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

Chapter 1: Introduction to Communication SystemsMULTIPLE CHOICE 1. The theory of radio waves was originated by: a.Marconi c. Maxwell b.Bell d. Hertz ANS: C 2. The person who sent the first radio signal across the Atlantic ocean was: a.Marconi c. Maxwell b.Bell d. Hertz ANS: A 3. The transmission of radio waves was first done by: a.Marconi c. Maxwell b.Bell d. Hertz ANS: D 4. A complete communication system must include: a.a transmitter and receiver b.a transmitter, a receiver, and a channel c.a transmitter, a receiver, and a spectrum analyzer d.a multiplexer, a demultiplexer, and a channel ANS: B 5. Radians per second is equal to: a. 2 f c. the phase angle 0 .f 2 d. none of the abovei r x ir

ANS: A 6. The bandwidth required for a modulated carrier depends on: a.the carrier frequency c. the signal-plus-noise to noise ratio b.the signal-to-noise ratio d. the baseband frequency range ANS: D 7. When two or more signals share a common channel, it is called: a.sub-channeling c. SINAD b.signal switching d. multiplexing ANS: D 8. TDM stands for: a.Time-Division Multiplexing c. Time Domain Measurement b.Two-level Digital Modulation d. none of the above

ANS: A 9. FDM stands for: a.Fast Digital Modulation c. Frequency-Division Multiplexing b.Frequency Domain Measurement d. none of the above ANS: C 10. The wavelength of a radio signal is: a.equal to f c b.equal to c c.the distance a wave travels in one period d.how far the signal can travel without distortion A ,

ANS: C 11. Distortion is caused by: a.creation of harmonics of baseband frequencies b.baseband frequencies "mixing" with each other c.shift in phase relationships between baseband frequencies d.all of the above ANS: D 12. The collection of sinusoidal frequencies present in a modulated carrier is called its: a.frequency-domain representation c. spectrum b.Fourier series d. all of the above ANS: D 13. The baseband bandwidth for a voice-grade (telephone) signal is: a.approximately 3 kHz c. at least 5 kHz b.20 Hz to 15,000 Hz d. none of the above ANS: A 14. Noise in a communication system originates in: a.the sender c. the channel b.the receiver d. all of the above ANS: D 15. "Man-made" noise can come from: a.equipment that sparks c. static b.temperature d. all of the above ANS: A 16. Thermal noise is generated in: a.transistors and diodes c. copper wire b.resistors d. all of the above ANS: D

17. Shot noise is generated in: a.transistors and diodes c. copper wire b.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 frequencies b.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 noise b.pink noise d. partition noise ANS: B 20. "Pink" noise has: a.equal power per Hertz b.equal power per octave ANS: B 21. When two noise voltages, V1 and V2, are combined, the total voltage VT is: a.VT = sqrt( V 1 V 1 + V2 V 2) c. V T = sqrt( V 1 V 2 ) b.VT = (V1 + V2)/2 d. V T = V 1 + V 2

c. constant power d. none of the above

ANS: A 22. Signal-to-Noise ratio is calculated as: a.signal voltage divided by noise voltage b.signal power divided by noise power c.first add the signal power to the noise power, then divide by noise power d.none of the above ANS: B 23. SINAD is calculated as: a.signal voltage divided by noise voltage b.signal power divided by noise power c.first add the signal power to the noise power, then divide by noise power d.none of the above ANS: D 24. Noise Figure is a measure of: a.how much noise is in a communications system b.how much noise is in the channel c.how much noise an amplifier adds to a signal d.signal-to-noise ratio in dB ANS: C

25. The part, or parts, of a sinusoidal carrier that can be modulated are: a.its amplitude c. its amplitude, frequency, and direction b.its amplitude and frequency d. its amplitude, frequency, and phase angle ANS: D COMPLETION 1. The telephone was invented in the year . ANS: 1863 2. Radio signals first were sent across the Atlantic in the year ANS: 1901 3. The frequency band used to modulate the carrier is called the ANS: base 4. The job of the carrier is to get the information through the ANS: channel 5. The bandwidth of an unmodulated carrier is ANS: zero 6. The 'B' in Hartley's Law stands for ANS: bandwidth 7. The more information per second you send, the the bandwidth required. ANS: greater larger wider 8. In signals. , you split the bandwidth of a channel into sub-channels to carry multiple . . . band. .

ANS: FDM 9. In , multiple signal streams take turns using the channel.

ANS: TDM 10. VHF stands for the frequency band.

ANS: very high 11. The VHF band starts at MHz. ANS: 30 12. The UHF band starts at MHz. ANS: 300 13. A radio signal's ANS: wavelength 14. In free space, radio signals travel at approximately 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 ANS: Fourier 17. Disabling a receiver during a burst of atmospheric noise is called ANS: noise blanking blanking 18. For satellite communications, noise can be a serious problem. ANS: solar 19. Thermal noise is caused by the random motions of ANS: electrons SHORT ANSWER 1.Name the five elements in a block diagram of a communications system. ANS: Source, Transmitter, Channel, Receiver, Destination 2.Name five types of internal noise. in a conductor. . series. . meters per second. is the distance it travels in one cycle of the carrier.

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 V from one noise source that is combined with 40 V from another noise source. Calculate the total noise voltage.

ANS: 50 V

6. If you have 100 mV of signal and 10 mV of noise, both across the same 100-ohm load, what is the signalto-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 CircuitsMULTIPLE CHOICE 1. The time it takes a charge carrier to cross from the emitter to the collector is called: a.base time c. charge time b.transit time d. Miller time ANS: B 2. A real capacitor actually contains: a.capacitance and resistance only b.capacitance and inductance only ANS: C 3. Bypass capacitors are used to: a.remove RF from non-RF circuits b.couple RF around an amplifier ANS: A 4. A resonant circuit is: a.a simple form of bandpass filter b.used in narrowband RF amplifiers ANS: C 5. Loading down a tuned-circuit amplifier will: a.raise the Q of the tuned circuit c. "multiply" the Q b.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 amplifier b.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 b.using a common-base amplifier ANS: B 8. In a BJT, the Miller Effect is due to: a.inductance of collector lead c. base-to-emitter capacitance b.collector-to-emitter capacitance d. base-to-collector capacitance ANS: D c. increasing the Q of the tuned circuit d. it cannot be avoided c. both a and b d. none of the above c. neutralize amplifiers d. reduce the Miller effect c. capacitance, inductance, and resistance d. reactance only

ANS: B

9. In RF amplifiers, impedance matching is usually done with: a.RC coupling c. direct coupling b.transformer coupling d. lumped reactance ANS: B 10. Neutralization cancels unwanted feedback by: a.adding feedback out of phase with the unwanted feedback b.bypassing the feedback to the "neutral" or ground plane c.decoupling it d.none of the above ANS: A 11. For a "frequency multiplier" to work, it requires: a.a nonlinear circuit b.a linear amplifier c.a signal containing harmonics d.an input signal that is an integer multiple of the desired frequency ANS: A 12. A sinusoidal oscillation from an amplifier requires: a.loop gain equal to unity b.phase shift around loop equal to 0 degrees c.both a and b, but at just one frequency d.none of the above ANS: C 13. The conditions for sinusoidal oscillation from an amplifier are called: a.the loop-gain criteria c. the Bode criteria b.the Hartley criteria d. the Barkhausen criteria ANS: D 14. The Hartley oscillator uses: a.a tapped inductor c. an RC time constant b.a two-capacitor divider d. a piezoelectric crystal ANS: A 15. The Colpitts VFO uses: a.a tapped inductor c. an RC time constant b.a two-capacitor divider d. a piezoelectric crystal ANS: B 16. The Clapp oscillator is: a.a modified Hartley oscillator c. a type of crystal-controlled oscillator b.a modified Colpitts oscillator d. only built with FETs

17. A varactor is: a.a voltage-controlled capacitor c. used in tuner circuits b.a dioded. all of the above ANS: D 18. Crystal-Controlled oscillators are: a.used for a precise frequency b.used for very low frequency drift (parts per million) c.made by grinding quartz to exact dimensions d.all of the above ANS: D 19. If two signals, Va = sin( t) and Vb = sin( bt), are fed to a mixer, the output: a.will contain 1 = + b and 2 = b b.will contain 1 = / b and 2 = b / c . w i l l c o nt a i n = ( + b ) / 2 d.none of the above ANS: Aco coa

w

w

w

c o

w

w

a

a

w

w

w

c o

w

w

a

a

co

co

co

a

20. In a balanced mixer, the output: a.contains equal (balanced) amounts of all input frequencies b.contains the input frequencies c.does not contain the input frequencies d.is a linear mixture of the input signals ANS: C 21. "VFO" stands for: a.Voltage-Fed Oscillator c. Varactor-Frequency Oscillator b.Variable-Frequency Oscillatord. Voltage-Feedback Oscillator ANS: B 22. A "frequency synthesizer" is: a.a VCO phase-locked to a reference frequency b.a VFO with selectable crystals to change frequency c.a fixed-frequency RF generator d.same as a mixer ANS: A COMPLETION 1. Generally, conductor lengths in RF circuits should be ANS: short 2. At UHF frequencies and above, elements must be considered as instead of as being "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 them. ANS: shielding 5. In high-frequency RF circuits, the placement of wires and 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 ANS: Q 9. A value of to be valid. ANS: 10 10. In a class C RF amplifier, the extracts one frequency from all the harmonics contained in the device current (e.g. collector current). ANS: tuned circuit 11. Using additional feedback to compensate for "stray" feedback is called . ANS: neutralization 12. A Colpitts oscillator uses a ANS: capacitive 13. Electrically, a piezoelectric crystal has both a resonant frequency. ANS: series, parallel and a voltage divider to provide feedback. or more for Q is required for the approximate tuned circuit equations of the tuned circuit. can be critical. between .

14.

To produce sum and difference frequencies, a mixer must be a nonANS: linear

circuit.

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 Hp.

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 20C, and a tempco of +10 ppm per degree Celsius. What will be the shift in frequency at 70C? What percentage is that? ANS: 50 kHz, 0.05% 7. Two sinusoidal signals, V1 and V2, are fed into an ideal balanced mixer. V1 is a 20-MHz signal; V2 is a 5MHz signal. What frequencies would you expect at the output of the mixer? ANS: 15 MHz and 25 MHz

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

Chapter 3: Amplitude Modulation

MULTIPLE CHOICE 1. AM stands for: a.Audio Modulation c. Angle Modulation b.Amplitude Modulation d. Antenna Modulation ANS: B 2. The "envelope" of an AM signal is due to: a.the baseband signal c. the amplitude signal b.the carrier signal d. none of the above ANS: A 3. If the audio Va sin( t) modulates the carrier Vc sin( t), then the modulation index, m, is: a.m = / c. m = (Va / Vc)2co ca c

co

a

c

b.m = Va / Vc ANS: B

d. m = V a /

ca

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

sin( t)com

sin( t)cc

b.v(t) = (Ec + Em ) sin( t) + sin( t) co cm c

d. v(t) = (E c + E m sin( t)) sin( t)co cm c

ANS: D 5. Overmodulation causes: a.distortion c. both a and b b.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( t) amplitude modulates the carrier Vc sin( t), it will produce the frequencies: a. + and a c. + and 2 + 2 0 . ( + ) / 2 a n d ( ) / 2 d. none of the aboveco ca c

c

c o

(

c o

c

c o

c

c

a

c

c

a

c

a

c

w

c

0 )

c

a

c

a

ANS: A 8. At 100% modulation, the total sideband power is: a.equal to the carrier power c. half the carrier power b.twice the carrier power d. 1.414 carrier power

ANS: C 9. If a 5-kHz signal modulates a 1-MHz carrier, the bandwidth of the AM signal will be: a.5 kHz c. 1.005 MHz b.10 kHz d. none of the above ANS: B 10. If an AM radio station increases its modulation index, you would expect: a.the audio to get louder at the receiver c. the signal-to-noise ratio to increase b.the received RF signal to increase d. all of the above ANS: D 11. The modulation index can be derived from: a.the time-domain signal c. both a and b b.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 radios b.requires too much power d. all of the above ANS: C 13. As compared to plain AM, SSB AM: a.is more efficient b.requires a more complex demodulator circuit c.requires less bandwidth d.all of the above ANS: D 14. The SC in SSB SC stands for: a.single-carrier c. sideband-carrier b.suppressed-carrier d. none of the above ANS: B 15. PEP stands for: a.Peak Envelope Power b.Peak Efficiency Power ANS: A 16. If an SSB transmitter radiates 1000 watts at peak modulation, what will it radiate with no modulation? a.1000 watts c. 250 watts b.500 watts d. 0 watts ANS: D 17. Music on AM radio stations is "low-fidelity" because: a. AM is susceptible to noise c. Peak Envelope Product d. none of the above

b.commercial AM stations use low power c.commercial AM stations have a narrow bandwidth d.all of the above ANS: C 18. The type of information that can be sent using AM is: a.audio c. digital data b.video d. all of the above ANS: D 19. Two tones modulate an AM carrier. One tone causes a modulation index of m1 and the other tone causes a modulation index of m2. The total modulation index is: a. m1 + m2 c. sqrt( m 1 m 2 + m 2 m 1 ) 0.( m 1 + m 2 ) / 2 d. sqrt( m 1 m 1 + m 2 m 2 )x x x x

ANS: D 20. To demodulate a USB SSB signal, the receiver must: a.be set to USB mode c. both a and b b.reinsert the carrier d. none of the above ANS: C COMPLETION 1.An advantage of AM is that the receiver can be very ANS: simple 2.A disadvantage of AM is its 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 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 . . sidebands. use of power. .

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 with 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: watts

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 ModulationMULTIPLE CHOICE 1. The FM modulation index: a.increases with both deviation and modulation frequency b.increases with deviation and decreases with modulation frequency c.decreases with deviation and increases with modulation frequency d.is equal to twice the deviation ANS: B 2. One way to derive FM from PM is: a.integrate the modulating signal before applying to the PM oscillator b.integrate the signal out of the PM oscillator c.differentiate the modulating signal before applying to the PM oscillator d.differentiate the signal out of the PM oscillator ANS: A 3. The bandwidth of an FM signal is considered to be limited because: a.there can only be a finite number of sidebands b.it is equal to the frequency deviation c.it is band-limited at the receiver d.the power in the outer sidebands is negligible ANS: D 4. Mathematically, the calculation of FM bandwidth requires the use of: a.ordinary trigonometry and algebra c. Taylor series b.Bessel functions d. fractals ANS: B 5. FM bandwidth can be approximated by: a.Armstrong's Rule c. Carson's Rule b.Bessel's Rule d. none of the above ANS: C 6. NBFM stands for: a.National Broadcast FM c. Near Band FM b.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 effect b.the threshold effect d. the limit effect ANS: B

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

ANS: D 11. FM stereo: a.uses DSBSC AM modulation c. has a higher S/N than mono FM b.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 monaural b.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 J 0 equals one b.using measurements at points where J 0 equals zero c.using measurements at points where the deviation equals zero d.only by using Bessel functions ANS: B COMPLETION 1.FM and PM are two forms of ANS: angle 2.PM is extensively used in communication. ANS: data modulation.

3. Compared to AM, the signal-to-noise ratio of FM is usually ANS: better 4. Compared to AM, the bandwidth of FM is usually ANS: wider greater .

.

5. FM transmitters can use Class amplifiers since amplitude linearity is not important. ANS: C 6. Both the power and amplitude of an FM signal ANS: stay constant 7. In FM, the frequency deviation is proportional to the instantaneous modulating signal. ANS: amplitude 8. The frequency deviation of an FM signal occurs at a rate equal to the modulating 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 . . . . of the of the as modulation is applied.

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 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. rule. .

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

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: TransmittersMULTIPLE CHOICE 1. The ability to change operating frequency rapidly without a lot of retuning is called: a.agility c. VFO b.expansion d. spread-spectrum ANS: A 2. The difference between the DC power into a transmitter and the RF power coming out: a.is a measure of efficiency c. may require water cooling b.heats the transmitter d. all of the above ANS: D 3. Baseband compression produces: a.a smaller range of frequencies from low to high b.a smaller range of amplitude from soft to loud c.a smaller number of signals d.none of the above ANS: B 4. ALC stands for: a.Amplitude Level Control b.Automatic Level Control ANS: B 5. In an AM transmitter, ALC is used to: a.keep the modulation close to 100% b.keep the modulation below 100% ANS: D 6. With high-level AM: a.all RF amplifiers can be nonlinear c. minimum RF power is required b.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 C b.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 b.the RF amplifiers must be Class B c. the RF amplifiers must be linear d. the RF amplifiers must be low-power c. maximize transmitted power d. all of the above c. Accurate Level Control d. none of the above

9. Power amplifiers must be linear for any signal that: a.is complex c. has variable frequency b.has variable amplitude d. all of the above ANS: B 10. In high-level AM, "high-level" refers to: a.the power level of the carrier c. the power level of the final RF amplifier b.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 stage b.the RF amplifier d. the carrier ANS: A 12. In an AM transmitter with 100% modulation, the voltage of the final RF stage will be: a.approximately half the DC supply voltage b.approximately twice the DC supply voltage c.approximately four times the DC supply voltage d.none of the above ANS: C 13. Practical transmitters are usually designed to drive a load impedance of: a.50 ohms resistive c. 300 ohms resistive b.75 ohms resistive d. 600 ohms resistive ANS: A 14. Which of the following can be used for impedance matching? a.pi network c. both a and b b.T network d. a bridge circuit ANS: C 15. When a transmitter is connected to a resistor instead of an antenna, the resistor is called: a.a heavy load c. a temporary load b.a dummy load d. a test load ANS: B 16. When a transmitter is connected to a resistor instead of an antenna, the resistor must be: a.wire-wound c. 1% tolerance or better b.noninductive d. all of the above ANS: B 17. A Class D amplifier is: a. very efficient c. essentially pulse-duration modulation

b. essentially pulse-width modulation ANS: D

d. all of the above

18. To generate a SSB signal: a.start with full-carrier AM c. start with a quadrature signal b.start with DSBSC d. all of the above ANS: B 19. The carrier is suppressed in: a.a balanced modulator c. a frequency multiplier b.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 b b.a crystal filter d. none of the above ANS: C 21. A direct FM modulator: a.varies the frequency of the carrier oscillator b.integrates the modulating signal c.both a and b d.none of the above ANS: A 22. An indirect FM modulator: a.requires a varactor in the carrier oscillator b.varies the phase of the carrier oscillator c.both a and b d.none of the above ANS: B 23. AFC stands for: a.Amplitude to Frequency Conversion c. Automatic Frequency Control b.Automatic Frequency Centering d. Audio Frequency Control ANS: C 24. Frequency multipliers are: a.essentially balanced modulators c. essentially mixers b.essentially Class C amplifiers d. none of the above ANS: B 25. With mixing: a.the carrier frequency can be raised b.the carrier frequency can be lowered c.the carrier frequency can be changed to any required value

d. the deviation is altered ANS: C COMPLETION 1. The accuracy and stability of a transmitter frequency is fixed by the ANS: carrier 2. In the USA, the sets requirements for accuracy and stability of a transmitter's frequency. ANS: FCC 3. In Canada, frequency. sets requirements for accuracy and stability of a transmitter's oscillator.

ANS: Industry Canada 4. Frequency retuning. 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. . . . is the ability of a transmitter to change frequency without a lot of

ANS: buffer 12. The peak collector voltage in a Class C RF amplifier is than the DC supply voltage. ANS: higher 13. Most practical transmitters are designed to operate into a ANS: 50 14. Transmitters built with transistor RF amplifiers often use a impedance matching. ANS: T 15. Matching networks also act as filters to help reduce ANS: harmonic 16. Severe impedance ANS: mismatch 17. Transceivers combine a transmitter and a ANS: receiver 18. To allow a high modulation percentage, it is common to modulate the the power amplifier in transistor modulators. ANS: driver 19. Pulse-width modulation is the same as pulseANS: duration 20. Switching amplifiers are sometimes called Class ANS: D 21. Because the sideband filter in a SSB transmitter is fixed, more than one frequency. ANS: mixing 22. To generate a SSB signal, it is common to start with a signal. ANS: DSBSC is used to operate at amplifiers. modulation. as well as into one "box". can destroy a transmitter's output stage. levels. network for -ohm load.

23. Indirect FM is derived from ANS: phase 24.

modulation.

Using a varactor to generate FM is an example of a ANS: reactance

modulator.

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: ReceiversMULTIPLE CHOICE 1. The two basic specifications for a receiver are: a.the sensitivity and the selectivity b.the number of converters and the number of IFs c.the spurious response and the tracking d.the signal and the noise ANS: A 2. The superheterodyne receiver was invented by: a.Foster c. Armstrong b.Seeley d. Hertz ANS: C 3. Trimmers and padders are: a.two types of adjusting tools b.small adjustable resistors ANS: D 4. "Skin effect" refers to: a.the way radio signals travel across a flat surface b.the tissue-burning effect of a strong RF signal c.the increase of wire resistance with frequency d.none of the above ANS: C 5. The "front end" of a receiver can include: a.the tuner c. the mixer b.the RF amplifier d. all of the above ANS: D 6. "IF" stands for: a.intermediate frequency b.intermodulation frequency ANS: A 7. AGC stands for: a.Audio Gain Control c. Active Gain Control b.Automatic Gain Control d. Active Gain Conversion ANS: B 8. The frequency of the local oscillator: a. is above the RF frequency c. indeterminate frequency d. image frequency c. small adjustable inductors d. small adjustable capacitors

b.is below the RF frequency c.can be either above of below the RF frequency d.is fixed, typically at 455 kHz. ANS: C 9. The local oscillator and mixer are combined in one device because: a.it gives a greater reduction of spurious responses b.it increases sensitivity c.it increases selectivity d.it is cheaper ANS: D 10. Basically, sensitivity measures: a.the weakest signal that can be usefully received b.the highest-frequency signal that can be usefully received c.the dynamic range of the audio amplifier d.none of the above ANS: A 11. Basically, selectivity measures: a.the range of frequencies that the receiver can select b.with two signals close in frequency, the ability to receive one and reject the other c.how well adjacent frequencies are separated by the demodulator d.how well the adjacent frequencies are separated in the mixer ANS: B 12. When comparing values for shape factor: a.a value of 1.414 dB is ideal c. a value of 1.0 is ideal b.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 b.a value of 4 is better than a value of 2 ANS: A 14. Distortion in a receiver can occur in: a.the mixer c. the IF amplifiers b.the detector d. all of the above ANS: D 15. Phase distortion is important in: a.voice communications systems c. monochrome video receivers b.color video receivers d. all of the above ANS: B c. both values are basically equivalent d. none of the above

16. The response of a receiver to weak signals is usually limited by: a.the AGC c. the dynamic range of the receiver b.noise generated in the receiver d. the type of detector circuit being used ANS: B 17. Image frequencies occur when two signals: a. are transmitted on the same frequency b. enter the mixer, with one being a reflected signal equal to the IF frequency c. enter the mixer, one below and one above the local oscillator by a difference equal to the IF d. enter the mixer, and the difference between the two signals is equal to twice the IF ANS: C 18. An image must be rejected: a.prior to mixing c. prior to detection b.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 factor b.having a wideband RF amplifier after the mixer c.having a narrowband RF amplifier before the mixer d.none of the above ANS: C 20. A common AM detector is the: a.PLL c. ratio detector b.envelope detector d. all of the above ANS: B 21. An FM detector is the: a.PLL c. quadrature detector b.ratio detector d. all of the above ANS: D 22. Germanium diodes are used in AM detectors because: a.they are faster than silicon diodes b.they are cheaper than silicon diodes c.they minimize distortion from nonlinearity d.all of the above ANS: C 23. A common SSB detector is: a.a PLL c. a BFO b.a dioded. a product detector ANS: D

24. BFO stands for: a.Beat Frequency Oscillator c. Bipolar Frequency Oscillator b.Barrier Frequency Oscillator d. Bistable Frequency Oscillator ANS: A 25. To demodulate both SSB and DSBSC, you need to: a.use a Foster-Seeley discriminator b.reinject the carrier c.use double conversion d.use one diode for SSB and two diodes for DSBSC ANS: B 26. Which would be best for DSBSC: a.carrier detection c. envelope detection b.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 detector b.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 range b.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. AFC b.squelch d. limiting ANS: B 30. LNA stands for: a.Limited-Noise Amplifier b.Low-Noise Amplifier ANS: B 31. AFC stands for: a.Audio Frequency Compensator c. Automatic Frequency Control b.Autodyne Frequency Compensation d. Autonomous Frequency Control ANS: C 32. The function of AFC is: a.maintain a constant IF frequency b.match the local oscillator to the received signal c. Low-Noise Audio d. Logarithmic Noise Amplification

c.lock the discriminator to the IF frequency d.none of the above ANS: B 33. SAW stands for: a.Symmetrical Audio Wave b.Surface Acoustic Wave ANS: B 34. The important property of a SAW is: a.it stabilizes the audio in a receiver b.it allows software radios to be built ANS: C 35. The main function of the AGC is to: a.keep the gain of the receiver constant b.keep the gain of the IF amplifiers constant c.keep the input to the detector at a constant amplitude d.all of the above ANS: C 36. DSP stands for: a.Dynamic Signal Properties c. Distorted Signal Packet b.Direct Signal Phase d. Digital Signal Processor ANS: D 37. SINAD stands for: a.Sinusoidal Amplitude Distortion b.Signal and Noise Amplitude Distortion c.Signal-plus-Noise-to-Noise Ratio d.Signal-plus-Noise and Distortion-to-Noise and Distortion Ratio ANS: D 38. TRF stands for: a.Tuned Radio Frequency b.Tracking Radio Frequency ANS: A COMPLETION 1. Almost all modern receivers use the ANS: superheterodyne 2. The first radio receiver of any kind was built in the year . principle. c. Transmitted Radio Frequency d. Tuned Receiver Function c. it is a stable bandpass filter d. none of the above c. Silicon-Activated Wafer d. Software-Activated Wave

ANS: 1887 3. When two tuned circuits each other, it means that when the frequency of one is adjusted, the other changes with it. ANS: track 4. The ANS: skin 5. The superhet was invented in the year . ANS: 1918 6. In a receiver, the ANS: front end 7. In a superhet, the output of the goes to the IF amplifiers. ANS: mixer 8. In a superhet, the frequency is the difference between the local oscillator frequency and the received signal frequency. ANS: intermediate IF 9. The circuit adjusts the gain of the IF amplifiers in response to signal strength. refers to the input filter and RF stage. effect causes the resistance of wire to increase with frequency.

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 ANS: lower 12. is the ability of a receiver to separate two signals that are close to each other in frequency. than the received signal frequency.

ANS: Selectivity 13. is the ability of a receiver to receive and successfully demodulate a very weak signal.

ANS: Sensitivity

14. A receiver with two different IF frequencies is called a double- receiver. ANS: conversion 15. A multiple-conversion receiver will have better rejection of ANS: image 16. A demodulator is also called a . ANS: detector 17. An detector uses a diode to half-wave rectify an AM signal. frequencies.

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 ANS: coherent 21. FM detectors have a characteristic ANS: S 22. While still commonly found, the Foster-Seeley and ratio detectors are . ANS: obsolescent 23. Unlike the PLL detector, the quadrature detector is sensitive to changes in input signal. 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 . of the -shaped curve. detection circuit. .

ANS: A 27. A double-tuned IF transformer is usually top and steep sides. ANS: over 28. Multiple IF stages can be ANS: stagger 29. Compared to tuned circuits, ceramic and crystal IF filters do not require ANS: adjustment 30. Up-conversion is when the output of the mixer is a signal. 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 ANS: IF 3 3 . A n -meter is designed to indicate signal strength in many communications receivers. ANS: S 34. The effectiveness of FM ANS: limiting 35. A refers to any kind of FM or PM detector. is measured by a receivers quieting sensitivity. amplifiers. . frequency than the incoming . -tuned to increase the bandwidth. coupled for the response to have a flat

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

ANS:

20 kHz 2. Using high-side injection for a 1-MHz IF, what is the frequency of the local oscillator when the receiver is tuned to 5 MHz? ANS: 6 MHz 3. An IF filter has a 60 dB bandwidth of 25 kHz and a 6 dB bandwidth of 20 kHz. What is the shape factor value? ANS: 1.25 4. Suppose a receiver uses a 5-MHz IF frequency. Assuming high-side injection, what would be the image frequency if the receiver was tuned to 50 MHz? ANS: 60 MHz 5. Suppose a SSB receiver requires an injected frequency of 1.5 MHz. What would be the acceptable frequency range of the BFO if the maximum acceptable baseband shift is 100 hertz? ANS: 1.5 MHz 100 hertz

6. The transformer of a double-tuned IF amplifier has a Q of 25 for both primary and secondary. What value of kc do you need to achieve optimal coupling? ANS: 0.06 7. What value of transformer coupling would a double-tuned 10-MHz IF amplifier with optimal coupling need to get a bandwidth of 100 kHz? ANS: 0.01

Chapter 7: Digital CommunicationsMULTIPLE CHOICE 1. The first digital code was the: a.ASCII code c. Morse code b.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 repeater b.a filter d. all of the above ANS: C 3. TDM stands for: a.Time-Division Multiplexing c. Ten-Digital Manchester b.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 = 2 f max ANS: A 5. The Shannon-Hartley theorem is: a.I = ktB c. C = B log2(1 + S/ N) b.C = 2B log2M d. SR = 2 f max 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 = 2 f max 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 = 2 f max ANS: D 8. Natural Sampling does not use: a.a sample-and-hold circuit c. a fixed sample rate b.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 second b.too many samples per second d. all of the above ANS: C 11. The immediate result of sampling is: a.a sample alias c. PCM b.PAM d. PDM ANS: B 12. Which of these is not a pulse-modulation technique: a.PDM c. PPM b.PWM d. PPS ANS: D 13. Quantizing noise (quantization noise): a.decreases as the sample rate increases b.decreases as the sample rate decreases c.decreases as the bits per sample increases d.decreases as the bits per sample decreases ANS: C 14. The dynamic range of a system is the ratio of: a.the strongest transmittable signal to the weakest discernible signal b.the maximum rate of conversion to the minimum rate of conversion c.the maximum bits per sample to the minimum bits per sample d.none of the above ANS: A 15. Companding is used to: a.compress the range of base-band frequencies b.reduce dynamic range at higher bit-rates c.preserve dynamic range while keeping bit-rate low d.maximize the useable bandwidth in digital transmission ANS: C 16. In North America, companding uses: a.the Logarithmic Law c. the Law (alpha law) b.the A Law d. the Law (mu law)cx

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

ANS: B 18. Codec stands for: a.Coder-Decoder b.Coded-Carrier ANS: A 19. A typical codec in a telephone system sends and receives: a.4-bit numbers c. 12-bit numbers b.8-bit numbers d. 16-bit numbers ANS: B 20. Compared to PCM, delta modulation: a.transmits fewer bits per sample c. can suffer slope overload b.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 high b.the signal does not change d. the sample is too large ANS: B 22. Compared to PCM, adaptive delta modulation can transmit voice: a.with a lower bit rate but reduced quality c. only over shorter distances b.with a lower bit rate but the same quality d. only if the voice is band-limited ANS: B 23. Which coding scheme requires DC continuity: a.AMI c. unipolar NRZ b.Manchester d. bipolar RZ ANS: C 24. Manchester coding: a.is a biphase code b.has a level transition in the middle of every bit period c.provides strong timing information d.all of the above ANS: D 25. The number of framing bits in DS-1 is: c. Code-Compression d. none of the above

a.1 c. 4 b.2 d. 8 ANS: A 26. Framing bits in DS-1 are used to: a.detect errors c. synchronize the transmitter and receiver b.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 receiver b.carry signaling d. all of the above ANS: B 28. The number of bits per sample in DS-1 is: a.1 b.2 ANS: D 29. The number of samples per second in DS-1 is: a.8 k c. 64 k d. 1.544 b.56 k ANS: A 30. The bit rate for each channel in DS-1 is: a.1.544 Mb/s c. 56 kb/s b.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/s b.64 kb/sd. 8 kb/s ANS: A 32. A T-1 cable uses: a.Manchester coding c. NRZ coding b.bipolar RZ AMI coding d. pulse-width coding ANS: B 33. The number of frames in a superframe is: a.6 c. 24 b.12 d. 48 ANS: B 34. A typical T-1 line uses: 0. a. 4 8

106

a.twisted-pair wire c. fiber-optic cable b.coaxial cable d. microwave ANS: A 35. "Signaling" is used to indicate: a.on-hook/off-hook condition c. ringing b.busy signal d. all of the above ANS: D 36. A vocoder implements compression by: a.constructing a model of the transmission medium b.constructing a model of the human vocal system c.finding redundancies in the digitized data d.using lossless techniques ANS: B 37. Compared to standard PCM systems, the quality of the output of a vocoder is: a.much better c. about the same b.somewhat better d. not as good ANS: D COMPLETION 1. Digitizing a signal often results in ANS: improved better 2. To send it over an analog channel, a digital signal must be 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 the length of the channel increases. ANS: decreases gets worse 5. The value of a pulse is the only information it carries on a digital channel. onto a carrier. transmission quality.

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 ANS: correct

some errors in digital transmission.

8.

Converting an analog signal to digital form is another source of in digital transmission systems. ANS: error noise

9.

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

10. All practical communications channels are bandANS: limited 11.

.

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

12. Ignoring noise, the for a given bandwidth. ANS: Shannon-Hartley

theorem gives the maximum rate of data transmission

13. The limit gives the maximum rate of data transmission for a given bandwidth and a given signal-to-noise ratio. ANS: Shannon 14. sampling is done without a sample-and-hold circuit. ANS: Natural 15. The format. Rate is the minimum sampling rate for converting analog signals to digital

ANS: Nyquist 16. distortion occurs when an analog signal is sampled at too slow a rate. ANS: Foldover

17.

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

18. The output of a sample-and-hold circuit is a pulseANS: amplitude 19.

modulated signal.

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 ANS:

-law equation.

mu 23. In Europe, compression is done using the 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 bits before being compressed to 8 bits. ANS: 12 26. The number of bits per sample transmitted in delta modulation is ANS: 1 one 27. Delta modulation requires a reproduction. ANS: higher sampling rate than PCM for the same quality of . -law equation.

28.

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

29. In delta modulation, overload can occur if the analog signal changes too fast. ANS: slope 30. The size varies in adaptive delta modulation.

ANS: step 31. Adaptive delta modulation can transmit PCM-quality voice at about of PCM. ANS: half 32. Unipolar NRZ is not practical because most channels do not have ANS: DC 33. In AMI, binary ones are represented by a voltage that alternates in ANS: polarity 34. Long strings of 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 and zeros. ANS: timing 37. Ther e ar e ANS: 24 38. DS-1 uses a ANS: framing 39. In DS-1, each channel is sampled ANS: 8000 40. Data is carried over a T-1 line at a rate of bits per second. times per second. bit to synchronize the transmitter and receiver. channels in a DS-1 frame. should be avoided in AMI. . continuity. the bit rate

ANS: 1.544 10 6

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 ANS: sixth 43. it. ANS: Lossless SHORT ANSWER 1. Use Hartley's Law to find how much time it would take to send 100,000 bits over a channel with a bandwidth of 2,000 hertz and a channel constant of k = 10. ANS: 5 seconds 2. Use the Shannon-Hartley theorem to find the bandwidth required to send 12,000 bits per second if the number of levels transmitted is 8. ANS: 2000 hertz 3. What is the Shannon Limit of a channel that has a bandwidth of 4000 hertz and a signal-to-noise ratio of 15? ANS: 16 kbps 4. What is the minimum required number of samples per second to digitize an analog signal with frequency components ranging from 300 hertz to 3300 hertz? ANS: 6600 samples/second 5. What is the approximate dynamic range, in dB, of a linear PCM system that uses 12 bits per sample? ANS: 74 dB 6. What is the approximate data rate for a system using 8 bits per sample and running at 8000 samples per second? compression transmits all the data in the original signal but uses fewer bits to do frame.

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 -law compressor if the input voltage is 0.388 volt?

ANS: 0.833 volt

Chapter 8: The Telephone SystemMULTIPLE CHOICE 1. DTMF stands for: a.Digital Telephony Multiple Frequency c. Dual-Tone Multifrequency b.Dial Tone Master Frequency d. Digital Trunk Master Frequency ANS: C 2. PSTN stands for: a.Public Switched Telephone Network c. Primary Service Telephone Network b.Private Switched Telephone Network d. Primary Service Telephone Numbers ANS: A 3. POTS stands for: a.Private Office Telephone System b.Primary Office Telephone Service ANS: D 4. LATA stands for: a.Local Access and Transport Area c. Local Area Telephone Access b.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 office b.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 b b.trunk lines d. none of the above ANS: B 7. Local loops terminate at: a.a tandem office c. a central office b.a toll station d. an interexchange office ANS: C 8. Call blocking: a.cannot occur in the public telephone network b.occurs on the local loop when there is an electrical power failure c.occurs only on long-distance cables d.occurs when the central office capacity is exceeded c. Primary Operational Test System d. Plain Old Telephone Service

ANS: D 9. In telephony, POP stands for: a.Post Office Protocol c. Power-On Protocol b.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 cable b.shielded twisted-pair copper wire d. fiber-optic ANS: A 11. FITL stands for: a.Framing Information for Toll Loops c. Framing In The Loop b.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 data b.reduce the attenuation of voice signals c.reduce crosstalk d.provide C-type conditioning to a local loop ANS: B 13. DC current flows through a telephone: a.when it is on hook c. as long as it is attached to a local loop b.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 A to 80 A c. 2 mA to 8 mA b. 200 A t o 800 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 control b.crossbar control d. ESS ANS: C 16. The typical voltage across a telephone when on-hook is: a.48 volts DC c. 90 volts DC b.48 volts, 20 hertz AC d. 90 volts, 20 hertz AC ANS: A 17. The typical voltage needed to "ring" a telephone is:

a.48 volts DC c. 90 volts DC b.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 multiplexed b.prevent "singing" d. all of the above ANS: C 19. VNL stands for: a.voltage net loss b.volume net loss ANS: C 20. Signal loss is designed into a telephone system to: a.eliminate reflections c. improve signal-to-noise ratio b.prevent oscillation d. reduce power consumption ANS: B 21. The reference noise level for telephony is: a.1 mW c. 1 pW b.0 dBm d. 0 dBr ANS: C 22. The number of voice channels in a basic FDM group is: a.6 c. 24 b.12 d. 60 ANS: B 23. Basic FDM groups can be combined into: a.supergroups c. jumbogroups b.mastergroups d. all of the above ANS: D 24. In telephone system FDM, voice is put on a carrier using: a.SSB c. PDM b.DSBSC d. PCM ANS: A 25. PABX stands for: a.Power Amplification Before Transmission b.Private Automatic Branch Exchange c.Public Automated Branch Exchange d.Public Access Branch Exchange ANS: B c. via net loss d. voice noise level

26. SLIC stands for: a.Single-Line Interface Circuit c. Subscriber Line Interface Card b.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 echoes b.carry signaling d. check for errors ANS: B 28. "Bit-stuffing" is more formally called: a.compensation c. justification b.rectification d. frame alignment ANS: C 29. ISDN stands for: a.Integrated Services Digital Network c. Integrated Services Data Network b.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 develop b.it is too slow c.it has been surpassed by newer technologies d.all of the above ANS: D 31. ADSL stands for: a.All-Digital Subscriber Line c. Allocated Digital Service Line b.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 expensive b.about the same speed d. none of the above ANS: A COMPLETION 1.A is a local calling area. ANS: LATA 2.Central offices are connected together by lines.

ANS: trunk 3. One central office can be connected to another through a office. ANS: tandem 4. With 7-digit phone numbers, office. ANS: ten 5. Call is when it becomes impossible for a subscriber to place a call due to an overload of lines being used. ANS: blocking 6. New switching equipment uses TDM to combine signals. thousand telephones can connect to a central

ANS: digital 7. Most local loops still use ANS: twisted-pair 8. As compared to a hierarchical network, a intermediate 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 ANS: green 13. A telephone is said to have ANS: seized 14. The functions are provided by a SLIC. the line when the central office sends it dial tone. wire is positive with respect to the other. . network never needs more than one copper wire.

ANS: BORSCHT 15. A coil prevents loss of signal energy within a telephone while allowing fullduplex operation over a single pair of wires. ANS: hybrid 16. In a crosspoint switch, not all can be in use at the same time. ANS: lines 17. The old carbon transmitters generated a relatively 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 ANS: suppressor 22. weighting is an attempt to adjust the noise or signal level to the response of a typical telephone receiver. ANS: C-message 23. In FDM telephony, the modulation is usually . ANS: SSB SSBSC 24. In FDM telephony, ANS: guard 25. Because of "bit robbing", a channel in a DS-1 frame allows only used to send digital data. ANS: 56 kbps when bands separate the channels in a group. converts a long-distance line from full-duplex to half-duplex operation. signal voltage.

26. A is a group of 12 DS-1 frames with signaling information in the sixth and twelfth frames. ANS: superframe 27. In DS-1C, ANS: stuff 28. Busy and dial tone are referred to as wires as the voice signal. ANS: in-channel 29. SS7 is the current version of signaling. ANS: common-channel 30. SS7 is a ANS: packet 31. In ISDN, the ANS: D 32. In ISDN, the ANS: B 33. Terminal equipment especially designed for ISDN is designated ANS: TE1 34. The A in ADSL stands for ANS: asymmetrical 35. In ADSL, the speed from the network to the subscriber is opposite direction. ANS: greater faster SHORT ANSWER than the speed in the . equipment. channels are used for voice or data. channel is used for common-channel signaling. -switched data network. signals because they use the same pair of bits are used to compensate for differences between clock rates.

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 TransmissionMULTIPLE CHOICE 1. In practical terms, parallel data transmission is sent: a.over short distances only c. over any distance b.usually over long distances d. usually over a coaxial cable ANS: A 2. The five-level teletype code was invented by: a.the Morkum Company c. Western Union b.the Teletype Company d. Emile Baudot ANS: D 3. Data codes are also called: a.character codes c. they do not have any other name b.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 data b. binary data d. all of the above ANS: B 5. Character codes include: a.alphanumeric characters b.data link control characters ANS: D 6. ASCII stands for: a.American Standard Character-set 2 b.American Standard Code for Information Interchange c.American Standard Code 2 d.Alphanumeric Standard Code for Information Interchange ANS: B 7. BS, FF, and CR are examples of: a.nonstandard character codes c. control characters b.escape characters d. none of the above ANS: C 8. LF stands for: a. Line Feed c. Line Forward c. graphic control characters d. all of the above

b. Link Feed ANS: A

d. Link Forward

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

ANS: A 16. BISYNC: a.is an IBM product c. requires the use of DLE b.is a character-oriented protocol d. all of the above ANS: D 17. HDLC: a.is an IBM product c. is identical to SDLC b.is a bit-oriented protocol d. all of the above ANS: B 18. The use of flags in SDLC requires: a."bit-stuffing" c. FEC b.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 queue b.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 buffer b.correct synchronization problems d. none of the above ANS: A 21. FEC stands for: a.Fixed Error Control c. Forward Error Correction b.Forward Error Control d. False Error Condition ANS: C 22. VRC is another name for: a.FEC c. LRC b.ARQ d. parity ANS: D 23. CRC stands for: a.Control Receiver Code c. Cyclic Redundancy Check b.Correct Received Character d. Cycle Repeat Character ANS: C 24. Huffman codes: a.allow errors to be detected but not corrected b.allow errors to be detected and corrected c.allow alphanumeric data to be corrected

d.

allow alphanumeric data to be compressed

ANS: D

correct data none of the above

25. Run-length encoding is used to: a. encrypt data c. b. compress data d. problem" all of the above avoids the "password ANS: B 26. Public-key encryption: a. allows the use of digital signatures b. is used to convey symmetric keys ANS: D 27. SDLC stands for: a. Synchronous Data Link Control b. Synchronous Data Line Control ANS: A 28. HDLC is: a.a bit-oriented protocolc. an ISO standard b.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 c. Synchronous Data Link Character d. Synchronous Data Line Character

c. d.

. ANS: Baudot 3. Data codes are also called ANS: character 4. The code is a 7-bit code commonly used in communication between personal computers. ANS: ASCII 5. The two letters designate the code character used to advance a printer to the next page. ANS: FF codes.

17. BCC stands for

check character.

6.

An asynchronous frame begins with the bit. ANS: start

7.

An asynchronous frame ends with the ANS: stop

bit.

8.

At the end of an asynchronous frame, the line will be at the ANS: mark binary 1

level.

9.

An integrated circuit called a is used in an asynchronous communication system to convert between parallel and serial data. ANS: UART

10. When receiving digital data, ANS: buffers

are used to hold data until they can be read.

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 synchronous transmission. ANS: transitions 13. Clock sync is derived from the stream of ANS: data 14. In the protocol, each frame begins with at least two SYN characters. bits in synchronous transmission.

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 bitANS: stuffing 20. errors cause many consecutive bits to be bad. to prevent accidental flags. .

ANS: Burst 21. FEC stands for ANS: forward 2 2 . A n ANS: ARQ 23. Parity fails when an number of bits are in error. ANS: even 24. CRC codes are particularly good at detecting errors. scheme corrects errors by requiring the retransmission of bad blocks. error correction.

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 ANS: long 29. Messages cannot be using a public key. enough, private-key encryption can be quite secure.

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 NetworksMULTIPLE CHOICE 1. CSMA stands for: a.Client-Server Multi-Access c. Carrier Server Master Application b.Carrier Sense Multiple Access d. none of the above ANS: B 2. The CD in CSMA/CD stands for: a.Carrier Detection c. Collision Detection b.Carrier Delay d. Collision Delay ANS: C 3. The Internet is: a.a network of networks c. a very large CSMA/CD network b.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 cable b.use CSMA/CD d. all of the above ANS: D 5. Dumb terminals are still used: a.in token-passing networks b.in networks requiring central monitoring c.in networks that cannot provide central monitoring d.none of the above ANS: B 6. In a circuit-switched network: a.communication is half-duplex only b.each channel carries only one data stream c.connection is usually done using a bus topology d.all of the above ANS: B 7. Each computer on a network is called a: a.hub c. node b.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 ANS: D

d. all of the above

9. The key feature of a star network is that individual workstations are connected to: a.a central ring c. a node b.a central bus d. none of the above ANS: D 10. On networks, long messages are divided into "chunks" called: a.packets c. carriers b.nodes d. tokens ANS: A 11. When two or more PCs try to access a baseband network cable at the same time, it is called: a.a collision c. excess traffic b.contention d. multiple access ANS: B 12. When two PCs send data over a baseband network cable at the same time, it is called: a.a collision c. excess traffic b.contention d. multiple access ANS: A 13. One type of network that never has a collision is: a.CSMA c. token-passing b.Ethernet d. all networks have collisions ANS: C 14. In an Ethernet-based network, a switch can be used to reduce the number of: a.nodes c. packets b.users d. collisions ANS: D 15. The effect of too many collisions is: a.the network goes down c. the cable overheats b.the network slows down d. data is lost ANS: B 16. MAU stands for: a.Multistation Access Unit c. Multiple Auxiliary Units b.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 ANS: C

d. CCITT ITU-E

18. Ethernet was invented by: a.IBM c. Xerox b.INTEL d. Digital Equipment Corporation ANS: C 19. An Ethernet running at 10 Mbits / second uses: a.Manchester encoding c. NRZ encoding b.Three-Level encoding d. AMI encoding ANS: A 20. A 100BaseT cable uses: a.fiber-optic cable c. RG-58U coaxial cable b.twisted-pair copper wires d. 50-ohm coaxial cable ANS: B 21. The word "Base" in 10BaseT means: a.the cable carries baseband signals b.the cable has a base speed of 10 Mbps c.it can be used as the base for a backbone cable system d.none of the above ANS: A 22. The reason a CSMA/CD network has a minimum length for packets is: a.to increase the data rate b.to prevent packets from reaching all other nodes during transmission c.to make sure all other nodes hear a collision in progress d.all of the above ANS: C 23. The reason a CSMA/CD network has a maximum length for cables is: a.to increase the data rate b.to prevent packets from reaching all other nodes during transmission c.to make sure all other nodes hear a collision in progress d.all of the above ANS: C 24. NIC stands for: a.Network Interface Card b.Network Interface Cable ANS: A 25. 10BaseT cable typically uses: a. a BNC connector c. an RJ45 connector c. Network Interface Code d. Network Internal Code

b. a T connector ANS: C

d. an RS11 connector

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

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

1.

The Internet is a network of ANS: 3. In a ANS: 4. In a communications. ANS: 5. The ANS: topology 6. Ring networks often use ANS: token 7. A ANS: packet -passing. circuit star networks

network, all nodes are connected to a central computer.

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

of a network describes how it is physically connected together.

is a short section of a message in digital form.

8.

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

9.

A occurs when two nodes transmit simultaneously on the same baseband cable. ANS: collision

10. In CSMA/CD networks, all collisions must be . ANS: detected 11. Carrier-Sense means that a node "listens" for the cable to be ANS: quiet free unused available 12. A " " cable links clusters of computers together. before using it.

ANS: backbone 13. 100BaseT cables can reliably carry up to ANS: 100 mega 14. In CSMA/CD, packets must have a ANS: minimum 15. In CSMA/CD, the ANS: length 16. A unique numerical address is provided to a node by its . ANS: NIC 17. A 100BaseTX cable is a ANS: fiber-optic 18. Hubs can be ANS: stacked 19. A switch looks at the ANS: address of each incoming packet. to form, in effect, one big hub. cable. of a cable is limited to ensure that collisions are detected. length to ensure that collisions are detected. bits per second.

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 InternetMULTIPLE CHOICE 1. MAN stands for: a.Manchester Access Network c. Metropolitan-Area Network b.Multiple-Area Network d. Multiple Access Network ANS: C 2. Packet switching is based on: a.store-and-forward c. real-time delivery b.switched circuits d. all of the above ANS: A 3. SNA stands for: a.Standard Network Access b.Small Network Access ANS: D 4. The number of layers in ISO OSI is: a.3 c. 7 b.5 d. 8 ANS: C 5. The lowest-level layer in ISO OSI is called the: a.physical layer c. cable layer b.link layer d. transport layer ANS: A 6. Bad frames are usually detected by the: a.frame layer c. error-check layer b.physical layer d. link layer ANS: D 7. A virtual circuit is set up by the: a.user c. network b.link layer d. frame ANS: C 8. Frame Relay: a.is faster than X.25 c. allows for variable length packets b.does less error checking than X.25 d. all of the above ANS: D c. Standard Network Architecture d. Systems Network Architecture

9. ATM stands for: a.Asynchronous Transfer Mode c. Asynchronous Transmission Model b.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 packet c.operate at the data-link level d.all of the above ANS: D 11. IP stands for: a.Internet Process b.Internet Protocol ANS: B 12. TCP stands for: a.Transmission Control Process c. Transfer Connection Protocol b.Transmission Control Protocol d. none of the above ANS: B 13. Together, TCP/IP consists of: a.5 layersc. an application and a process b.7 layers d. datagrams ANS: A 14. IP is a: a.connection-oriented protocol c. connectionless protocol b.virtual circuit d. non-robust protocol ANS: C 15. The "lifetime" of a packet in an IP network: a.is essentially forever b.depends on elapsed time since transmission c.depends on number of "hops" between nodes d.is approximately 200 milliseconds ANS: C 16. UDP stands for: a.User Datagram Protocol c. User Data Packet b.User Data Protocol d. Universal Data Packet ANS: A 17. HTTP stands for: a. High-speed Transmission Test Procedure c. Interconnect Protocol d. Interconnect Procedure

b.High-Level Transfer Test Procedure c.Hypertext Transmission and Transport Procedure d.Hypertext Transport Protocol ANS: D 18. HTTP allows the use of: a.dumb terminals c. browsers b.file transport d. none of the above ANS: C 19. HTML stands for: a.Hypertext Markup Language c. Hypertext Transfer-Mode Layer b.Hypertext Transfer-Mode Level d. High-speed Transfer-Mode Language ANS: A 20. HTML allows: a. telneting c. web page layout b.high-speed file transfer d. all of the above ANS: C 21. FTP stands for: a.File Transfer Protocol c. File Test Procedure b.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 user b.test files to see if their data has been "corrupted" c.transport packets at maximum speed through the network d.none of the above ANS: A 23. SMTP stands for: a.Short Message Transport Protocol b.Simple Message Transport Protocol ANS: C 24. ISP stands for: a.Internet Service Protocol b.Internet Service Provider ANS: B 25. The standard Internet address (or URL) is: a.a 32-bit binary number c. running out of available values b.four groups of base-ten numbers d. all of the above c. Internet Service Procedure d. none of the above c. Simple Mail Transport Protocol d. Secondary Mail Transfer Procedure

ANS: D 26. DNS stands for: a.Domain Name Server c. Domain Numbering System b.Domain Name System d. Domain Naming System ANS: A 27. A DNS: a.has become obsolete on the Internet b.translates words to numbers c.stores all domain addresses d.describes the Internet address-naming procedure ANS: B 28. An intranet connected to the Internet is often protected by: a.a DNS c. a "firewall" b.a "brick wall" d. the use of "spoofing" protocols ANS: C 29. OSI stands for: a.Open Systems Interconnectionc. Open Systems Internet b.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 ANS: leased 4. The use of digital circuitANS: switched 5. Packet switching is done on a store-and- network. ANS: forward 6. A is a hierarchy of procedures for implementing digital communications. lines is cheaper than dedicated lines. on a monthly basis.

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

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

ANS: packet 13. The physical route of a ANS: virtual 14. Frame Relay requires channels with low rates. circuit changes each time it is used.

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 ANS: real 18. simply regenerate and retransmit packets in a network. ANS: Repeaters -time communications.

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 ANS: ARPANET DARPANET

of the 1970s.

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 ANS: hyperlinks 25. The Internet "backbone" mostly uses high-speed ANS: fiber-optic 26. A translates words in an Internet address to numbers. ANS: DNS 27. Intranets usually connect to the Internet through a ANS: firewall 28. Voice over 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 . is telephony done over the Internet. for security. cables. that jump to other pages on the web.

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 ModemsMULTIPLE CHOICE 1. FSK stands for: a.Full-Shift Keying c. Full-Signal Keying b.Frequency-Shift Keying d. none of the above ANS: B 2. PSK stands for: a.Pulse-Signal Keying c. Phase-Signal Keying b.Pulse-Shift Keying d. Phase-Shift Keying ANS: D 3. QAM stands for: a.Quadrature Amplitude Modulation b.Quadrature Amplitude Masking ANS: A 4. In the equation I = ktB, I is measured in: a.amperes c. bits b.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 symbol b.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 open b.the eye is maximally closed d. the eye alternately opens and closes ANS: A 7. What you see in an eye pattern is the effect of: a.too many bits high c. intermodulation distortion b.too many bits low d. intersymbol interference ANS: D 8. High-frequency radioteletype systems commonly use: a.FSK c. PSK b.AFSK d. QAM ANS: A c. Quadrature Amplitude Marking d. none of the above

9. Instead of a single bit, a QPSK symbol contains: a.a byte c. a dibit b.4 bits d. a Q-bit ANS: C 10. To reduce the need for linearity, /4 DQPSK uses: a.angles of 0, 90, 180, and 270 degrees c. angles of /4, 2 /4, 3 /4, and 4 /4 b.angles of 45, 135, 225, and 315 degrees d. double phase-shift anglesir ir ir ir ir

ANS: B 11. For QAM, a "constellation diagram" shows: a.location of symbols in "symbol space" c. effects of noise on symbols b.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 angle b.amplitude and phase angle d. I-bits and Q-bits ANS: B 13. The specs of the old Bell type 103 modem were: a.300 bps, full-duplex, FSK c. 1200 bps, full-duplex, FSK b.600 bps, full-duplex, FSK d. 1200 bps, half-duplex, FSK ANS: A 14. ITU is an abbre