An antenna is the interface between the transmission line and .

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

Chapter 1: Introduction to Communication Systems

MULTIPLE CHOICE

1. The theory of radio waves was originated by:a.Marconi c. Maxwellb.Bell d. Hertz

ANS: C

2. The person who sent the first radio signal across the Atlantic ocean was:a.Marconi c. Maxwellb.Bell d. Hertz

ANS: A

3. The transmission of radio waves was first done by:a.Marconi c. Maxwellb.Bell d. Hertz

ANS: D

4. A complete communication system must include:a.a transmitter and receiverb.a transmitter, a receiver, and a channelc.a transmitter, a receiver, and a spectrum analyzerd.a multiplexer, a demultiplexer, and a channel

ANS: B

5. Radians per second is equal to:a.2 i r x f c. the phase angle0 .f ÷ 2 i r 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 ratiob.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. SINADb.signal switching d. multiplexing

ANS: D

8. TDM stands for:a.Time-Division Multiplexing c. Time Domain Measurementb.Two-level Digital Modulation d. none of the above

ANS: A

9. FDM stands for:a.Fast Digital Modulation c. Frequency-Division Multiplexingb.Frequency Domain Measurement d. none of the above

ANS: C

10. The wavelength of a radio signal is:a . e q u a l t o f ÷ cb . e q u a l t o c ÷ A ,

c.the distance a wave travels in one periodd.how far the signal can travel without distortion

ANS: C

11. Distortion is caused by:a.creation of harmonics of baseband frequenciesb.baseband frequencies "mixing" with each otherc.shift in phase relationships between baseband frequenciesd.al l of the above

ANS: D

12. The collection of sinusoidal frequencies present in a modulated carrier is called its:a.frequency-domain representation c. spectrumb.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 kHzb.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 channelb. the receiver d. all of the above

ANS: D

15. "Man-made" noise can come from:a.equipment that sparks c. staticb.temperature d. all of the above

ANS: A

16. Thermal noise is generated in:a.transistors and diodes c. copper wireb.resistors d. all of the above

ANS: D

17. Shot noise is generated in:a.transistors and diodes c. copper wireb.resistors d. none of the above

ANS: A

18. The power density of "flicker" noise is:a.the same at all frequencies c. greater at low frequenciesb.greater at high frequencies d. the same as "white" noise

ANS: C

19. So called "1/f" noise is also called:a.random noise c. white noiseb.pink noise d. partition noise

ANS: B

20. "Pink" noise has:a.equal power per Hertz c. constant powerb.equal power per octave 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)b.VT = (V1 + V2)/2 d. VT = V1 + V2

ANS: A

22. Signal-to-Noise ratio is calculated as:a.signal voltage divided by noise voltageb.signal power divided by noise powerc.first add the signal power to the noise power, then divide by noise powerd.none of the above

ANS: B

23. SINAD is calculated as:a.signal voltage divided by noise voltageb.signal power divided by noise powerc.first add the signal power to the noise power, then divide by noise powerd.none of the above

ANS: D

24. Noise Figure is a measure of:a.how much noise is in a communications systemb.how much noise is in the channelc.how much noise an amplifier adds to a signald.signal-to-noise ratio in dB

ANS: C

25. The part, or parts, of a sinusoidal carrier that can be modulated are:a. i ts amplitude c. its amplitude, frequency, and directionb.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 . I n , you split the bandwidth of a channel into sub-channels to carry multiplesignals.

ANS: FDM

9 . I n , 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 in a conductor.

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.

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 timeb.transit t ime d. Miller time

ANS: B

2. A real capacitor actually contains:a.capacitance and resistance only c. capacitance, inductance, and resistanceb.capacitance and inductance only d. reactance only

ANS: C

3. Bypass capacitors are used to:a.remove RF from non-RF circuits c. neutralize amplifiersb.couple RF around an amplifier d. reduce the Miller effect

ANS: A

4. A resonant circuit is:a.a simple form of bandpass filter c. both a and bb.used in narrowband RF amplifiers d. none of the above

ANS: C

5. Loading down a tuned-circuit amplifier will:a.raise the Q of the tuned circuit c. "multiply" the Qb.lower the Q of the tuned circuit d. have no effect on Q

ANS: B

6. The "Miller Effect" can:a.cause an amplifier to oscillate c. reduce the bandwidth of an amplifierb.cause an amplifier to lose gain d. all of the above

ANS: D

7. The Miller Effect can be avoided by:a.using a common-emitter amplifier c. increasing the Q of the tuned circuitb.using a common-base amplifier d. it cannot be avoided

ANS: B

8. In a BJT, the Miller Effect is due to:a.inductance of collector lead c. base-to-emitter capacitanceb.collector-to-emitter capacitance d. base-to-collector capacitance

ANS: D

ANS: B

9. In RF amplifiers, impedance matching is usually done with:a.RC coupling c. direct couplingb.transformer coupling d. lumped reactance

ANS: B

10. Neutralization cancels unwanted feedback by:a.adding feedback out of phase with the unwanted feedbackb.bypassing the feedback to the "neutral" or ground planec.decoupling itd.none of the above

ANS: A

11. For a "frequency multiplier" to work, it requires:a.a nonlinear circuitb.a l inear amplifierc.a signal containing harmonicsd.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 unityb.phase shift around loop equal to 0 degreesc.both a and b, but at just one frequencyd.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 criteriab.the Hartley criteria d. the Barkhausen criteria

ANS: D

14. The Hartley oscillator uses:a.a tapped inductor c. an RC time constantb.a two-capacitor divider d. a piezoelectric crystal

ANS: A

15. The Colpitts VFO uses:a.a tapped inductor c. an RC time constantb.a two-capacitor divider d. a piezoelectric crystal

ANS: B

16. The Clapp oscillator is:a.a modified Hartley oscillatorc. a type of crystal-controlled oscillatorb.a modified Colpitts oscillator d. only built with FETs

17. A varactor is:a.a voltage-controlled capacitor c. used in tuner circuitsb.a dioded. all of the above

ANS: D

18. Crystal-Controlled oscillators are:a.used for a precise frequencyb.used for very low frequency drift (parts per million)c.made by grinding quartz to exact dimensionsd.all of the above

ANS: D

19. If two signals, Va = sin(co

a

t) and Vb = sin(cobt), are fed to a mixer, the output:a . w i l l c o n t a i n w 1 = w

a

+ w b a n d c o 2 = wa

– w b

b . w i l l c o n t a i n w 1 = wa

/ w b a n d c o 2 = w b / wa

c.wi l l conta in c o = ( c oa

+ c o b ) / 2d.none of the

above ANS: A

20. In a balanced mixer, the output:a.contains equal (balanced) amounts of all input frequenciesb.contains the input frequenciesc.does not contain the input frequenciesd.is a linear mixture of the input signals

ANS: C

21. "VFO" stands for:a.Voltage-Fed Oscillator c. Varactor-Frequency Oscillatorb.Variable-Frequency Oscillatord. Voltage-Feedback Oscillator

ANS: B

22. A "frequency synthesizer" is:a.a VCO phase-locked to a reference frequencyb.a VFO with selectable crystals to change frequencyc.a fixed-frequency RF generatord.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 instead of asbeing "lumped".

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 betweenthem.

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 or more for Q is required for the approximate tuned circuit equationsto be valid.

ANS: 10

10. In a class C RF amplifier, the extracts one frequency from all the harmonicscontained 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 and aresonant frequency.

ANS: series, parallel

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 p .H

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 5- MHz 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 c. Angle Modulationb.Amplitude Modulation d. Antenna Modulation

ANS: B

2. The "envelope" of an AM signal is due to:a.the baseband signal c. the amplitude signalb.the carrier signal d. none of the above

ANS: A

3. If the audio Va sin(coa

t) modulates the carrier Vc sin(cc

t), then the modulation index, m, is:a.m = c o

a

/ c

c. m = (Va / Vc)2

b.m = Va / Vc d. m = Va / ca

ANS: B

4. The equation for full-carrier AM is:a.v(t) = (Ec + Em) × sin(c

c

t) c. v(t) = (E c × Em) × s in( c om

t) × s in( cc

t)

b.v(t) = (Ec + Em) × sin(com

t) + sin( cc

t) d. v(t) = (Ec + Em sin( c om

t)) × sin( cc

t)

ANS: D

5. Overmodulation causes:a.distortion c. both a and bb.splatter 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(coa

t) amplitude modulates the carrier Vc sin(cc

t), it will produce the frequencies:a . c

c

+ c oa

a n d (c

– c o a c . cc

+ c oa

a n d 2 cc

+ 2 a

0 . ( cc

+ wa

) / 2 a n d ( cc

– 0 )a

) / 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 powerb.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 MHzb.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 increaseb.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 c. both a and bb.the frequency-domain signal 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 radiosb.requires too much power d. all of the above

ANS: C

13. As compared to plain AM, SSB AM:a. is more eff icientb.requires a more complex demodulator circuitc.requires less bandwidthd.al l of the above

ANS: D

14. The SC in SSB SC stands for:a.single-carrier c. sideband-carrierb.suppressed-carrier d. none of the above

ANS: B

15. PEP stands for:a.Peak Envelope Power c. Peak Envelope Productb.Peak Efficiency Power 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 wattsb.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 powerc.commercial AM stations have a narrow bandwidthd.al l of the above

ANS: C

18. The type of information that can be sent using AM is:a.audio c. digital datab.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 x m 2 + m2 x m 1)0.(m1 + m2) / 2 d. sqrt(m1 x m 1 + m2 x m 2)

ANS: D

20. To demodulate a USB SSB signal, the receiver must:a.be set to USB mode c. both a and bb.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

0.6

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 wattswith 100% modulation.

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:

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 frequencyb.increases with deviation and decreases with modulation frequencyc.decreases with deviation and increases with modulation frequencyd.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 oscillatorb.integrate the signal out of the PM oscillatorc.differentiate the modulating signal before applying to the PM oscillatord.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 sidebandsb.it is equal to the frequency deviationc.it is band-limited at the receiverd.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 seriesb.Bessel functions d. fractals

ANS: B

5. FM bandwidth can be approximated by:a.Armstrong's Rule c. Carson's Ruleb.Bessel's Rule d. none of the above

ANS: C

6. NBFM stands for:a.National Broadcast FM c. Near Band FMb.Non-Broadcast 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 effectb.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" effectb.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 frequenciesb.increase the signal to noise ratio for lower audio frequenciesc.increase the signal to noise ratio for all audio frequenciesd.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 workb.the "dead time" before de-emphasis occursc.the time delay between the L and R channelsd.the time-constant of the filter circuits used

ANS: D

11. FM stereo:a.uses DSBSC AM modulation c. has a higher S/N than mono FMb.is implemented using an SCA signal d. is not compatible with mono FM

ANS: A

12. An SCA signal:a.can use amplitude modulation c. is monauralb.can use FM modulation 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 oneb.using measurements at points where J0 equals zeroc.using measurements at points where the deviation equals zerod.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 communication.

ANS: data

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:widergreater

5. FM transmitters can use Class amplifiers since amplitude linearity is notimportant.

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 of themodulating signal.

ANS: amplitude

8. The frequency deviation of an FM signal occurs at a rate equal to the of themodulating signal.

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

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?

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 usingfunctions.

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 areclose 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

ANS: C

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: = 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 is 11 kHz.

ANS: C

Chapter 5: Transmitters

MULTIPLE CHOICE

1. The ability to change operating frequency rapidly without a lot of retuning is called:a.agility c. VFOb.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 coolingb.heats the transmitter d. all of the above

ANS: D

3. Baseband compression produces:a.a smaller range of frequencies from low to highb.a smaller range of amplitude from soft to loudc.a smaller number of signalsd.none of the above

ANS: B

4. ALC stands for:a.Amplitude Level Control c. Accurate Level Controlb.Automatic 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% c. maximize transmitted powerb.keep the modulation below 100% d. all of the above

ANS: D

6. With high-level AM:a.all RF amplifiers can be nonlinear c. minimum RF power is requiredb.minimum modulation power is required d. all of the above

ANS: A

7. With high-level AM:a.the RF amplifiers are typically Class A c. the RF amplifiers are typically Class Cb.the RF amplifiers are typically Class B d. the RF amplifiers are typically Class AB

ANS: C

8. With low-level AM:a.the RF amplifiers must be Class A c. the RF amplifiers must be linearb.the RF amplifiers must be Class B d. the RF amplifiers must be low-power

9. Power amplifiers must be linear for any signal that:a.is complex c. has variable frequencyb.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 c. the power level of the final RF amplifierb.the power level of the modulation 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 stageb.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 voltageb.approximately twice the DC supply voltagec.approximately four times the DC supply voltaged.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 resistiveb.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 bb.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 loadb.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 betterb.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 c. start with a quadrature signalb.start with DSBSC d. all of the above

ANS: B

19. The carrier is suppressed in:a.a balanced modulator c. a frequency multiplierb.a mixer 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 bb.a crystal filter d. none of the above

ANS: C

21. A direct FM modulator:a.varies the frequency of the carrier oscillatorb.integrates the modulating signalc.both a and bd.none of the above

ANS: A

22. An indirect FM modulator:a.requires a varactor in the carrier oscillatorb.varies the phase of the carrier oscillatorc.both a and bd.none of the above

ANS: B

23. AFC stands for:a.Amplitude to Frequency Conversion c. Automatic Frequency Controlb.Automatic Frequency Centering d. Audio Frequency Control

ANS: C

24. Frequency multipliers are:a.essentially balanced modulators c. essentially mixersb.essentially Class C amplifiers d. none of the above

ANS: B

25. With mixing:a.the carrier frequency can be raisedb.the carrier frequency can be loweredc.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 sets requirements for accuracy and stability of a transmitter'sfrequency.

ANS: FCC

3. In Canada, sets requirements for accuracy and stability of a transmitter'sfrequency.

ANS: Industry Canada

4. Frequency is the ability of a transmitter to change frequency without a lot ofretuning.

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 than the DC supplyvoltage.

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 network forimpedance matching.

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 as well asthe power amplifier in transistor modulators.

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, is used to operate atmore than one frequency.

ANS: mixing

22. To generate a SSB signal, it is common to start with a signal.

ANS: DSBSC

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 selectivityb.the number of converters and the number of IFsc.the spurious response and the trackingd.the signal and the noise

ANS: A

2. The superheterodyne receiver was invented by:a.Foster c. Armstrongb.Seeley d. Hertz

ANS: C

3. Trimmers and padders are:a.two types of adjusting tools c. small adjustable inductorsb.small adjustable resistors d. small adjustable capacitors

ANS: D

4. "Skin effect" refers to:a.the way radio signals travel across a flat surfaceb.the tissue-burning effect of a strong RF signalc.the increase of wire resistance with frequencyd.none of the above

ANS: C

5. The "front end" of a receiver can include:a.the tuner c. the mixerb.the RF amplifier d. all of the above

ANS: D

6. "IF" stands for:a.intermediate frequency c. indeterminate frequencyb.intermodulation frequency d. image frequency

ANS: A

7. AGC stands for:a.Audio Gain Control c. Active Gain Controlb.Automatic Gain Control d. Active Gain Conversion

ANS: B

8. The frequency of the local oscillator: a. is above the RF frequency

b.is below the RF frequencyc.can be either above of below the RF frequencyd.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 responsesb.it increases sensitivityc.it increases selectivityd.it is cheaper

ANS: D

10. Basically, sensitivity measures:a.the weakest signal that can be usefully receivedb.the highest-frequency signal that can be usefully receivedc.the dynamic range of the audio amplifierd.none of the above

ANS: A

11. Basically, selectivity measures:a.the range of frequencies that the receiver can selectb.with two signals close in frequency, the ability to receive one and reject the otherc.how well adjacent frequencies are separated by the demodulatord.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 c. a value of 1.0 is idealb.a value of 0.707 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 c. both values are basically equivalentb.a value of 4 is better than a value of 2 d. none of the above

ANS: A

14. Distortion in a receiver can occur in:a.the mixer c. the IF amplifiersb. the detector d. all of the above

ANS: D

15. Phase distortion is important in:a.voice communications systems c. monochrome video receiversb.color video receivers d. all of the above

ANS: B

16. The response of a receiver to weak signals is usually limited by:a.the AGC c. the dynamic range of the receiverb.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 frequencyc. 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 c. prior to detectionb.prior to IF amplification d. images cannot be rejected

ANS: A

19. Image frequency problems would be reduced by:a.having an IF amplifier with the proper shape factorb.having a wideband RF amplifier after the mixerc.having a narrowband RF amplifier before the mixerd.none of the above

ANS: C

20. A common AM detector is the:a.PLL c. ratio detectorb.envelope detector d. all of the above

ANS: B

21. An FM detector is the:a.PLL c. quadrature detectorb.ratio detector d. all of the above

ANS: D

22. Germanium diodes are used in AM detectors because:a.they are faster than silicon diodesb.they are cheaper than silicon diodesc.they minimize distortion from nonlinearityd.all of the above

ANS: C

23. A common SSB detector is:a.a PLL c. a BFOb.a dioded. a product detector

ANS: D

24. BFO stands for:a.Beat Frequency Oscillator c. Bipolar Frequency Oscillatorb.Barrier Frequency Oscillatord. Bistable Frequency Oscillator

ANS: A

25. To demodulate both SSB and DSBSC, you need to:a.use a Foster-Seeley discriminatorb.reinject the carrierc.use double conversiond.use one diode for SSB and two diodes for DSBSC

ANS: B

26. Which would be best for DSBSC:a.carrier detection c. envelope detectionb.coherent 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 detectorb.a quadrature detector d. all of the above

ANS: C

28. The function of a limiter is:a.to remove amplitude variations c. to limit dynamic rangeb.to limit spurious responses d. to limit noise response

ANS: A

29. Suppressing the audio when no signal is present is called:a.AGC c. AFCb.squelch d. limiting

ANS: B

30. LNA stands for:a.Limited-Noise Amplifier c. Low-Noise Audiob.Low-Noise Amplifier d. Logarithmic Noise Amplification

ANS: B

31. AFC stands for:a.Audio Frequency Compensator c. Automatic Frequency Controlb.Autodyne Frequency Compensation d. Autonomous Frequency Control

ANS: C

32. The function of AFC is:a.maintain a constant IF frequencyb.match the local oscillator to the received signal

c.lock the discriminator to the IF frequencyd.none of the above

ANS: B

33. SAW stands for:a.Symmetrical Audio Wave c. Silicon-Activated Waferb.Surface Acoustic Wave d. Software-Activated Wave

ANS: B

34. The important property of a SAW is:a.it stabilizes the audio in a receiver c. it is a stable bandpass filterb.it allows software radios to be built d. none of the above

ANS: C

35. The main function of the AGC is to:a.keep the gain of the receiver constantb.keep the gain of the IF amplifiers constantc.keep the input to the detector at a constant amplituded.all of the above

ANS: C

36. DSP stands for:a.Dynamic Signal Properties c. Distorted Signal Packetb.Direct Signal Phase d. Digital Signal Processor

ANS: D

37. SINAD stands for:a.Sinusoidal Amplitude Distortionb.Signal and Noise Amplitude Distortionc.Signal-plus-Noise-to-Noise Ratiod.Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio

ANS: D

38. TRF stands for:a.Tuned Radio Frequency c. Transmitted Radio Frequencyb.Tracking 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 each other, it means that when the frequency of one isadjusted, the other changes with it.

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 oscillatorfrequency 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 infrequency.

ANS: Selectivity

13. is the ability of a receiver to receive and successfully demodulate a very weaksignal.

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 of theinput signal.

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 coupled for the response to have a flattop and steep sides.

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 frequency than the incomingsignal.

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

3 3 . A n -meter is designed to indicate signal strength in many communicationsreceivers.

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 k

c 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 c. Morse codeb.Baudot code d. none of the above

ANS: C

2. In digital transmission, signal degradation can be removed using:a.an amplifier c. a regenerative repeaterb.a filter d. all of the above

ANS: C

3. TDM stands for:a.Time-Division Multiplexing c. Ten-Digital Manchesterb.Time-Domain Multiplexing d. Ten Dual-Manchester

ANS: A

4. Hartley's Law is:a.I = ktB c. C = B log2(1 + S/N)b.C = 2B log2M d. SR = 2fmax

ANS: A

5. The Shannon-Hartley theorem is:a.I = ktB c. C = B log2(1 + S/N)b.C = 2B log2M d. SR = 2fmax

ANS: B

6. The Shannon Limit is given by:a.I = ktB c. C = B log2(1 + S/N)b.C = 2B log2M d. SR = 2fmax

ANS: C

7. The Nyquist Rate can be expressed as:a.I = ktB c. C = B log2(1 + S/N)b.C = 2B log2M d. SR = 2fmax

ANS: D

8. Natural Sampling does not use:a.a sample-and-hold circuit c. a fixed sample rateb.true binary numbers d. an analog-to-digital converter

ANS: A

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

ANS: C

11. The immediate result of sampling is:a.a sample alias c. PCMb.PAM d. PDM

ANS: B

12. Which of these is not a pulse-modulation technique:a.PDM c. PPMb.PWM d. PPS

ANS: D

13. Quantizing noise (quantization noise):a.decreases as the sample rate increasesb.decreases as the sample rate decreasesc.decreases as the bits per sample increasesd.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 signalb.the maximum rate of conversion to the minimum rate of conversionc.the maximum bits per sample to the minimum bits per sampled.none of the above

ANS: A

15. Companding is used to:a.compress the range of base-band frequenciesb.reduce dynamic range at higher bit-ratesc.preserve dynamic range while keeping bit-rate lowd.maximize the useable bandwidth in digital transmission

ANS: C

16. In North America, companding uses:a.the Logarithmic Law c. the c x Law (alpha law)b.the A Law d. the µ Law (mu law)

ANS: D

17. In Europe, companding uses:a.the Logarithmic Law c. the c x Law (alpha law)b.the A Law d. the µ Law (mu law)

ANS: B

18. Codec stands for:a.Coder-Decoder c. Code-Compressionb.Coded-Carrier d. none of the above

ANS: A

19. A typical codec in a telephone system sends and receives:a.4-bit numbersc. 12-bit numbersb.8-bit numbers d. 16-bit numbers

ANS: B

20. Compared to PCM, delta modulation:a.transmits fewer bits per sample c. can suffer slope overloadb.requires a much higher sampling rate 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 highb.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 distancesb.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 NRZb.Manchester d. bipolar RZ

ANS: C

24. Manchester coding:a. is a biphase codeb.has a level transition in the middle of every bit periodc.provides strong timing informationd.al l of the above

ANS: D

25. The number of framing bits in DS-1 is:

29.

a.1 c. 4b.2 d. 8

ANS: A

26. Framing bits in DS-1 are used to:a.detect errors c. synchronize the transmitter and receiverb.carry signaling d. all of the above

ANS: C

27. So-called "stolen" bits in DS-1 are used to:a.detect errors c. synchronize the transmitter and receiverb.carry signaling d. all of the above

ANS: B

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

ANS: D

The number of samples per second in DS-1 is:a.8 kb . 5 6 k

0.a.

c.d.

48

64 k1.544

×106

ANS: A

30. The bit rate for each channel in DS-1 is:a.1.544 Mb/s c. 56 kb/sb.64 kb/sd. 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/sb.64 kb/sd. 8 kb/s

ANS: A

32. A T-1 cable uses:a.Manchester coding c. NRZ codingb.bipolar RZ AMI coding d. pulse-width coding

ANS: B

33. The number of frames in a superframe is:a.6 c. 24b.12 d. 48

ANS: B

34. A typical T-1 line uses:

a.twisted-pair wire c. fiber-optic cableb.coaxial cable d. microwave

ANS: A

35. "Signaling" is used to indicate:a.on-hook/off-hook condition c. ringingb.busy signal d. all of the above

ANS: D

36. A vocoder implements compression by:a.constructing a model of the transmission mediumb.constructing a model of the human vocal systemc.finding redundancies in the digitized datad.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 sameb.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 as thelength of the channel increases.

ANS:

decreases gets worse

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

ANS: binary

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 in digitaltransmission systems.

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 theorem gives the maximum rate of data transmissionfor a given bandwidth.

ANS: Shannon-Hartley

13. The limit gives the maximum rate of data transmission for a given bandwidthand a given signal-to-noise ratio.

ANS: Shannon

14. sampling is done without a sample-and-hold circuit.

ANS: Natural

15. The Rate is the minimum sampling rate for converting analog signals to digitalformat.

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 theidentity" 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 bitsbefore being compressed to 8 bits.

ANS: 12

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

ANS: 1one

27. Delta modulation requires a sampling rate than PCM for the same quality ofreproduction.

ANS: higher

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 the bit rateof PCM.

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 information regardless of the pattern of ones andzeros.

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.

ANS: 1.544 × 106

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 doit.

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 c. Dual-Tone Multifrequencyb.Dial Tone Master Frequency d. Digital Trunk Master Frequency

ANS: C

2. PSTN stands for:a.Public Switched Telephone Network c. Primary Service Telephone Networkb.Private Switched Telephone Network d. Primary Service Telephone Numbers

ANS: A

3. POTS stands for:a.Private Office Telephone System c. Primary Operational Test Systemb.Primary Office Telephone Service d. Plain Old Telephone Service

ANS: D

4. LATA stands for:a.Local Access and Transport Area c. Local Area Telephone Accessb.Local Access Telephone Area d. Local Area Transport Access

ANS: A

5. A LATA is a:a.a local calling area c. a way of accessing a tandem officeb.a type of digital local network d. a way of accessing a central office

ANS: A

6. Central offices are connected by:a.local loops c. both a and bb. trunk l ines d. none of the above

ANS: B

7. Local loops terminate at:a.a tandem office c. a central officeb.a toll station d. an interexchange office

ANS: C

8. Call blocking:a.cannot occur in the public telephone networkb.occurs on the local loop when there is an electrical power failurec.occurs only on long-distance cablesd.occurs when the central office capacity is exceeded

ANS: D

9. In telephony, POP stands for:a.Post Office Protocol c. Power-On Protocolb.Point Of Presence d. none of the above

ANS: B

10. The cable used for local loops is mainly:a.twisted-pair copper wire c. coaxial cableb.shielded twisted-pair copper wire d. fiber-optic

ANS: A

11. FITL stands for:a.Framing Information for Toll Loops c. Framing In The Loopb.Fiber In the Toll Loop d. Fiber-In-The-Loop

ANS: D

12. Loading coils were used to:a.increase the speed of the local loop for digital datab.reduce the attenuation of voice signalsc.reduce crosstalkd.provide C-type conditioning to a local loop

ANS: B

13. DC current flows through a telephone:a.when it is on hook c. as long as it is attached to a local loopb.when it is off hook d. only when it is ringing

ANS: B

14. The range of DC current that flows through a telephone is:a . 20 µ A to 80 µ A c. 2 mA to 8 mAb.200 µ A to 800 µ A 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 controlb.crossbar control d. ESS

ANS: C

16. The typical voltage across a telephone when on-hook is:a.48 volts DC c. 90 volts DCb.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 c. 90 volts DCb.48 volts, 20 hertz AC 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 multiplexedb.prevent "singing" d. all of the above

ANS: C

19. VNL stands for:a.voltage net loss c. via net lossb.volume 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 ratiob.prevent oscillation d. reduce power consumption

ANS: B

21. The reference noise level for telephony is:a.1 mW c. 1 pWb.0 dBm d. 0 dBr

ANS: C

22. The number of voice channels in a basic FDM group is:a.6 c. 24b.12 d. 60

ANS: B

23. Basic FDM groups can be combined into:a.supergroups c. jumbogroupsb.mastergroups d. all of the above

ANS: D

24. In telephone system FDM, voice is put on a carrier using:a.SSB c. PDMb.DSBSC d. PCM

ANS: A

25. PABX stands for:a.Power Amplification Before Transmissionb.Private Automatic Branch Exchangec.Public Automated Branch Exchanged.Public Access Branch Exchange

ANS: B

26. SLIC stands for:a.Single-Line Interface Circuit c. Subscriber Line Interface Cardb.Standard Line Interface Card d. Standard Local Interface Circuit

ANS: C

27. In DS-1, bits are "robbed" in order to:a.provide synchronization c. cancel echoesb.carry signaling d. check for errors

ANS: B

28. "Bit-stuffing" is more formally called:a.compensation c. justificationb.rectification d. frame alignment

ANS: C

29. ISDN stands for:a.Integrated Services Digital Network c. Integrated Services Data Networkb.Information Services Digital Network d. Information Systems Digital Network

ANS: A

30. Basic ISDN has not been widely adopted because:a.it took to long to developb.it is too slowc.it has been surpassed by newer technologiesd.al l of the above

ANS: D

31. ADSL stands for:a.All-Digital Subscriber Line c. Allocated Digital Service Lineb.Asymmetrical Digital Subscriber 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 expensiveb.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, thousand telephones can connect to a centraloffice.

ANS: ten

5 . Cal l is when it becomes impossible for a subscriber to place a call due to anoverload 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 network never needs more than oneintermediate switch.

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 full-duplex 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 atypical telephone receiver.

ANS: C-message

23. In FDM telephony, the modulation is usually .

ANS:SSBSSBSC

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 kbps whenused to send digital data.

ANS: 56

26. A is a group of 12 DS-1 frames with signaling information in the sixth andtwelfth frames.

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 signals because they use the same pair ofwires as the voice signal.

ANS: in-channel

29. SS7 is the current version of signaling.

ANS: common-channel

3 0 . S S 7 i s 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 than the speed in theopposite direction.

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 distanceb.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 Unionb.the Teletype Company d. Emile Baudot

ANS: D

3. Data codes are also called:a.character codes c. they do not have any other nameb.character sets 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 datab.binary data d. all of the above

ANS: B

5. Character codes include:a.alphanumeric characters c. graphic control charactersb.data link control characters d. all of the above

ANS: D

6. ASCII stands for:a.American Standard Character-set 2b.American Standard Code for Information Interchangec.American Standard Code 2d.Alphanumeric Standard Code for Information Interchange

ANS: B

7. BS, FF, and CR are examples of:a.nonstandard character codes c. control charactersb.escape 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-Transmitterb.Unidirectional Asynchronous Receiver-Transmitterc.Unaltered Received Textd.Universal Automatic Receiver for Text

ANS: A

10. In asynchronous transmission, the transmitter and receiver are:a.frame-by-frame synchronized using the data bitsb.frame-by-frame synchronized using a common clockc.frame-by-frame synchronized using the start and stop bitsd.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-timesb.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 framesb.much longer than asynchronous framesc.128 bytes longd.1024 bytes long

ANS: B

13. Synchronous transmission is used because:a.no start and stop bits means higher efficiencyb.it is cheaper than asynchronous since no UARTS are requiredc.it is easier to implement than asynchronousd.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 bitsb.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 allowedb.transmission must stop periodically for resynchronizationc.the clock circuits must be precisely adjustedd.the channel must be noise-free

ANS: A

16. BISYNC:a.is an IBM product c. requires the use of DLEb.is a character-oriented protocol d. all of the above

ANS: D

17. HDLC:a.is an IBM product c. is identical to SDLCb.is a bit-oriented protocol d. all of the above

ANS: B

18. The use of flags in SDLC requires:a."bit-stuffing" c. FECb.different flags at either end of a frame d. ARQ

ANS: A

19. The initials ARQ are used to designate:a.automatic request for resynchronization c. automatic receiver queueb.automatic request for retransmission d. automatic request for queue

ANS: B

20. ARQ is used to:a.correct bit errors c. put data into a temporary bufferb.correct synchronization problems d. none of the above

ANS: A

21. FEC stands for:a.Fixed Error Control c. Forward Error Correctionb.Forward Error Control d. False Error Condition

ANS: C

22. VRC is another name for:a.FEC c. LRCb.ARQ d. parity

ANS: D

23. CRC stands for:a.Control Receiver Code c. Cyclic Redundancy Checkb.Correct Received Character d. Cycle Repeat Character

ANS: C

24. Huffman codes:a.allow errors to be detected but not correctedb.allow errors to be detected and correctedc.allow alphanumeric data to be corrected

correct datanone of the above

avoids the "password problem" all of the above

Synchronous Data Link CharacterSynchronous Data Line Character

d. allow alphanumeric data to be compressed

ANS: D

25. Run-length encoding is used to:

a. encrypt data c.b. compress data d.

ANS: B

26. Public-key encryption:

a. allows the use of digital signatures c.b. is used to convey symmetric keys d.

ANS: D

27. SDLC stands for:

a. Synchronous Data Link Control c.b. Synchronous Data Line Control d.

ANS: A

28. HDLC is:

a.a bit-oriented protocolc. an ISO standardb.based on SDLC 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 code is a 7-bit code commonly used in communication between personalcomputers.

ANS: ASCII

5. The two letters designate the code character used to advance a printer to the nextpage.

ANS: FF

17. BCC stands for check character.

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 is used in an asynchronous communication systemto convert between parallel and serial data.

ANS: UART

10. When receiving digital data, are used to hold data until they can be read.

ANS: buffers

11. Synchronous communication is more than asynchronous since there are fewer"overhead" bits.

ANS: efficient

12. There must be sufficient 1-to-0 to maintain synchronization in synchronoustransmission.

ANS: transitions

13. Clock sync is derived from the stream of bits in synchronous transmission.

ANS: data

14 . In t he 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

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

2 2 . A n 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.

17. BCC stands for check character.

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 c. Carrier Server Master Applicationb.Carrier Sense Multiple Access d. none of the above

ANS: B

2. The CD in CSMA/CD stands for:a.Carrier Detection c. Collision Detectionb.Carrier Delay d. Collision Delay

ANS: C

3. The Internet is:a.a network of networks c. a very large CSMA/CD networkb.a very large client-server network d. not really a network at all

ANS: A

4. Most LANs:a.are based on Ethernet c. use UTP cableb.use CSMA/CD d. all of the above

ANS: D

5. Dumb terminals are still used:a.in token-passing networksb.in networks requiring central monitoringc.in networks that cannot provide central monitoringd.none of the above

ANS: B

6. In a circuit-switched network:a.communication is half-duplex onlyb.each channel carries only one data streamc.connection is usually done using a bus topologyd.all of the above

ANS: B

7. Each computer on a network is called a:a.hub c. nodeb.token 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 nodeb.a central bus d. none of the above

ANS: D

10. On networks, long messages are divided into "chunks" called:a.packets c. carriersb.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 trafficb.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 trafficb.contention d. multiple access

ANS: A

13. One type of network that never has a collision is:a.CSMA c. token-passingb.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. packetsb.users d. collisions

ANS: D

15. The effect of too many collisions is:a.the network goes down c. the cable overheatsb.the network slows down d. data is lost

ANS: B

16. MAU stands for:a.Multistation Access Unit c. Multiple Auxiliary Unitsb.Multiple Access Unit 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 c. Xeroxb.INTEL d. Digital Equipment Corporation

ANS: C

19. An Ethernet running at 10 Mbits / second uses:a.Manchester encoding c. NRZ encodingb.Three-Level encoding d. AMI encoding

ANS: A

20. A 100BaseT cable uses:a.fiber-optic cable c. RG-58U coaxial cableb.twisted-pair copper wires d. 50-ohm coaxial cable

ANS: B

21. The word "Base" in 10BaseT means:a.the cable carries baseband signalsb.the cable has a base speed of 10 Mbpsc.it can be used as the base for a backbone cable systemd.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 rateb.to prevent packets from reaching all other nodes during transmissionc.to make sure all other nodes hear a collision in progressd.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 rateb.to prevent packets from reaching all other nodes during transmissionc.to make sure all other nodes hear a collision in progressd.all of the above

ANS: C

24. NIC stands for:a.Network Interface Card c. Network Interface Codeb.Network Interface Cable 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 c. Uninterruptible Terminal Packetb.Unshielded Twisted-Pair copper wire d. Unicode Text Packet

ANS: B

27. Compared to twisted-pair telephone cables, CAT-5 cables:a.are cheaper c. allow faster bit ratesb.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 itb.sends incoming packets out to specific portsc.cannot be used in an Ethernet-type networkd.are more common in token-passing networks

ANS: A

29. A switch:a.sends incoming packets out to all other terminals connected to itb.sends incoming packets out to specific portsc.cannot be used in an Ethernet-type networkd.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 networksb.it is faster when used in large networksc.it reduces the number of collisions in large networksd.al l of the above

ANS: C

31. Broadband LANs:a.modulate the data onto a carrierb.use coaxial cablesc.are provided by cable TV companies for Internet accessd.al l 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 bb.client-server networks d. none of the above

ANS: B

33. Record locking is used to:a.store records securely on a serverb.prevent multiple users from looking at a document simultaneouslyc.prevent one user from reading a record that another user is writing tod.none of the above

ANS: C

34. The software that runs a client-server network must be:a.UNIX-based c. multitaskingb.WINDOWS-based d. Novell certified

ANS: C

35. A "thin" client is:a.basically, a PC with no disk drives c. same as a "dumb" terminalb.a node that rarely sends data d. all of the above

ANS: A

COMPLETION

1. A LAN is a Area Network.

ANS: Local

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

communications.

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 is a short section of a message in digital form.

ANS: packet

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:quietfreeunusedavailable

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 of each incoming packet.

ANS: address

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 c. Metropolitan-Area Networkb.Multiple-Area Network d. Multiple Access Network

ANS: C

2. Packet switching is based on:a.store-and-forward c. real-time deliveryb.switched circuits d. all of the above

ANS: A

3. SNA stands for:a.Standard Network Access c. Standard Network Architectureb.Small Network Access d. Systems Network Architecture

ANS: D

4. The number of layers in ISO OSI is:a.3 c. 7b.5 d. 8

ANS: C

5. The lowest-level layer in ISO OSI is called the:a.physical layer c. cable layerb.link layer d. transport layer

ANS: A

6. Bad frames are usually detected by the:a.frame layer c. error-check layerb.physical layer d. link layer

ANS: D

7. A virtual circuit is set up by the:a.user c. networkb.link layer d. frame

ANS: C

8. Frame Relay:a.is faster than X.25 c. allows for variable length packetsb.does less error checking than X.25 d. all of the above

ANS: D

9. ATM stands for:a.Asynchronous Transfer Mode c. Asynchronous Transmission Modelb.Asynchronous Transmission Mode d. Automatic Test Mode

ANS: A

10. A bridge:a.separates a network into "collision domains"b.looks at the address of each packetc.operate at the data-link leveld.all of the above

ANS: D

11. IP stands for:a.Internet Process c. Interconnect Protocolb.Internet Protocol d. Interconnect Procedure

ANS: B

12. TCP stands for:a.Transmission Control Process c. Transfer Connection Protocolb.Transmission Control Protocol d. none of the above

ANS: B

13. Together, TCP/IP consists of:a.5 layersc. an application and a processb.7 layersd. datagrams

ANS: A

14. IP is a:a.connection-oriented protocol c. connectionless protocolb.virtual circuit d. non-robust protocol

ANS: C

15. The "lifetime" of a packet in an IP network:a.is essentially foreverb.depends on elapsed time since transmissionc.depends on number of "hops" between nodesd.is approximately 200 milliseconds

ANS: C

16. UDP stands for:a.User Datagram Protocol c. User Data Packetb.User Data Protocol d. Universal Data Packet

ANS: A

17. HTTP stands for:a. High-speed Transmission Test Procedure

b.High-Level Transfer Test Procedurec.Hypertext Transmission and Transport Procedured.Hypertext Transport Protocol

ANS: D

18. HTTP allows the use of:a.dumb terminals c. browsersb.file transport d. none of the above

ANS: C

19. HTML stands for:a.Hypertext Markup Language c. Hypertext Transfer-Mode Layerb.Hypertext Transfer-Mode Level d. High-speed Transfer-Mode Language

ANS: A

20. HTML allows:a. telneting c. web page layoutb.high-speed file transfer d. all of the above

ANS: C

21. FTP stands for:a.File Transfer Protocol c. File Test Procedureb.File Transport Protocol d. Fast Transport Packet

ANS: A

22. FTP is used to:a.transfer files between a server on the network and a userb.test files to see if their data has been "corrupted"c.transport packets at maximum speed through the networkd.none of the above

ANS: A

23. SMTP stands for:a.Short Message Transport Protocol c. Simple Mail Transport Protocolb.Simple Message Transport Protocol d. Secondary Mail Transfer Procedure

ANS: C

24. ISP stands for:a.Internet Service Protocol c. Internet Service Procedureb.Internet Service Provider d. none of the above

ANS: B

25. The standard Internet address (or URL) is:a.a 32-bit binary number c. running out of available valuesb.four groups of base-ten numbers d. all of the above

ANS: D

26. DNS stands for:a.Domain Name Server c. Domain Numbering Systemb.Domain Name System d. Domain Naming System

ANS: A

27. A DNS:a.has become obsolete on the Internetb.translates words to numbersc.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 Interconnectionc. Open Systems Internetb.Open Standard Interconnection 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 c. Full-Signal Keyingb.Frequency-Shift Keying d. none of the above

ANS: B

2. PSK stands for:a.Pulse-Signal Keying c. Phase-Signal Keyingb.Pulse-Shift Keying d. Phase-Shift Keying

ANS: D

3. QAM stands for:a.Quadrature Amplitude Modulation c. Quadrature Amplitude Markingb.Quadrature Amplitude Masking d. none of the above

ANS: A

4. In the equation I = ktB, I is measured in:a.amperes c. bitsb.amperes per second d. bits per second

ANS: C

5. In the equation C = 2Blog2M, M is the:a.margin of noise c. number of possible states per symbolb.modulation index 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 openb.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 distortionb.too many bits low d. intersymbol interference

ANS: D

8. High-frequency radioteletype systems commonly use:a.FSK c. PSKb.AFSK d. QAM

ANS: A

9. Instead of a single bit, a QPSK symbol contains:a.a byte c. a dibitb.4 bits d. a Q-bit

ANS: C

10. To reduce the need for linearity, ir/4 DQPSK uses:a.angles of 0, 90, 180, and 270 degrees c. angles of i r/4, 2 i r/4, 3 i r/4, and 4 i r/4b.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" c. effects of noise on symbolsb.separation of symbols in "symbol space" 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 angleb.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, FSKb.600 bps, full-duplex, FSK d. 1200 bps, half-duplex, FSK

ANS: A

14. ITU is an abbreviation for:a.International Telephony Unit c. International Telecommunications Unionb.International Telephony Union d. International Telecommunications Units

ANS: C

15. The ITU is under the auspices of:a.CCITT c. IEEEb.the U.N. d. ANSI

ANS: B

16. High-speed modems equalize the line to compensate for:a.noise and interferenceb.uneven phase and frequency responsec . low SNRd.inconsistent bit rates at either end of channel

ANS: B

17. The bits sent to allow equalization are called:a.Gaussian bi ts c. a training sequenceb.random bits d. a random sequence

ANS: C

18. The V.90 standard is issued by:a.the EIA c. the ITUb.the TIA d. the ISO

ANS: C

19. MNP2, MNP3, MNP4, and MNP10 are all:a.data-compression schemes c. both a and bb.error-correction protocols d. none of the above

ANS: B

20. MNP5 and V.42 bis are both:a.data-compression schemes c. both a and bb.error-correction protocols d. none of the above

ANS: A

21. In RS-232, flow control is done using:a.RTS/CTS handshake c. both a and bb.XON/XOFF characters d. none of the above

ANS: C

22. The official name for RS-232C is:a.RS-232C c. ISO-232C/Db.EIA-232D d. ANSI-232C

ANS: B

23. In RS-232, a modem would be:a.a DTR c. a DCEb.a DSR d. a DTE

ANS: C

24. In RS-232, a personal computer would be:a.a DTR c. a DCEb.a DSR d. a DTE

ANS: D

25. On a DB-9 RS-232 connector, signal ground is pin:a.1 c. 5b.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: C

27. The minimum lines required for RS-232 are:a.TD and RD c. TD, RD, DSR, and signal groundb.TD, RD, and signal ground d. TD, RD, RTS, CTS, and signal ground

ANS: B

28. Hardware flow control uses:a.XON and XOFF c. RTS and CTSb.TD and RD d. DSR and DCD

ANS: C

29. Software flow control uses:a.XON and XOFF c. RTS and CTSb.TD and RD d. DSR and DCD

ANS: A

30. Which voltage represents a binary zero on an RS-232 data pin:a.+15 volts c. +9 voltsb.+12 volts d. all of the above

ANS: D

31. DSL stands for:a.Data Signal Line c. Digital Subscriber Lineb.Digital Signal Line d. Double-Speed Loop

ANS: C

32. ADSL stands for:a.Asynchronous DSL c. Analog DSLb.Asymmetrical DSL d. All DSL

ANS: B

33. In a CATV system, HFC stands for:a.Head Frequency Control c. Hybrid Fiber-Coaxb.Hybrid Frequency Control d. Hybrid Fiber Control

ANS: C

34. In a CATV system, CMTS stands for:a.Cable Modem Terminal Server c. Cable Modem Terminal Systemb.Cable Modem Transmission 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 Liteb.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, coding adds extra bits to improve performance on a noisyline.

ANS: Trellis

13. is used in a high-speed modem to compensate for uneven frequency and phaseresponse 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 line is asserted when the analog carrier from another modem isbeing received.

ANS: CD

DCD RLSD

17. Between hardware flow control and software flow control, flow control ispreferred.

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 is used to put several channels of dataonto a fiber-optic backbone.

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 dial-up 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 orbins 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 c. Tone Division Multiple Accessb.Time-Division Multiple Access d. none of the above

ANS: B

2. CDMA stands for:a.Code-Division Multiple Access c. Compact Digital Multiplex Arrangementb.Carrier Division Multiple Access d. none of the above

ANS: A

3. TDMA is used instead of TDM when:a.all the signals come from the same sourceb.the signals come from different sourcesc.TDM is used in RF communicationsd.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 signalb.the length of the channel d. all of the above

ANS: C

5. A DS-1 signal contains:a.12 channels c. 32 channelsb.24 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 Mbpsb.256 kbps d. 1.544 Mbps

ANS: D

7. Besides data bits, a DS-1 frame contains a:a.timing bit c. signaling bitb.T-bit d. framing bit

ANS: D

8. In DS-1, a bit is "stolen" out of each channel:a.every frame c. every sixth frameb.every other frame d. every twelfth frame

ANS: C

9. Moving signals from one line to another is called:a.t ime switching c. line switchingb.space switching d. cross-point switching

ANS: B

10. Moving PCM samples from one time-slot to another is called:a.t ime switching c. signal switchingb.space switching d. crosspoint switching

ANS: A

11. A digital space switch is a:a.multiplexer c. computerized Strowger switchb.TDM switch d. crosspoint switch

ANS: D

12. Spread-spectrum can be done by using:a.computer-controlled frequency reuse c. direct-sequence methodb.frequency-hopping d. all of the above

ANS: D

13. The term "chip rate" is used in describing:a.computer-controlled frequency reuse c. direct-sequence methodb.frequency-hopping 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 bandwidthb.much more bandwidth d. approximately double the bandwidth

ANS: B

15. "Processing gain" is another term for:a.RF gain c. spreading gainb.computer speed 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 ratiob.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 receiverb.a wideband receiver d. a "chip-rate" receiver

ANS: B

19. CDMA:a.cannot be used with frequency-hopping spread-spectrumb.cannot be used with direct-sequence spread-spectrumc.cannot be used on an RF channeld.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 sequencesb.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 -division multiplexing.

ANS: frequency

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 ofbits 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 calledfading.

ANS: Rayleigh

17. A PN sequence is a -random noise sequence.

ANS: pseudo

18. One method of spread-spectrum is frequency .

ANS: hopping

1 9 . I t i s to jam a spread-spectrum signal.

ANS: difficult

2 0 . I t i s to eavesdrop on a spread-spectrum signal.

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 spread-spectrum 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 c. Shorted Wire Regionb.Sine Wave Response d. none of the above

ANS: D

2. TDR stands for:a.Total Distance of Reflection c. Time-Domain Responseb.Time-Domain Reflectometer d. Transmission Delay Ratio

ANS: B

3. An example of an unbalanced line is:a.a coaxial cable c. an open-wire-line cableb.300-ohm twin-lead TV 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 reactancesb.distributed d. ideal elements

ANS: B

5. As frequency increases, the resistance of a wire:a.increases c. stays the sameb.decreases d. changes periodically

ANS: A

6. The effect of frequency on the resistance of a wire is called:a.I2R loss c. the skin effect0.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 sameb.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 usedb.the resistance per foot and the inductance per footc.the resistance per foot and the capacitance per footd.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 c. increases with voltageb.increases with frequency 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 footb.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 pulseb.would reflect as a negative pulsec.would reflect as a positive pulse followed by a negative pulsed.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 pulseb.would reflect as a negative pulsec.would reflect as a positive pulse followed by a negative pulsed.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 pulseb.would reflect as a negative pulsec.would reflect as a positive pulse followed by a negative pulsed.would not reflect at all

ANS: A

15. The optimum value for SWR is:a.zero c. as large as possibleb.one d. there is no optimum value

ANS: B

16. A non-optimum value for SWR will cause:a.standing waves c. higher voltage peaks on cableb.loss of power to load d. all of the above

ANS: D

17. VSWR stands for:a.variable SWR c. voltage SWR

b.vacuum SWR d. none of the above

ANS: C

18. The impedance "looking into" a matched line:a.is infinite c. is the characteristic impedanceb.is zero d. 50 ohms

ANS: C

19. A Smith Chart is used to calculate:a.transmission line impedances c. optimum length of a transmission lineb.propagation velocity 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 sameb.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 zeroc. multiplying it by 2

b.dividing i t by 2 t d. dividing it by Z0

ANS: D

23. The radius of the circle you draw on a Smith Chart represents:a.the voltage c. the impedanceb.the current d. none of the above

ANS: D

24. The center of the Smith Chart always represents:a.zero c. the characteristic impedanceb.one d. none of the above

ANS: C

25. A TDR is commonly used to:a.measure the characteristic impedance of a cableb.find the position of a defect in a cable

c.replace a slotted-lined.al l 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 lines since both wires are symmetrical withrespect to ground.

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 parameters instead oflumped ones.

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 field insidethe wire.

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 impedance.

ANS: surge

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

21. Besides heat from I2R, the power a cable can carry is limited by the voltage ofits dielectric.

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 Er

= 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. Maxwellb.Hertz d. Marconi

ANS: C

2. Radio waves were first demonstrated experimentally by:a.Armstrong c. Maxwellb.Hertz d. Marconi

ANS: B

3. The technology that made cell phones practical was:a.the microprocessor chip c. high-power microwave transmittersb.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 frequenciesb.high antennasd. all of the above

ANS: C

5. Which of the following are electromagnetic:a.radio waves c. gamma wavesb. l ight 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 bb.perpendicular to the direction of travel d. none of the above

ANS: C

7. TEM stands for:a.Transverse Electromagnetic c. True Electromagneticb.Transmitted Electromagnetic d. none of the above

ANS: A

8. In free space, radio waves travel at a speed of:a.3 x 106 meters per second c. 3 x 106 miles per secondb.300 x 106 meters per second d. 300 x 106 miles per second

ANS: B

9. Which is a possible polarization for an electromagnetic wave:a.vertical c. circularb.horizontal d. all of the above

ANS: D

10. Which polarization can be reasonably well received by a circularly polarized antenna:a.vertical c. circularb.horizontal d. all of the above

ANS: D

11. The number of circular polarization modes (directions) is:a.1 c. 3b.2 d. many

ANS: B

12. An antenna has "gain" as compared to:a.an isotropic radiator c. a ground-wave antennab.a vertically polarized radiator d. none of the above

ANS: A

13. EIRP stands for:a.the E and I fields of the Radiated Powerb.the Effective Isotropic Radiated Powerc.the Effective Internal Reflected Powerd.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 spaceb.losses due to absorption in the upper atmospherec.the decrease in energy per square meter due to expansion of the wavefrontd.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 c. at microwave frequenciesb.above about 20 MHz 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 c. a flat metallic surface of the right sizeb.a flat dielectric surface of the right size d. a flat body of water

ANS: C

17. Radio waves sometimes "bend" around a corner because of:

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

a. reflection c. refraction

b. diffusion d. diffraction

ANS: D

18. Space waves are:a.line-of-sightb.reflected off the ionospherec.same as sky wavesd.radio waves used for satellite communications

ANS: A

19. Sky waves:a.are l ine-of-sightb."bounce" off the ionospherec.are same as space wavesd.are radio waves used for satellite communications

ANS: B

20. Sky waves cannot be "heard":a.close to the transmitter c. in the "silent" zoneb.far from the transmitter 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 diversityb.diffraction d. spatial diversity

ANS: A

22. "Ghosts" on a TV screen are an example of:a.fading c. multipath distortionb.diffraction d. cancellation due to reflection

ANS: C

23. A "repeater" is used to:a.send a message multiple times over a channelb.send a message over multiple channels at the same timec.extend the range of a radio communications systemd.cancel the effects of fading

ANS: C

24. Cellular phone systems rely on:a.high power c. the radio horizonb.repeaters 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 callb.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 receiversb.a "rake" receiver d. none of the above

ANS: B

28. The troposphere is the:a.highest layer of the atmosphere c. lowest layer of the atmosphereb.middle layer of the atmosphere d. the most ionized layer of the atmosphere

ANS: C

29. Meteor-trail propagation is:a.used for radio telephony c. also called "ducting"b.used to send data by radio 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.

ANS: 300 × 106

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.

ANS: 3 × 106

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 to its propagationdirection.

ANS: perpendicular

14 . Wi th polarization, the direction of a radio wave's electric field rotates as ittravels through space.

ANS: circular

15. An antenna is said to have in a certain direction if it radiates more power in thatdirection than in other directions.

ANS: gain

16. The watts per square meter of a radio wave as the wave-front moves throughspace.

ANS: decrease

17. Reflection of plane-waves from a smooth surface is called reflection.

ANS: specular

18. is the "bending" of radio waves as they travel across the boundary between twodifferent 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 waves interferingwith direct waves.

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 thecell area, to reduce interference.

ANS: Sectoring

29. The use of chips makes cell phones a practical technology.

ANS: microprocessor

SHORT ANSWER

1. A certain dielectric has permittivity of 6.3 × 10–10 F/m and the same permeability as free space. What is the characteristic impedance of that dielectric?

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:796 pW/m2

3. What power must a point-source of radio waves transmit so that the power density at 3000 meters from the source is 1 µW/m2?

ANS:113 watts

4. If a radio receiver needs 1 nW/m2 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 SWRb.the reflected signal d. all of the above

ANS: A

2. A half-wave dipole is sometimes called:a.a Marconi antenna c. a Yagi antennab.a Hertz 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-wavelengthb.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 antennab.SWR along the feed cable d. I2R 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 directionsb.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 antennab.selectivity d. resonance

ANS: A

7. The front-to-back ratio of a half-wave dipole antenna is:a.0 dB c. 10 dBb.3 dB d. infinite

ANS: A

8. An antenna's beamwidth is measured:a . f rom +90 ° to –90 ° c. between half-power pointsb.from front to back d. between the minor side-lobes

ANS: C

9. ERP stands for:a.Equivalent Radiation Pattern c. Equivalent Radiated Power

b.Effective Radiation Pattern 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 groundb.buildings and other structures on the groundc . f a d i n gd.faulty connection of the feed cable ground

ANS: A

11. A 1-MHz monopole antenna must be:a.mounted vertically c. at least one half-wavelength longb.mounted horizontally d. at least one wavelength long

ANS: A

12. The typical antenna in an AM radio is a:a.dipole c. ferrite "loop-stick"b.folded dipole 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 rotationb.Faraday Rotation d. the distance traveled

ANS: B

14. A nonresonant antenna:a.will not transmit c. will cause SWR on the feed cableb.will not receive d. all of the above

ANS: C

15. At resonance, the input impedance to a lossless antenna should be:a.resistive c. capacitiveb.inductive d. infinite

ANS: A

16. An antenna can be matched to a feed line using:a.a shorted stub c. an LC networkb.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

An antenna is the interface between the transmission line and .

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

b. the number of nodes decreases d. none of the above

ANS: A

18. Arrays can be:a.phased c. parasiticb.driven 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 Dipoleb.Yagi d. stacked array

ANS: B

20. LPDA stands for:a.Low-Power Dipole Array c. Log-Periodic Dipole Arrayb.Low-Power Directed Array d. Log Power Dipole Array

ANS: C

21. The radiated beam from a parabolic "dish" transmitting antenna is:a.collimated c. dispersedb.phased d. none of the above

ANS: A

22. The energy picked up by a parabolic antenna is concentrated at the:a.center c. focusb.edges d. horn

ANS: C

23. Antennas are often tested in:a.an echo chamber c. a vacuum chamberb.an anechoic 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 meterb.a dipole d. a field-strength meter

ANS: D

COMPLETION

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 transmittedradio waves leaving the antenna.

ANS: radiation

5. Input impedance at the center feed point of a resonant half-wave dipole is about.

ANS: 70

6. Input impedance at the center feed point of a resonant folded dipole is about .

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

ANS: beamwidth

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:widergreater 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 element.

ANS: parasitic

25. An LPDA is a dipole array.

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

3 0 . A n 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 GHzb.1 GHz d. 100 GHz

ANS: B

2. The UHF range is:a.below the microwave range c. above the microwave rangeb.inside 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 injectionb.the power level of the signal d. none of the above

ANS: A

4. The dominant mode of a rectangular waveguide is:a .TE 0 1 c. TE 1 0

b.TM 0 1 d. TM1 0

ANS: C

5. The dominant mode of a circular waveguide is:a .TE 0 1 c. TE 11

b.TM 0 1 d. TM11

ANS: C

6. Circular waveguides use TM 01 mode because:a.i t is dominantc. it is the only mode possibleb.of its circular symmetry d. it is more efficient

ANS: B

7. The characteristic impedance of a waveguide:a . i s f i x e db.depends on the frequency it carriesc.depends on the longer dimension of its cross sectiond.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 waveguideb.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 directivityb.their coupling specification d. all of the above

ANS: D

10. Striplines and microstrips are used to:a.couple sections of waveguide c. couple components on a circuit boardb.couple waveguides to antennas d. none of the above

ANS: C

11. A resonant cavity is a type of:a. tuned circuit c. antennab.defect in a waveguide d. none of the above

ANS: A

12. A TEE connector used with waveguides is:a.an H-plane TEE c. a "magic" TEEb.an E-plane TEE d. all of the above

ANS: D

13. TWT stands for:a.Transverse Wave Transmissionc. Traveling-Wave Tubeb.Transverse-Wave Tube d. Traveling-Wave Transmission

ANS: C

14. An "isolator" is a device that:a.isolates frequencies in a waveguideb.allows a signal to pass in one direction onlyc.separates signals among various portsd.prevents microwaves from leaking out of a waveguide

ANS: B

15. A "circulator" is a device that:a.rotates signal polarity in a waveguideb.allows a signal to pass in one direction onlyc.separates signals among various portsd.prevents microwaves from being "trapped" in a waveguide

ANS: C

16. GaAs stands for:a.gallium arsenide c. gallium asteniteb.gallium assembly d. none of the above

ANS: D

17. IMPATT stands for:a.impact avalanche and transit time c. implied power at transmission terminalb.induced mobility at transmission time d. none of the above

ANS: A

18. YIG stands for:a.Yttrium-Iron-Gallium c. Yttrium-Iron-Garnetb.Yttrium-Iron-Germanium d. none of the above

ANS: C

19. A YIG can be tuned by applying:a.an electric field c. mechanical pressureb.a magnetic field d. an "exciter" signal

ANS: B

20. The device commonly used in microwave ovens is the:a.TWT c. magnetronb.klystron d. YIG

ANS: C

21. The device commonly used in satellite communications is the:a.TWT c. magnetronb.klystron d. YIG

ANS: A

22. The device commonly used in UHF transmitters is the:a.TWT c. magnetronb.klystron d. YIG

ANS: B

23. A microwave phased array is often made using:a.slots c. Fresnel lensesb.Yagis d. all of the above

ANS: A

24. RADAR stands for:a.radio ranging c. radio detection and rangingb.radio depth and ranging d. remote detection and ranging

ANS: C

25. RADAR uses:a.pulsed transmission c. the Doppler effectb.continuous transmission d. all of the above

ANS: D

26. The maximum effective range for pulsed radar:a.increases with increasing repetition rate c. decreases with increasing pulse periodb.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 rangeb.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 antenna is a flat piece of copper on an insulating substrate with a groundplane on the other side.

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 than the transmitted signal if thetarget is moving toward the radar antenna.

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:260 × 106 meters per second

3.Calculate the phase velocity in a waveguide carrying a signal that is twice its cutoff frequency.

ANS:346 × 106 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. skipb.hop d. jump

ANS: B

2. Microwave systems use:a.FM c. QAMb.SSB 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 wattsc. 200 wattsb.20 watts d. none of the above

ANS: A

5. In analog microwave systems, additional repeaters increase the:a.reliability c. jitterb.noise level d. all of the above

ANS: B

6. In digital microwave systems, additional repeaters increase the:a.reliability c. jitterb.noise level d. all of the above

ANS: C

7. LOS stands for:a.Loss Of Skip c. Line-Of-Sightb.Loss Of Signal d. Line-Of-Signal

ANS: C

8. Too much antenna gain causes:a.a very narrow microwave beam c. excessive noiseb.a very wide microwave beam d. jitter

ANS: A

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 towerb.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 valueb.an ERP level that exceeds a given valuec.an energy-per-hertz level that exceeds a given valued.none of the above

ANS: A

11. Satisfactory performance of a digital microwave system requires a:a.low level of transmitted powerb.high level of ERPc.good energy per bit per transmitted Watt ratiod.good energy per bit per noise density ratio

ANS: D

12. Fading is caused by:a.multipath reception c. ductingb.attenuation due to weather 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 antennasb.power d. all of the above

ANS: A

14. Repeaters are used in a microwave system:a.always c. above 10 GHzb.when distance exceeds line-of-sight d. below 10 GHz

ANS: B

15. Microwave repeaters can be:a.IF type c. regenerative typeb.baseband 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 powerb.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 Systemc.Multichannel Multipoint Distribution Systemd.Multiple Microwave Distribution Systems

ANS: C

18. LMDS stands for:a.Local Microwave Distribution Systemb.Local Multipoint Distribution Systemc.Local Multichannel Distribution Systemd.Low-power Microwave Distribution System

ANS: B

19. LMDS is:a.bidirectional c. multidirectionalb.unidirectional 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 noisethan noise figure incalculations.

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 diversityin a microwave system.

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-sightdistance.

ANS: Repeaters

12. Analog microwave systems use both IF and repeaters.

ANS: baseband

13. Microwave digital radio techniques reduce the accumulation of as a signal goesfrom link to link.

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 carrier-to-noise power ratio?

ANS: 40 dB

Chapter 19: Television

MULTIPLE CHOICE

1. NTSC stands for:a.National Television Systems Commissionb.National Television Systems Committeec.National Television Systems Councild.Nippon Television Systems Commission

ANS: B

2. The NTSC specification was drawn up by the:a.FCC c. EIAb.IRE d. IEEE

ANS: C

3. RGB stands for:a.Red-Green Burst c. Red-Green Bandwidthb.Red-Green Brightness d. Red-Green-Blue

ANS: D

4. The number of scan lines in an NTSC signal is:a.525 c. 1024b.625 d. 1250

ANS: A

5. The number of NTSC frames sent per second is:a.25 c. 50b.30 d. 60

ANS: B

6. The number of NTSC fields sent per second is:a.25 c. 50b.30 d. 60

ANS: D

7. The aspect ratio of a standard TV receiver is:a.3 : 4 c. 525 : 625b.4 : 3 d. 625 : 525

ANS: B

8. Luminance refers to:a.brightness c. chromab.contrast d. raster

ANS: A

9. Luminance is measured in:a.foot-candles c. IRE unitsb.lumins d. NTSC units

ANS: C

10. The maximum luminance level is called:a.max white c. all whiteb.peak white d. whiter than white

ANS: B

11. The blanking level corresponds to a luminance of:a.white c. whiter than whiteb.black d. blacker than black

ANS: B

12. The sync pulse level corresponds to a luminance of:a.white c. whiter than whiteb.black d. blacker than black

ANS: D

13. The vertical blanking pulse is serrated to:a.maintain horizontal sync c. equalize the DC levelb.maintain vertical sync d. all of the above

ANS: A

14. When measured in lines, horizontal resolution:a.is greater than vertical resolutionb.is about the same as vertical resolutionc.is less than vertical resolutiond.horizontal resolution is not measured in lines

ANS: B

15. The smallest picture element is called a:a.dot c. pixelb.pic 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 componentb.composite color signal, in-phase color component, quadrature phase color componentc.composite video signal, in-phase video component, quadrature video color componentd.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 lessb.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 AMb.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 AMb.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 AMb.vestigial sideband AM d. FM

ANS: C

21. The function of the "color burst" is to:a.detect the presence of a color video signalb.regenerate the color sub-carrierc.to synchronize the color demodulation line by lined.al l of the above

ANS: D

22. SAP stands for:a.separate audio program c. sync amplitude pulseb.separate audio pulse d. sync audio pulse

ANS: A

23. The horizontal output transformer is also called:a.the isolation transformer c. the flyback transformerb.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 lowerb.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 horizontalb.electrostatically for both vertical and horizontalc.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 c. automatic frequency and picture controlb.automatic frequency and phase 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:lumaluminance

8. Color information is called .

ANS:chromachrominance

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 co lor turns off the color circuitry when a color TV is receiving amonochrome signal.

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

ANS: purity

31. The controls in a color TV adjust the electron beams to strike the correct triad ofphosphor dots.

ANS: convergence

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 kmb.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 downlinkb.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. footprintb.downlink d. plate

ANS: C

4. The velocity required to stay in orbit:a. is constantb.is zero (freefall)c.is lower close to the earth than far from the earthd.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 elevationc. declination and elevationb.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 wattsb.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:a.101 watts c. 103 wattsb.102 watts d. 104 watts

ANS: C

8. The "payload" on a communications satellite consists of:a. t ransponders c. solar cellsb.batteries d. all of the above

ANS: A

9. "Station-keeping" refers to:a.antenna maintenance c. orbital adjustmentsb.power-level adjustments d. none of the above

ANS: C

10. DBS stands for:a.decibels of signal c. direct-broadcast systemb.down-beam signal d. direct-broadcast satellite

ANS: D

11. LNA stands for:a.low-noise amplifier c. low-noise amplitudeb.low north angle d. low-noise array

ANS: A

12. A reduction in TWT power for linearity is called:a.backdown c. power-downb.backoff d. EIRP drop

ANS: B

13. TVRO stands for:a.television receive only c. television remote originb.television repeater only d. none of the above

ANS: A

14. TDMA stands for:a.transponder-directed multiple antennas c. time-division multiple accessb.television distribution master antenna d. transmit delay minimum aperture

ANS: C

15. VSAT stands for:a.video satellite c. very small antenna terminalb.video signal 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 antennab.low power to a small antenna d. LEO satellites

ANS: B

17. A typical VSAT system is configured as a:a . s t ar c. ringb.mesh d. repeater

ANS: A

18. LEO stands for:a.long elliptic orbit c. lateral earth orbitb.low-earth orbit d. longitudinal earth orbit

ANS: B

19. For real-time communication, LEO systems require:a.a constellation of satellites c. very high powerb.tracking dish antennasd. 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 GHzb.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 than Ku-band antennas.

ANS: larger

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 c. Advanced Mobile Phone Systemb.Analog Mobile Phone Service d. Advanced Mobile Phone Service

ANS: D

2. PCS stands for:a.Personal Communications Service c. Personal Cell phone Serviceb.Personal Communications Systems d. Portable Communications Systems

ANS: B

3. RCC stands for:a.Radio Common Carrier c. Regional Cellular Carrierb.Radio Cellular Carrierd. none of the above

ANS: A

4. MSC stands for:a.Mobile Switching Center c. Maximum Signal Carrierb.Mobile Service Cellular d. Minimum Signal Carrier

ANS: A

5. MTSO stands for:a.Minimum Transmitted Signal Output c. Mobile Telephone Switching Officeb.Maximum Transmitted Signal Output d. Mobile Transmission Time-Out

ANS: C

6. MIN stands for:a.Manual Identification Numberc. Maximum In-band Noiseb.Mobile Identification Number d. Minimum In-band Noise

ANS: B

7. NAM stands for:a.Numerical Access Mode c. Number Access Moduleb.Numerical Assignment Mode d. Number Assignment Module

ANS: D

8. ESN stands for:a.Electronic Serial Number c. Emission Strength Numberb.Emitted Signal Number d. none of the above

ANS: A

9. SCM stands for:a.Service Class Mark c. Signal Class Markb.Station Class Mark d. Serial-Code Mode

ANS: B

10. SCM identifies the:a.code number of a cell phone c. signal classification (analog or digital)b.base-station class d. maximum power level of a cell phone

ANS: D

11. SID stands for:a.Sequential Interrupt Demand c. System Identification Numberb.Standard 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 systemc.set its transmitted power leveld.recognize that it is "roaming"

ANS: D

13. DCC stands for:a.Digital Color Code c. Digital Communications Carrierb.Digital Communications Code d. Direct Channel Code

ANS: A

14. SAT stands for:a.Station Antenna Tower c. Supervisory Access Toneb.Supervisory Audio Tone d. none of the above

ANS: B

15. CMAC stands for:a.Control Mobile Attenuation Code c. Central Mobile Access Controlb.Control Mobile Access Code d. Carrier Mode Attenuation Control

ANS: A

16. The CMAC is used to:a.control access to the cell siteb.set the access code of the cell phonec.set the transmit power of the cell phoned.select the transmit channel for the cell phone

ANS: C

COMPLETION

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. FSKb.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 wattsb.less than 600 mW. d. 4 watts

ANS: B

20. BSC stands for:a.Base Station Controller c. Basic Service Contractb.Base Signal Controller 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 interfaceb.MTSO d. air interface

ANS: D

22. The optimum cell-site radius is:a.2 km c. as small as possibleb.0.5 km d. none of the above

ANS: D

23. Phone traffic is measured in:a.cal ls c. number of usersb.erlangs 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 ERPb.decrease the number of cells d. decrease the ERP

ANS: A

25. CDPD stands for:a.Code-Division Packet Data c. Coded Digital Packet Datab.Cellular Digital Packet Data d. Cellular Digital Pulse Data

ANS: B

COMPLETION

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: Ione

8. The maximum ERP of class III cell phones is .

ANS: 600 mW

9. A portable, handheld cell phone would be ERP class .

ANS: IIIthree

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

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 c. third-generationb.second-generation d. digital-generation

ANS: B

2. The frequency band designated for PCS in North America is:a.800 MHz c. 1.9 GHzb.900 MHz d. 12 GHz

ANS: C

3. The "forward" PCS channel is:a.from the base to the mobile c. from mobile to mobileb.from the mobile to the base d. same as the uplink

ANS: A

4. Compared to AMPS, PCS cell sites are:a.bigger c. distributedb.smaller d. higher-power

ANS: B

5. AMPS was designed for:a.POTS c. use built into an automobileb.voice d. all of the above

ANS: D

6. The number of competing PCS systems in North America is:a.2 c. 4b.3 d. many

ANS: B

7. CDMA technology was invented by:a.AT&T c. Bell Labsb.Lucent d. Qualcomm

ANS: D

8. GSM is used in:a.Asia c. North Americab.Europe d. all of the above

ANS: D

9. In GSM, voice channels are called:a.traffic channels c. bearer channelsb.voice channelsd. talking channels

ANS: A

10. AMPS uses:a.CDMA c. spread-spectrumb.TDMA 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 phoneb.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 onlyb.GSM only d. both GSM and TDMA

ANS: D

13. GSM uses:a.frequency hopping c. CDMAb.direct-sequence modulation d. all of the above

ANS: A

14. In GSM, SIM stands for:a.Short Inbound Message c. Subscriber ID Moduleb.Subscriber-Initiated Message d. Subscriber ID Method

ANS: C

15. IMSI stands for:a.Integrated Mobile Subscriber Identificationb.International Mobile Subscriber Identificationc.Interim Mobile Subscriber Identificationd.Intermodulation System Interference

ANS: B

16. IS-95 uses:a.frequency hopping c. CDMAb.TDMA d. all of the above

ANS: C

17. IS-136 uses:a.frequency hopping c. CDMAb.TDMA d. all of the above

ANS: B

18. In CDMA:a.all frequencies are used in all cellsb.each cell uses half the available frequenciesc.each cell is assigned a frequency by the based.the frequency is selected by the mobile phone

ANS: A

19. CDMA uses a set of PN sequences that are:a.common c. rotatingb.unique d. orthogonal

ANS: D

20. The next generation of PCS is expected to have:a.faster data rates c. wider roaming areab.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:CDMAdirect 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 Personal Telecommunications.

ANS: Universal

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 onlyb.the UHF band onlyc.both the VHF and UHF bandsd.the VHF band, the UHF band, and the ISM band

ANS: C

2. ISM stands for:a.IEEE Standard Message c. Industrial, Scientific, and Messagingb.IEEE Secure Messaged. Industrial, Scientific, and Medical

ANS: D

3. CAPCODE is:a.an encryption scheme used for pagersb.an addressing scheme used for pagersc.an error-detection scheme used for pagersd.a digital modulation scheme used for pagers

ANS: B

4. In a one-way pager system:a.all pages are sent from all transmittersb.each transmitting antenna covers a wide areac.transmitters use relatively high powerd.all of the above

ANS: D

5. POCSAG stands for:a.Pager Operations Common Standards Advisory Groupb.Pager Operations Code Standardization Advisory Groupc.Post Office Code Standardization Advisory Groupd.Post Office Common Standards Advisory Group

ANS: C

6. A typical pager system does not:a.require "handoffs" c. require error detectionb.allow "roaming" 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 bandb.UHF band d. infrared band

ANS: C

9. The IEEE 802 document for wireless LANs specifies the use of:a.CSMA/CA c. CDMAb.CSMA/CD d. all of the above

ANS: A

10. BSS stands for:a.Basic Service Set c. Bluetooth Service Systemb.Basic Service System d. none of the above

ANS: A

11. Bluetooth uses:a.CDMA c. QPSKb.frequency hopping d. all of the above

ANS: B

12. Bluetooth uses the:a.VHF band c. ISM bandb.UHF band d. infrared band

ANS: C

13. TDD stands for:a.Time-Division Duplex c. Time Delay Differenceb.Time-Delayed Duplex d. Total Distance Delay

ANS: A

14. A Bluetooth "piconet" has:a.2 nodes c. 2 to 8 nodesb.2 to 4 nodes d. 2 to 16 nodes

ANS: C

15. Two or more connected piconets forms a:a.micronet c. TDD netb.multinet 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 c. Infrared Restricted Data Areab.Infrared Digital Association d. Infrared Roaming Data Area

ANS: A

18. The range of an IRDA system is:a.1 meter c. 1 footb.10 meters d. 10 feet

ANS: A

19. Infrared networks:a.cannot penetrate walls c. can use reflected infrared beamsb.can use diffused 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 metersb.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. lessb.greater d. doesn't have an index of refraction

ANS: C

2. Fiber-optic cables do not:a.carry current c. generate EMIb.cause crosstalk d. all of the above

ANS: D

3. Single-mode fiber is made from:a.glass c. both a and bb.plastic d. none of the above

ANS: A

4. Fiber-optic cable cannot be used:a.in an explosive environmentb.to connect a transmitter to an antennac.to isolate a medical patient from a shock hazardd.none of the above

ANS: B

5. A single-mode cable does not suffer from:a.modal dispersion c. waveguide dispersionb.chromatic dispersion d. all of the above

ANS: A

6. Scattering causes:a. loss c. intersymbol interferenceb.dispersion 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 kmb.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 dBb.0.2 db d. 3 dB

ANS: B

10. Which of the following is a type of fiber connector:a.ST c. SMAb.SC d. all of the above

ANS: D

11. The quantum of light is called:a.an erg c. a photonb.an e-v d. a phonon

ANS: C

12. LASER stands for:a.Light Amplification by Simulated Emission of Radiationb.Light Amplification by Stimulated Emission of Radiationc.Light Amplification by Simulated Emitted Raysd.Light Amplification by Stimulated Emitted Rays

ANS: B

13. APD stands for:a.Avalanche Photodiode c. Avalanche Photo Detectorb.Advanced Photodiode 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 currentb.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 joule0.µW per amp d. µ sec 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 ofrather 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 acable.

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 at the end of an optical fiber unless you know it isnot connected to a light source.

ANS: look

Chapter 25: Fiber-Optic Systems

MULTIPLE CHOICE

1. FDDI stands for:a.Fiber Digital Data Interface c. Fiber Distribution Delay Interfaceb.Fiber Distributed Data Interface d. Frequency-Division Data Interface

ANS: B

2. FITL stands for:a.Fiber In The Loop c. Frequency Input to The Loopb.Fiber Input Timing Loss d. Fiber Input Timing Loop

ANS: A

3. FTTC stands for:a.Fiber Transmission Timing Constraintb.Fiber Transmission Technology Committeec.Fiber Telephone Transmission Cabled.Fiber To The Curb

ANS: D

4. SONET stands for:a.Simple Optical Network c. Synchronous Optical Networkb.Standard Optical Network d. none of the above

ANS: C

5. DWDM stands for:a.Digital Wavelength-Division Modulationb.Dense Wavelength-Division Modulationc.Double Wavelength-Division Modulationd.Dense Wavelength-Division Multiplexing

ANS: D

6. A Soliton is a:a.defect in the glass c. type of pulseb.type of particle d. type of optical network

ANS: C

7. Adding bits to synchronize one digital signal to another is called:a.bi t s tuffing c. SDHb.bit-synch d. WDM

ANS: A

8. Power above the minimum required by an optical receiver is called:

2. FITL stands for Fiber In The .

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 kmb.100 miles d. 10 km

ANS: C

10. In SONET, OC-1 stands for:a.Optical Carrier level one c. Optical Channel oneb.Optical Coupler unidirectional d. Optical Cable type 1

ANS: A

11. In SONET, STS stands for:a.Synchronous Transport Signal c. Synchronous Transmission Signalb.Synchronous Transport System d. Synchronous Transmission System

ANS: A

12. A commonly used fiber-based system for LANs is:a.FDDI c. gigabit Ethernetb.high-speed Ethernet d. all of the above

ANS: D

13. The use of solitons on fiber-optic cables is:a.common c. obsoleteb.experimental d. not possible

ANS: B

14. OTDR stands for:a.Optical Time-Delay Response c. Optical Time-Domain Reflectometerb.Optical Timing Delay Requirement 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. FITLb.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 directions.

ANS: opposite

1 5 . E a c h in an FDDI system acts as a regenerative repeater.

ANS: node

16. FDDI uses mode cables.

ANS: multi17. The data rate of an FDDI system is________________________bps.

ANS: 100 M

18. SONET frames have considerably more than do DS frames for informationabout signal routing and setup.

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