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Communications MCQ Set 1

1. What we use for impedance matching in RF amplifiers?
a) RC coupling
b) Transformer coupling
c) Direct coupling
d) RF coupling

View Answer

Answer: b [Reason:] Impedance matching is the input impedance of an electrical load or the output impedance of corresponding electrical signal source to maximize power transfer or minimize signal reflection from the load. Transformer coupling is basically used for impedance matching in RF amplifiers.

2. Neutralization cancels unwanted feedback by bypassing the feedback to the neutral or ground plane.
a) True
b) False

View Answer

Answer: b [Reason:] Neutralization cancels unwanted feedback by adding feedback out of phase with the unwanted feedback.

3. In a receiver, distortion can occur in ________
a) Mixer
b) Detector
c) IF amplifiers
d) Either mixer or detector or IF amplifiers

View Answer

Answer: d [Reason:] Distortion in a receiver can occur in either mixer or in detector. It can also occur in IF amplifiers.

4. How we limit the response of a receiver to a weak signal?
a) by the AGC
b) by the noise that is generated in the receiver
c) by the dynamic range of the receiver
d) by the type of detector circuit being used

View Answer

Answer: b [Reason:] The response of a receiver to weak signals is limited by the noise. This noise is generated in the receiver only.

5. When aliasing will takes place?
a) Sampling signals less than Nyquist Rate
b) Sampling signals more than Nyquist Rate
c) Sampling signals equal to Nyquist Rate
d) Sampling signals at a rate which is twice of Nyquist Rate

View Answer

Answer: a [Reason:] Aliasing causes different signals to become indistinguishable when sampled. It happens when sampling rate is less than Nyquist rate.

6. A resonant circuit is a simple form of bandpass filter.
a) True
b) False

View Answer

Answer: a [Reason:] he quality factor Q, of a resonant circuit is a measure of quality of resonant circuit. We can also say that it tells about “goodness” of resonant circuit. A higher value for Q means a more narrow bandwidth, which we want in many application.

7. Which statement is true for high level amplitude modulation?
a) all RF amplifiers are of class A
b) all RF amplifiers can be nonlinear
c) minimum RF power is required
d) maximum RF power is required

View Answer

Answer: b [Reason:] In amplitude modulated system, amplitude of carrier is varied in proportion with the wave being transmitted. For high level amplitude modulation, modulating amplifiers is used to give power to sideband. All RF amplifiers in amplitude modulations are nonlinear.

8. Which statement is true for low level amplitude modulation?
a) all RF amplifiers are of class A
b) all RF amplifiers can be linear
c) minimum RF power is required
d) maximum RF power is required

View Answer

Answer: b [Reason:] In amplitude modulated system, amplitude of carrier is varied in proportion with the wave being transmitted. All RF amplifiers in low level amplitude modulations must be linear.

9. Which two networks can be used for impedance matching?
a) pi network and T network
b) pi network and bridge network
c) bridge network and T network
d) pi network and omega network

View Answer

Answer: a [Reason:] If a source with low impedance is connected with a load with high impedance then the power that can pass through the connection is limited by higher impedance. Generally the two networks, pi and T are used for impedance matching.

10. Which statement is true about frequency multipliers?
a) they are essentially balanced modulators
b) they are essentially class C amplifiers
c) they are essentially class AB amplifiers
d) they are essentially mixers

View Answer

Answer: b [Reason:] Frequency multiplier multiplies the frequency of a circuit by an integer. Frequency multipliers are generally class C amplifiers.

Communications MCQ Set 2

1. Which of the following does not cause losses in optical fibre cables?
a) Stepped index operation
b) Impurities
c) Microbending
d) Attenuation in glass

View Answer

Answer: a [Reason:] In Stepped index operation, refractive index within the core is uniform. There is also a sharp decrease in refractive index at the core-cladding interface. It generally does not cause any type os losses in optical fibre cables.

2. In case of FM, if the modulating frequency is lowered and the modulating voltage remains constant then the amplitude of distant sidebands first increases and then decreases.
a) True
b) False

View Answer

Answer: b [Reason:] If the modulating frequency in FM lowered and the modulating voltage remains constant then the amplitude of distant sidebands only increases.

3. It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using ________
a) space diversity
b) frequency diversity
c) directional antenna
d) oscillator

View Answer

Answer: b [Reason:] It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using diverse frequency.

4. What is the characteristic impedance of a twin wire feeder used in television?
a) 1000 ohm
b) 100 ohm
c) 10 ohm
d) 300 ohm

View Answer

Answer: d [Reason:] For a twin wire feeder the characteristic impedance should be close to 300 ohm.

5. A buffer amplifier is a cathode follower double tuned amplifier.
a) True
b) False

View Answer

Answer: b [Reason:] A buffer amplifier is basically a high gain DC amplifier. It is generally used to transfer voltage from a circuit having high output impedance level to a circuit with a low input impedance level.

6. What is the direction of rotation of a CD?
a) anticlockwise
b) clockwise
c) either clockwise or anticlockwise depend on data stored
d) mostly anticlockwise but sometimes clockwise

View Answer

Answer: a [Reason:] CD stands for compact disk. The direction of rotation of Compact Disk is anticlockwise.

7. According to Fourier Analysis a square wave can be represented as a fundamental sine wave and even harmonics.
a) True
b) False

View Answer

Answer: b [Reason:] According to Fourier Analysis a square wave can be represented as a fundamental sine wave and odd harmonics.

8. Filter method is the one and only method to produce SSB?
a) True
b) False

View Answer

Answer: b [Reason:] SSB can be produced by filter method. But it can also be produced by phase cancellation method.

9. Impulse noise can be reduced in _________
a) FM
b) AM
c) Both AM and FM
d) PM

View Answer

Answer: a [Reason:] Impulse noise includes unwanted, almost instantaneous sharp sounds. It is only in frequency modulated circuits that allows reduction in impulse noise.

10. In televisions, equalizing pulses are sent during __________
a) horizontal blanking
b) vertical blanking
c) serrations
d) horizontal retrace

View Answer

Answer: a [Reason:] The duration of an equalizing pulse is approximately 2.5 microseconds. The repetition frequency of equalizing pulses is twice the line frequency. It is necessary to sent equalizing pulses during horizontal blanking in televisions.

Communications MCQ Set 3

1. Frequency Modulated system needs less bandwidth?
a) True
b) False

View Answer

Answer: b [Reason:] In frequency modulation, frequency of carrier varies with the modulated wave. It does not require much less bandwidth.

2. When bandwidth is the major consideration a narrow and wide band FM can be approximated to?
a) PM
b) SSB
c) VSB
d) AM

View Answer

Answer: d [Reason:] For narrow and wide bands frequency modulation, modulation index is respectively smaller and greater than 1. When bandwidth is considered it can be approximated to AM.

3. Power density from an isotropic antenna is equal to ________
analog-communications-questions-answers-applications-vsb-q3

View Answer

Answer: a [Reason:] Power of a transmitter that is radiated from an isotropic antenna will have a uniform power density in all direction. The power density at any distance ‘R’ for an isotropic antenna is equal to analog-communications-questions-answers-applications-vsb-q3a.

4. Which modulation is used in microwave band?
a) Amplitude Modulation
b) Pulse Modulation
c) Frequency Modulation
d) Phase Modulation

View Answer

Answer: b [Reason:] In pulse modulation, message information is encoded in the amplitude of series of signal pulse. It is mostly used for radio navigation, microwave band and for many others.

5. All the output pulses are at full transmitter power for a strong signal in all of the following except ________
a) PAM
b) PFM
c) PCM
d) PWM

View Answer

Answer: a [Reason:] Pulse amplitude modulation varies amplitude of pulses for transmission of data. Its output pulses are not at full transmitter power for a strong signal and thus it is a exception.

6. In pulse transmitter, the ratio of time on to time off is called ________
a) base
b) bandwidth
c) duty cycle
d) efficiency

View Answer

Answer: c [Reason:] Duty cycle is the fraction of one period in which the system is active. It can also be defined as the ratio of time on to time off of a system.

7. In which of the following modulated systems, quantization noise occurs?
a) TDM
b) FM
c) PWD
d) PCM

View Answer

Answer: d [Reason:] Pulse code modulation (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only.

8. Signal to quantization noise ratio in PCM system depends on _________
a) sampling rate
b) signal bandwidth
c) number of quantization levels
d) nature of carrier wave

View Answer

Answer: c [Reason:] Pulse code modulation (PCM) is a digital form of communication. For demodulation of PCM, it is necessary to convert it into PAM. Quantization noise occurs in PCM only. Signal to quantization noise ratio depends on number of quantization levels.

9. Pulse Modulation can be used in automatic landing equipments.
a) True
b) False

View Answer

Answer: a [Reason:] In pulse modulation, message information is encoded in the amplitude of series of signal pulse. It is mostly used for radio navigation, microwave band, automatic landing equipments and in many others.

10. Which of the following modulation is used in data communication?
a) Pulse Modulation
b) Amplitude Modulation
c) Phase Modulation
d) Frequency Modulation

View Answer

Answer: a [Reason:] In pulse modulation, message information is encoded in the amplitude of series of signal pulse. It is mostly used for radio navigation, microwave band, automatic landing equipments and in many others. It is also highly used in data communication.

Communications MCQ Set 4

1. What is the modulation index of an AM signal if the peak voltage goes from E_max to E_min?
analog-communications-questions-answers-aptitude-test-q1

View Answer

Answer: c [Reason:] Modulation index describes the variation of carrier signal modulation around its unmodulated level. It is defined as analog-communications-questions-answers-aptitude-test-q1a where Emax and Emin is respectively the maximum and minimum voltage.

2. Which frequencies is produced if Va sin⁡(ωa t) amplitude modulates the carrier Vc sin⁡(ωc t)?
a) (ωc + ωa) and (ωc – ωa)
b) (ωc) and (ωa)
c) (ωc + ωa) and (2ωc + 2ωa)
d) (2ωc) and (2ωa)

View Answer

Answer: a [Reason:] If we modulate the carrier having frequency ωc with wave having frequency ωa then the resultant wave has frequency (ωc + ωa) and (ωc – ωa).

3. What is the total sideband power if there is 100% modulation?
a) half the carrier wave
b) twice the carrier wave
c) equal to the carrier wave
d) one-fourth of the carrier wave

View Answer

Answer: a [Reason:] For 100% modulation, value of modulation index should be equal to 1. If modulation index, m=1 then total sideband power is equal to the half of carrier wave.

4. If AM radio station increases its modulation index then there is an increase in receiving RF signal.
a) True
b) False

View Answer

Answer: a [Reason:] Modulation index describes the variation of carrier signal modulation around its unmodulated level. Increase in it also increase the ability of increase reception of RF signals.

5. How an AM radio station increase its signal-to-noise ratio?
a) by increasing its modulation index
b) by decreasing its modulation index
c) by maintaining a constant modulation index
d) by increasing the frequency

View Answer

Answer: a [Reason:] Signal to noise ratio is the ratio of signal power to the noise power. It is often described in decibels. It is directly proportional with modulation index and thus it increases with modulation index.

6. What is the main problem in using quadrature amplitude modulation?
a) high bandwidth is required
b) high power is required
c) incompability with ordinary AM radio waves
d) bandwidth required is less

View Answer

Answer: c [Reason:] It is widely used for modulating data signals onto a carrier which is used for radio communication. It is both an analogue and digital modulation technique. It has many advantages over other modulations such as PSK but its disadvantage is its incompability with ordinary radio waves.

7. A single sideband modulation system requires a more complex demodulator circuit?
a) True
b) False

View Answer

Answer: a [Reason:] Single side band uses only one of its sideband among two sidebands. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on our signal. Due to the removal of one sideband total bandwidth required also decreases which makes it more efficient than others. For its demodulation it requires a complex demodulator circuit.

8. A narrow band noise can exist in _________
a) AM only
b) PCM only
c) FM only
d) AM and FM both

View Answer

Answer: d [Reason:] Narrow band filter is used to isolate a narrow band of frequencies from a wider bandwidth signal. It is a combination of band pass and band reject filter. So it can be used in both AM and FM.

9. To demodulate a USB SSB signal, the receiver must ________
a) be set to USB mode
b) reinsert the carrier
c) both a and b
d) have low-fidelity

View Answer

Answer: c [Reason:] Single side band uses only one of its sideband among two sidebands. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on our signal. To demodulate upper sideband of signal it is necessary that the receiver must be set to USB mode and have the ability to reinsert the carrier.

10. The __________ of an AM signal resembles the shape of baseband signal.
a) upperband
b) lowerband
c) efficiency
d) envelope

View Answer

Answer: d [Reason:] Envelope is basically a smooth curve that outlines the extremes of any baseband signal. So basically it is message or baseband signal that determines the envelope.

Communications MCQ Set 5

1. What is the full form of PEP in communication?
a) Peak Efficiency Power
b) Peak Envelope Power
c) Peak Efficiency Product
d) Peak Envelope Power

View Answer

Answer: d [Reason:] PEP in communication stands for peak envelope power. It is the highest envelope power that is transmitted to antenna transmission line by a transmitter.

2. Only audio can be sent using Amplitude Modulation.
a) True
b) False

View Answer

Answer: b [Reason:] Amplitude modulation has the capability to sent audio, video and digital data. So the statement that audio signal can sent by amplitude modulation is wrong.

3. What is the total modulation index, if one wave has a modulation index of m1 and other wave has a modulation index of m2?
analog-communications-questions-answers-chopper-circuit-q3

View Answer

Answer: d [Reason:] The total modulation index of two waves having modulation index m1 and m2 is analog-communications-questions-answers-chopper-circuit-q3a

4. How many sidebands is produced with a single tone in an amplitude modulated system?
a) One
b) Two
c) Three
d) Four

View Answer

Answer: b [Reason:] Single toned modulation is that in which modulation is carried out by single frequency. It has two sidebands.

5. If we compared to the USB, the information in LSB is ________
a) different
b) twice
c) same
d) little different

View Answer

Answer: c [Reason:] The two bands i.e. upper sideband and lower sideband generally contains same information. They also has same power.

6. In amplitude modulated system, total sideband power is ________ than the carrier power.
a) always more
b) always less
c) sometimes more
d) sometimes less

View Answer

Answer: b [Reason:] If we take the total power by considering all the sidebands produced in signal that it will always less than carrier power.

7. An amplitude modulated system requires less bandwidth than single side band system.
a) True
b) False

View Answer

Answer: b [Reason:] Single side band uses only one of its sideband among two sidebands. The two sidebands carries exactly the same information and thus removing a sideband does not have any effect on our signal. Due to the removal of one sideband total bandwidth required decreases which also makes it more efficient than others.

8. In SC in DSB-SC stands for _________
a) suppressed-carrier
b) single-carrier
c) sideband-carrier
d) super-carrier

View Answer

Answer: a [Reason:] DSB-SC stands for Double Side Band- Suppressed Carrier. It is used to produce Single Side Band. IN DSB-SC all the frequencies produced by amplitude modulation are symmetrically arranged above and below the carrier frequency.

9. What is the correct statement about FM modulation index?
a) increases with both modulation frequency and deviation
b) decreases with modulation frequency and increases with deviation
c) it increase with modulation frequency and decreases with deviation
d) it is equal to twice the deviation

View Answer

Answer: b [Reason:] Frequency modulated modulation index increases as deviation increase. It also decreases with modulation frequency.

10. Which mathematically term is used for calculating FM bandwidth?
a) Bessel functions
b) Trigonometry
c) Taylor series
d) Fractals

View Answer

Answer: a [Reason:] Bessel function are the solution of Bessel differential equation which are non-singular at the origin. In communication it is used to calculate FM bandwidth.

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