Frenzel

Ans: Baseband signal

Ans: reflected radio signals

Chapter 1: Introduction to Elec Comm 11. 11. The The proc proces ess s of modi modifyi fying ng a high high frequency carrier with the information to be transmitted is called

1. Communicatio Communication n is the process of

Ans: exchanging information 2. Two key barriers communication are

Ans: modulation to

12. The process process of transm transmitti itting ng two or more information signals simultaneously over the same channel is called

3. Elec Electr tron onic ic comm commun unic icat atio ions ns discovered in which century?

was was

Ans: 19th

Contin Continuou uous s voice voice or video video signal signals s are referred to as being

Ans: Water

Ans: noise

6. The communication communications s medium causes the signal to be

Ans: attenuated

Ans: Another communications signal

8. One-way One-way communications communications is called called

Ans: simplex

from from

a

Ans: Detection

15. Transmission of graphical information over the telephone network is accomplished by

Ans: facsimile

Measuring ing physic physical al condit condition ions s at 16. Measur some remote location location and transmitting transmitting this data for analysis is the process of

Ans: Telemetry

17. Receiving elec tr trom ag agnetic emissions from stars is called

Ans: Radio-astronomy two-way

Ans: Full duplex

10. The origin original al electri electrical cal informa information tion signal to be transmitted is called the ©2008 Created by Kai Raimi – BHC

a

Ans: 11m

Ans: Electric and magnetic fields

22. The voice frequency frequency range is

Ans: 300 to 3000 Hz

23. Another Another name for signals signals in the HF range is

Ans: shortwaves

24. Televi Television sion broadc broadcasti asting ng occurs occurs in which ranges?

Ans: VHF

25. Electro Electromag magnet netic ic waves waves primarily by heat are called

produc produced ed

Ans: infrared rays 26. A micron micron is

7. Which of the following following is not a source of noise?

Ans: Baseband

14. 14. Reco Recove veri ring ng info inform rmat atio ion n carrier is known as

5. Random Random interf interfere erence nce to transmit transmitted ted signals is called

9. Si S imultaneous communications is called

Ans: Multiplexing 13.

4. Which of the following following is not a major major communications medium?

has

21. Radio signals signals are made up up of

human

Ans: distance and language

20. A frequency of 27M Hz Hz wavelength of approximately

18. A person personal al commun communica icatio tions ns hobby hobby for individuals is

Ans: ham radio

Ans: One-millionth of a meter 27. The frequency frequency range of infrared infrared rays is approximately

Ans: 0.7 to 100μm

28. The approx approxima imatel tely y wavele wavelengt ngth h of red light is

Ans: 7000 Ǻ

29. Which of the following following is not used for communications

Ans: X-rays

19. Radar is based based upon ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

1

30. 30. A sign signal al occu occupi pies es the the spec spectru trum m space space from from 1.115 1.115 to 1.122 1.122 GHz. GHz. The bandwidth is

Ans: 7 MHz

the united states, the 31. In electromagn electromagnetic etic spectrum spectrum is regulated regulated and managed by

Ans: FCC

32. For a given bandwidth bandwidth signal, signal, more channel space is available for signals in the range of

Ans: EHF

Chapter 2: AM and SSB Modulation 1. Having an information signal change some characteristic of a carrier signal is called

6. The The rati ratio o of the the peak peak modu modula lati ting ng signal voltage to the peak carrier voltage is referred to as

Ans: the modulation index If m is grea greate terr 7. happens?

than than 1, what what

Ans: information signal is distorted

Ans: The carrier frequency changes 3.

Ans: m = 1

9. The The outl outlin ine e of the the pea peaks ks of of a carr carrie ier r has the shape of the modulating signal and is called the

Ans: envelop

10. Overmo Overmodul dulati ation on occur occurs s when when

11. 11. The The value values s of Vmax Vmax and Vmin Vmin as read from an AM wave on an osci oscill llos osco cope pe are are 2.8 2.8 and and 0.3. 0.3. The The percentage of modulation is

Ans: 80.6 %

4. The circuit used modulation is called a

to

produced

Ans: demodulator

5. A modul modulat ator or circ circui uitt perf perfor orms ms what what math mathem emat atic ical al oper operat atio ion n on its its two inputs?

Ans: Multiplication

produ roduce ced d

©2008 Created by Kai Raimi – BHC

Ans: 25 percent

18. An AM transmitter has a percen percentag tage e of modula modulatio tion n of 88. The carrier power is 440 W. The power in one sideband is

19. An AM transm transmiit iiter er antenn antenna a current current is measur measured ed with with no modula modulation tion and found to be 2.6 A. With modulation, the current rises to 2.9 A. The percentage of modulation is

by

Ans: sidebands

13. 13. A carri carrier er of 880 880 kHz is modul modulate ated d by a 3.5 kHz sine wave. The LSB and USB are, respectively,

Ans: 876.5 and 883.5 kHz

14. A disp displlay of sig signal nal ampl mplitu itude versus frequency is called the

Ans: frequency domain

17. 17. For For 100 100 perc percen entt modu modula lati tion on,, what what percent ag age of power is in eac h sideband?

Ans: 70 percent

The The opp oppos osit ite e of of mod modul ulati ation on is

Ans: Demodulation

16. 16. An AM signa signall has a carr carrie ierr power power of 5 W. The percentage of modulation is 80 percent. The total sideband power is

Ans: 85 W

Ans: Vm > Vc

12. The The new new sign signal als s modulation are called

Ans: Carrier

Ans: 1.6 W

8. For For idea ideall AM, AM, whic which h of the the fol follo lowin wing g is true?

Ans: modulation

2. Whic Which h of the the follo followi wing ng is not not true true about AM?

15. Most of of the powe powerr in an AM AM signal signal is the

ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

20. 20. What What is the the carr carrie ierr powe powerr in the problem above if the antenna resistance is 75 ohms?

Ans: 507 W

21. 21. In an AM sign signal al,, the the tran transm smit itte ted d information is contained within the

Ans: sidebands

22. An AM signa signall without without the the carrie carrierr is called a(n) 2

Ans: DSB 23. What is the minimum AM signal needed to transmit information?

Ans: One sideband

24. The main advantage of SSB over standard AM or DSB is

Ans: Less spectrum space is used

25. In SSB, which sideband is the best to use?

Ans: neither upper or lower

26. The typical audio modulating frequency range used in radio and telephone communications is

Ans: 300 Hz to 3 kHz

27. An AM signal with a maximum modulating signal frequency of 4.5 kHz has a total bandwidth of

Ans: 9 kHz

28. Distortion of the modulating signal produces harmonics which cause an increase in the signal

Ans: bandwidth

29. The process of translating a signal, with or without modulation, to a higher or lower frequency for processing is called

Ans: frequency conversion

30. Frequency translation is carried out by a circuit called a

Ans: converter


31.

An input signal of 1.8 MHz is mixed with a local oscillation of 5 MHz. A filter selects the difference signal. The output is

Ans: 3.2 MHz

32. The output of an SSB transmitter with a 3.85 MHz carrier and a 1.5 kHz sine wave modulating tone is

Ans: 3.85, 3.8485, and 3.8515 MHz

33. An SSB transmitter produces a 400 V peak-to-peak signal across a 52 ohms antenna load. The PEP output is

Ans: 384.5 W

400V

= 384.5W 52 Ω

34. The output power of an SSB transmitter is usually expressed in terms of

Ans: Peak envelope power

35. An SSB transmitter has a PEP rating of 1 kW. The average output power is in the range of

Ans: 250 to 333 W

Vavg 1 =

3 PEP Vavg 2 = 4

Amplitude modulation is the same

Ans: Analog multiplication 2. In a diode modulator, the negative half of the AM wave is supplied by a(n)

Ans: Tuned circuit 3. Amplitude produced by

modulation

can

be

Ans: Having the carrier vary a resistance

Ans: Variable resistance 5.

In Fig. 3-4, D1 is a

Ans: Variable resistor

6. The component used to produce AM at very high frequencies is a

Ans: Varactor

7. Amplitude modulation generated at a very low voltage or power amplitude is known as

Ans: Low-level modulation

Solution: PEP

1. as

4. Amplitude modulators that vary the carrier amplitude with the modulating signal by passing it through an attenuator work on the principle of

Solution: PEP = 2 2

Chapter 3: AM Circuits

=

333W ,

=

250W

8. A collector modulator has a supply voltage of 48 V. The peak-to-peak amplitude of the modulating signal for 100 percent modulation is

Ans: 96 V Solution:


3

Vmp-p = 2Vc . m = 96 V

16. The output of a balanced modulator is

9. A collector modulated transmitter has a supply voltage of 24 V and a collector current of 0.5 A. The modulator power for 100 percent modulation is

Ans: 12 W Solution:

Ans: demodulator

12. A circuit that generates the upper and lower sidebands but no carrier is called a(a)

Ans: Balanced modulator

13. The inputs to a balanced modulator are 1 MHz and a carrier of 1.5 MHz. The outputs are

Ans: 500 kHz and 2.5 MHz

14. A widely used balanced modulator is called the

Ans: lattice modulator

15. In a diode ring modulator, the diodes act like


Ans: Differential amplifier

19. The equivalent circuit of a quartz crystal is a

Ans: Series resonant circuit and parallel resonant circuit

used

Ans: Envelope detector

17. The principal circuit in the popular 1496/1596 IC balanced modulator is a

Ans: RC networks and op-amps

10. The c irc uit t hat recovers the original modulating information from an AM signal is known as a

Ans: switches

23. A balanced modulator used to demodulate a SSB signal is called a(n)

18. The most commonly used filter in SSB generator uses

P = VI = 24 x 0.5 = 12 W

11. The most commonly amplitude demodulator is the

Ans: DSB

Ans: phase shift

20. A crystal lattice filter has crystal frequencies of 27.5 and 27.502 MHz. The bandwidth is approximately

Ans: 2 kHz

Ans: converter

24. Frequency translation is done with a circuit called a

Ans: mixer 25.

The inputs to a mixer are f o and f m. In down conversion, which of the following mixer output signals is selected

Ans: f o - f m

26. Mixing for frequency conversion is the same as

Ans: Liner summing

27. Which of the following can be used as a mixer

Solution: BW = f 2 – f 1 = 27.502MHz–27.5MHz = 2 kHz 21. An SSB generator has a sideband filter cent ered at 3. 0 M Hz. The modulating signal is 3 kHz. To produce both upper and lower sidebands, the following carrier frequencies must be produced:

Ans: 2997 and 3003 kHz

Ans: Balanced modulator, FET and Diode modulator 28. The desired output from a mixer is usually selected with a

Ans: Crystal filter 29.

The two main inputs to a mixer are the signal to be translated and a signal from a(n)

Ans: Local oscillator

Solution: LSB = 3.0 MHz – 3 kHz = 2997 kHz USB = 3.0 MHz + 3 kHz = 3003 kHz 22. In the phasing method of SSB generation, one sideband is canceled out due to COMMUNICATION ELECTRONIC 2EDITION - FRENZEL ND

30. An NE602 mixer IC has a difference output of 10.7 MHz. The input is 146.8 MHz. The local oscillator frequency is

Ans: 157.5 MHz

4

Solution: f o = 146.8 MHz + 10.7 MHz

Chapter 4: FM 1. The amount of frequency deviation from the carrier center frequency in an FM transmitter is proportional to what characteristic of the modulating signal?

8. To compensate for increases in carrier frequency deviation with an increase in modulating signal frequency, what circuit is used between the modulating signal and the phase modulator?

Ans: Low-pass filter 9.

The FM produced by PM is called

Ans: Indirect FM

Ans: Amplitude

2. Both FM and PM are types of kind of modulation?

Ans: Angle

3. If the amplitude of the modulating signal decreases, the carrier deviation

Ans: decreases

4. On an FM signal, maximum deviation occurs at what point on the modulating signal?

10. If the amplitude of the modulating signal applied to a phase modulator is constant, the output signal will be

Ans: The carrier frequency

11. A 100 MHz carrier is deviated 50 kHz by a 4 kHz signal. The modulation index is

Ans: 12.5 Solution:

Ans: Both positive and negative peak amplitude

5. I n P M, a frequency s hif t o cc urs while what characteristic of the modulating signal is changing?

Ans: Amplitude

6. Maximum frequency deviation of a PM signal occurs at

Ans: Zero crossing points

Ans: Carrier amplitude and frequency


Ans: 7

Solution: m 4 000 4 1000 =

=

By using Bessel’s Table, a modulation index of 4, has 7 significant sidebands. 14. What is the bandwidth of the FM signal described in question 13 above?

Ans: 14 kHz Solution:

BW = 2Nf max BW = 2 (7) (1000) = 14 kHz 15. What is the relative amplitude of the third pair of sidebands of an FM signal with m = 6

Ans: 0.11 m 5 00 0 0 12.5 4000 =

=

12. The maximum deviation of an FM carrier is 2 kHz by a maximum modulating signal of 400 Hz. The deviation ratio is

Ans: 5

16. A 200 kHz carrier is modulated by a 2.5 kHz signal. The fourth pair of sidebands are spaced from the carrier by


4th sideband = 4 (2.5 kHz) = 10 kHz

Solution: m 2000 5 4 00 =

7. In PM, carrier frequency deviation is not proportional to:

signal. How many significant sideband pairs are produced?

=

13. A 70 kHz carrier has a frequency deviation of 4 kHz with a 1000 Hz ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

17. An FM transmitter has a maximum deviation of 12 kHz and a maximum modulating frequency of 12 kHz. The bandwidth by Carson’s rule is

Ans: 48 kHz

5

Solution: BW = 2 (δmax + f max) BW = 2 (12 kHz + 12 kHz) = 48 kHz 18.

The maximum allowed deviation of the FM sound signal in TV is 25 kHz. If the actual deviation is 18 kHz, the percent modulation is

Ans: 72%

25. Frequency modulation transmitters are more efficient because their power is increased by what type of amplifier

Ans: class C

26. Noise interf eres m ainly modulating signals that are

wit h

Ans: high frequencies

4. The capacitance of a diode is in what general range

varactor

Ans: pF

5. In Fig. 5-3, the varactor diode is biased by which components?

Ans: R1, R2 6.

Solution: m 1 8 00 0 0.72 25000 =

=

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


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 preemphasis and de-emphasis circuits is

In Fig. 5-3, if the reverse bias on D1 is reduced, the resonant frequency of C1

Ans: decreases

7. The frequency change of a crystal oscillator produced by a varactor diode is

Ans: small

8. A phase modulator phase shift of the

varies

9. The widest phase obtained with a(n)

variation

Ans: carrier

Ans: 2.122 kHz

Ans: LC resonant circuit

Chapter 5: FM Circuits

Ans: deviation control

10.

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

3. Increasing the reverse bias on a varactor diode will cause its capacitance

Ans: decrease


the

is

In Fig. 5-7, R4 is the

11. The sm all frequency change produced by a phase modulator can be increased by using a(n)

Ans: frequency multiplier

12. A crystal oscillator whose frequency can be changed by an input voltage is called a(n)

Ans: VXO

6

13. Which oscillators are preferred for carrier generators because of their good frequency stability?

Ans: crystal

Ans: Foster-Seeley discriminator

averages

Ans: Quadrature detector

16. Which frequency demodulator is considered the best overall?

Ans: PLL

17. In Fig. 5-8, the voltage at point A when the input frequency is below the FM center frequency is

Ans: positive 18.

In Fig. 5-8, R3 and C6 form which kind of circuit?

Ans: De-emphasis 19.

In Fig. 5-10, the voltage across C6

is

Ans: directly proportional to frequency deviation 20. In a pulse averaging discriminator, the pulses are produced by a(n)

Ans: zero crossing detector 21.

A reactance modulator looks like a capacitance of 35 pF in parallel with the oscillator-tuned circuit whose inductance is 50 μH and capacitance is 40 pF. What


Ans: 206 MHz

28. The band of frequencies over which a PLL will acquire or recognize an input signal is called the

f = 1 2Π LC CT = 35 pF + 40 pF =75 pF 1 f 2.6MHz µ 2Π (50 H)(75pF) =

27. The range of frequencies over which a PLL will track input signal variations is known as the

Ans: lock range

Solution:

14. Which of the following frequency demodulators requires an input limiter?

15. Which discriminator pulses in a low-pass filter?

is the center frequency of the oscillator prior to FM?

=

22. Which of the following is true about the NE566 IC?

Ans: it is a VCO

23. An FM demodulator that uses a differential amplifier and tuned circuits to convert frequency variations into voltage variations is the

Ans: Differential peak detector

24. The output amplitude of the phase detector in a quadrature detector is proportional to

Ans: pulse width

25. The input to a PLL is 2 MHz. In order for the PLL to be locked, the VCO output must be

Ans: 2 MHz

26. Decreasing the input frequency to a locked PLL will cause the VCO output to

Ans: jump to the free-running frequency

Ans: capture range

29. Over a narrow range frequencies, the PLL acts like a

of

Ans: Bandpass filter

30. The output of a PLL frequency demodulator is taken from

Ans: low-pass filter

Chapter 6: Radio Transmitters 1. Which of the following circuits is not typically part of every radio transmitter?

Ans: mixer

2. Class C amplifiers are not used in which type of transmitter?

Ans: SSB

3. A circuit that isolates the carrier oscillator from load changes is called a

Ans: buffer amplifier

4. A class B amplifier conducts for how many degrees of an input sine wave?

Ans: 180o ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

7

5. Bias for a class C amplifier produced by an input RC network is known as

Ans: signal bias

6. An F M t ransm it ter h as a 9 M Hz crystal carrier oscillator and frequency multipliers of 2, 3, 4. The output frequency is

Ans: 216 MHz Solution

f = 9 MHz x 2 x 3 x 4 = 216 MHz

Ans: Zi = Zl 13. Which of the following is not a benefit of a toroid RF inductor?

Ans: Self-supporting 14. A toroid is a

Ans: Magnetic core 15. Which of t he f ollowi ng is not commonly used for impedance matching in a transmitter?

Ans: Resistive attenuator

7. The most efficient RF power amplifier is which class amplifier?

16.

8. Collector current in a class C amplifier is a

Ans: 0.289

Ans: C

Ans: Pulse

9. The maximum power of ty pical transistor RF power amplifiers is in what range?

Ans: Hundreds of watts

10. Self-oscillation in a transistor amplifier is usually caused by

Ans: internal capacitance

11. Neutralization is the process of

Ans: cancelling the effect of internal device capacitance

2.5 A. Its efficiency is 80 %. The RF output power is

ZP

Ns

72

=

0.28

17. Impedance matching in broadband linear RF amplifier handled with a(n)


The gain of a transistor amplifier is

23. What values of L and C in an L network are required to match a 10 Ω transistor amplifier impedance to a 50 Ω load at 27 MHz?

a is

12.

Ans: splatter

22.

Ans: balun Maximum power transfer occurs when what relationship exists between the generator impedance ZI and the load impedance Zl?

20. In an AM transmitter, a clipper circuit eliminates

Ans: directly proportional to collector current

ZS 6

Ns

19. Which of the following is not a benefit of speech-processing circuits?

Ans: excessive signal bandwidth

=

=

@ 100 %: P100 = VI = 60 W @ 80 %: P80 = 0.8 P100 P80 = 0.8 (60) = 48 W

21. In a speech-processing circuit, a low-pass filter prevents

Solution:

NP

Solution:

Ans: improved frequency stability

To a match a 6 Ω amplifier impedance to a 72 Ω antenna load, a transformer must have a turns ration NP/NS of

NP

Ans: 48

18.

A class C amplifier has a supply voltage of 24 V and a collector current of ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

Ans: L = 118 nH, C = 236 pF Solution: XL

=

R1R2

2 R1

−

XL= 2πfL 2

XL = (10)(50)− 10

=

20Ω 8

L=

XC C=

XL = 117.89nH ≅ 118n 2π ( 2 7 M ) =

R1R2

10(50) =

XL 1

2π f XC

=

20 1

=

25

=

2π (27M)(25)

235.78p

The simplest receiver is a(n)

Ans: tuned circuit 2.

The key conceptual circuit in a superhet receiver is the

Ans: mixer

3. Most of the gain and selectivity in a superhet is obtained in the

Ans: IF amplifier

4. The sensitivity of a receiver depends upon the receiver’s overall

Ans: Gain

5. The ability of a receiver to separate one signal from others on closely adjacent frequencies is called the

Ans: selectivity

6. A mixer has a signal input of 50 MHz and an LO frequency of 59 MHz. The IF is

Ans: 9 MHz

IF = f o – f s = 59 MHz – 50 MHz = 9 MHz 7.

A signal 2 times the IF away from the desired s ignal t hat causes interference is referred to as a(n)

Ans: Image

Chapter 7: Communications Receivers 1.

Ans: 5.38

Solution:


8. A receiv er has a desired input signal of 18 MHz and an LO frequency of 19.6 MHz. The image frequency is

Ans: 21.2 MHz

Shape factor = 60 dB BW / 6 dB BW Shape factor = 14 kHz / 2.6 kHz = 5.38 13. Most internal noise comes from

Ans: thermal agitation

14. Which of the following is not a source of external noise

Ans: thermal agitation

15. Noise can be reduced by

Ans: narrowing the BW

Solution: IF = 19.6 MHz – 18 MHz = 1.6 MHz f si = f s + 2IF f si = 18 MHz + 2 (1.6 MHz) f si = 21.2 MHz 9. The main interference is

Solution:

cause

of

16. Noise at the input to a receiver can be as high as several

Ans: microvolts

image

Ans: Poor front-end selectivity 10. For best image rejection, the IF for a 30 MHz signal would be

Ans: 55 MHz

11. A tuned circuit is resonant at 4 MHz. Its Q is 100. The bandwidth is


BW = f r / Q = 4 MHz / 100 = 40 kHz 12. A crystal filter has a 6 dB bandwidth of 2.6 kHz and a 60 dB bandwidth of 14 kHz. The shape factor is ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

17. Which circuit contributes most to the noise in a receiver?

Ans: mixer

18. Which noise figure represents the lowest noise

Ans: 1.6 dB (smallest value)

19. Which filter shape factor represents the best skirt selectivity?

Ans: 1.6 (smallest value) 20.

Which input signal below represents the best receiver sensitivity?

Ans: 0.5 μV

21. Transistor with the lowest noise figure in the microwave region is a(n) 9

Ans: MESFET 22. The AGC circuits usually control the gain of the

Ans: IF amplifier

23. Selectivity is obtained receivers from

in most

Ans: double-tuned circuits 24.

Widest bandwidth in a doubletuned circuit is obtained with

Ans: overcoupling

25. Automatic gain control permits a wide range of signal amplitudes to be accommodated by controlling the gain of the

Ans: IF amplifier 26.

In an IF amplifier with reverse AGC, a strong signal will cause the collector current to

Ans: decrease

27. Usually AGC voltage is derived by the

Ans: demodulator

28. An AFC circuit is used to correct for

Ans: frequency drift in the LO

29. A circuit keeps the audio cut off until a signal is received is known as

Ans: a squelch

30. A BFO is used in the demodulation of which types of signals?

Ans: SSB or CW


31. Which of the following circuits are not t ypic ally shared in an SSB transceiver?

Ans: mixers

32. The basic frequency synthesizer circuit is a(n)

Ans: PLL

38.

The noise voltage across a 300 Ω input resistance to a TV set with a 6 MHz bandwidth and a temperature of 30oC is

Ans: 5.5 μV Solution:

33. The output frequency increment of a frequency synthesizer is determined by the

Ans: reference input to the phase detector 34. The out put of the frequency synthesizer is changed by varying the

Ans: frequency division ratio 35.

In Fig 7-28, if the input reference is 25 kHz and the divide ratio is 144, the VCO output frequency

Ans: 3.6 MHz

36. The bandwidth of a parallel LC circuit can be increased by

Ans: decreasing XL

37. The upper and lower cutoff frequencies of a tuned circuit are 1.7 and 1.5 MHz respectively. The circuit Q is

Ans: 8

Solution: BW = 1.7 MHz – 1.5 MHz = 200 kHz fr = 1.5 MHz + (200 kHz / 2) = 100 kHz Q = fr / BW = 8 ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

V

=

V

=

4kTBWR 4k(273

30)(6 MHz)(300)

+

Where k = 1.3806503 x 10 -23V = 5.5 μV 39.

The stage gains in a superheterodyne are follows RF amplifier, 10dB; mixer, 6dB; two IF amplifiers, each 33 dB; detector, -4 dB; AF amplifier, 28 dB. The total gain is

Ans: 106

Solution: GT = G1 + G2 + .. + Gn GT = 10 + 6 + 33 + 33 + -4 + 28 = 106 dB 40.

A tuned circuit resonates at 12 MHz with an inductance of 5 μH whose resistance is 6 Ω. The circuit bandwidth is


XL = 2πfL = 2π(12 MHz)( 5 μH) = 376.99 Q = XL / R = 376.99 / 6 = 62.83 BW = fr / Q = 12 MHz / 62.83 = 190.99 kHz 41.

In a receiver with noise-derived squelch, the presence of an audio signal causes the audio amplifier to be 10

Ans: enabled

10. The FDM telephone sys tem s accommodate many channels by

Ans: using multiplexing

Chapter 8: Multiplexing 1.

Multiplexing is the process of

Ans: sending multiple signals simultaneously over a single channel 2.

In FDM, multiple signals

of

11. In FM stereo broadcasting, the L + R signal

Ans: modulates the FM carrier

13. The SCA signal if us ed in FM broadcasting is transmitted via

Ans: VCO

Ans: A 67 kHz subcarrier

21. Transmitting data as serial binary words is called

22. Converting analog signals to digital is done by sampling and

Ans: Quantizing

Ans: take turns transmitting

Ans: secure communications

23. A quantizer is a(n)

Ans: A/D converter

15. In TDM, each signal may use he full bandwidth of the channel

Ans: True

6. The circuit the performs demultiplexing in an FDM system is a(n)


16. Sampling produces

an

analog

signal

Ans: PAM

Most FDM telemetry systems use

Ans: FM

8. The best frequency demodulator is the

Ans: PLL discriminator

17. The maximum bandwidth that an analog signal use with a sampling frequency of 108 kHz is


used

Ans: SSB

in

FDM

f n = f b / 2 = 108 kHz / 2 = 54 kHz 18. Pulse-amplitude modulation signals are multiplexed by using

Ans: FET switches

20. In PAM/TDM system, keeping the multiplexer and DEMUX channels step with one another is done by a

14. In TDM, multiple signals

5. Which of the f ollowing is not a typical FDM application

9. The modulation telephone systems is

Ans: The PAM signal itself

Ans: PCM

Each signal in a an FDM system

4. Frequenc y modulat ion in FDM systems is usually accomplished with a

19. In PAM demultiplexing, the receiver clock is derived from

Ans: Sync pulse

Ans: DSB modulates a subcarrier

Ans: modulates a subcarrier

7.

levels

12. In FM stereo broadcasting, the L – R signal

Ans: share a common bandwidth 3.

multiple



24. Emphasizing low-level signals and compressing higher-level signals is called

Ans: Companding

25. Which of the following is not a benefit of companding?

Ans: Minimizes signal bandwidth

26. A telephone system using TDM and PCM is called

Ans: T-1 27.

An IC that contains A/D and D/A converters, companders and parallel-toserial converters is called

Ans: Codec

11

28. Pulse-code modulation is preferred to PAM because of its

Ans: Superior noise immunity

6. A pattern of voltage and current variations along a transmission line not terminated in its characteristic impedance is called

Ans: Standing waves Chapter 9: Antennas and Transmission lines 1. The most commonly transmission line is a

used

Ans: Coax

SWR

on

a

Ans: 1 8.

A 50 Ω coax is connected to a 73 Ω antenna. The SWR is

2. The characteristic impedance of a transmission line does not depend upon its

Ans: none of the above

Ans: 1.46

Diameter

and

3.

Which of the following is not a common transmission line impedance?

Ans: 120 Ω

9. The most coefficient is

desirable

reflection

Ans: 0 10.

A ratio expressing the percentage of incident voltage reflected on a transmission line is know as the

4.

Ans: ZO = Zl 5.

The mismatch between antenna and transmission line impedances cannot be corrected for by

Ans: Adjusting transmission line

the

length


11. The minimum voltage along a transmission line is 260 V, while the maximum voltage is 390 V. The SWR is

Ans: 1.5

of SWR

Ans: Tuned Circuits

14. A shorted quarter-wave line at the operating frequency acts like a(n)

Ans: Parallel Resonant

16. A popular half-wavelength antenna is the

Ans: Dipole

17. The length of a doublet at 27 MHz is

Ans: 17.33 ft

Solution: 468 468 L= = = 17.33ft. 27 f MHz 18. A popular vertical antenna is the

Ans: Ground plane

Solution: | Γ |=

13. At very high frequencies, transmission lines are used as

Ans: Series Resonant Circuit

Ans: Reflection coefficient

For maximum absorption of power at the antenna, the relationship between the characteristic impedance of the line ZO and the load impedance Zl should be

Ans: 328 MHz

15. A shorted half-wave line at the operating frequency acts like a(n)

Solution: If RL > ZO : SWR = RL / ZO = 73 / 50 = 1.46

Choices were: Length, Conductor Conductor spacing

7. The desirable transmission line is

12. Three feet is one wavelength at a frequency of

Vmax - Vmin Vmax

=

+

Vmin

1+ | Γ | 1− | Γ |

=

=

390 - 260 390

1 + 0.2 1 − 0.2

+

260

=

0.2

= 1.5


19. The magnetic field of an antenna is perpendicular to the earth. The antenna’s polarization

Ans: is horizontal

12

20. An ant enna that t ransm it s or receives equally well in all directions is said to be

Ans: Omnidirectional

28. A coax has an attenuation of 2.4 db per 100 ft. The attenuation for 275 ft is

Ans: 6.6 db

2.4db A dB = 100 ft × 275

Ans: figure of 8

22. t he lengt h of a vertical at 146 MHz is

ground

plane

Ans: 1.6 ft

Solution: L 468 = 2 2 f MHz

Ans: 3 to 30 MHz

= 6.6dB

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

=

468 2(146)

= 1.6ft.

Ans: 73 Ω

24. A direction antenna with two or more elements is known as a(n)

Ans: Array 25.

The horizontal radiation pattern o a vertical dipole is

Ans: circle

26. I n a Yagi ant enna, m ax im um direction of radiation is toward the

Ans: Director

27. Conduc tors in multielement antennas that do not receive energy directly from the transmission line are known as

Ans: Parasitic elements


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 radiation pattern and gain

Ans: Yagi

multielement

Ans: Log-periodic

34. Ground-wave communications is most effective in what frequency range?

Ans: 300 kHz to 3 MHz

35. The ionosphere signals to be

Ans: Skywave

Ans: Direct wave

P = GTPT = (15)(32) = 480 W

33. A wide-bandwidth driven array is the

37. The type of radio wave responsible for long-distance communications by multiple skips is the

38. Microwave signals propagate by way of the

Solution:

23. The impedance of a dipole is about

36. The ionosphere has its greatest effect on signals in what frequency range?

Solution:

21. The horizontal radiation pattern of a dipole is a

Ans: refracted

causes

radio


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: d = 2 ht d=

+

2 hr

2(550 ) + 2(400)

=

53.16mi

41. To increase the transmission distance of a UHF signal, which of the following should be done?

Ans: Increase antenna height

42. A coax has a velocity factor of 0.68. What is the length of a half wave at 30 MHz? 13

Ans: 11.2 ft 4.

Which of t he microwave frequency

Solution: λ 2 λ 2

=

Vp 2f MHz

f ollowing

is

a

Ans: 22 GHz =

c V f

2f MHz 3.28ft = 3.4m × 1m

=

=

(300)(0.68 )f 2(30)

=

3.4m

Ans: mobile radio

11.152ft

43. Which transmission line has the lowest attenuation?

Ans: Twin lead

Ans: 60o

Ans: Repeater

benefit

of

8. The most common cross section of a wave guide is a

Ans: rectangular

Ans: 5.9 GHz using

Ans: More spectrum space 2. Radio communications are regulated in the United States by the

Communications

3. Which of the f ollowing is not a disadvantage of microwaves?

Solution: 1 in = 0.0254 m c 3 ×108 m/s = f = 2Width 2(0.0254)


13. The dominant waveguides is

mode

in

most

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)

16. Decreasing the volume of a cavity causes its resonant frequency to

Ans: Increase

17. A popular microwave mixer diode is the

= 5.9GH

Ans: Gunn 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

Ans: higher-cost equipment

12. When the electric field in a waveguide is perpendicular to the direction of wave propagation, the mode is said to be

Ans: Cavity resonator

9. A rect angular waveguide has a width of 1 in. and a height of 0.6 in. Its cutoff frequency is

Chapter 10: Microwave Techniques

Ans: Federal Commission

7. Stripline and microstrip transmission lines are usually made with

Ans: PCBs

45. A receiver-transmitter station used to increase the communications range of VHF, UHF, and microwave signals is called a(n)

Ans: Electric and magnetic fields

Ans: Transverse electric

6. Coaxial cable is not widely used for long microwave transmission lines because of its

Ans: high loss

44. Refer to Fig. 9-39. The beam width of this antenna patter is approximately

1. The main microwaves is

5. Which of the f ollowing is not a common microwave application?

11. Signal propagation in a waveguide is by


18. Varactor and step-recovery diodes are widely used in what type of circuit

Ans: Frequency multiplier 19. Which diode microwave oscillator

is

a

popular

Ans: Gunn

14

20. Which t ype of diode does not ordinarily operate with reverse bias

Ans: Tunnel

21. Low-power replacing

Gunn

diodes

are

Ans: Reflex klystrons

30. The main advantage of a TWT over a klystron for microwave amplification is

Ans: Wider bandwidth

Ans: Cathode-ray tube

23. In a klystron amplifier, velocity modulation of the electron beam is produced by the

Ans: Buncher cavity

32.

The most widely used microwave antenna is a

Ans: horn antenna

33. What happens when antenna is made longer?

24. A reflex klystron is used as a(n)

horn

Ans: Gain increases

Ans: 10.5 db

25. For proper operation, a magnetron must be accompanied by a

Ans: Permanent magnet

4π A

 (7)(9)    10000  = 10.9956 2  3 × 108    9   5 × 10 

4π (0.5 )

G=

27. A magnetron is used only as a(n)

GdB = 10 log 10.9956 = 10.41 dB

λ2

Ans: Cavity resonator Ans: oscillator

application

for

Ans: Radar

29. In a TWT, the electron beam is density-modulated by a

=

35. Given the frequency and dimensions in Question 34 above the beamwidth is about

Ans: 53o

Solution:

Ans: Helix


80

=

w

= 53.33 o

  3 × 10 8    5 × 10 9   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

Solution:

26. The operating frequency of klystrons and magnetrons is set by the

28. A common magnetrons is in

a

34. A pyramidal horn used at 5 GHz has an aperture that is 7 by 9 cm. The gain is about

Ans: Oscillator

80 w/λ

31. High-power TWTs are replacing what in microwave amplifiers?

Ans: klystrons

22. Which of the following is not a microwave tube?

G=

39.

Increasing the diameter of a parabolic reflector causes which of the following

Ans: Decreasing increasing gain

beamwidth

and

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

42. A common omnidirectional microwave antenna is the

Ans: Bicone ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

15

10. Batteries are used to power all satellite subsystems

Chapter 11: Introduction to Sat-Com

Ans: During eclipse periods

1. As the height of a satellite orbit gets lower, the speed of the satellite

Ans: Increases

2. The main functions of communications satellite is a a(a)

a

Ans: Repeater

3. The key electronic component in a communications satellite is the

Ans: Transponder

4. A circular orbit around the equator with a 24 h period is called a(n)

Ans: Geostationary orbit

5. A satellite stays in orbit because the following 2 factor are balanced

Ans: Gravitational pull and inertia

6. The height of a satellite in a synchronous equatorial orbit is

Ans: 22300 mi

7. Most satellites operate in which frequency band?

Ans: 3 GHz to 30 GHz

8. The main power sources for a satellite are

Ans: Solar cells

9. The maximum height of an elliptical orbit is called

Ans: Apogee


Ans: Latitude and longtitude

11. The s at ellite subs yst em that monitors and controls the satellite is the

Ans: Telemetry, tracking and command subsystem 12. The basic technique stabilize a satellite is

20. The physical location of a satellite is determined by its

used

to

Ans: Spin

13. The jet thrusters are usually fired to

Ans: Maintain altitude

14. Most commercial satellite activity occurs in which bands?

Ans: C and Ku

15. How can multiple earth stations share a satellite on the same frequency

Ans: Frequency reuse

16. The typical bandwidth of a satellite band is

Ans: 500 MHz

17. Which of the following is not usually a part of a transponder

Ans: Modulator

18. The satellite communications channels in a transponder are defined by the


19. The HPAs in most satellites are

Ans: Klystrons


21. The receive GCE system in an earth station performs what function(s)

Ans: Demodulation and demultiplexing

22. Which of the following types of HPA is not used in earth stations

Ans: Magnetron

23. A common up-converter and downconverter IF is

Ans: 70 MHz

24. The type of modulation used on voice and video signals is

Ans: FM 25.

The modulation normally used with digital data is

Ans: QPSK

26. Which of the following is not a typical output from a GPS receiver?

Ans: Speed

---------------------------------------------------------Chapter 12: Data Communications 1. Data communications refer to the transmission of

Ans: Voice, Video, and Computer data 2.

Data communications uses

Ans: Digital methods

16

12. Which of the following is correct?

3. Which of the following is not primarily a type of data communications

Ans: The bit rate may be greater than the baud rate

4. The main reason that serial transmission is preferred to parallel transmission is that

Ans: both analog signals to digital and digital signals to analog signals

Ans: Teletype

Ans: Protocol 22. A popular PC protocol is

Ans: Xmodem

13. A modem converts

Ans: Serial requires multiple channels 5. to

Ans: DPSK

Ans: Baud rate

7. Data transmission of one character at a time with start and stop bits is known as what type of transmission?

Ans: Asynchronous 8.

The mos t widely communications code is

used

data

Ans: ASCII 9.

The ASCII code has

Ans: 7 bits

10. Digital signals may be transmitted over the telephone network if

Ans: they are converted to analog first.

11. Start and stop bits, respectively, are

Ans: Space and mark

Ans: FSK

15. A carrier recovery circuit is not needed with

6. The number of amplitude, frequency, or phase changes that take place per second is known ad the


Ans: SYN

14. Slow-speed modems use

Mark and space refer respectively

Ans: Binary 1 and binary 0

23. A synchronous t ransm is sion usually begins with which character?

16. The basic modulator demodulator circuits in PSK are

and

Ans: Balanced modulators

17. The carrier used with a BPSK demodulator is

Ans: The BPSK signal itself

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) ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

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

27. Which of the following words has the correct parity bit? Assume odd parity. The last bit is the parity bit

Ans: 1100110 1

28. Another name for parity is

Ans: Vertical redundancy check

29. Ten bit errors occur in two million transmitted. The bit error rate is

Ans: 5 x 10-6 Solution:

e=

10 2 × 10 6

= 5 × 10 −6 17

30. The building block of a parity or BCC generator is a(n)

Ans: XOR

Ans: Block check character

Ans: CRC

generat or

uses

which

Ans: Shift register 34. Which of the following is not a LAN?

Ans: Cable TV system

35. The fastest LAN topology is the

Ans: Bus

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?


BW = f b/2 = 56 kbits/2 = 28 kHz

36. Which is not a common LAN medium?

Ans: Twin Lead

37. A mainframe computer connected to multiple terminals and PCs usually uses which configuration?

Ans: Star

38. A small telephone switching system that can be used as a LAN is called a

Ans: PBX

39. Which medium susceptible to noise?

Ans: Twisted pair

41. Transmitting the data signal directly over the medium is referred to as

32. Dividing the data block by a constant produces a remainder that is used for error detection. It is called the

Solution:

40. Which medium is the most widely used in LANs?

31. A longitudinal redundancy check produces a(n)

33. A CRC components?

Ans: Fiber-optic cable

is


the

least

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

S N

= 10

BW

=

 S   N dB  10  

     

= 630.96

10Mbits/s log 2 (1 + 630.96 )

= 1.075MHz

46. Which circuit is common to bot frequency-hopping and direct-sequence SS transmitters?

Ans: Frequency of operation

47. Spread spectrum stations sharing a band are identified by and distinguished from one another by

Ans: PSN code

48. The type of modulation most often used with direct-sequence SS is

Ans: PSK

49. The main generator is a(n)

circuit

in

a

PSN

Ans: XOR

50. To a conventional narrowband receiver, an SS signal appears to be like

Solution C = 2BWlog 2M C = 2(36MHz) (log 2 (16))

C = BW log2(1+S/N) S/NdB = 10 log (S/N)

Ans: Noise =

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

51. Which of the following is not a benefit of SS?

Ans: Noise proof

52. Spread s pect rum is a f orm of multiplexing

Ans: true

COMMUNICATION ELECTRONIC 2EDITION - FRENZEL ND

18

53. The most critical and difficult part of receiving a direct-sequence SS signal is

Ans: Synchronism

8. The core of a fiber-optic cable is made of

Ans: Glass

9. The core of a fiber-optic cable is surrounded by

Chapter 13: Fiber Optic Communications 1. Which of the f ollowing is not a common application of fiber-optic cable?

Ans: Consumer TV

2. Total internal reflection takes place if the light ray strikes the interface at an angle with what relationship to the critical angle?

Ans: greater than

3. The operation of a fiber-optic cable is based on the principle of

Ans: Reflection

4. Which of the f ollowing is not a common type of fiber-optic cable?

Ans: Single-mode grade-index 5. Cable attenuation expressed in terms of

is

usually

Ans: Cladding

10. The s peed of light in plas tic 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

Ans: dB/km

15. The speed of light is

6. Which cable length has the highest attenuation?

Ans: 2 km

7. The upper pulse rate and information-carrying capacity of a cable is limited by

Ans: Attenuation


Ans: 300,000,000 m/s

18. A popular light wavelength in fiberoptic 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 Solution:

1000ft = 0.3048 km σ = 15 × 0.3048 = 4.57dB

16. Refraction is the

Ans: Bending of light waves 17.

The ratio of the speed of light in air to the s peed of light in anot her substance is called the

Ans: Index of refraction


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 Solution:

19

LossT = 1.8 + 3.4 + 5.9 + 18 = 29.1 dB 26. Which light emitter is preferred for high-speed data in a fiber-optic system?

Ans: Laser

Ans: Visible

and

ILDs

operat e

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

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:

20 Gbits - km/s 5 km

= 400bits/s

35. Which fiber-optic system is better?


Ans: Scanning

2. The most c om monly us ed light sensor in a modern fax machine is a

Ans: Charge coupled device

Ans: 1500 and 2300 Hz

4. Which resolution produces the best quality fax?

Ans: 400 lines per inch

uses

which

The most widely used fax standard

Ans: 56 kbits/s

12. The master control center for a cellular telephone system is the

Ans: Mobile telephone switching office Ans: Repeater

14. Multiple cells within an area may use the same channel frequencies

Ans: True

15. Cellular telephones use which type of operation?

Ans: Full-duplex

Ans: 12 kHz

17. The maximum output power of a cellular transmitter is

Ans: Group 3 7. Group modulation?

11. The transmission speed of group 4 fax is

16. The maximum frequency deviation of an FM cellular transmitter is

Ans: Vestigial sideband AM 6. is

Facsimile standards are set by the

13. Each cell site contains a

3. In FM fax, the frequencies for black and white are

fax

9.

Ans: CCITT

Ans: Satellite weather photos

1. Printed documents to be transmitted by fax are converted into a baseband electrical signal by the process of

2

Most fax printers are of which type?

10. What type of graphics is commonly transmitted by radio fax?

Chapter 14: Modern Comm Apps

5. Group modulation?

8.

Ans: Thermal

Ans: 3 repeaters

27. Most fiber-optic light sources emit light in which spectrum?

28. Both LEDs correctly with

Ratemax =

3

fax

uses

which

Ans: QAM


Ans: 3 W

18. Receive channel 22 is 870.66 MHz. Receive channel 23 is 20

Ans: 870.69 MHz Solution: f CH 23 = f CH 22 + 30 kHz* f CH 23 = 870.66 MHz + 30 kHz f CH 23 = 870.69 MHz *in cellular radio systems, receive channels are spaced 30 kHz apart

19. A transmit channel has a frequency of 837.6 MHz. The receive channel frequency is

Ans: 882.6 MHz

Ans: The unit is “handed off” to a closer cell 23. In a cellular radio, the duplexer is a

Ans: Pair of sharp bandpass filter

24. The time from the transmission of a radar pulse to its reception is 0.12 ms. The distance to the target is how many nautical miles?

Ans: 9.7 nmi

f receive = f transmit + 45 MHz* f receive = 837.6 MHz + 45 MHz f receive = 882.6 MHz *in cellular radio systems, the transmit and receive frequencies are spaced 30 kHz apart

20. A receive channel frequency is 872.4 MHz. To develop an 82.2 MHz IF, the frequency synthesizer must supply an LO signal of

D=

T 12.36

Solution:

Ans: MTSO

22. When the signal from a mobile cellular unit drops below a certain level, what action occurs?


12.36

=

9.7nmi

PRT =

1 PRF

Duty Cycle =

Duty Cycle =

Ans: Speed

29. The Doppler Effect is a change in what signal characteristic produced by relative motion between the radar set and a target?

30. The most widely used transmitter component is a

radar

Ans: Magnetron

26. The pulse duration of a radar signal is 600 ns. The PRF is 185 pulses per second. The duty cycle is

Solution:

21. The output power of a cellular radio is controlled by the

120μ2

Ans: Antenna directivity

Ans: 1.1 %

f LO = f r + IF f LO = 872.4 MHz + 82.2 MHz f LO = 954.6 MHz

=

25. The ability of a radar to determine the bearing to a target depends upon the

Ans: 954.6 MHz

28. The Doppler Effect allows which characteristics of a target to be measured?

Ans: Frequency

Solution:

Solution:

Ans: CW (Continuous-wave)

31. Low-power radar transmitters and receiver LOs use which component?

Ans: Gunn diode

32. What component in a duplexer protects the receiver from the highpower transmitter output?

Ans: Spark gap

33. Most radar antennas usa a

=

1 185

Ans: Horn and parabolic reflector

= 5.405ms

34. The most common radar display is the

PWT PRT 600ns 5.405ms

Ans: Plan position indicator 100

×

=

0.0111

27. The Doppler eff ect is us ed t o produce modulation of which type of radar signal? ND COMMUNICATION ELECTRONIC 2EDITION - FRENZEL

35. A radar antenna using multiple dipoles or slot antennas in a matrix with variable phase shifters is called a(n)

Ans: Phased array

36. Police radars use which technique? 21

Ans: CW (Continuous-wave) 37. Which of the following is a typical radar operating frequency?

Ans: 10 GHz

38. The TV signal uses which types of modulation for picture and sound respectively?

Ans: AM, FM

39. If a TV sound transmitter has a carrier frequency of 197.75 MHz, the picture carrier is

Ans: 193.25 MHz Solution:

SCARRIER = PCARRIER + 4.5 MHz PCARRIER = SCARRIER - 4.5 MHz PCARRIER = 197.75 MHz - 4.5 MHz PCARRIER = 193.25 MHz 40. The total bandwidth of an NTSC TV signal is

Ans: 6 MHz

Ans: Luminance Y 44. What is the name of the solid-state imaging device used int TV cameras that converts the light in a scene into an electrical signal?

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

51. What ensures proper synchronization at the receiver?

color

Ans: 3.58 MHz color burst

52. Which of the following is not a benefit of cable TV?

Ans: Lower-cost reception

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

41. What is the total number of interlaced scan lines in one complete frame of a NTSC U.S. TV signal?

Ans: 41.25 MHz

42. What keeps the scanning process at the receiver in step with the scanning in the picture tube at receiver?

Ans: Balanced demodulator

43. What is the black-and-white or monochrome brightness signal in TV called

Ans: horizontal output

Ans: 525

Ans: Sync pulses


49. What type of circuit is used to modulate and demodulate the color signals?

50. What circuit in the TV receiver is used to develop the high voltage needed to operate the picture tube?


22

Frenzel

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