# MCQs in Modulation Part VIII

(Last Updated On: December 8, 2017) This is the Multiples Choice Questions Part 8 of the Series in Modulation as one of the Communications Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies, Communications Books, Journals and other Communications References.

### Online Questions and Answers Topic Outline

• MCQs in Amplitude Modulation
• MCQs in Phase Modulation
• MCQs in Sound Pressure Level
• MCQs in Frequency Modulation
• MCQs in Pulse Modulation

### MCQs in Modulation Series

Following is the list of multiple choice questions in this brand new series:

Modulation MCQs
PART 1: MCQs from Number 1 – 50                        Answer key: PART I
PART 2: MCQs from Number 51 – 100                   Answer key: PART II
PART 3: MCQs from Number 101 – 150                 Answer key: PART III
PART 4: MCQs from Number 151 – 200                 Answer key: PART IV
PART 5: MCQs from Number 201 – 250                 Answer key: PART V
PART 6: MCQs from Number 251 – 300                 Answer key: PART VI
PART 7: MCQs from Number 301 – 350                 Answer key: PART VII
PART 8: MCQs from Number 351 – 400                 Answer key: PART VIII
PART 9: MCQs from Number 401 – 450                 Answer key: PART IX
PART 10: MCQs from Number 451 – 500                 Answer key: PART X

### Continue Practice Exam Test Questions Part VIII of the Series

351. Determine the resonant frequency of a series combination of a 0.001 microfarad capacitor and a 2 – milihenry inductor.

• a. 112.5 kHz
• b. 35.59 kHz
• c. 1125.4 MHz
• d. 3.26 MHz

352. Which of the following is not a typical part of every radio transmitter?

• a. Carrier oscillator
• b. Driver amplifier
• c. Mixer
• d. Final power amplifier

353. What is the approximate magnitude of the impedance of a parallel RLC circuit at resonance?

• a. Approximately equal to the circuit resistance
• b. Approximately equal to XL
• c. Low, as compared to the circuit resistance
• d. Approximately equal to XC

354. What are the three major oscillator circuits often used in radio equipment?

• a. Taft, Pierce, and negative feedback
• b. Colpitts, Hartley, and Taft
• c. Taft, Hartley, and Pierce
• d. Colpitts, Hartley, and Pierce

355. How is a positive feedback coupled to the input in a Hartley oscillator?

• a. Through a neutralizing capacitor
• b. Through a capacitive divider
• c. Through a link coupling
• d. Through a tapped coil

356. How is the positive feedback coupled to the input in a Colpitts oscillator?

• a. Through a tapped coil
• b. Trough link coupling
• c. Through a capacitive divider
• d. Through a neutralizing capacitor

357. How is a positive feedback coupled to the input in a Pierce oscillator?

• a. Through a tapped coil
• b. Trough link coupling
• c. Through a capacitive divider
• d. Through a neutralizing capacitor

358. Which of the three major oscillator circuits used in radio equipment utilizes a quartz crystal?

• a. Negative feedback
• b. Hartley
• c. Colpitts
• d. Pierce

359. What is the piezoelectric effect?

• a. Mechanical vibration of a crystal by the application of a voltage
• b. Mechanical deformation of a crystal by the application of a magnetic field
• c. The generation of electrical energy by the application of light
• d. Reversed conduction states when pn-junction is exposed to light

360. What is the major advantage of a Pierce oscillator?

• a. It is easy to neutralize
• b. It doesn’t require an LC tank circuit
• c. It can be tuned over a wide range
• d. It has high output power

361. Which type of oscillator circuit is commonly used in a VFO?

• a. Pierce
• b. Colpitts
• c. Hartley
• d. Negative feedback

362. Why is the Colpitts oscillator circuit commonly used in a VFO?

• a. The frequency is a linear function of the load impedance
• b. It can be used with or without crystal lock-in
• c. It is stable
• d. It has high output power

363. How is the efficiency of a power amplifier determined?

• a. Efficiency = (RF power out / dc power in) x 100%
• b. Efficiency = (RF power in / RF power out) x 100%
• c. Efficiency = (RF power in / dc power in) x 100%
• d. Efficiency = (dc power in / RF power in) x 100%

364. For reasonably efficient operation of a transistor amplifier, what should be the load resistance be with 12 volts at the collector and a 5 watts power output?

• a. 100.3 ohms
• b. 14.4 ohms
• c. 10.3 ohms
• d. 144 ohms

365. What order of Q is required by a tank circuit sufficient to reduce harmonics to an acceptable level?

• a. Approximately 120
• b. Approximately 12
• c. Approximately 1200
• d. Approximately 1.2

366. What is the flywheel effect?

• a. The continued motion of a radio wave through space when the transmitter is turned off
• b. The back and forth oscillation of electrons in an LC circuit
• c. The use of a capacitor in a power supply to filter rectified AC
• d. The transmission of a radio signal to a distant station by several hops through the ionosphere

367. How can parasitic oscillations be eliminated from a power amplifier?

• a. By tuning for maximum SWR
• b. By tuning for maximum power output
• c. By neutralization
• d. By tuning the output

368. If the spectrum is shifted in frequency with no other changes, this is known as

• a. Frequency multiplication
• b. Sideband movement
• c. Baseband orientation
• d. Frequency translation

369. A device which is capable of causing frequency translation

• a. High-Q tank circuit
• b. Balanced modulator
• c. Low-Q tank circuit
• d. IF strip

370. If the frequency of each component in a signal spectrum is increased by the same fixed amount, this is known as

• a. Up conversion
• b. Demodulation
• c. Frequency translation
• d. Both a and c

371. A particular amplifier is designed to be a frequency doubler. If the input signal frequency is 15.4 MHz, a circuit in the output will be tuned to

• a. 7.7 MHz
• b. 15.4 MHz
• c. 30.8 MHz
• d. 61.6 MHz

372. Any device to be used as a frequency multiplier must be

• a. Active
• b. Passive
• c. Linear
• d. Nonlinear

373. A particular amplifier circuit used for frequency coupling is known as

• a. Push-push
• b. Push-pull
• c. Pull-push
• d. Pull-pull

374. Frequency division is useful in the implementation of a

• a. AM demodulation
• b. Frequency synthesizer
• c. FM demodulator
• d. AGC circuit

375. Indirect frequency synthesizers will include

• a. phase-locked loop
• b. voltage-controlled oscillators
• c. multiple bank crystals
• d. both A and B

376. A particular frequency synthesizer contains only a single crystal. What words describe this synthesizer?

• a. Crystal modulated
• b. Inexact
• c. Indirect
• d. Deficient

377. A recognizable feature of a CW transmitter is

• a. Keyed transmitter
• b. Power amplification
• c. Frequency generation
• d. All of the above

378. The term “pulling” refers to

• a. The change of the crystal oscillator frequency by loading
• b. One-half cycle operation of a push-pull amplifier
• c. Loading on the transmitter caused by the antenna connection
• d. Reduction of the power supply terminal voltage as the transmitter is keyed

379. An AM broadcast transmitter in the multi-kilowatt operating range will have what form of final amplifier?

• a. Solid-state devices
• b. Vacuum tubes
• c. Travelling wave tubes
• d. Both a and b

380. In a broadcast station, the AGC is referred to as

• a. Automatic gain control limiter
• b. Compression amplifier
• c. Loudness controller
• d. All of the above

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

• a. AM
• b. SSB
• c. CW
• d. FM

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

• a. Final amplifier
• b. Driver amplifier
• c. Linear amplifier
• d. Buffer amplifier

383. Bias for class c amplifier produced by an input RC network is known as

• a. Signal bias
• b. Self-bias
• c. Fixed external bias
• d. Threshold bias

384. Collector current in a class C amplifier is

• a. Sine wave
• b. Half-sine wave
• c. Pulse
• d. Square wave

385. Neutralizing is the process of

• a. Cancelling the effect of internal device capacitance
• b. Bypassing undesired alternating current
• c. Reducing gain
• d. Eliminating harmonics

386. In an AM transmitter, a clipper circuit eliminates

• a. Harmonics
• b. Splatter
• c. Over-deviation
• d. Excessive gain

387. The final power amplifier in an FM transmitter usually operates class

• a. A
• b. B
• c. C
• d. D

388. A transistor RF power amplifier can be tuned for

• a. Minimum IC in the next stage
• b. Zero signal in the next stage
• c. Minimum IC in the same stage
• d. Maximum IC in the same stage

389. The purpose of a balanced modulator circuit is to eliminate the

• a. Carrier
• b. Upper sideband
• c. Lower sideband
• d. Baseband signal

390. A frequency multiplier circuit

• a. Operates class A
• b. Is tuned to a harmonic of the input signal
• c. Needs parasitic oscillations
• d. Is usually pulse modulated

391. An IF transformer of a radio receiver operates at 456 kHz. The primary circuit has a Q of 50 and the secondary has a Q of 40. Find the bandwidth using the optimum coupling factor.

• a. 10.192 kHz
• b. 15.288 kHz
• c. 152.88 kHz
• d. 101.92 kHz

392. A varactor has a maximum capacitance of 80pF and is used in a tuned circuit with a 100 microhenry inductor. Find the tuning voltage necessary for the circuit to resonate at twice its resonant frequency with no tuning voltage applied.

• a. 5 V
• b. 2.5 V
• c. 7.5 V
• d. 4.25 V

393. A phase-locked loop has a VCO with a free-running frequency of 14 MHz. As the frequency of the reference input is gradually raised from zero, the loop locks at 12 MHz and comes out of lock again at 18 MHz. Calculate the capture range.

• a. 4 MHz
• b. 2 MHz
• c. 12 MHz
• d. 8 MHz

394. If the frequency fed to the pre-amplifier of a basic transmitter with multipliers is composed of a pair of triplers and a doubler is 198 MHz, what frequency should the oscillator operate?

• a. 11 MHz
• b. 33 MHz
• c. 22 MHz
• d. 66 MHz

395. A phase-locked loop has a VCO with a free running frequency of 14 MHz. As the frequency of the reference input is gradually raised from zero, the loop locks at 12 MHZ and comes out of lock again at 18 MHz. Calculate the lock range.

• a. 4 MHz
• b. 2 MHz
• c. 12 MHz
• d. 8 MHz

396. A crystal oscillator is accurate within 0.0005%. How far off frequency could its output be at 37 MHz?

• a. 135 Hz
• b. 150 Hz
• c. 185 Hz
• d. 224 Hz

397. A transmitter has a carrier power output of 10 W at an efficiency of 80%. How much power must be supplied by the modulating amplifier for 100% modulation?

• a. 6.25 W
• b. 7.14 W
• c. 12.5 W
• d. 14.3 W

398. A transmitter operates from a 16 V supply, with a collector current of 2 A. The modulation transformer has a turns ratio of 4:1. What is the load impedance seen by the audio amplifier?

• a. 96 ohms
• b. 128 ohms
• c. 6 ohms
• d. 8 ohms

399. A collector-modulated class C amplifier has a carrier output power of 150 W and an efficiency of 80%. Calculate the transistor power dissipation with 100% modulation.

• a. 93. 75 W
• b. 120 W
• c. 64 W
• d. 56. 25 W

400. An AM transmitter is required to produce 20 W of carrier power when operating from a 25 V supply. What is the required load impedance as seen from the collector?

• a. 15.625 ohms
• b. 22.5 ohms
• c. 11.25 ohms
• d. 31.25 ohms

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