, as it is in spread-spectrum. 6. What is meant by "orthogonal sequences" in CDMA? ANS: During transmission, the PN sequences determine which parts of the available bandwidth the spreadspectrum signal will occupy. Assume you have two PN sequences: PN1 and PN2. At some point in time, suppose PN1 would cause a transmission to occupy frequencies f11, f12, f13, and so forth. Now suppose PN2 would cause the transmission to occupy frequencies f21, f22, f23, and so forth. If the two sets of frequencies, (f11, f12, f13, ...) and (f21, f22, f23, ...), have no frequencies in common, then the two PN sequences are said to be orthogonal.

Chapter 14: Transmission Lines MULTIPLE CHOICE 1. SWR stands for: a. Shorted Wave Radiation b. Sine Wave Response

c. Shorted Wire Region d. none of the above

ANS: D 2. TDR stands for: a. Total Distance of Reflection b. Time-Domain Reflectometer

c. Time-Domain Response d. Transmission Delay Ratio

ANS: B 3. An example of an unbalanced line is: a. a coaxial cable b. 300-ohm twin-lead TV cable

c. an open-wire-line cable d. all of the above

ANS: A 4. When analyzing a transmission line, its inductance and capacitance are considered to be: a. lumped c. equal reactances b. distributed d. ideal elements ANS: B 5. As frequency increases, the resistance of a wire: a. increases c. stays the same b. decreases d. changes periodically ANS: A 6. The effect of frequency on the resistance of a wire is called: 2 a. I R loss c. the skin effect b. the Ohmic effect d. there is no such effect ANS: C 7. As frequency increases, the loss in a cable's dielectric: a. increases c. stays the same b. decreases d. there is no loss in a dielectric ANS: A 8. The characteristic impedance of a cable depends on: a. the resistance per foot of the wire used b. the resistance per foot and the inductance per foot c. the resistance per foot and the capacitance per foot d. the inductance per foot and the capacitance per foot

ANS: D 9. For best matching, the load on a cable should be: a. lower than Z0 c. equal to Z0 b. higher than Z0 d. 50 ohms ANS: C 10. The characteristic impedance of a cable: a. increases with length b. increases with frequency

c. increases with voltage d. none of the above

ANS: D 11. The velocity factor of a cable depends mostly on: a. the wire resistance c. the inductance per foot b. the dielectric constant d. all of the above ANS: B 12. A positive voltage pulse sent down a transmission line terminated in a short-circuit: a. would reflect as a positive pulse b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all ANS: B 13. A positive voltage pulse sent down a transmission line terminated with its characteristic impedance: a. would reflect as a positive pulse b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all ANS: D 14. A positive voltage-pulse sent down a transmission line terminated in an open-circuit: a. would reflect as a positive pulse b. would reflect as a negative pulse c. would reflect as a positive pulse followed by a negative pulse d. would not reflect at all ANS: A 15. The optimum value for SWR is: a. zero b. one

c. as large as possible d. there is no optimum value

ANS: B 16. A non-optimum value for SWR will cause: a. standing waves b. loss of power to load

c. higher voltage peaks on cable d. all of the above

ANS: D 17. VSWR stands for: a. variable SWR b. vacuum SWR

c. voltage SWR d. none of the above

ANS: C 18. The impedance "looking into" a matched line: a. is infinite c. is the characteristic impedance b. is zero d. 50 ohms ANS: C 19. A Smith Chart is used to calculate: a. transmission line impedances b. propagation velocity

c. optimum length of a transmission line d. transmission line losses

ANS: A 20. Compared to a 300-ohm line, the loss of a 50-ohm cable carrying the same power: a. would be less c. would be the same b. would be more d. cannot be compared ANS: B 21. A balanced load can be connected to an unbalanced cable: a. directly c. by using a "balun" b. by using a filter d. cannot be connected ANS: C 22. On a Smith Chart, you "normalize" the impedance by: a. assuming it to be zero c. multiplying it by it by Z0 b. dividing it by 2π d. dividing 2π ANS: D 23. The radius of the circle you draw on a Smith Chart represents: a. the voltage c. the impedance b. the current d. none of the above ANS: D 24. The center of the Smith Chart always represents: a. zero c. the characteristic impedance b. one d. none of the above ANS: C 25. A TDR is commonly used to: a. measure the characteristic impedance of a cable b. find the position of a defect in a cable

c. replace a slotted-line d. all of the above ANS: B COMPLETION 1. A cable that lacks symmetry with respect to ground is called

.

ANS: unbalanced 2. Parallel lines are usually operated as respect to ground.

lines since both wires are symmetrical with

ANS: balanced 3. Normally, a transmission line is terminated with a load equal to its

impedance.

ANS: characteristic 4. Twisted-pair cables are transmission lines for relatively

frequencies.

ANS: low 5. To analyze a transmission line, it is necessary to use lumped ones.

parameters instead of

ANS: distributed 6. The increase of a wire's resistance with frequency is called the

effect.

ANS: skin 7. The increase of a wire's resistance with frequency is caused by the the wire.

field inside

ANS: magnetic 8. Dielectrics become more

as the frequency increases.

ANS: lossy 9. The inductance and capacitance of a cable are given per unit

.

ANS: length 10. Characteristic impedance is sometimes called ANS: surge

impedance.

11. A cable that is terminated in its characteristic impedance is called a

line.

ANS: matched 12. A pulse sent down a cable terminated in a short-circuit will reflect with the polarity. ANS: opposite 13. The apparently stationary pattern of waves on a mismatched cable is called a wave. ANS: standing 14. SWR stands for

-wave ratio.

ANS: standing 15. The ideal value for SWR is

.

ANS: one 16. Transmission line impedances can be found using a

chart.

ANS: Smith 17. Short transmission-line sections called

can be used as capacitors or inductors.

ANS: stubs 18. Any cable that radiates energy can also

energy.

ANS: absorb 19. A

-dB loss in a cable means only half the power sent reaches the load.

ANS: 3 20. It is often best to measure SWR at the

end of a cable.

ANS: load 2

21. Besides heat from I R, the power a cable can carry is limited by the its dielectric.

voltage of

ANS: breakdown 22. To normalize an impedance on a Smith Chart, you divide it by ANS: Z0

.

23. The

of a Smith Chart always represents the characteristic impedance.

ANS: center 24. A

wavelength transmission line can be used a transformer.

ANS: one-quarter 25. A slotted line is used to make measurements in the

domain.

ANS: frequency SHORT ANSWER 1. A transmission line has 2.5 pF of capacitance per foot and 100 nH of inductance per foot. Calculate its characteristic impedance. ANS: Z0 = 200 ohms 2. Two wires with air as a dielectric are one inch apart. The diameter of the wire is .04 inch. Calculate, approximately, its characteristic impedance. ANS: 386 ohms 3. If a coaxial cable uses plastic insulation with a dielectric constant ∈r = 2.6 , what is the velocity factor for the cable? ANS: 0.62 4. If a cable has a velocity factor of 0.8, how long would it take a signal to travel 3000 kilometers along the cable? ANS: 12.5 ms 5. If a cable has a velocity factor of 0.8, what length of cable is required for a 90° phase shift at 100 MHz? ANS: 0.6 meters 6. A cable has a VSWR of 10. If the minimum voltage along the cable is 20 volts, what is the maximum voltage along the cable? ANS: 200 volts

7. A lossless line has a characteristic impedance of 50 ohms, but is terminated with a 75-ohm resistive load. What SWR do you expect to measure? ANS: 1.5 8. If a cable has an SWR of 1.5, what will be the absolute value of its voltage coefficient of reflection? ANS: 0.2 9. A generator matched to a line with a voltage coefficient of reflection equal to 0.2 transmits 100 watts into the line. How much power is actually absorbed by the load? ANS: 96 watts 10. Using a Smith Chart to analyze a 50-ohm cable, what would be the normalized value of an impedance equal to 200 + j50 ohms? ANS: 4 + j1

Chapter 15: Radio-Wave Propagation MULTIPLE CHOICE 1. Radio waves were first predicted mathematically by: a. Armstrong c. Maxwell b. Hertz d. Marconi ANS: C 2. Radio waves were first demonstrated experimentally by: a. Armstrong c. Maxwell b. Hertz d. Marconi ANS: B 3. The technology that made cell phones practical was: a. the microprocessor chip c. high-power microwave transmitters b. the miniature cell-site d. all of the above ANS: A 4. Cell phones reduce much of the problems of mobile communications with: a. high power levels c. reuse of frequencies b. high antennas d. all of the above ANS: C 5. Which of the following are electromagnetic: a. radio waves b. light

c. gamma waves d. all of the above

ANS: D 6. The electric and magnetic fields of a radio wave are: a. perpendicular to each other c. both a and b b. perpendicular to the direction of travel d. none of the above ANS: C 7. TEM stands for: a. Transverse Electromagnetic b. Transmitted Electromagnetic

c. True Electromagnetic d. none of the above

ANS: A 8. In free space, radio waves travel at a speed of: a. 3 × 106 meters per second c. 3 × 106 miles per second 6 d. 300 × 106 miles per second b. 300 × 10 meters per second ANS: B

9. Which is a possible polarization for an electromagnetic wave: a. vertical c. circular b. horizontal d. all of the above ANS: D 10. Which polarization can be reasonably well received by a circularly polarized antenna: a. vertical c. circular b. horizontal d. all of the above ANS: D 11. The number of circular polarization modes (directions) is: a. 1 c. 3 b. 2 d. many ANS: B 12. An antenna has "gain" as compared to: a. an isotropic radiator b. a vertically polarized radiator

c. a ground-wave antenna d. none of the above

ANS: A 13. EIRP stands for: a. the E and I fields of the Radiated Power b. the Effective Isotropic Radiated Power c. the Effective Internal Reflected Power d. the Electric-field Intensity of the Radiated Power ANS: B 14. The "attenuation of free space" is due to: a. losses in the characteristic impedance of free space b. losses due to absorption in the upper atmosphere c. the decrease in energy per square meter due to expansion of the wavefront d. the decrease in energy per square meter due to absorption of the wavefront ANS: C 15. Ground waves are most effective: a. below about 2 MHz b. above about 20 MHz

c. at microwave frequencies d. when using horizontally polarized waves

ANS: A 16. Radio waves would most strongly reflect off: a. a flat insulating surface of the right size b. a flat dielectric surface of the right size

c. a flat metallic surface of the right size d. a flat body of water

ANS: C 17. Radio waves sometimes "bend" around a corner because of: a. reflection c. refraction

b. diffusion

d. diffraction

ANS: D 18. Space waves are: a. line-of-sight b. reflected off the ionosphere c. same as sky waves d. radio waves used for satellite communications ANS: A 19. Sky waves: a. are line-of-sight b. "bounce" off the ionosphere c. are same as space waves d. are radio waves used for satellite communications ANS: B 20. Sky waves cannot be "heard": a. close to the transmitter b. far from the transmitter

c. in the "silent" zone d. in the "skip" zone

ANS: D 21. A 20-dB reduction in the strength of a radio wave due to reflection is called: a. fading c. frequency diversity b. diffraction d. spatial diversity ANS: A 22. "Ghosts" on a TV screen are an example of: a. fading b. diffraction

c. multipath distortion d. cancellation due to reflection

ANS: C 23. A "repeater" is used to: a. send a message multiple times over a channel b. send a message over multiple channels at the same time c. extend the range of a radio communications system d. cancel the effects of fading ANS: C 24. Cellular phone systems rely on: a. high power b. repeaters

c. the radio horizon d. the reuse of frequencies

ANS: D 25. If the number of cell-phone users within a cell increases above some limit: a. the cell area is increased c. the power levels are increased

b. the cell area is split

d. the number of channels is reduced

ANS: B 26. As a cell-phone user passes from one cell to another: a. a "handoff" process occurs c. both cells will handle the call b. a "sectoring" process occurs d. nothing occurs ANS: A 27. To receive several data streams at once, a CDMA spread-spectrum system uses: a. a "funnel" receiver c. multiple receivers b. a "rake" receiver d. none of the above ANS: B 28. The troposphere is the: a. highest layer of the atmosphere b. middle layer of the atmosphere

c. lowest layer of the atmosphere d. the most ionized layer of the atmosphere

ANS: C 29. Meteor-trail propagation is: a. used for radio telephony b. used to send data by radio

c. also called "ducting" d. not possible

ANS: B COMPLETION 1. Radio waves were mathematically predicted by

.

ANS: Maxwell 2. Radio waves were first demonstrated by

.

ANS: Hertz 3. Radio waves are

electromagnetic waves.

ANS: transverse 4. The propagation speed of radio waves in free space is

m/sec.

6

ANS: 300 × 10

5. Electromagnetic radiation can be thought of as a stream of particles called

.

ANS: photons 6. Unlike sound or water waves, radio waves do not need a

to travel through.

ANS: medium 7. The dielectric strength of clean dry air is about

volts per meter.

6

ANS: 3 × 10

8. Waves from an

source radiate equally in all directions.

ANS: isotropic 9. The wavefront of a point source would have the shape of a

.

ANS: sphere 10. At a far distance from the source, a radio wavefront looks like a flat

-wave.

ANS: plane 11. The polarization of a radio wave is the direction of its

field.

ANS: electric 12. The electric field of a radio wave is

to its magnetic field.

ANS: perpendicular 13. Both the electric and magnetic fields of a radio wave are direction.

to its propagation

ANS: perpendicular 14. With travels through space.

polarization, the direction of a radio wave's electric field rotates as it

ANS: circular 15. An antenna is said to have direction than in other directions.

in a certain direction if it radiates more power in that

ANS: gain 16. The watts per square meter of a radio wave space.

as the wave-front moves through

ANS: decrease 17. Reflection of plane-waves from a smooth surface is called ANS: specular

reflection.

18.

is the "bending" of radio waves as they travel across the boundary between two different dielectrics. ANS: Refraction

19. The process of

makes radio waves appear to "bend around a corner".

ANS: diffraction 20.

waves travel from transmitter to receiver in a "line-of-sight" fashion. ANS: Space

21.

waves are vertically polarized radio waves that travel along the earth's surface. ANS: Ground

22.

waves are radio waves that "bounce off" the ionosphere due to refraction. ANS: Sky

23. The

zone is a region where sky waves cannot be received.

ANS: skip 24. "Ghosts" on a TV screen are an example of

distortion.

ANS: multipath 25. The "fast fading" seen in mobile communications is caused by with direct waves.

waves interfering

ANS: reflected 26. Cell phones typically operate at a

power level.

ANS: low 27. The

of frequencies allows many cell-phone users to share a geographical area.

ANS: reuse 28.

is when a cell-site uses three directional antennas, each covering a third of the cell area, to reduce interference. ANS: Sectoring

29. The use of ANS: microprocessor

chips makes cell phones a practical technology.

SHORT ANSWER –10

1. A certain dielectric has permittivity of 6.3 × 10 the characteristic impedance of that dielectric?

F/m and the same permeability as free space. What is

ANS: 45 ohms 2. If a point source of radio waves transmits 1 watt, what is the power density 10,000 meters from the source? ANS: 2 796 pW/m 3. What power must a point-source of radio waves transmit so that the power density at 3000 meters from 2 the source is 1 µW/m ? ANS: 113 watts 2

4. If a radio receiver needs 1 nW/m of power density to function, how far away from a 1-watt point source will it continue to work? ANS: 8.9 km 5. A line-of-sight radio link over flat terrain needs to use antenna towers 50 km apart. What, approximately, is the minimum height for the towers assuming all the towers are the same? ANS: 37 meters 6. A mobile radio is being used at 1 GHz in an urban environment with lots of reflecting structures. If the car is traveling 36 km/hour, what is the expected time between fades? ANS: 15 msec

Chapter 16: Antenna

MULTIPLE CHOICE 1. The real part of an antenna's input impedance is due to: a. the radiated signal c. the SWR b. the reflected signal d. all of the above ANS: A 2. A half-wave dipole is sometimes called: a. a Marconi antenna b. a Hertz antenna

c. a Yagi antenna d. none of the above

ANS: B 3. The end-to-end length of a half-wave dipole antenna is actually: a. one wavelength c. slightly longer than a half-wavelength b. one half-wavelength d. slightly shorter than a half-wavelength ANS: D 4. The radiation of energy from an antenna can be seen in the: a. standing wave pattern around the antenna c. radiation resistance of the antenna 2 b. SWR along the feed cable d. I R loss of the antenna ANS: C 5. Measured on the ground, the field strength of a horizontally polarized half-wave dipole antenna is strongest: a. in one direction c. in all directions b. in two directions d. depends on the number of elements ANS: B 6. The ability of an antenna to radiate more energy in one direction than in other directions is called: a. directivity c. active antenna b. selectivity d. resonance ANS: A 7. The front-to-back ratio of a half-wave dipole antenna is: a. 0 dB c. 10 dB b. 3 dB d. infinite ANS: A 8. An antenna's beamwidth is measured: a. from +90° to –90° b. from front to back

c. between half-power points d. between the minor side-lobes

ANS: C 9. ERP stands for: a. Equivalent Radiation Pattern b. Effective Radiation Pattern

c. Equivalent Radiated Power d. Effective Radiated Power

ANS: D 10. "Ground Effects" refers to the effects on an antenna's radiation pattern caused by: a. radio signals reflecting off the ground b. buildings and other structures on the ground c. fading d. faulty connection of the feed cable ground ANS: A 11. A 1-MHz monopole antenna must be: a. mounted vertically b. mounted horizontally

c. at least one half-wavelength long d. at least one wavelength long

ANS: A 12. The typical antenna in an AM radio is a: a. dipole b. folded dipole

c. ferrite "loop-stick" d. none of the above

ANS: C 13. The polarization of plane waves received from a satellite is changed by: a. gamma rays c. helical rotation b. Faraday Rotation d. the distance traveled ANS: B 14. A nonresonant antenna: a. will not transmit b. will not receive

c. will cause SWR on the feed cable d. all of the above

ANS: C 15. At resonance, the input impedance to a lossless antenna should be: a. resistive c. capacitive b. inductive d. infinite ANS: A 16. An antenna can be matched to a feed line using: a. a shorted stub c. an LC network b. a loading coil d. all of the above ANS: D 17. As the length of a "long-wire" antenna is increased: a. the number of lobes increases c. efficiency decreases

b. the number of nodes decreases

d. none of the above

ANS: A 18. Arrays can be: a. phased b. driven

c. parasitic d. all of the above

ANS: D 19. An array with one driven element, a reflector, and one or more directors is called a: a. Marconi c. Log-Periodic Dipole b. Yagi d. stacked array ANS: B 20. LPDA stands for: a. Low-Power Dipole Array b. Low-Power Directed Array

c. Log-Periodic Dipole Array d. Log Power Dipole Array

ANS: C 21. The radiated beam from a parabolic "dish" transmitting antenna is: a. collimated c. dispersed b. phased d. none of the above ANS: A 22. The energy picked up by a parabolic antenna is concentrated at the: a. center c. focus b. edges d. horn ANS: C 23. Antennas are often tested in: a. an echo chamber b. an anechoic chamber

c. a vacuum chamber d. an RF reflective chamber

ANS: B 24. Field strength at a distance from an antenna is measured with: a. a slotted line c. an EIRP meter b. a dipole d. a field-strength meter ANS: D COMPLETION 1. An antenna is the interface between the transmission line and

.

ANS: space 2. Hertz antenna is another name for a half-wave

.

ANS: dipole 3. The length of a half-wave dipole is about

% of a half-wave in free space.

ANS: 95 4. The resistance is the portion of an antenna's input impedance due to transmitted radio waves leaving the antenna. ANS: radiation 5. Input impedance at the center feed point of a resonant half-wave dipole is about Ω. ANS: 70 6. Input impedance at the center feed point of a resonant folded dipole is about

Ω.

ANS: 280 – 300 7. The vertical angle of radiation is called the angle of

.

ANS: elevation 8. Antenna radiation patterns are typically drawn on graphs with

coordinates.

ANS: polar 9. As compared to a

source, a half-wave dipole has a gain of about 2 dBi.

ANS: point isotropic 10. Antenna gain measured in

is with reference to a half-wave dipole.

ANS: dBd 11.

is the same as the gain for a lossless antenna. ANS: Directivity

12. The front-to-back ratio of a half-wave dipole is

dB.

ANS: 0 13. The ANS: beamwidth

of a directional antenna is the angle between its half-power points.

14. ERP stands for

radiated power.

ANS: effective 15. ERP is the power input to the antenna multiplied by the antenna's

.

ANS: gain 16. A

is required to connect a coaxial cable to a center-fed dipole antenna.

ANS: balun 17. A horizontally mounted dipole will radiate waves with

polarization.

ANS: horizontal 18. A folded dipole has

bandwidth than a standard dipole.

ANS: wider greater more 19. A monopole antenna is typically mounted in the

direction.

ANS: vertical 20. The length of a typical monopole antenna is

wavelength.

ANS: one-quarter 1/4 21. A monopole antenna mounted high on a tower typically uses a

plane.

ANS: ground 22. A vertical antenna has an

radiation pattern for ground-based receivers.

ANS: omnidirectional 23. The number of driven elements in a Yagi antenna is typically

.

ANS: one 24. The reflector on a Yagi antenna is called a ANS: parasitic 25. An LPDA is a

dipole array.

element.

ANS: log-periodic 26. If an LPDA had five elements, the number of driven elements it had would be

.

ANS: five 27. All the waves that hit the surface of a parabolic antenna merge at the

.

ANS: focus 28. A

beam has all its individual rays parallel to each other.

ANS: collimated 29. A microwave

antenna is essentially an extension of a waveguide.

ANS: horn 30. An

chamber is often used to test microwave antennas.

ANS: anechoic SHORT ANSWER 1. Calculate the physical length of a half-wave dipole for use at 300 MHz. ANS: 475 millimeters 2. How much power will a 95% efficient antenna radiate if driven with 100 watts? ANS: 95 watts 3. If an antenna has 10.14 dB of gain compared to a point source, how much gain does it have compared to a half-wave dipole? ANS: 8 dB 4. What is the ERP of an antenna with 10 dBd of gain and driven by one watt? ANS: 10 watts 5. A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS current in the antenna? ANS: 1 ampere

6. A resonant antenna has an input impedance of 100 ohms and is driven by 100 watts. What is the RMS voltage at the feed-point of the antenna? ANS: 100 volts

Chapter 17: Microwave Devices MULTIPLE CHOICE 1. The microwave frequency range is considered to start at: a. 100 MHz c. 10 GHz b. 1 GHz d. 100 GHz ANS: B 2. The UHF range is: a. below the microwave range b. inside the microwave range

c. above the microwave range d. same as the microwave range

ANS: A 3. The dominant mode of a waveguide depends on: a. the shape of the waveguide c. the point of signal injection b. the power level of the signal d. none of the above ANS: A 4. The dominant mode of a rectangular waveguide is: a. TE 01 c. TE 10 b. TM 01 d. TM10 ANS: C 5. The dominant mode of a circular waveguide is: a. TE 01 c. TE 11 b. TM 01 d. TM11 ANS: C 6. Circular waveguides use TM 01 mode because: a. it is dominant c. it is the only mode possible b. of its circular symmetry d. it is more efficient ANS: B 7. The characteristic impedance of a waveguide: a. is fixed b. depends on the frequency it carries c. depends on the longer dimension of its cross section d. both b and c ANS: D 8. Power can be coupled into or out of a waveguide: a. with a magnetic field probe c. through a hole in the waveguide b. with an electric field probe d. all of the above

ANS: D 9. Directional couplers for waveguides are characterized by: a. their insertion loss c. their directivity b. their coupling specification d. all of the above ANS: D 10. Striplines and microstrips are used to: a. couple sections of waveguide b. couple waveguides to antennas

c. couple components on a circuit board d. none of the above

ANS: C 11. A resonant cavity is a type of: a. tuned circuit b. defect in a waveguide

c. antenna d. none of the above

ANS: A 12. A TEE connector used with waveguides is: a. an H-plane TEE b. an E-plane TEE

c. a "magic" TEE d. all of the above

ANS: D 13. TWT stands for: a. Transverse Wave Transmission b. Transverse-Wave Tube

c. Traveling-Wave Tube d. Traveling-Wave Transmission

ANS: C 14. An "isolator" is a device that: a. isolates frequencies in a waveguide b. allows a signal to pass in one direction only c. separates signals among various ports d. prevents microwaves from leaking out of a waveguide ANS: B 15. A "circulator" is a device that: a. rotates signal polarity in a waveguide b. allows a signal to pass in one direction only c. separates signals among various ports d. prevents microwaves from being "trapped" in a waveguide ANS: C 16. GaAs stands for: a. gallium arsenide b. gallium assembly ANS: A

c. gallium astenite d. none of the above

17. IMPATT stands for: a. impact avalanche and transit time b. induced mobility at transmission time

c. implied power at transmission terminal d. none of the above

ANS: A 18. YIG stands for: a. Yttrium-Iron-Gallium b. Yttrium-Iron-Germanium

c. Yttrium-Iron-Garnet d. none of the above

ANS: C 19. A YIG can be tuned by applying: a. an electric field b. a magnetic field

c. mechanical pressure d. an "exciter" signal

ANS: B 20. The device commonly used in microwave ovens is the: a. TWT c. magnetron b. klystron d. YIG ANS: C 21. The device commonly used in satellite communications is the: a. TWT c. magnetron b. klystron d. YIG ANS: A 22. The device commonly used in UHF transmitters is the: a. TWT c. magnetron b. klystron d. YIG ANS: B 23. A microwave phased array is often made using: a. slots c. Fresnel lenses b. Yagis d. all of the above ANS: A 24. RADAR stands for: a. radio ranging b. radio depth and ranging

c. radio detection and ranging d. remote detection and ranging

ANS: C 25. RADAR uses: a. pulsed transmission b. continuous transmission ANS: D

c. the Doppler effect d. all of the above

26. The maximum effective range for pulsed radar: a. increases with increasing repetition rate c. decreases with increasing pulse period b. decreases with increasing repetition rate d. none of the above ANS: B 27. The minimum effective range for pulsed radar: a. increases with increasing pulse duration c. is always a tenth of the maximum range b. decreases with increasing pulse duration d. none of the above ANS: A COMPLETION 1.

is the effect of a pulse "spreading out" as it travels through a waveguide. ANS: Dispersion

2. The electric field is

along the walls of a rectangular waveguide.

ANS: zero 3. The waveguide mode with the lowest cutoff frequency is the

mode.

ANS: dominant 4. In TE10 mode, the

field peaks in the middle of the waveguide cross section.

ANS: electric 5. In TE20 mode, the electric field has

peaks in the waveguide cross section.

ANS: two 6. In a circular waveguide,

mode is used because of its circular symmetry.

ANS: TM01 7. A waveguide acts as a

-pass filter.

ANS: high 8. In a waveguide, group velocity is always

than the speed of light.

ANS: slower 9. In a waveguide, phase velocity is always

than the speed of light.

ANS: faster 10. In a waveguide, impedance

as frequency increases.

ANS: decreases 11. A

TEE is a combination of E-plane and H-plane TEES.

ANS: hybrid 12. The Q of a resonant cavity is very

compared to lumped LC circuits.

ANS: high 13. A wavemeter is a resonant

with an adjustable plunger.

ANS: cavity 14. A Gunn device oscillates because of its negative

.

ANS: resistance 15. Both magnetrons and TWTs are slow

tubes.

ANS: wave 16. Both klystrons and TWTs are

-beam tubes.

ANS: linear 17. A

antenna is just a waveguide with a hole in it.

ANS: slot 18. A plane on the other side.

antenna is a flat piece of copper on an insulating substrate with a ground

ANS: patch 19. The radar cross section of a target is typically

than its actual size.

ANS: smaller 20. The frequency of the returned signal will be target is moving toward the radar antenna.

than the transmitted signal if the

ANS: higher SHORT ANSWER 1. Calculate the TE10 cutoff frequency for a rectangular waveguide if the longer dimension of its cross section is 5 cm.

ANS: 3 GHz 2. Calculate the group velocity in a waveguide carrying a signal that is twice its cutoff frequency. ANS: 6 260 × 10 meters per second 3. Calculate the phase velocity in a waveguide carrying a signal that is twice its cutoff frequency. ANS: 6 346 × 10 meters per second 4. Calculate the wavelength of a 2-GHz signal in a waveguide with a 1-GHz cutoff frequency. ANS: 173 millimeters 5. Find the gain in dBi of a 10-GHz horn antenna with dE = dH= 60 mm. ANS: 14.8 6. Find the maximum unambiguous range for a pulsed radar sending 10k pulses per second. ANS: 15 km 7. Find the minimum unambiguous range for a pulsed radar sending 2-µsec duration pulses. ANS: 300 meters

Chapter 18: Terrestrial Microwave Communication Systems MULTIPLE CHOICE 1. Another term for a single microwave link is a: a. section c. skip b. hop d. jump ANS: B 2. Microwave systems use: a. FM b. SSB

c. QAM d. all of the above

ANS: D 3. The typical reliability of a microwave system is: a. 90% c. 99.9% b. 99% d. 99.99% ANS: D 4. A typical microwave system uses a transmitted power of about: a. 2 watts c. 200 watts b. 20 watts d. none of the above ANS: A 5. In analog microwave systems, additional repeaters increase the: a. reliability c. jitter b. noise level d. all of the above ANS: B 6. In digital microwave systems, additional repeaters increase the: a. reliability c. jitter b. noise level d. all of the above ANS: C 7. LOS stands for: a. Loss Of Skip b. Loss Of Signal

c. Line-Of-Sight d. Line-Of-Signal

ANS: C 8. Too much antenna gain causes: a. a very narrow microwave beam b. a very wide microwave beam ANS: A

c. excessive noise d. jitter

9. The microwave signal path should clear obstacles by at least: a. 60% of the Faraday zone c. 60% of the height of the antenna tower b. 60% of the Fresnel zone d. 60% of the highest obstacle height ANS: B 10. Satisfactory performance of an analog microwave system is defined as: a. a carrier-to-noise ratio that exceeds a given value b. an ERP level that exceeds a given value c. an energy-per-hertz level that exceeds a given value d. none of the above ANS: A 11. Satisfactory performance of a digital microwave system requires a: a. low level of transmitted power b. high level of ERP c. good energy per bit per transmitted Watt ratio d. good energy per bit per noise density ratio ANS: D 12. Fading is caused by: a. multipath reception b. attenuation due to weather

c. ducting d. all of the above

ANS: D 13. The effects of fading due to multipath reception are often reduced using: a. diversity c. high-gain antennas b. power d. all of the above ANS: A 14. Repeaters are used in a microwave system: a. always b. when distance exceeds line-of-sight

c. above 10 GHz d. below 10 GHz

ANS: B 15. Microwave repeaters can be: a. IF type b. baseband type

c. regenerative type d. all of the above

ANS: D 16. An advantage of digital techniques over analog in a microwave system is: a. less bandwidth is required c. it requires less power b. accumulation of noise is reduced d. all of the above ANS: B 17. MMDS stands for: a. Multichannel Microwave Distribution System

b. Multipoint Microwave Distribution System c. Multichannel Multipoint Distribution System d. Multiple Microwave Distribution Systems ANS: C 18. LMDS stands for: a. Local Microwave Distribution System b. Local Multipoint Distribution System c. Local Multichannel Distribution System d. Low-power Microwave Distribution System ANS: B 19. LMDS is: a. bidirectional b. unidirectional

c. multidirectional d. none of the above

ANS: A COMPLETION 1. One microwave link is called a

.

ANS: hop 2. STL stands for

-to-transmitter links.

ANS: studio 3. A typical microwave system has about one hour per

or less of downtime.

ANS: year 4. Adding more links causes

in a digital microwave system.

ANS: jitter 5. In microwave systems, it is more convenient to use noise calculations.

than noise figure in

ANS: temperature 6. In digital microwave systems, the energy per bit per

is a key parameter.

ANS: noise density 7. Multipath reception can cause 20 dB or more of ANS: fading

.

8. Two antennas stacked one above the other on a tower is an example of in a microwave system.

diversity

ANS: space 9. The ability to use two frequencies simultaneously is an example of

.

ANS: diversity 10. Microwave systems generally use less than

watts of power.

ANS: ten 11.

are necessary in a microwave system that extends beyond the line-of-sight distance. ANS: Repeaters

12. Analog microwave systems use both IF and

repeaters.

ANS: baseband 13. Microwave digital radio techniques reduce the accumulation of from link to link.

as a signal goes

ANS: noise 14. MMDS is unidirectional, but

is bidirectional.

ANS: LMDS SHORT ANSWER 1. If the line-of-sight distance for an optical beam is 12 km, what would it be, approximately, for a microwave beam? ANS: 16 km 2. A line-of-sight microwave link operating at 4 GHz has a separation of 40 km between antennas. An obstacle in the path is located midway between the two antennas. By how much must the beam clear the obstacle? ANS: 16.4 meters 3. A transmitter and receiver operating at 1 GHz are separated by 10 km. How many dBm of power gets to the receiver if the transmitter puts out 1 Watt, and both the sending and receiving antennas have a gain of 20 dBi?

ANS: –42.4 dBm 4. A microwave system has a feed-line loss of 2 dB and sees a sky temperature of 150 K. Calculate the noise temperature of the antenna/feed-line system referenced to the receiver input. ANS: 201 K 5. A microwave receiver receives –60 dBm of signal. The noise power is –100 dBm. What is the carrierto- noise power ratio? ANS: 40 dB

Chapter 19: Television MULTIPLE CHOICE 1. NTSC stands for: a. National Television Systems Commission b. National Television Systems Committee c. National Television Systems Council d. Nippon Television Systems Commission ANS: B 2. The NTSC specification was drawn up by the: a. FCC c. EIA b. IRE d. IEEE ANS: C 3. RGB stands for: a. Red-Green Burst b. Red-Green Brightness

c. Red-Green Bandwidth d. Red-Green-Blue

ANS: D 4. The number of scan lines in an NTSC signal is: a. 525 c. 1024 b. 625 d. 1250 ANS: A 5. The number of NTSC frames sent per second is: a. 25 c. 50 b. 30 d. 60 ANS: B 6. The number of NTSC fields sent per second is: a. 25 c. 50 b. 30 d. 60 ANS: D 7. The aspect ratio of a standard TV receiver is: a. 3 : 4 b. 4 : 3

c. 525 : 625 d. 625 : 525

ANS: B 8. Luminance refers to: a. brightness b. contrast

c. chroma d. raster

ANS: A 9. Luminance is measured in: a. foot-candles b. lumins

c. IRE units d. NTSC units

ANS: C 10. The maximum luminance level is called: a. max white b. peak white

c. all white d. whiter than white

ANS: B 11. The blanking level corresponds to a luminance of: a. white c. whiter than white b. black d. blacker than black ANS: B 12. The sync pulse level corresponds to a luminance of: a. white c. whiter than white b. black d. blacker than black ANS: D 13. The vertical blanking pulse is serrated to: a. maintain horizontal sync b. maintain vertical sync

c. equalize the DC level d. all of the above

ANS: A 14. When measured in lines, horizontal resolution: a. is greater than vertical resolution b. is about the same as vertical resolution c. is less than vertical resolution d. horizontal resolution is not measured in lines ANS: B 15. The smallest picture element is called a: a. dot b. pic

c. pixel d. none of the above

ANS: C 16. In a color TV receiver, Y I Q refers to: a. luminance signal, in-phase color component, quadrature phase color component b. composite color signal, in-phase color component, quadrature phase color component c. composite video signal, in-phase video component, quadrature video color component d. a method of demodulating stereo sound ANS: A

17. Compared to the luminance signal, the horizontal resolution for color is: a. much greater c. much less b. about the same d. resolution does not apply to color ANS: C 18. The modulation used for the video signal in a standard NTSC color TV receiver is: a. SSB c. suppressed-carrier AM b. vestigial sideband AM d. FM ANS: B 19. The modulation used for the audio signal in a standard NTSC color TV receiver is: a. SSB c. suppressed-carrier AM b. vestigial sideband AM d. FM ANS: D 20. The modulation used for the chroma signal in a standard NTSC color TV receiver is: a. SSB c. suppressed-carrier AM b. vestigial sideband AM d. FM ANS: C 21. The function of the "color burst" is to: a. detect the presence of a color video signal b. regenerate the color sub-carrier c. to synchronize the color demodulation line by line d. all of the above ANS: D 22. SAP stands for: a. separate audio program b. separate audio pulse

c. sync amplitude pulse d. sync audio pulse

ANS: A 23. The horizontal output transformer is also called: a. the isolation transformer c. the flyback transformer b. the video transformer d. the yoke ANS: C 24. Compared to a monochrome CRT, the accelerating voltage on a color CRT is: a. about the same c. much lower b. much higher d. color CRTs use magnetic acceleration ANS: B 25. Deflection in CRTs used in TV receivers is done: a. magnetically for both vertical and horizontal b. electrostatically for both vertical and horizontal c. electrostatically for vertical and magnetically for horizontal

d. magnetically for vertical and electrostatically for horizontal ANS: A 26. AFPC stands for: a. allowed full picture chroma b. automatic frequency and phase control

c. automatic frequency and picture control d. none of the above

ANS: B COMPLETION 1.

is a conductive coating on both the inside and outside of the CRT in a TV. ANS: Aquadag

2. The

standard for TV has been in use since 1953.

ANS: NTSC 3. Video systems form pictures by a

process.

ANS: scanning 4. During the horizontal blanking interval, the electron beam

from right to left.

ANS: retraces 5. The NTSC specifies a

video signal.

ANS: composite 6. The

ratio of a CRT screen is the ratio of width to height.

ANS: aspect 7. Brightness information is called

.

ANS: luma luminance 8. Color information is called

.

ANS: chroma chrominance 9. The blanking period before the sync pulse is called the front ANS: porch

.

10. Odd and even fields are identified by the

of the vertical sync pulse.

ANS: position 11. Each horizontal scan line takes

microseconds, not including blanking.

ANS: 62.5 12. Horizontal blanking lasts

microseconds.

ANS: 10 13. Vertical blanking lasts about

milliseconds.

ANS: 1.3 14. Picture elements are called

.

ANS: pixels 15. The maximum number of scan lines under NTSC is

.

ANS: 525 16. The human eye is most sensitive to the color

.

ANS: green 17. The color sub-carrier frequency is approximately

MHz.

ANS: 3.58 18. SAP stands for

audio program.

ANS: separate 19. The second anode of a CRT is often called the

.

ANS: ultor 20. The accelerating voltage for a color CRT is about

kV.

ANS: 20 to 30 21. The inside of a CRT's face-plate is coated with

to generate the picture.

ANS: phosphor 22. The horizontal output transformer is called the

transformer.

ANS: flyback 23. A good way to separate luma from chroma is to use a

filter.

ANS: comb 24. The color monochrome signal.

turns off the color circuitry when a color TV is receiving a

ANS: killer 25. Signal levels in cable TV systems are usually measured in

.

ANS: dBmV 26. The antenna for a CATV system is located at the

end.

ANS: head 27. A

shows a color-bar signal with predetermined levels and phases.

ANS: vectorscope 28. Color intensity is called

.

ANS: saturation 29. The

of the chroma signal represents the color hue.

ANS: phase 30. The phosphor dots.

controls in a color TV adjust the electron beams to strike the correct color

ANS: purity 31. The phosphor dots. ANS: convergence

controls in a color TV adjust the electron beams to strike the correct triad of

Chapter 20: Satellite Communications MULTIPLE CHOICE 1. The height of the geosynchronous orbit above the equator is about: a. 3,578 km c. 357,800 km b. 35,780 km d. depends on satellite velocity ANS: B 2. The high and low points of a satellite's orbit are called, respectively,: a. apogee and perigee c. uplink and downlink b. perigee and apogee d. downlink and uplink ANS: A 3. The area on the earth that is "covered" by a satellite is called its: a. earth station c. footprint b. downlink d. plate ANS: C 4. The velocity required to stay in orbit: a. is constant b. is zero (freefall) c. is lower close to the earth than far from the earth d. is higher close to the earth than far from the earth ANS: D 5. An antenna is aimed by adjusting the two "look angles" called: a. azimuth and elevation c. declination and elevation b. azimuth and declination d. apogee and perigee ANS: A 6. The power per transponder of a typical Ku-band satellite is in the range: a. 5 to 25 watts c. 500 to 2500 watts b. 50 to 250 watts d. depends on its orbit ANS: B 7. The power level for an earth station to transmit to a satellite is on the order of: 1 3 a. 10 watts c. 10 watts 2 4 b. 10 watts d. 10 watts ANS: C 8. The "payload" on a communications satellite consists of: a. transponders c. solar cells b. batteries d. all of the above

ANS: A 9. "Station-keeping" refers to: a. antenna maintenance b. power-level adjustments

c. orbital adjustments d. none of the above

ANS: C 10. DBS stands for: a. decibels of signal b. down-beam signal

c. direct-broadcast system d. direct-broadcast satellite

ANS: D 11. LNA stands for: a. low-noise amplifier b. low north angle

c. low-noise amplitude d. low-noise array

ANS: A 12. A reduction in TWT power for linearity is called: a. backdown c. power-down b. backoff d. EIRP drop ANS: B 13. TVRO stands for: a. television receive only b. television repeater only

c. television remote origin d. none of the above

ANS: A 14. TDMA stands for: a. transponder-directed multiple antennas b. television distribution master antenna

c. time-division multiple access d. transmit delay minimum aperture

ANS: C 15. VSAT stands for: a. video satellite b. video signal antenna terminal

c. very small antenna terminal d. very small aperture terminal

ANS: D 16. On the uplink from a terminal, a VSAT system uses: a. high power to a small antenna c. low power to a large antenna b. low power to a small antenna d. LEO satellites ANS: B 17. A typical VSAT system is configured as a: a. star b. mesh

c. ring d. repeater

ANS: A 18. LEO stands for: a. long elliptic orbit b. low-earth orbit

c. lateral earth orbit d. longitudinal earth orbit

ANS: B 19. For real-time communication, LEO systems require: a. a constellation of satellites c. very high power b. tracking dish antennas d. all of the above ANS: A 20. The frequency bands used by Ku-band satellites are: a. 4 GHz and 6 GHz c. 20 GHz and 30 GHz b. 12 GHz and 14 GHz d. none of the above ANS: B COMPLETION 1. A satellite in geosynchronous orbit takes

hours to complete one orbit.

ANS: 24 2. The

is the signal path from the earth station to the satellite.

ANS: uplink 3. The

is the signal path from the satellite to the earth station.

ANS: downlink 4. A satellite in a

orbit appears to stay directly above one spot on the equator.

ANS: geostationary 5. Non-geostationary satellites are sometimes called

satellites.

ANS: orbital 6. A geosynchronous orbit is about

km above the earth.

ANS: 35,780 7. A

is an outline of the area on the earth's surface that a satellite broadcasts to.

ANS: footprint 8. All satellite orbits are

in shape.

ANS: elliptical 9. The

is the distance of a satellite's closest approach to the earth.

ANS: perigee 10. The

is a satellite's farthest distance from the earth.

ANS: apogee 11. An antenna's

is its angular direction between east and west.

ANS: azimuth 12. An antenna's

is its vertical angle with respect to the earth's surface.

ANS: elevation 13. An antenna's

is the angle by which it is offset from the earth's axis.

ANS: declination 14. Satellites using the

band operate on 12 GHz.

ANS: Ku 15. The time for a signal to make a round trip via satellite is about

milliseconds.

ANS: 500 16. A

is a type of repeater used on communications satellites.

ANS: transponder 17. Both the gain and the beamwidth of a dish antenna depend on its

.

ANS: diameter 18. VSAT systems commonly use a

network configuration.

ANS: star 19. To date, LEO satellite systems have been a financial ANS: failure 20. C-band antennas are ANS: larger

than Ku-band antennas.

.

SHORT ANSWER 1. A receiving antenna with a gain of 44.4 dBi looks at a sky with a noise temperature of 15 K. The loss between the output of the antenna and the input of the LNA is 0.4 dB, and the LNA has a noise temperature of 40 K. Calculate the G/T. ANS: 25 dB 2. A receiver has a noise figure of 1.7 dB. Find its equivalent noise temperature. ANS: 139 K. 3. A receiving antenna with a G/T of 25 dB is used to receive signals from a satellite 38,000 km away. The satellite has a 100-watt transmitter and an antenna with a gain of 30 dBi. The signal has a bandwidth of 1 MHz at a frequency of 12 GHz. Calculate the C/N at the receiver. ANS: 38 dB

Chapter 21: Cellular Radio MULTIPLE CHOICE 1. AMPS stand for: a. American Mobile Phone System b. Analog Mobile Phone Service

c. Advanced Mobile Phone System d. Advanced Mobile Phone Service

ANS: D 2. PCS stands for: a. Personal Communications Service b. Personal Communications Systems

c. Personal Cell phone Service d. Portable Communications Systems

ANS: B 3. RCC stands for: a. Radio Common Carrier b. Radio Cellular Carrier

c. Regional Cellular Carrier d. none of the above

ANS: A 4. MSC stands for: a. Mobile Switching Center b. Mobile Service Cellular

c. Maximum Signal Carrier d. Minimum Signal Carrier

ANS: A 5. MTSO stands for: a. Minimum Transmitted Signal Output b. Maximum Transmitted Signal Output

c. Mobile Telephone Switching Office d. Mobile Transmission Time-Out

ANS: C 6. MIN stands for: a. Manual Identification Number b. Mobile Identification Number

c. Maximum In-band Noise d. Minimum In-band Noise

ANS: B 7. NAM stands for: a. Numerical Access Mode b. Numerical Assignment Mode

c. Number Access Module d. Number Assignment Module

ANS: D 8. ESN stands for: a. Electronic Serial Number b. Emitted Signal Number ANS: A

c. Emission Strength Number d. none of the above

9. SCM stands for: a. Service Class Mark b. Station Class Mark

c. Signal Class Mark d. Serial-Code Mode

ANS: B 10. SCM identifies the: a. code number of a cell phone b. base-station class

c. signal classification (analog or digital) d. maximum power level of a cell phone

ANS: D 11. SID stands for: a. Sequential Interrupt Demand b. Standard Identification Number

c. System Identification Number d. Signal Intensity Descriptor

ANS: C 12. The SID is used by a cell phone to: a. identify the type of system (analog or digital) b. recognize an AMPS system c. set its transmitted power level d. recognize that it is "roaming" ANS: D 13. DCC stands for: a. Digital Color Code b. Digital Communications Code

c. Digital Communications Carrier d. Direct Channel Code

ANS: A 14. SAT stands for: a. Station Antenna Tower b. Supervisory Audio Tone

c. Supervisory Access Tone d. none of the above

ANS: B 15. CMAC stands for: a. Control Mobile Attenuation Code b. Control Mobile Access Code

c. Central Mobile Access Control d. Carrier Mode Attenuation Control

ANS: A 16. The CMAC is used to: a. control access to the cell site b. set the access code of the cell phone c. set the transmit power of the cell phone d. select the transmit channel for the cell phone ANS: C 17. In an AMPS system, voice is sent using: a. AM

c. FSK

b. FM

d. CDMA

ANS: B 18. In an AMPS system, control-channel signals are sent using: a. AM c. FSK b. FM d. CDMA ANS: C 19. The ERP of a typical handheld AMPS cell phone is: a. less than 600 µW. c. between 1 and 2 watts b. less than 600 mW. d. 4 watts ANS: B 20. BSC stands for: a. Base Station Controller b. Base Signal Controller

c. Basic Service Contract d. Basic Service Code

ANS: A 21. The combination of the mobile cell phone and the cell site radio equipment is called the: a. BSC c. RF interface b. MTSO d. air interface ANS: D 22. The optimum cell-site radius is: a. 2 km b. 0.5 km

c. as small as possible d. none of the above

ANS: D 23. Phone traffic is measured in: a. calls b. erlangs

c. number of users d. number of blocked calls

ANS: B 24. One way to increase the capacity of a cell phone system is: a. increase the number of cells c. increase the ERP b. decrease the number of cells d. decrease the ERP ANS: A 25. CDPD stands for: a. Code-Division Packet Data b. Cellular Digital Packet Data ANS: B COMPLETION

c. Coded Digital Packet Data d. Cellular Digital Pulse Data

1. AMPS uses the

-MHz band.

ANS: 800 2.

is still the most common cellular phone system in North America. ANS: AMPS

3. Frequency

is what makes cellular phone systems complex.

ANS: reuse 4. A

occurs when an in-use cell-phone moves from one cell site to another.

ANS: handoff 5. If a cell-site radius drops below

km, handoffs will occur too frequently.

ANS: 0.5 6. The number of ERP classes in AMPS is

.

ANS: three 7. A cell phone permanently installed in a car would be ERP class

.

ANS: I one 8. The maximum ERP of class III cell phones is

.

ANS: 600 mW 9. A portable, handheld cell phone would be ERP class

.

ANS: III three 10. Mobile transmitter power is controlled by the

.

ANS: land station 11. A MAC is a mobile

code.

ANS: attenuation 12. For security, you should always assume that AMPS transmissions are

.

ANS: public 13. A mobile switching center is also called an

.

ANS: MTSO 14. The optimum size of a cell site depends on the amount of

.

ANS: traffic 15. Telephone call traffic is measured in

.

ANS: erlangs 16. A cell phone moving into a site with no available frequencies will have a

call.

ANS: dropped 17. The reduction in cell size to increase traffic is called cell

.

ANS: splitting 18. A

site is a very small unit that can mount on a streetlight pole.

ANS: microcell 19. Very small cells called

are used for reliable indoor reception.

ANS: picocells 20. Compared with AMPS, digital cellular phones require

bandwidth.

ANS: less SHORT ANSWER 1. Give two reasons why digital cell phone systems are more secure than analog cell phone systems. ANS: 1. Digital is inherently more secure because of its format. 2. Digitized voice signals are easily encrypted. 2. If a 28.8-kbps modem is being used over a cell phone, how many words of text would be lost during a 100-msec handoff interruption assuming 10 bits per letter and 5 letters per word? ANS: 57.6 3. A certain cell site contains 200 cell phones. The probability that a given cell phone is being used is 15%. What is the traffic in erlangs?

ANS: 30 4. What is "trunking gain"? ANS: For a given probability of being blocked, the maximum allowable traffic per channel increases as the number of channels increases.

Chapter 22: Personal Communications Systems

MULTIPLE CHOICE 1. Current PCS systems are referred to as: a. first-generation b. second-generation

c. third-generation d. digital-generation

ANS: B 2. The frequency band designated for PCS in North America is: a. 800 MHz c. 1.9 GHz b. 900 MHz d. 12 GHz ANS: C 3. The "forward" PCS channel is: a. from the base to the mobile b. from the mobile to the base

c. from mobile to mobile d. same as the uplink

ANS: A 4. Compared to AMPS, PCS cell sites are: a. bigger b. smaller

c. distributed d. higher-power

ANS: B 5. AMPS was designed for: a. POTS b. voice

c. use built into an automobile d. all of the above

ANS: D 6. The number of competing PCS systems in North America is: a. 2 c. 4 b. 3 d. many ANS: B 7. CDMA technology was invented by: a. AT&T b. Lucent

c. Bell Labs d. Qualcomm

ANS: D 8. GSM is used in: a. Asia b. Europe ANS: D

c. North America d. all of the above

9. In GSM, voice channels are called: a. traffic channels b. voice channels

c. bearer channels d. talking channels

ANS: A 10. AMPS uses: a. CDMA b. TDMA

c. spread-spectrum d. none of the above

ANS: D 11. Other things being equal, battery life in a GSM phone should be: a. less than in a TDMA phone c. greater than in a TDMA phone b. no better than in an AMPS phone d. no better than a TDMA phone ANS: C 12. It is necessary to send control information on traffic channels in: a. no PCS system c. TDMA only b. GSM only d. both GSM and TDMA ANS: D 13. GSM uses: a. frequency hopping b. direct-sequence modulation

c. CDMA d. all of the above

ANS: A 14. In GSM, SIM stands for: a. Short Inbound Message b. Subscriber-Initiated Message

c. Subscriber ID Module d. Subscriber ID Method

ANS: C 15. IMSI stands for: a. Integrated Mobile Subscriber Identification b. International Mobile Subscriber Identification c. Interim Mobile Subscriber Identification d. Intermodulation System Interference ANS: B 16. IS-95 uses: a. frequency hopping b. TDMA

c. CDMA d. all of the above

ANS: C 17. IS-136 uses: a. frequency hopping b. TDMA

c. CDMA d. all of the above

ANS: B 18. In CDMA: a. all frequencies are used in all cells b. each cell uses half the available frequencies c. each cell is assigned a frequency by the base d. the frequency is selected by the mobile phone ANS: A 19. CDMA uses a set of PN sequences that are: a. common b. unique

c. rotating d. orthogonal

ANS: D 20. The next generation of PCS is expected to have: a. faster data rates c. wider roaming area b. Internet access d. all of the above ANS: D COMPLETION 1. PCS stands for

Communications System.

ANS: Personal 2. Current PCS systems are called

-generation systems.

ANS: second 3. In North America, PCS is assigned the

-MHz band.

ANS: 1900 4. Compared to AMPS, PCS cells are

in size.

ANS: smaller 5. Besides TDMA and CDMA,

is also used in North America for PCS.

ANS: GSM 6. The spread-spectrum technique used in IS-95 PCS is ANS: CDMA direct sequence

.

7. The spread-spectrum technique used in GSM is

.

ANS: frequency hopping 8. Unlike AMPS, CDMA allows for a

handoff.

ANS: soft 9. The orthogonal PN sequences used in CDMA are called a

code.

ANS: Walsh 10. Unlike other systems, in CDMA

frequencies are used in all cells.

ANS: all 11. PN stands for Pseudo-

Noise.

ANS: random 12.

diversity is inherent in any spread-spectrum system. ANS: Frequency

13. RF channel S/N ratios

than zero are typical in CDMA systems.

ANS: less 14. CDMA uses a

-rate vocoder.

ANS: variable 15. A phone user typically talks less than

% of the time during a conversation.

ANS: 50 16. CDMA requires

-loop power control to work properly.

ANS: closed 17. GPRS stands for General

Radio Service.

ANS: Packet 18. IMT stands for International

Telecommunications.

ANS: Mobile 19. UPT stands for ANS: Universal

Personal Telecommunications.

20. UWT stands for Universal

Telecommunications.

ANS: Wireless 21. W-CDMA stands for

CDMA.

ANS: Wideband SHORT ANSWER 1. What is the advantage of a "soft" handoff? ANS: No calls are dropped. 2. If CDMA receivers hear all frequencies all the time, how do they pick a specific frequency? ANS: Each frequency is modulated using a separate orthogonal PN sequence. To demodulate, the receiver uses the PN sequence specific to the channel it wants. 3. What is the effect of cochannel interference in CDMA? ANS: It increases the background noise level, but CDMA can tolerate a lot of such noise. 4. How does GSM achieve frequency diversity? ANS: It uses limited frequency hopping. 5. Why was PCS assigned to 1.9 GHz instead of the 800-MHz band used for AMPS? ANS: The 800 MHz band was already overcrowded. 6. Why would a battery in a GSM phone be expected to last longer than a battery in a TDMA phone? ANS: A TDMA phone is active during one out of every three time slots. A GSM phone is active during one out of every eight. 7. What is the advantage of using offset QPSK over standard QPSK? ANS: With standard QPSK, the transmitted power repeatedly goes to zero. With offset QPSK, it never goes to zero. Linearity requirements are less strict for offset QPSK transmitters. 8. What is the "near/far" effect in CDMA, and what causes it?

ANS: A stronger station farther away can "drown out" a weaker station that is near. This happens when the power transmitted by mobile units is not well controlled by the base.

Chapter 23: Paging and Wireless Data Networking

MULTIPLE CHOICE 1. Pagers use: a. the VHF band only b. the UHF band only c. both the VHF and UHF bands d. the VHF band, the UHF band, and the ISM band ANS: C 2. ISM stands for: a. IEEE Standard Message b. IEEE Secure Message

c. Industrial, Scientific, and Messaging d. Industrial, Scientific, and Medical

ANS: D 3. CAPCODE is: a. an encryption scheme used for pagers b. an addressing scheme used for pagers c. an error-detection scheme used for pagers d. a digital modulation scheme used for pagers ANS: B 4. In a one-way pager system: a. all pages are sent from all transmitters b. each transmitting antenna covers a wide area c. transmitters use relatively high power d. all of the above ANS: D 5. POCSAG stands for: a. Pager Operations Common Standards Advisory Group b. Pager Operations Code Standardization Advisory Group c. Post Office Code Standardization Advisory Group d. Post Office Common Standards Advisory Group ANS: C 6. A typical pager system does not: a. require "handoffs" b. allow "roaming"

c. require error detection d. all of the above

ANS: A 7. The IEEE specification covering wireless LANs is: a. 802.10 c. 802.12

b. 802.11

d. 802.13

ANS: B 8. The IEEE 802 spec for wireless LANs uses the: a. VHF band c. ISM band b. UHF band d. infrared band ANS: C 9. The IEEE 802 document for wireless LANs specifies the use of: a. CSMA/CA c. CDMA b. CSMA/CD d. all of the above ANS: A 10. BSS stands for: a. Basic Service Set b. Basic Service System

c. Bluetooth Service System d. none of the above

ANS: A 11. Bluetooth uses: a. CDMA b. frequency hopping

c. QPSK d. all of the above

ANS: B 12. Bluetooth uses the: a. VHF band b. UHF band

c. ISM band d. infrared band

ANS: C 13. TDD stands for: a. Time-Division Duplex b. Time-Delayed Duplex

c. Time Delay Difference d. Total Distance Delay

ANS: A 14. A Bluetooth "piconet" has: a. 2 nodes b. 2 to 4 nodes

c. 2 to 8 nodes d. 2 to 16 nodes

ANS: C 15. Two or more connected piconets forms a: a. micronet b. multinet

c. TDD net d. scatternet

ANS: D 16. The basic range of a Bluetooth device is: a. 10 cm to 1 meter

c. 10 cm to 100 meters

b. 10 cm to 10 meters

d. within 10 feet

ANS: B 17. IRDA stands for: a. Infrared Data Association b. Infrared Digital Association

c. Infrared Restricted Data Area d. Infrared Roaming Data Area

ANS: A 18. The range of an IRDA system is: a. 1 meter b. 10 meters

c. 1 foot d. 10 feet

ANS: A 19. Infrared networks: a. cannot penetrate walls b. can use diffused infrared beams

c. can use reflected infrared beams d. all of the above

ANS: D 20. The maximum range of a typical wireless modem is: a. 1 meter c. several hundred meters b. several meters d. several thousand meters. ANS: D COMPLETION 1. Each pager has a unique address called a

.

ANS: capcode 2. Many pagers can share a frequency using

.

ANS: TDMA 3. The POCSAG was devised by the British

Office.

ANS: Post 4. A POCSAG message uses a

-bit error correction code.

ANS: 10 5. IEEE

covers wireless LANs.

ANS: 802.11 6. The IEEE document specifies a maximum power of

for wireless LANs.

ANS: 1 watt 7. Bluetooth uses the

band.

ANS: ISM 8. A network of 2 to 8 Bluetooth devices is called a

.

ANS: piconet 9. A Bluetooth scatternet consists of 2 or more

.

ANS: piconets 10. An IRDA system is deliberately restricted to a range of ANS: 1 meter

.

Chapter 24: Fiber Optics

MULTIPLE CHOICE 1. Compared to the core, the index of refraction of the cladding must be: a. the same c. less b. greater d. doesn't have an index of refraction ANS: C 2. Fiber-optic cables do not: a. carry current b. cause crosstalk

c. generate EMI d. all of the above

ANS: D 3. Single-mode fiber is made from: a. glass b. plastic

c. both a and b d. none of the above

ANS: A 4. Fiber-optic cable cannot be used: a. in an explosive environment b. to connect a transmitter to an antenna c. to isolate a medical patient from a shock hazard d. none of the above ANS: B 5. A single-mode cable does not suffer from: a. modal dispersion b. chromatic dispersion

c. waveguide dispersion d. all of the above

ANS: A 6. Scattering causes: a. loss b. dispersion

c. intersymbol interference d. all of the above

ANS: A 7. The loss in single-mode fiber-optic cable due to the glass is about: a. 40 dB per km c. 0.4 dB per km b. 4 db per km d. zero loss ANS: C 8. The loss in single-mode fiber-optic cable due to a splice is about: a. 0.02 dB c. 1 dB

b. 0.2 db

d. 3 dB

ANS: A 9. The loss in single-mode fiber-optic cable due to a connector is about: a. 0.02 dB c. 1 dB b. 0.2 db d. 3 dB ANS: B 10. Which of the following is a type of fiber connector: a. ST c. SMA b. SC d. all of the above ANS: D 11. The quantum of light is called: a. an erg b. an e-v

c. a photon d. a phonon

ANS: C 12. LASER stands for: a. Light Amplification by Simulated Emission of Radiation b. Light Amplification by Stimulated Emission of Radiation c. Light Amplification by Simulated Emitted Rays d. Light Amplification by Stimulated Emitted Rays ANS: B 13. APD stands for: a. Avalanche Photodiode b. Advanced Photodiode

c. Avalanche Photo Detector d. Advanced Photo Detector

ANS: A 14. In a PIN diode, leakage current in the absence of light is called: a. baseline current c. dark current b. zero-point current d. E-H current ANS: C 15. For a light detector, responsivity is measured in: a. amps per watt c. mA per joule b. µW per amp d. µsec per µW ANS: A COMPLETION 1. In the core, the angle of incidence equals the angle of ANS: reflection

.

2. The core is surrounded by the

.

ANS: cladding 3. The

angle is where refraction changes to reflection.

ANS: critical 4. An electron-volt is a measure of

.

ANS: energy 5. The numerical aperture is the

of the angle of acceptance.

ANS: sine 6. Optical fiber relies on total

reflection.

ANS: internal 7. Chromatic dispersion is also called

dispersion.

ANS: intramodal 8. With optical fiber,

light is more common than visible light.

ANS: infrared 9. In multimode fiber,

index has less dispersion than step index.

ANS: graded 10. For laser diodes, the term

is used instead of bandwidth.

ANS: linewidth 11. Dispersion can be expressed in units of

rather than bandwidth.

ANS: time 12.

interference is when one pulse merges with the next pulse. ANS: Intersymbol

13. The optical fiber is free to move around in a

cable.

ANS: loose-tube 14. The optical fiber is not free to move around in a

cable.

ANS: tight-buffer 15. A

is a short length of fiber that carries the light away from the source.

ANS: pigtail 16. Good connections are more critical with

-mode fiber.

ANS: single 17. A

diode is the usual light source for single-mode cable.

ANS: laser 18. The quantum of light is called the

.

ANS: photon 19. A

diode is the usual light detector for single-mode cable.

ANS: PIN 20. For safety, you should never not connected to a light source. ANS: look

at the end of an optical fiber unless you know it is

Chapter 25: Fiber-Optic Systems MULTIPLE CHOICE 1. FDDI stands for: a. Fiber Digital Data Interface b. Fiber Distributed Data Interface

c. Fiber Distribution Delay Interface d. Frequency-Division Data Interface

ANS: B 2. FITL stands for: a. Fiber In The Loop b. Fiber Input Timing Loss

c. Frequency Input to The Loop d. Fiber Input Timing Loop

ANS: A 3. FTTC stands for: a. Fiber Transmission Timing Constraint b. Fiber Transmission Technology Committee c. Fiber Telephone Transmission Cable d. Fiber To The Curb ANS: D 4. SONET stands for: a. Simple Optical Network b. Standard Optical Network

c. Synchronous Optical Network d. none of the above

ANS: C 5. DWDM stands for: a. Digital Wavelength-Division Modulation b. Dense Wavelength-Division Modulation c. Double Wavelength-Division Modulation d. Dense Wavelength-Division Multiplexing ANS: D 6. A Soliton is a: a. defect in the glass b. type of particle

c. type of pulse d. type of optical network

ANS: C 7. Adding bits to synchronize one digital signal to another is called: a. bit stuffing c. SDH b. bit-synch d. WDM ANS: A 8. Power above the minimum required by an optical receiver is called: a. gain margin c. excess gain

b. system margin

d. overdrive

ANS: B 9. Typically, repeaters are not required for fiber-optic cable lengths up to: a. 1000 miles c. 100 km b. 100 miles d. 10 km ANS: C 10. In SONET, OC-1 stands for: a. Optical Carrier level one b. Optical Coupler unidirectional

c. Optical Channel one d. Optical Cable type 1

ANS: A 11. In SONET, STS stands for: a. Synchronous Transport Signal b. Synchronous Transport System

c. Synchronous Transmission Signal d. Synchronous Transmission System

ANS: A 12. A commonly used fiber-based system for LANs is: a. FDDI c. gigabit Ethernet b. high-speed Ethernet d. all of the above ANS: D 13. The use of solitons on fiber-optic cables is: a. common b. experimental

c. obsolete d. not possible

ANS: B 14. OTDR stands for: a. Optical Time-Delay Response b. Optical Timing Delay Requirement

c. Optical Time-Domain Reflectometer d. Optical Time-Division Relay

ANS: C 15. Using fiber-optic cable in a telephone system except for the connection to the subscriber's phone is called: a. FDDI c. FITL b. FTTC d. SONET ANS: B COMPLETION 1. FTTC stands for Fiber To The

.

ANS: Curb 2. FITL stands for Fiber In The

.

ANS: Loop 3. SDH stands for Synchronous Data

.

ANS: Hierarchy 4. WDM stands for

-division multiplexing.

ANS: Wavelength 5. SONET stands for

Optical Network.

ANS: Synchronous 6. FDDI stands for Fiber

Data Interface.

ANS: Distributed 7. Optical amplifiers use

-doped glass.

ANS: erbium 8. Optical amplifiers use a

laser.

ANS: pump 9. Dense

allows many different wavelengths of light to share a cable.

ANS: WDM 10. The OC-1 line rate is

Mbps.

ANS: 51.84 11. SONET does not use bit

to synchronize two digital signals.

ANS: stuffing 12. SONET uses a

to denote the starting position of an information frame.

ANS: pointer 13. FDDI systems use two

rings to carry signals.

ANS: token 14. The two rings of an FDDI system carry data in ANS: opposite

directions.

15. Each

in an FDDI system acts as a regenerative repeater.

ANS: node 16. FDDI uses

mode cables.

ANS: multi 17. The data rate of an FDDI system is

bps.

ANS: 100 M 18. SONET frames have considerably more about signal routing and setup.

than do DS frames for information

ANS: overhead 19. The number of bytes in a SONET frame is

.

ANS: 810 20. The number of bytes in the payload of a SONET frame is

.

ANS: 774 21. The number of rows in a SONET frame is

.

ANS: 9 22. The total number of overhead bytes in a SONET frame row is

.

ANS: 4 23. The number of path overhead bytes in a SONET frame row is

.

ANS: 1 24. SONET frame rows contain path overhead and

overhead.

ANS: transport 25. In SONET, SPE stands for synchronous payload

.

ANS: envelope SHORT ANSWER 1. What is the bandwidth of a first-order LPF with a rise time of 350 nanoseconds? ANS:

1 MHz 2. Calculate the total rise time for a fiber-optic system if the transmitter, receiver, and cable each have a rise time of 50 nanoseconds. ANS: 86.6 nanoseconds