Ans: Baseband signal
Ans: reflected radio signals
11. The process of modifying a high frequency carrier with the information to be transmitted is called Ans: modulation
20. A frequency of 27MHz has a wavelength of approximately Ans: 11m
Chapter 1: Introduction to Elec Comm 1. Communication is the process of Ans: exchanging information 2. Two key barriers to communication are Ans: distance and language
human
3. Electronic communications discovered in which century? Ans: 19th
was
4. Which of the following fol lowing is not a major communications medium? Ans: Water 5. Random interference interferenc e signals is called Ans: noise
to
transmitted
6. The communications medium causes the signal to be Ans: attenuated 7. Which of the following is not a source of noise? Ans: Another communications signal 8. One-way communications is called Ans: simplex 9. Simultaneous two-way communications is called Ans: Full duplex 10. The original electrical information signal to be transmitted is called the ©2008 Created Created by Kai Kai Raimi Raimi – BHC BHC
21. Radio signals are made up of Ans: Electric and magnetic fields
12. The process of transmitting two or more information signals simultaneously over the same channel is called Ans: Multiplexing
22. The voice frequency range is Ans: 300 to 3000 Hz
13. Continuous voice or video signals sig nals are referred to as being Ans: Baseband
23. Another name for f or signals s ignals in the t he HF range is Ans: shortwaves
14. Recovering information from a carrier is known as Ans: Detection
24. Television broadcasting occurs in which ranges? Ans: VHF
15. Transmission Transmissi on of graphical information over the telephone network is accomplished by Ans: facsimile
25. Electromagnetic waves primarily by heat are called Ans: infrared rays
16. Measuring physical conditions at some remote location and transmitting this data for analysis is the process of Ans: Telemetry 17. Receiving electromagnetic from stars is called Ans: Radio-astronomy Radio-astronomy
produced
26. A micron is Ans: One-millionth of a meter 27. The frequency range of infrared rays is approximately Ans: 0.7 to 100µm
emissions
18. A personal per sonal communications hobby for f or individuals individuals is Ans: ham radio
28. The approximately wavelength of red r ed light is Ans: 7000 Ǻ 29. Which of the following is not used for communications Ans: X-rays
19. Radar is based upon COMMUNICAT COMMUNICATION ION ELECTRONIC ELECTRONIC 2
ND
EDITION - FRENZEL
1
m = 18 000
25000
=
0.72
19. Which of the following is not a major benefit of FM over AM? Ans: Lower complexity and cost 20. The primary disadvantage of FM is its Ans: Excessive use of spectrum space 21. Noise is primarily Ans: High frequency spikes 22. The receiver circuit that rids FM of noise is the Ans: Limiter 23. The phenomenon of a strong FM signal dominating a weaker signa on a common frequency is referred to as the Ans: capture effect 24. The AM signals generated at a low level may only be amplified by what type of amplifier? Ans: Linear 25. Frequency modulation transmitters are more efficient because their power is increased by what type of amplifier Ans: class C 26. Noise interferes mainly with modulating signals that are Ans: high frequencies
27. Pre-emphasis circuits boost what modulating frequencies before modulation? Ans: high frequencies 28. A pre-emphasis circuit is a Ans: high pass filter 29. Pre-emphasis is compensated for at the receiver by Ans: low-pass filter 30. The cut-off frequency of pre-emphasis and de-emphasis circuits is Ans: 2.122 kHz
Chapter 5: FM Circuits 1. Another name for a VVC is Ans: varactor diode 2. The depletion region in a junction diode forms what part of a capacitor Ans: dielectric
6. In Fig. 5-3, if the reverse reduced, the resonant frequ Ans: decreases
7. The frequency change o oscillator produced by a va is Ans: small
8. A phase modulator varies shift of the Ans: carrier
9. The widest phase variation with a(n) Ans: LC resonant circuit 10. In Fig. 5-7, R 4 is the Ans: deviation control
11. The small frequency chan by a phase modulator can by using a(n) Ans: frequency multiplier
3.
12. A crystal oscillator whose fr be changed by an input volt a(n) Ans: VXO
4. The capacitance of a varactor diode is in what general range Ans: pF
13. Which oscillators are carrier generators because frequency stability? Ans: crystal
5. In Fig. 5-3, the varactor diode is biased by which components?
14. Which
Increasing the reverse bias on a varactor diode will cause its capacitance Ans: decrease
of
the
following
7. The most efficient RF power amplifier is which class amplifier? Ans: C 8. Collector current in a class C amplifier is a Ans: Pulse 9. The maximum power of typical transistor RF power amplifiers is in what range? Ans: Hundreds of watts
16. To a match a 6 Ω amplifier impedance to a 72 Ω antenna load, a transformer must have a turns ration N P /NS of Ans: 0.289
22. The gain of a transistor amp Ans: directly proportional current
Solution:
NP
=
Ns NP Ns
ZP ZS
=
6 72
=
0.289
10. Self-oscillation in a transistor amplifier is usually caused by Ans: internal capacitance
17. Impedance matching in a broadband linear RF amplifier is handled with a(n) Ans: balun
11. Neutralization is the process of Ans: cancelling the effect of internal device capacitance
18. A class C amplifier has a supply voltage of 24 V and a collector current of 2.5 A. Its efficiency is 80 %. The RF output power is Ans: 48
12. Maximum power transfer occurs when what relationship exists between the generator impedance ZI and the load impedance Zl? Ans: Zi = Zl 13. Which of the following is not a benefit of a toroid RF inductor? Ans: Self-supporting
21. In a speech-processing ci pass filter prevents Ans: excessive signal bandw
Solution: @ 100 %: P100 = VI = 60 W @ 80 %: P80 = 0.8 P100 P80 = 0.8 (60) = 48 W
14. A toroid is a Ans: Magnetic core
19. Which of the following is not a benefit of speech-processing circuits? Ans: improved frequency stability
15. Which of the following is not commonly used for impedance matching in a
20. In an AM transmitter, a clipper circuit
23. What values of L and C in a are required to match a 10 amplifier impedance to a 50 MHz? Ans: L = 118 nH, C = 236 pF Solution:
XL
R1R2 − R12
=
XL= 2πfL
(10)(50) − 10
XL
=
L=
XL 2π (27M)
XC =
C=
R1R2 XL
1 2π f XC
=
=
2
=
= 117.89nH
10(50) 20
=
25
1 2π (27M)(25)
Chapter 7: Communications R
1. The simplest receiver is a(n Ans: tuned circuit
17. The maximum bandwidth that an analog signal use with a sampling frequency of 108 kHz is Ans: 54 kHz
7. Most FDM telemetry systems use Ans: FM 8. The best frequency demodulator is the Ans: PLL discriminator 9. The modulation used in FDM telephone systems is Ans: SSB 10. The FDM telephone systems accommodate many channels by Ans: using multiple levels of multiplexing 11. In FM stereo broadcasting, the L + R signal Ans: modulates the FM carrier 12. In FM stereo broadcasting, the L – R signal Ans: DSB modulates a subcarrier 13. The SCA signal if used broadcasting is transmitted via Ans: A 67 kHz subcarrier
in
18. Pulse-amplitude modulation signals are multiplexed by using Ans: FET switches 19. In PAM demultiplexing, the receiver clock is derived from Ans: The PAM signal itself 20. In PAM/TDM system, keeping the multiplexer and DEMUX channels step with one another is done by a Ans: Sync pulse 21. Transmitting data as serial binary words is called Ans: PCM
FM
14. In TDM, multiple signals Ans: take turns transmitting 15. In TDM, each signal may use he full bandwidth of the channel Ans: True 16. Sampling an analog signal produces
Solution: fn = fb / 2 = 108 kHz / 2 = 54 kHz
22. Converting analog signals to digital is done by sampling and Ans: Quantizing
Ans: Minimizes signal bandw
26. A telephone system usin PCM is called Ans: T-1
27. An IC that contains converters, companders an serial converters is called Ans: Codec
28. Pulse-code modulation i PAM because of its Ans: Superior noise immunity
Chapter 9: Antennas and T lines 1. The most commonly used line is a Ans: Coax 2.
The characteristic imped transmission line does not d its Ans: none of the above Choices were:
23. A quantizer is a(n) Ans: A/D converter 24. Emphasizing low-level signals and compressing higher-level signals is called Ans: Companding
Length, Conductor Conductor spacing
Diam
3. Which of the following is transmission line impedance Ans: 120 Ω
characteristic impedance of the line Z O and the load impedance Z l should be Ans: ZO = Zl 5. The mismatch between antenna and transmission line impedances cannot be corrected for by Ans: Adjusting the length of transmission line 6. A pattern of voltage and current variations along a transmission line not terminated in its characteristic impedance is called Ans: Standing waves 7. The desirable SWR on a transmission line is Ans: 1 8. A 50 Ω coax is connected to a 73 Ω antenna. The SWR is Ans: 1.46 Solution: If RL > ZO : SWR = RL / ZO = 73 / 50 = 1.46 9. The most desirable reflection coefficient is Ans: 0 10. A ratio expressing the percentage of incident voltage reflected on a transmission line is know as the Ans: Reflection coefficient
11. The minimum voltage along a transmission line is 260 V, while the maximum voltage is 390 V. The SWR is Ans: 1.5 Solution:
| Γ |=
Vmax - Vmin Vmax + Vmin
SWR
=
1+ | Γ | 1− | Γ |
=
=
390 - 260 390 + 260
1 + 0.2 1 − 0.2
=
0.2
= 1.5
12. Three feet is one wavelength at a frequency of Ans: 328 MHz 13. At very high frequencies, transmission lines are used as Ans: Tuned Circuits 14. A shorted quarter-wave line at the operating frequency acts like a(n) Ans: Parallel Resonant 15. A shorted half-wave line at the operating frequency acts like a(n) Ans: Series Resonant Circuit 16. A popular half-wavelength antenna is the Ans: Dipole 17. The length of a doublet at 27 MHz is Ans: 17.33 ft
L=
468 f MHz
=
468 27
= 17.33ft.
18. A popular vertical antenna is Ans: Ground plane
19. The magnetic field of an perpendicular to the antenna’s polarization Ans: is horizontal
20. An antenna that transmits equally well in all directions Ans: Omnidirectional 21. The horizontal radiation dipole is a Ans: figure of 8
22. the length of a ground plan 146 MHz is Ans: 1.6 ft Solution:
L 2
=
468 2 f MHz
=
468 2(146)
23. The impedance of a dipole i Ans: 73 Ω
24. A direction antenna with t elements is known as a(n) Ans: Array
26. In a Yagi antenna, maximum direction of radiation is toward the Ans: Director 27. Conductors in multielement antennas that do not receive energy directly from the transmission line are known as Ans: Parasitic elements 28. A coax has an attenuation of 2.4 db per 100 ft. The attenuation for 275 ft is Ans: 6.6 db Solution:
A dB
=
2.4db × 275 = 6.6dB 100 ft
29. An antenna has a power gain of 15. The power applied to the antenna is 32 W. The effective radiated power is Ans: 480 W Solution: P = GTPT = (15)(32) = 480 W 30. Which beamwidth represents the best antenna directivity Ans: 7O 31. The radiation pattern of collinear and broadside antennas Ans: Bidirectional 32. Which antenna has a unidirectional
33. A wide-bandwidth multielement driven array is the Ans: Log-periodic 34. Ground-wave communications is most effective in what frequency range? Ans: 300 kHz to 3 MHz 35. The ionosphere causes radio signals to be Ans: refracted
41. To increase the transmissio a UHF signal, which of t should be done? Ans: Increase antenna height
42. A coax has a velocity fac What is the length of a hal MHz? Ans: 11.2 ft Solution:
36. The ionosphere has its greatest effect on signals in what frequency range? Ans: 3 to 30 MHz 37. The type of radio wave responsible for long-distance communications by multiple skips is the Ans: Skywave 38. Microwave signals propagate by way of the Ans: Direct wave 39. The line-of-sight communications is not a factor in which frequency range? Ans: HF 40. A microwave-transmitting antenna is 550 ft high. The receiving antenna is 200 ft high. The maximum transmission distance is Ans: 53.2 mi. Solution:
Vp
c Vf (300)(0 = 2 2fMHz 2fMHz 2(3 λ 3.28ft = 3.4m × = 11.152 2 1m λ
=
=
43. Which transmission line ha attenuation? Ans: Twin lead
44. Refer to Fig. 9-39. The be this antenna patter is approx Ans: 60o
45. A receiver-transmitter stat increase the communicatio VHF, UHF, and microwav called a(n) Ans: Repeater
Chapter 10: Microwave Techn
2. Radio communications are regulated in the United States by the Ans: Federal Communications Commission 3. Which of the following is disadvantage of microwaves? Ans: higher-cost equipment
not
a
4. Which of the following is a microwave frequency Ans: 22 GHz 5. Which of the following is not a common microwave application? Ans: mobile radio 6. Coaxial cable is not widely used for long microwave transmission lines because of its Ans: high loss 7. Stripline and microstrip transmission lines are usually made with Ans: PCBs 8. The most common cross section of a wave guide is a Ans: rectangular 9. A rectangular waveguide has a width of 1 in. and a height of 0.6 in. Its cutoff frequency is Ans: 5.9 GHz Solution:
f
=
c 2Width
=
3 × 108 m/s 2(0.0254)
=
5.9GH z
10. A waveguide has a cutoff frequency of 17 GHz. Which of the signals will not be passed by the waveguide? Ans: 15 GHz 11. Signal propagation in a waveguide is by Ans: Electric and magnetic fields 12. When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be Ans: Transverse electric 13. The dominant mode in most waveguides is Ans: TE0,1 14. A magnetic field is introduced into a waveguide by a Ans: Probe 15. A half-wavelength, closed section of a waveguide that acts as a parallel resonant circuit is known as a(n) Ans: Cavity resonator 16. Decreasing the volume of a cavity causes its resonant frequency to Ans: Increase 17. A popular microwave mixer diode is the Ans: Gunn
Ans: Frequency multiplier
19. Which diode is a popular oscillator Ans: Gunn
20. Which type of diode does n operate with reverse bias Ans: Tunnel
21. Low-power Gunn diodes are Ans: Reflex klystrons 22. Which of the following microwave tube? Ans: Cathode-ray tube
23. In a klystron amplifie modulation of the electro produced by the Ans: Buncher cavity 24. A reflex klystron is used as Ans: Oscillator
25. For proper operation, a mag be accompanied by a Ans: Permanent magnet
26. The operating frequency and magnetrons is set by th Ans: Cavity resonator
27. A magnetron is used only as Ans: oscillator
Ans: Bicone 29. In a TWT, the electron beam is densitymodulated by a Ans: Helix 30. The main advantage of a TWT over a klystron for microwave amplification is Ans: Wider bandwidth 31. High-power TWTs are replacing what in microwave amplifiers? Ans: klystrons 32. The most widely antenna is a Ans: horn antenna
used
microwave
33. What happens when a horn antenna is made longer? Ans: Gain increases 34. A pyramidal horn used at 5 GHz has an aperture that is 7 by 9 cm. The gain is about Ans: 10.5 db Solution:
G=
4π A λ2
(7)(9) 10000 2 3 × 10 8 9 5 × 10
4π (0.5 ) =
= 10.9956
GdB = 10 log 10.9956 = 10.41 dB 35. Given the frequency and dimensions in
Solution:
G=
80 w/ λ
=
80 w
=
53.33 o
3 × 10 8 9 5 × 10 36. The diameter of a parabolic reflector should be at least how many wavelengths at the operating frequency? Ans: 10 37. The point where the antenna is mounted with respect to the parabolic reflector is called Ans: Focal point 38. Using a small reflector to beam waves to the larger parabolic reflector is known as Ans: Cassegrain feed 39. Increasing the diameter of a parabolic reflector causes which of the following Ans: Decreasing beamwidth and increasing gain 40. A helical antenna is made up of a coil and a Ans: Reflector 41. The output of a helical antenna is Ans: Circularly polarized
Chapter 11: Introduction to S
1. As the height of a satellit lower, the speed of the sate Ans: Increases
2. The main functions of a com satellite is a a(a) Ans: Repeater
3. The key electronic comp communications satellite is Ans: Transponder 4. A circular orbit around the a 24 h period is called a(n) Ans: Geostationary orbit
5. A satellite stays in orbit following 2 factor are balanc Ans: Gravitational pull and in
6. The height of a sate synchronous equatorial orbi Ans: 22300 mi 7. Most satellites operate frequency band? Ans: 3 GHz to 30 GHz 8. The main power sources are Ans: Solar cells
Ans: The bit rate may be greater than the baud rate 13. A modem converts Ans: both analog signals to digital and digital signals to analog signals 14. Slow-speed modems use Ans: FSK 15. A carrier recovery circuit is not needed with Ans: DPSK 16. The basic modulator and demodulator circuits in PSK are Ans: Balanced modulators 17. The carrier used with demodulator is Ans: The BPSK signal itself
a
23. A synchronous transmission begins with which character? Ans: SYN
usually
24. The characters making up the message in a synchronous transmission are collectively referred to as a data Ans: Block 25. Bit errors in data transmission are usually cause by Ans: Noise 26. Which of the following is not a commonly used method of error detection? Ans: Redundancy
31. A longitudinal redunda produces a(n) Ans: Block check character
32. Dividing the data block by produces a remainder that error detection. It is called th Ans: CRC 33. A CRC generator components? Ans: Shift register
34. Which of the following is not Ans: Cable TV system
35. The fastest LAN topology is Ans: Bus
BPSK
18. A 9600 baud rate signal can pass over the voice-grade telephone line if which kind of modulation is used? Ans: QAM 19. Quadrature amplitude modulation is Ans: AM plus QPSK 20. A QAM modulator does not use a(n) Ans: XNOR 21. A rule or procedure that defines how data is to be transmitted is called a(n) Ans: Protocol
27. Which of the following words has the correct parity bit? Assume odd parity. The last bit is the parity bit Ans: 1100110 1
36. Which is not a common LAN Ans: Twin Lead
28. Another name for parity is Ans: Vertical redundancy check
37. A mainframe computer multiple terminals and PCs which configuration? Ans: Star
29. Ten bit errors occur in two million transmitted. The bit error rate is Ans: 5 x 10 -6
38. A small telephone switching can be used as a LAN is ca Ans: PBX
Solution:
39. Which medium is the leas to noise? Ans: Fiber-optic cable
e=
10 2 × 10 6
=
5 × 10 −6
40. Which medium is the most
41. Transmitting the data signal directly over the medium is referred to as Ans: Baseband 42. The techniques of using modulation and FDM to transmit multiple data channels of a common medium is known as Ans: Broadband 43. What is the minimum bandwidth required to transmit a 56 kbits/s binary signal with no noise? Ans: 28 kHz
S N
= 10
BW
=
S N dB 10
=
53. The most critical and diff receiving a direct-sequence Ans: Synchronism
630.96
10Mbits/s = 1.075MHz log 2 (1 + 630.96 )
Chapter 13: Fiber Optic Comm
46. Which circuit is common to bot frequency-hopping and direct-sequence SS transmitters? Ans: Frequency of operation
Solution: BW = f b /2 = 56 kbits/2 = 28 kHz
47. Spread spectrum stations sharing a band are identified by and distinguished from one another by Ans: PSN code
44. Sixteen different levels (symbols) are used to encode binary data. The channel bandwidth is 36 MHz. The maximum channel capacity is Ans: 288 Mbits/s
48. The type of modulation most often used with direct-sequence SS is Ans: PSK
Solution
49. The main circuit in a PSN generator is a(n) Ans: XOR
C = 2BWlog 2M C = 2(36MHz) (log 2 (16)) = 288 Mbits/s 45. What is the bandwidth required to transmit at a rate of 10Mbits/s in the presence of a 28-db S/N ratio? Ans: 1.075 MHz Solution: C = BW log2(1+S/N) S/NdB = 10 log (S/N)
50. To a conventional narrowband receiver, an SS signal appears to be like Ans: Noise 51. Which of the following is not a benefit of SS? Ans: Noise proof 52. Spread spectrum multiplexing
is
a
form
of
1. Which of the following is application of fiber-optic cab Ans: Consumer TV
2. Total internal reflection take light ray strikes the interface with what relationship to angle? Ans: greater than
3. The operation of a fiber-o based on the principle of Ans: Reflection
4. Which of the following is type of fiber-optic cable? Ans: Single-mode grade-inde
5. Cable attenuation is usual in terms of Ans: dB/km 6. Which cable length has attenuation? Ans: 2 km
7. The upper pulse rate and carrying capacity of a cable Ans: Attenuation
Ans: Glass 9. The core of a fiber-optic cable is surrounded by Ans: Cladding 10. The speed of light in plastic compared to the speed of light in air is Ans: Less 11. Which of the following is not a major benefit of fiber-optic cable? Ans: Lower cost 12. The main benefit of light-wave communications over microwaves or any other communications media are Ans: Wider bandwidth 13. Which of the following is not part of the optical spectrum Ans: X-rays 14. The wavelength of visible light extends from Ans: 400 to 750 nm 15. The speed of light is Ans: 300,000,000 m/s 16. Refraction is the Ans: Bending of light waves 17. The ratio of the speed of light in air to the speed of light in another substance is called the Ans: Index of refraction
18. A popular light wavelength in fiber-optic cable is Ans: 1.3 µm 19. Which type of fiber-optic cable is the most widely used? Ans: Multimode step-index 20. Which type of fiber-optic cable is best for very high speed data? Ans: Single mode step-index 21. Which type of fiber-optic cable has the least modal dispersion? Ans: Single mode step-index 22. Which of the following is not a factor in cable light loss? Ans: Reflection 23. A distance of 8 km is the same as Ans: 5 mi 24. A fiber-optic cable has a loss of 15 db/km. The attenuation in a cable 1000ft long is Ans: 4.57 dB
25. Fiber-optic with attenuations of 1.8, 3.4, 5.9 and 18 dB are linked together. The total loss is Ans: 29.1 dB
COMMUNICATION ELECTRONIC 2
ND
27. Most fiber-optic light sources emit light in which spectrum? Ans: Visible 28. Both LEDs and ILDs operate correctly with Ans: Forward bias 29. Single-frequency light is called Ans: Monochromatic 30. Laser light is very bright because it is Ans: Coherent 31. Which of the following is not a common detector? Ans: Photovoltaic diode 32. Which of the following is the fastest light sensor? Ans: Avalanche photodiode 33. Photodiodes operate properly with Ans: Reverse bias
Solution: 1000ft = 0.3048 km σ = 15 × 0.3048 = 4.57dB
Solution: LossT = 1.8 + 3.4 + 5.9 + 18 = 29.1 dB ©2008 Created by Kai Raimi – BHC
26. Which light emitter is preferred for highspeed data in a fiber-optic system? Ans: Laser
EDITION - FRENZEL
34. The product of the bit rate and distance of a fiber-optic system is 2Gbits-km/s. What is the maximum rate at 5 km? Ans: 400 Mbits/s Solution: Ratemax =
20 Gbits - km/s 5 km
=
400bits/s 19
Ans: CCD 45. The I and Q composite color signals are multiplexed onto the picture carrier by modulating a 3.58 MHz subcarrier using Ans: DSB AM
53. What technique is used to permit hundreds of TV signals to share a common cable? Ans: FDM
46. The assembly around the neck of a picture tube that produces the magnetic fields that deflect and scan the electron beams is called the Ans: Yoke 47. The picture and sound carrier frequencies in a TV receiver IF are respectively Ans: 45.75 and 41.25 MHz 48. The sound IF in a TV receiver is Ans: 41.25 MHz 49. What type of circuit is used to modulate and demodulate the color signals? Ans: Balanced demodulator 50. What circuit in the TV receiver is used to develop the high voltage needed to operate the picture tube? Ans: horizontal output 51. What ensures proper synchronization at the receiver? Ans: 3.58 MHz color burst
color
52. Which of the following is not a benefit of cable TV? Ans: Lower-cost reception
©2008 Created by Kai Raimi – BHC
COMMUNICATION ELECTRONIC 2
ND
EDITION - FRENZEL
22
