Analog Communications Questions and Answers – Instantaneous Frequency and Frequency Modulation

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This set of Analog Communications Multiple Choice Questions & Answers focuses on “Instantaneous Frequency and Frequency Modulation”.

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
Explanation: 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. It is usually used with a small load for power amplification.

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

Answer: b
Explanation: Neutralization cancels unwanted feedback by adding feedback out of phase with the unwanted feedback. It is a method of filtering noise out of signals.

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
Explanation: Distortion in a receiver can occur in either mixer or in the detector. It can also occur in IF amplifiers. Distortion is the change in the shape of the waveform.
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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
Explanation: The response of a receiver to weak signals is limited by the noise. This noise is generated in the receiver only. Noise is the unwanted signal that is present in the passband of the signal.

5. When aliasing will take 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
Explanation: Aliasing causes different signals to become indistinguishable when sampled. It happens when the sampling rate is less than Nyquist rate. To prevent aliasing, sampling signals should be at a rate which is twice of Nyquist Rate.
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6. A resonant circuit is a simple form of bandpass filter.
a) True
b) False
View Answer

Answer: a
Explanation: The quality factor Q, of a resonant circuit is a measure of quality of resonant circuit, thus indicating the performance of the resonant circuit. Bandwidth can be seen as the ratio of the resonant frequency to quality factor. A higher value for Q means a more narrow bandwidth, which we want in many applications.

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
Explanation: In high level AM, modulation is done at high power of carrier and modulating signal therefore output power is high. Therefore, power amplifiers are not used to boost the carrier and modulating signal. Thus, all RF amplifiers are non-linear.
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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
Explanation: For low level AM, modulation is done at low power of carrier and modulating signal, so power amplifiers are used to boost the carrier and modulating signal. Therefore, output power is low. Thus, the amplifiers used are 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
Explanation: 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.
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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
Explanation: Frequency multiplier multiplies the frequency of the input by an integer, such that the output is a multiple of the input. Frequency multipliers are generally class C amplifiers.

Sanfoundry Global Education & Learning Series – Analog Communications.

To practice all areas of Analog Communications, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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