250+ TOP MCQs on Modulation and Multiplexing and Answers

Avionics Multiple Choice Questions on “Modulation and Multiplexing”.

1. The process of making the signal more compatible with the medium is called as?
a) Modulation
b) Transmission
c) Encrypting
d) Multiplexing
Answer: a
Clarification: Modulation is the process of making the information signal more compatible with the medium. Modulation is the reason why we can have different channels on radio.

2. The information signal is otherwise referred to as ___________
a) Digital signal
b) Analog signal
c) Baseband signal
d) Broadband signal
Answer: c
Clarification: The information signal, regardless of analog or digital type, is referred to as baseband signals. It could be voice, video or digital data and is modulated before transmission. In some case, baseband signals can be transmitted without modulation.

3. Voice signals cannot be directly transmitted by radio.
a) True
b) False
Answer: a
Clarification: Baseband signals are, in many cases, incompatible with the medium. Theoretically, it is possible to transmit voice signals directly by radio, but due to the low frequency of these waves the antenna size required form transmission is too big.

4. In frequency modulation, carrier frequency is always greater than baseband frequency.
a) True
b) False
Answer: a
Clarification: In frequency modulation, the baseband signal is overlapped or impressed in the carrier signal. The carrier can never have a lower frequency than the baseband signal as it would result in a huge data loss of the baseband signal.

5. Which one of the following is not a type of modulation?
a) Frequency modulation
b) Amplitude Modulation
c) Pulse modulation
d) Phase amplitude modulation
Answer: c
Clarification: Modulation is of three types, frequency modulation, amplitude modulation and phase modulation. Pulse modulation is a type of amplitude modulation.

6. In amplitude modulation, which of the following varies?
a) Frequency of the carrier
b) Frequency of the information signal
c) Amplitude of the carrier wave
d) Amplitude of the information signal
Answer: c
Clarification: In amplitude modulation, the amplitude of the carrier wave is modulated with respect to the information signal. The frequency and the phase of both the carrier and the information signal remain constant.

7. You have 5 information signals and only one transmitter. What technique will help in transmitting all the 5 signals?
a) Frequency modulation
b) Multiplexing
c) Amplification
d) Amplitude modulation
Answer: b
Clarification: Multiplexing is the process of transmitting more than one signal via a common transmitting medium. A device called a multiplexer is used for this purpose. The signal can be demultiplexed at the receiver end to retrieve the original information.

8. What type of multiplexing is used in mobile phones?
a) Frequency division multiplexing
b) Time division multiplexing
c) Code division multiplexing
d) Phase multiplexing
Answer: c
Clarification: In code-division multiplexing, the signals to be transmitted are converted to digital data that is then uniquely coded with a faster binary code. The signals modulate a carrier on the same frequency. All use the same communications channel simultaneously. The unique coding is used at the receiver to select the desired signal.

9. Which one of the following is not true with respect to amplitude modulation?
a) Less noise
b) Longer range
c) Lower bandwidth
d) Less complex circuits
Answer: a
Clarification: Although AM is much simpler and has a wider range due to atmospheric propagation, one of its major disadvantages is due to noise. Noise directly affects the amplitude of the signal and its hard to retrieve the original information.

10. What type of multiplexing is used in serial buses?
a) Time division multiplexing
b) Code division multiplexing
c) Frequency division multiplexing
d) Phase multiplexing
Answer: a
Clarification: In serial buses, time division multiplexing is used to split the digital data, which is in binary numbers, into individual bits which occupy a particular time slot and is transmitted. The use of serial buses increases the limit on transmission speed and reduces noise.