ECE - Radio Receivers Quiz (or) MCQ | Questions and Answers

1 .

In a ratio detector______

A)

the linearity is worse than in phase discriminator

B)

stabilization against signal strength variations is provided

C)

the output is twice that obtainable from a similar phase discriminator

D)

the circuit is the same as in a discriminator, except that the diodes are reversed

Correct Answer : the linearity is worse than in phase discriminator

2 .

In a superheterodyne receiver

A)

the RF stage has same selectivity than IF stage

B)

the RF stage has better selectivity than IF stage

C)

the IF stage has better selectivity than RF stage

D)

None of the above

Correct Answer : the IF stage has better selectivity than RF stage

3 .

The function of an AM detector circuit is to

A)

discard the carrier

B)

provide audio signal

C)

rectify the input signal

D)

All of the above

Correct Answer : All of the above

4 .

A)

433 kHz

B)

455 kHz

C)

545 kHz

D)

555 kHz

Correct Answer : 455 kHz

5 .

An AM receiver uses a diode detector for demodulation. This enables it satisfactorily to receive_____

A)

ISB

B)

Single-sideband, full-carrier

C)

Single-sideband, reduced-carrier

D)

Single-sideband, suppressed-carrier

Correct Answer : Single-sideband, full-carrier

6 .

To prevent overloading of the IF amplifier in a receiver, one should use_______

A)

Variable sensitivity

B)

Squelch

C)

Variable selectivity

D)

Double conversion

Correct Answer : Variable sensitivity

7 .

A low ratio of the ac to the dc load impedance of a diode detector results in

A)

Diagonal clipping

B)

Poor AF response

C)

Negative-peak clipping

D)

Poor AGC operation

Correct Answer : Negative-peak clipping

8 .

Indicate which of the following circuits could not demodulate SSB:

A)

BFO

B)

Product modulator

C)

Balance modulator

D)

Phase discriminator

Correct Answer : Phase discriminator

9 .

One of the following cannot be used to demodulate SSB:

A)

Product detector

B)

Diode Balance modulator

C)

Complete phase-shift generator

D)

Bipolar transistor balanced modulator

Correct Answer : Bipolar transistor balanced modulator

10 .

The noise generated by a resistor depends upon

A)

its resistance value

B)

its operating temperature

C)

both its resistance value and operating temperature

D)

None of the above

Correct Answer : its operating temperature

11 .

Noise limiter is provided on AM receivers to

A)

reduce noise due to electrical storms

B)

reduce interfering noise due to ignition system

C)

reduce interference due to electrical machinery

D)

All of the above

Correct Answer : All of the above

12 .

In superheterodyne receivers, the local oscillator is used to

A)

detect the modulating signal

B)

amplify the received modulated carrier

C)

shift the frequency of the received modulated carrier to the IF band

D)

None of the above

Correct Answer : shift the frequency of the received modulated carrier to the IF band

13 .

Which of the following statement about the amplitude limiter is not valid?

A)

Output must be tuned

B)

Leak type bias must be used

C)

The circuit is always biased in class C, by virtue of the leak type bias

D)

When the input increases past the threshold of limiting, the gain decreases to keep the output constant

Correct Answer : The circuit is always biased in class C, by virtue of the leak type bias

14 .

A trimmer is basically a

A)

capacitor

B)

inductor

C)

insulator

D)

variable resistor

Correct Answer : Capacitor

15 .

In a radio receiver

A)

RF stage has no effect on S/N ratio

B)

all stages contribute equally to noise

C)

mixer stage contributes most of the noise generated

D)

None of the above

Correct Answer : mixer stage contributes most of the noise generated

16 .

The sensitivity of a superheterodyne receiver is determined by

A)

the noise figure

B)

the gain IF amplifier

C)

the gain of RF amplifier

D)

All of the above

Correct Answer : All of the above

17 .

In a radio receiver______

A)

the local oscillator frequency is made equal to the incoming signal frequency

B)

the local oscillator frequency is made higher than the incoming signal frequency

C)

the local oscillator frequency is made lower than the incoming signal frequency

D)

None of the above

Correct Answer : the local oscillator frequency is made higher than the incoming signal frequency

18 .

In radio receiver, the maximum contribution to noise is from

A)

mixer stage

B)

power supply

C)

power amplifier

D)

equally from above three

Correct Answer : power amplifier

19 .

In a FM waveform, the side bands are spaced at intervals equal to

A)

modulating frequency

B)

half the modulating frequency

C)

twice the modulating frequency

D)

four times the modulating frequency

Correct Answer : half the modulating frequency

20 .

Power spectral density of white noise

A)

is constant with frequency

B)

increases with frequency

C)

decreases with frequency

D)

None of the above

Correct Answer : is constant with frequency

21 .

In a receiver, at higher frequencies

A)

tracking will be poor

B)

selectivity will be poor

C)

image frequency rejection will be poor

D)

tracking will be improved

Correct Answer : tracking will be improved

22 .

A communication channel with additive white Gaussian noise, has a bandwidth of 4 kHz and an SNR of 15. Its channel capacity is

A)

1.6 kbps

B)

16 kbps

C)

32 kbps

D)

256 kbps

Correct Answer : 16 kbps

23 .

The typical squelch circuit

A)

cuts off an IF amplifier when the AGC is maximum

B)

cuts off an IF amplifier when the AGC is minimum

C)

cuts off an audio amplifier when the carrier is absent

D)

eliminates the RF interference when the signal is weak

Correct Answer : cuts off an audio amplifier when the carrier is absent

24 .

Indicate which of the following statements about the advantages of the phase discriminator over the slope detector is false:

A)

Better linearity

B)

Fewer tuned circuits

C)

Greater limiting

D)

Much easier alignment

Correct Answer : Greater limiting

25 .

The controlled oscillator synthesizer is sometimes preferred over the direct one because

A)

Its frequency stability is better

B)

It is a simpler piece of equipment

C)

It does not require crystal oscillator

D)

It is relatively free of spurious frequency

Correct Answer : It is relatively free of spurious frequency

26 .

A superheterodyne receiver with an IF of 450 kHz is tuned to a signal at 1200 kHz. The image frequency is

A)

2100 kHz

B)

1650 kHz

C)

900 kHz

D)

750 kHz

Correct Answer : 2100 kHz

27 .

A receiver has poor IF selectivity. It will therefore also have poor

A)

Blocking

B)

Sensitivity

C)

Double-spotting

D)

Diversion reception

Correct Answer : Blocking

28 .

Show which of the following statements about the amplitude limiter is untrue:

A)

The output must be tuned

B)

Leak-type bias must be used

C)

The circuit is always biased in class C, by virtue of the leak-type bias.

D)

When the input increases past the threshold of the limiting, the gain decreases to keep the output constant.

Correct Answer : The circuit is always biased in class C, by virtue of the leak-type bias.

29 .

The local oscillator of a broadcast receiver is tuned to a frequency higher than the incoming frequency

A)

To permit easier tracking

B)

To allow adequate frequency coverage without switching

C)

To help the image frequency rejection

D)

Because otherwise an intermediate frequency could not be produced

Correct Answer : To allow adequate frequency coverage without switching

30 .

A heterodyne frequency changer is called a

A)

Mixer

B)

Modulator

C)

Demodulator

D)

Frequency translator

Correct Answer : Mixer

31 .

RF amplifiers are used in radio receivers for

A)

improved image frequency rejection

B)

improved rejection of adjacent unwanted signals

C)

prevention of re-radiation of the local oscillator through the antenna of the receiver

D)

All of the above

Correct Answer : All of the above

32 .

Which are the popular IF frequencies for microwave and radar receivers operating on frequencies in the range 1 to 10 GHz

A)

3, 6 and 7 kHz

B)

3, 6 and 7 GHz

C)

30, 60 and 70 kHz

D)

30, 60 and 70 MHz

Correct Answer : 30, 60 and 70 MHz

33 .

Neutralization is used in RF amplifiers to_______

A)

improve selectivity

B)

increase bandwidth

C)

stop oscillation

D)

All of the above

Correct Answer : stop oscillation

34 .

It is known that noise phase modulates the FM wave. As the noise side band frequency approaches the carrier frequency, the noise amplitude

A)

will increase

B)

will decrease

C)

will remain constant

D)

will reduce to negligible value

Correct Answer : will decrease

35 .

A notch filter is sometimes used in communication receivers to

A)

reduce receiver gain at some specific frequency

B)

spread the bandwidth

C)

made selectivity more precise

D)

increase receiver gain at some specific frequency

Correct Answer : reduce receiver gain at some specific frequency

36 .

Which one of the following is not a useful quantity for comparing the noise performance of receivers?

A)

Noise figure

B)

Input noise voltage

C)

Noise temperature

D)

Equivalent noise resistance

Correct Answer : Input noise voltage

37 .

Which of the following is same in AM and FM receivers?

A)

AGC

B)

Demodulator

C)

IF amplifier

D)

All of the above

Correct Answer : IF amplifier

38 .

The selectivity of a radio receiver is

A)

its ability to suppress noise.

B)

its ability to amplify weak signals

C)

its ability to reject adjacent unwanted signals

D)

the frequency at which it gives maximum amplification to signal.

Correct Answer : its ability to reject adjacent unwanted signals

39 .

EM 84 tube is used in radio receivers as

A)

magic eye

B)

RF amplifier

C)

audio amplifier

D)

full wave rectifier

Correct Answer : magic eye

40 .

Modulated carrier power in FM

A)

increases with modulating signal power

B)

decreases with modulating signal power

C)

is independent of the modulating signal power

D)

None of the above

Correct Answer : is independent of the modulating signal power

41 .

A receiver having an RF amplifier and an IF of 450 kHz, has Q of the coils 65 and an incoming frequency of 1200 kHz. The image rejection of the receiver is

A)

13.3

B)

236

C)

3655

D)

5870

Correct Answer : 236

42 .

In a radio receiver, the local oscillator is always tuned to a frequency higher than the incoming frequency to

A)

allow permit adequate frequency coverage without switching

B)

facilitate tracking

C)

facilitate image frequency rejection

D)

All of the above

Correct Answer : allow permit adequate frequency coverage without switching

43 .

When a superheterodyne receiver is tuned to 455 kHz, its local oscillator provides a mixer with the input at 1010 kHz. The image frequency is

A)

555 kHz

B)

1010 kHz

C)

1465 kHz

D)

1920 kHz

Correct Answer : 1465 kHz

44 .

In a broadcast superheterodynes receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 100. If the intermediate frequency is 455 kHz. The image frequency at 1000 kHz will be

A)

545 kHz

B)

1010 kHz

C)

1455 kHz

D)

1910 kHz

Correct Answer : 1910 kHz

45 .

FM receivers using the standard 88 to 108 MHz band use IF of

A)

12.2 MHz

B)

10.7 MHz

C)

9.9 MHz

D)

8 MHz

Correct Answer : 10.7 MHz

46 .

The problem associated with tuned-radio frequency receiver is

A)

instability

B)

bandwidth variation

C)

insufficient adjacent frequency rejection

D)

All of the above

Correct Answer : All of the above

47 .

Superheterodyne receiver can be used in

A)

AM

B)

FM

C)

SSB

D)

All of the above

Correct Answer : All of the above

48 .

An unmodulated voltage 10 V effective is applied to a dioxide detector in which load resistance is 4 x 10^-5 ohms. A micrometer shows that the rectified DC current in this resistance is 30 A. The efficiency of detection is

A)

34%

B)

55.5%

C)

68.8%

D)

84.7%

Correct Answer : 84.7%

49 .

Selectivity varies with receiving frequency, frequency is raised.

A)

Somewhat better at intermediate frequency

B)

Somewhat better when the receiving frequency is raised

C)

Somewhat worse when the receiving frequency is raised

D)

Somewhat worse when the receiving frequency is lowered

Correct Answer : Somewhat worse when the receiving frequency is raised

50 .

In a receiver, which of the following device has IF input but RF output?

A)

Demodulator

B)

Loudspeaker

C)

Audio amplifier

D)

Frequency changer

Correct Answer : Demodulator

51 .

Standard AM radio broadcasts are confined to

A)

HF

B)

MF

C)

UHF

D)

VHF

Correct Answer : MF

52 .

In a radio receiver with simple AGC

A)

an increase in signal strength produces more AGC

B)

the audio stage gain is normally controlled by AGC

C)

the highest AGC voltage is produced between stations

D)

the faster the AGC time constant, the more accurate the output

Correct Answer : an increase in signal strength produces more AGC

53 .

A transmitter serial current contains

A)

audio frequencies

B)

carrier frequencies

C)

Both (A) and (B)

D)

radio frequencies

Correct Answer : radio frequencies

54 .

In a broadcast superheterodynes receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 100. If the intermediate frequency is 455 kHz. The image frequency at 25 MHz will be

A)

24.09 MHz

B)

24.54 MHz

C)

25.45 MHz

D)

25.91 MHz

Correct Answer : 25.91 MHz

55 .

In a communication system, noise is most likely to affect the signal

A)

in the channel

B)

at the transmitter

C)

at the destination

D)

in the information source

Correct Answer : in the channel

56 .

In a radio receiver, if the intermediate frequency is too high

A)

Tracking difficulties will be least

B)

Selectivity will be poor

C)

Adjacent channel rejection will improve

D)

All of the above will occur

Correct Answer : Selectivity will be poor

57 .

In a radio receiver, if the intermediate frequency is too low

A)

Selectivity will be too sharp

B)

Image-frequency rejection will improve

C)

The frequency selectivity of the local oscillator will have to be lowered

D)

All of the above

Correct Answer : Selectivity will be too sharp

58 .

In a radio receiver, the local oscillator is tuned to a frequency

A)

equal to incoming frequency

B)

lower than the incoming frequency

C)

higher than the incoming frequency

D)

None of the above

Correct Answer : higher than the incoming frequency

59 .

Which of the following oscillator is generally not used at VHF?

A)

Clapp oscillator

B)

Colpitts oscillator

C)

Ultra Audio oscillator

D)

Armstrong oscillator

Correct Answer : Armstrong oscillator

60 .

In a superheterodyne receiver, the IF stage has better selectivity than RF stage because

A)

of high L/C ratio

B)

of lower frequency

C)

of constant passband

D)

of higher frequency

Correct Answer : of constant passband

61 .

The image frequency of a superheterodyne receiver is

A)

typical to FM receivers only

B)

not rejected by the IF tuned circuits

C)

always outside the operating range of the receiver

D)

independent of the frequency at which the receiver is tuned

Correct Answer : typical to FM receivers only

62 .

The purpose of incorporating a pre-selector stage in a receiver is to

A)

improve linearity

B)

provide higher selectivity

C)

larger passband

D)

provide higher fidelity

Correct Answer : provide higher selectivity

63 .

Which of the following statement about the advantage of phase discriminator over the slope detector is false?

A)

Better linearity

B)

Greater limiting

C)

Fewer tuned circuits

D)

Much easier alignment

Correct Answer : Greater limiting

64 .

Which of the following produces upper and lower side frequencies?

A)

Microphone

B)

Oscillator in a receiver

C)

Modulator in a. radio transmitter

D)

Demodulator in a superheterodyne receiver

Correct Answer : Microphone

65 .

The passband of the tuned circuits of a radio receiver should be equal to

A)

20 kHz

B)

455 kHz

C)

1455 kHz

D)

None of the above

Correct Answer : 20 kHz

66 .

In a receiver, which of the following device has RF input but IF output?

A)

Demodulator

B)

Loudspeaker

C)

Audio amplifier

D)

Frequency changer

Correct Answer : Frequency changer

67 .

The IF stage of a receiver employs

A)

impedance coupling

B)

capacitive coupling

C)

double-tuned transformer coupling

D)

single-tuned transformer coupling

Correct Answer : double-tuned transformer coupling

68 .

Statement 1 : Diode is the most common device used for demodulation.
Statement 2 : A discriminator is a FM detector.

A)

Statement 1 is true but statement 2 is false

B)

Statement 1 is false but statement 2 is true

C)

Both the statements are true

D)

Both the statements are false

Correct Answer : Both the statements are true

69 .

A receiver having poor IF selectivity will also have poor

A)

sensitivity

B)

blocking

C)

double spotting

D)

All of the above

Correct Answer : blocking

70 .

The source of which of the following noise is different from that of the remaining?

A)

Solar noise

B)

Cosmic noise

C)

Galactic noise

D)

Atmospheric noise

Correct Answer : Atmospheric noise

71 .

In a transistor receiver, the use of FET as the first stage amplifier is likely to

A)

improve selectivity of the receiver

B)

improve the effectiveness of the AGC

C)

reduce the effect of negative peak clipping

D)

reduce the effect of noise at all frequencies

Correct Answer : reduce the effect of negative peak clipping

72 .

In a broadcast superheterodynes receiver having no RF amplifier, the loaded Q of the antenna coupling circuit is 100. If the intermediate frequency is 455 kHz. The rejection ratio at 25 MHz will be

A)

1.116

B)

1.386

C)

2.116

D)

2.386

Correct Answer : 1.116

73 .

As compared to tuned radio frequency receivers which of the following is the advantage of using superheterodyne receivers?

A)

Stability

B)

Noise suppression

C)

High gain and better sensitivity

D)

Better selectivity at high frequencies

Correct Answer : High gain and better sensitivity

74 .

The selectivity of most receivers is determined largely by

A)

sensitivity

B)

antenna direction

C)

characteristics of IF section

D)

All of the above

Correct Answer : characteristics of IF section

75 .

In a superheterodyne receiver, the IF is 455 kHz. If it is tuned to 1200 kHz, the image frequency will be

A)

745 kHz

B)

910 kHz

C)

1655 kHz

D)

2110 kHz

Correct Answer : 2110 kHz

Explanation : A signal (image) can interfere with a superheterodyne receiver if fits the following equation.

Image = Signal +/- 2 x I.F.

Which says that a signal has the capacity to interfere with a superhet receiver if its frequency is equal to the signal frequency (1200 kHz in our question) plus or minus twice the IF (455 kHz in our question).

So one possible image is : 1200 + ( 2 x 455 ) = 2110 kHz (possible).

And the other: 1200 - ( 2 x 455 ) = 290 kHz (not likely).