# Avionics Questions and Answers – Pulse Modulation

This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Pulse Modulation”.

1. The process of using a pulse signal to represent information is called _______
a) Pulse modulation
b) Frequency modulation
c) Amplitude modulation
d) Phase modulation

Explanation: In pulse modulation, the information to be transmitted is represented by a series of binary pulses. Since the pulse information is binary in nature analog signal shave to be converted to digital before transmitting.

2. Which of the following is false with respect to pulse modulation?
a) Less power consumption
b) Low noise
c) Degraded signal can be regenerated
d) Can transmit analog as well as digital waves

Explanation: Analog values cannot be transmitted as such by pulse modulation since it can only transmit binary data. However, the analog signal can be converted into digital using an ADC and then transmitted via pulse modulation.

3. Which of the following is not a form of pulse modulation?
a) Pulse amplitude modulation
b) Pulse width modulation
c) Pulse position modulation
d) Pulse frequency modulation

Explanation: There are four basic forms of pulse modulation. They are: pulse amplitude modulation, pulse width modulation, pulse position modulation pulse code modulation. In any form of pulse modulation, the frequency of the signal is not changed.

4. How many voltage levels are present in a PWM signal?
a) 0
b) 1
c) 2
d) 3

Explanation: The amplitude of PWM is binary in nature meaning that it has only two levels. The amplitude of the modulating signals varies the width of the pulses generated.

5. Power consumption is low in pulse modulation.
a) True
b) False

Explanation: In pulse modulation, the carrier is not transmitted continuously but in pulses whose width is determined by the amplitude of the modulating signal. The duty cycle is made in such a way that the carrier is off for a longer time than it bursts hence the average power consumption is low.

6. Which pulse modulation technique is least expensive?
a) Pulse amplitude modulation
b) Pulse width modulation
c) Pulse position modulation
d) Pulse code modulation

Explanation: Out of all the pulse modulation techniques, Pulse amplitude modulation is the least expensive and simplest to implement. In pulse amplitude modulation, the amplitude of the pulse varies with the amplitude of the modulating signal.

7. Which of the following is false with respect to pulse position modulation?
a) Can be transmitted in broadband
b) Modulates a high frequency carrier
c) Pulse is narrow
d) Pulse width changes in accordance with the amplitude of modulating signal

Explanation: In PPM, the pulses change position according to the amplitude of the analog signal. The pulses are very narrow. These pulse signals may be transmitted in a baseband form, but in most applications, they modulate a high-frequency radio carrier.

8. Pulse modulation is not used in which of the following?
a) Telemetry systems
b) Remote control models
c) Switch power modes
d) Communication of airplane with ATC

Explanation: Pulse modulation is used in telemetry systems to monitor spacecraft or missile, RC models, for switching power supplies like regulators and also as audio switching power amplifiers. Communication of airplane with ATC is amplitude modulated waves.

9. The process of signal compression and expansion used to reduce distortion and noise is called _____
a) Amplification
b) Companding
c) Compressing
d) Modulating

Explanation: To reduce the effects of noise and distortion in pulse modulation, a process called companding is done. Companding is a process of signal compression and expansion.

10. What type of digital modulation is widely used for digital data transmission?
a) Pulse amplitude modulation
b) Pulse width modulation
c) Pulse position modulation
d) Pulse code modulation

Explanation: The most widely used technique for digitizing information signals for electronic data transmission is pulse code modulation. It has uniform transmission quality and also can be used when the signal traffic is high.

11. What is the output voltage if the input voltage of a compander with a maximum voltage range of 1 V and a μ of 255 is 0.25?
a) 0V
b) 0.25V
c) 0.5V
d) 0.75V

Explanation:

12. What is the output voltage if the input voltage of a compander with a maximum voltage range of 1 V and a μ of 255 is 0.8V0?
a) 0.08V
b) 0.458V
c) 1.02V
d) 1.54V

Explanation:

Sanfoundry Global Education & Learning Series – Avionics.

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