# Analog Communications Questions and Answers – Bandwidth of FM Signal with Arbitrary m(t)

This set of Analog Communications test focuses on “Bandwidth of FM Signal with Arbitrary m(t)”.

1. When two or more signals share a common channel, it is called ________
a) sub-channeling
b) channeling
c) switching
d) multiplexing

Explanation: Multiplexing is a method by which multiple analog or digital signals are combined to form a single complex signal. In multiplexing, many signals are combined into one signal and passed through a single channel, thus sharing the same medium.

2. One of the reason of distortion is shift in phase relationships between baseband frequencies.
a) True
b) False

Explanation: Phase distortion is the change in shape of the waveform. Thus, if we shift the phase relationships between baseband frequencies, it will ultimately result in distortion.

3. Miller effect can cause an amplifier to oscillate.
a) True
b) False

Explanation: Miller effect is responsible for limiting the gain of an amplifier at higher frequencies due to Miller capacitance between the output and input. Also, oscillations in amplifier occur due to input/output feedback.

4. How can we successfully avoid Miller effect?
a) using a common-base amplifier
b) using a common-emitter amplifier
c) by increasing the Q factor
d) by decreasing the Q factor

Explanation: Miller effect is responsible for the increase in equivalent input capacitance of an inverting voltage amplifier. The increase equivalent input capacitance is given by, CM = C(1 + AV). Miller effect can be avoided by using a common-base amplifier.

5. What is the two basic specifications of a receiver?
a) sensitivity and selectivity
b) superious response and tracking
c) signal and noise
d) number of convertors and number of IFs

Explanation: Sensitivity and selectivity are the two key specifications for any receiver, which is used for the purpose in communication. Sensitivity is the ability of the receiver to amplify weak signals, whereas Selectivity is the ability of the receiver to reject unwanted signals.
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6. Who invented the superheterodyne receivers?
a) Hertz
b) Armstrong
c) Foster
d) Seeley

Explanation: Superheterodyne uses frequency mixing to convert a received RF signal to a fixed IF(intermediate frequency). This method is known as heterodyning. This IF can be processed more easily than the original carrier frequency. It was invented by Armstrong.

7. Skin effect refers ________
a) the increase of wire resistance with frequency
b) the decrease of wire resistance with frequency
c) the uniform nature of wire resistance with frequency
d) the way radio signals travel across a flat surface

Explanation: Skin effect becomes more and more apparent as frequency increases as skin depth becomes smaller. It is due to alternating current flowing through the outer surface of conducting material. It refers to the increase of wire resistance with frequency.

8. The frequency of local oscillator ________
a) can be either below or above the RF frequency
b) is below the RF frequency
c) is above the RF frequency
d) is fixed typically at 450KHz

Explanation: The frequency of the local oscillator is not fixed. It is mostly above the RF frequency.

9. Phase distortion is important in ________
a) voice communication systems

Explanation: Phase distortion is a change in the shape of the waveform. It occurs when filter’s do not have a sharp cut off frequency thus not properly filtering a wave. Thus, phase distortion is important in color video receivers.

Sanfoundry Global Education & Learning Series – Analog Communications.

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