# MCQ in Modulation Part 6 | ECE Board Exam

(Last Updated On: February 24, 2021) This is the Multiples Choice Questions Part 6 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.

#### MCQ Topic Outline included in ECE Board Exam Syllabi

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

#### Continue Practice Exam Test Questions Part 6 of the Series

251. A method that applied the modulated wave to the vertical deflection circuit of the oscilloscope and the modulating signal to the horizontal deflection circuit.

a. Trapezoidal method

b. Circular method

c. Square method

d. Any method

Solution:

252. The heart of all methods of single-sideband modulation and demodulation

a. Modulator

b. Balanced modulator

c. Modulation

d. demodulation

Solution:

253. If the frequency and phase are parameters of carrier angle, which is a function of time, the general term ___________-cover both.

a. Amplitude modulation

b. Frequency modulation

c. Phase modulation

d. Angle modulation

Solution:

254. In FM radio communication system, narrow-band (NBFM) is used rather than wideband (WBFM), because it,

a. Improves signal to noise ration

b. Reduces interchannel interference

c. Provides maximum coverage for a given amount of power

d. All of the above

Solution:

255. Radio transmitter basically consists of two principal parts, one reproducing a carrier frequency and one for __________.

a. IF Frequency

b. RF Frequency

c. Modulating Frequency

d. Power

Solution:

256. Is a measure of its ability to maintain as nearly a fixed frequency as possible over as long as time interval as possible.

b. Selectivity

c. Sensitivity

d. Frequency stability

Solution:

257. Is the effect of two-transmitter when they are in close proximity. This results into the sum and difference frequencies of two carriers.

a. Intermodulation effect

b. Intermodulation interference

c. Intermodulation product

d. intermodulation

Solution:

258. _________ is a continuous frequency capable of being modulated or impressed with a second information carrying signal.

a. Carrier frequency

b. Center frequency

c. IF frequency

d. RF frequency

Solution:

259. The varactor diode used in FM may be represented by the approximate equivalent circuit of the _____ in series with a ________.

a. Diode, capacitor

b. Diode, resistor

c. Capacitor, resistor

d. Any of these

Solution:

260. The name varactor comes from variable _________.

a. Resistor

b. Capacitor

c. Diode

d. reactor

Solution:

261. 75 microseconds pre-emphasis time is used in __________.

a. FM

b. AM

c. TV

d. None of these

Solution:

262. Recovers the modulating voltage from the frequency modulation by utilizing the phase angle shift between primary and secondary voltages of tuned oscillators.

a. Direct method

b. Indirect method

c. Foster-Seeley discriminator

d. Slope detector

Solution:

263. Is used in FM receivers to “lock onto” the received signal and stabilized receptions.

a. Automatic Gain Control

b. Automatic Frequency Control

c. Muscle Control

d. Automatic Frequency Gain Control

Solution:

264. Are amplifier circuits that are used to eliminate amplitude modulation and amplitude-modulated noise from received FM Signals before detection.

a. Demodulators

b. Diode detector

c. Amplitude limiters

d. None of these

Solution:

265. If the total sideband power is 12.5% of the total radiated power, find the modulation index.

a. 50 percent

b. 53.4 percent

c. 26.2 percent

d. 32.3 percent

Solution:

266. Carriers are spaced at 20 kHz, beginning at 100 kHz. Each carrier is modulated by a signal with a 5 kHz bandwidth. Is there interference from the sideband?

a. Yes

b. No

c. Maybe

d. Secret

Solution:

267. For an unmodulated carrier of 150 V and a modulated peak value of 230 V. What is the modulation index

a. 0.35

b. 0.533

c. 0.652

d. 0.42

Solution:

268. New frequencies outside the regular AM spectrum are called ___________.

a. Distortion

b. Interference

c. Splatter

d. Harmonic

Solution:

269. A DSB-SC has a total power of 350 watts with 100% modulation suppresses 50% of the carrier, and the suppressed carrier power goes to the sidebands. How much power is in the sidebands?

a. 116.67 W

b. 233.33 W

c. 175 W

d. 350 W

Solution:

270. A DSB-SC system must suppress the carrier by 30 dB from its original value of 30 W. What value must the carrier be reduced?

a. 30000 W

b. 0.03 W

c. 300 W

d. 0.003 W

Solution:

271. ___________, which further amplifies the signal and has the bandwidth and passband shaping appropriate for the received signal.

a. RF stage

b. Mixer and local oscillator stage

c. IF stage

d. AF stage

Solution:

272. In FM, a bandwidth estimate 98 percent level of Bessel functions

a. Approximate bandwidth

b. Narrow-band Bandwidth

c. Carson’s rule

d. Wideband bandwidth

Solution:

273. The complete series of stages for reproducing the FM signal with the desired carrier and deviation is the _______.

a. Modulator

b. Exciter

c. IF stage

d. RF stage

Solution:

274. Is the ability of FM system to provide low-noise, high fidelity music background/broadcast..

a. Monophonic

b. Stereophonic

c. Stereonic

d. SCA

Solution:

275. It make use of the shape of IF filter frequency response roll-off versus frequency.

a. Foster Seeley

b. Slope detector

c. Diode detector

Solution:

276. In AM, modulation index is a number lying between ____ and 1.

a. 2

b. 5

c. 0

d. 3

Solution:

277. This form of modulation is also known as independent sideband emission.

a. A3E

b. R3E

c. H3E

d. B8E

Solution:

278. An attenuated carrier is reinserted into the SSB signal to facilitate receiver tuning and demodulation.

a. A3E

b. R3E

c. H3E

d. B8E

Solution:

279. Standard AM used for broadcasting

a. A3E

b. R3E

c. H3E

d. B8E

Solution:

280. Single sideband, suppressed carrier in which the carrier is suppressed by at least 45 dB in the transmitter.

a. A3E

b. R3E

c. H3E

d. B8E

Solution:

281. The shift in the carrier frequency from the resting point compared to the amplitude of the modulating signal is called _______.

a. Index

b. Deviation ratio

c. Carrier frequency

d. Deviation frequency

Solution:

282. In FM, the amplitude of the modulated frequency wave remains ___________ at all times.

a. Varying

b. Dependent

c. Constant

d. variable

Solution:

283. An AM has a maximum span of 30 V, what is the required minimum span to attain 100% modulation?

a. 30 V

b. 20 V

c. 0 V

d. None of these

Solution:

284. DZMM having a carrier frequency of 630 kHz is modulated by 2.6 kHz audio signal having an amplitude of 37.5 V. What is the amplitude voltage of 630 kHz carrier frequency at 0.35 modulation index?

a. 57.6 V

b. 107.14 V

c. 206.5 V

d. 86.2 V

Solution:

285. If the sideband power is 50% of the carrier power, what is the modulation index?

a. 50%

b. 75%

c. 90%

d. 100%

Solution:

286. If the increase power is 180 watts at 1 kW unmodulated output power the modulation index is _________.

a. 75%

b. 60%

c. 50%

d. 25%

Solution:

287. In AM, if the unmodulated power carrier is 10 kW, and the total power is 15 kW, what is the upper sideband power at 100% modulation index?

a. 25 kW

b. 2 kW

c. 2.5 kW

d. 4 kW

Solution:

288. If the input resistance of the base station of AM broadcast produced 20 kW carrier power, at what modulation index should the antenna rise at 108.63 A?

a. 20%

b. 50%

c. 60%

d. 80%

Solution:

289. ________ used a phase detector to compare the phase and frequency of the received signal to the VCO output.

a. PIL

b. PAL

c. PLL

d. PLI

Solution:

290. A filter with a roll-off of 6 dB/kHz is used as a slope detector. The input signal varies with +3 kHz deviation from center carrier frequency. How many dB down is the output at full deviation?

a. 9 dB

b. -18 dB

c. 18 dB

d. -9 dB

Solution:

291. A receiver limiter requires a 20 mV signal for quieting operation. The voltage gain between the RF input and the limiter is 57.7 dB, what is the input at the antenna terminal assuming equal resistance?

a. 75.6 mV

b. 26.67 uV

c. 52.3 uV

d. 49.6 uV

Solution:

292. A 1-MHz carrier is modulated with a resulting 100 Hz deviation. It undergoes x36 multiplication, followed by mixing with a 34.5 MHz signal and re-multiplication by 72. What is the final carrier and deviations?

a. 5076 MHz, ± 2592 MHz

b. 2592 MHz, ± 259.2 kHz

c. 2592MHz, ± 5076 MHz

d. 259.2 MHz, ± 108 kHz

Solution:

293. For standard commercial broadcast FM, the deviation ratio is ________.

a. 15

b. 75

c. 5

d. 10

Solution:

294. A system has 150 kHz of bandwidth available for 10 kHz modulation signal. What is the approximate deviation to be used?

a. 35 kHz

b. 65 kHz

c. 25 kHz

d. 15 kHz

Solution:

295. An FM has a deviation of 100 kHz and a modulating frequency of 15 kHz, what happen to m if the deviation triples?

a. 6.66

b. 2.22

c. 4.12

d. 0.20

Solution:

296. A receiver for a signal at 100 MHz uses a 10.7 MHz IF and low tracking. What is the image frequency?

a. 89.3 MHz

b. 78.6 MHz

c. 52.5 MHz

d. 35.2 MHz

Solution:

297. What is the change in resonant frequency of the actual varactor capacitance value differs by -5% (0.05) of the nominal value?

a. 2.06

b. 3.02

c. 1.03

d. 5.06

Solution:

298. An oscillator resonate at 1 MHz with a nominal 100 pF capacitor and 0.25 mH inductor, what is the resonant frequency of the actual capacitor value is +20% of the nominal value?

a. 1.006 MHz

b. 0.9188 MHz

c. 3.625 MHz

d. 2.00123 MHz

Solution:

299. “Front end” is also called _________.

a. IF stage

b. AF stage

c. RF stage

d. None of these

Solution:

300. Undesired signal on the other side of the local oscillator output will have the same difference frequency and pass into the IF amplifier.

a. Carrier frequency

b. Sum frequency

c. Difference frequency

d. Image frequency

Solution:

#### Questions and Answers in Modulation Series

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

MCQ in Modulation
PART 1: MCQ from Number 1 – 50                        Answer key: PART 1
PART 2: MCQ from Number 51 – 100                   Answer key: PART 2
PART 3: MCQ from Number 101 – 150                 Answer key: PART 3
PART 4: MCQ from Number 151 – 200                 Answer key: PART 4
PART 5: MCQ from Number 201 – 250                 Answer key: PART 5
PART 6: MCQ from Number 251 – 300                 Answer key: PART 6
PART 7: MCQ from Number 301 – 350                 Answer key: PART 7
PART 8: MCQ from Number 351 – 400                 Answer key: PART 8
PART 9: MCQ from Number 401 – 450                 Answer key: PART 9
PART 10: MCQ from Number 451 – 500                 Answer key: PART 10