Modulation, Multiplexing and Sensor Networks - Communication and Optical Instrumentation - Instrumentation Engineering Previous Year Questions

1

2009 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2009

A 50% duty cycle square wave with zero mean is used as a baseband signal in an ideal frequency modulator with a sinusoidal carrier of frequency ω_c. The modulated signal is given as an input to an ideal phase demodulator (a circuit that produces an output proportional to the difference in phase of the modulated signal from that of the carrier). The output of the circuit is

A

a square wave

B

a train of impulses with alternating signs

C

a triangular wave

D

a sinusoidal wave

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2

2010 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2010

In a pulse code modulated (PCM) signal sampled at \( f_s \) and encoded into an \( n \)-bit code, the minimum bandwidth required for faithful reconstruction is

A

\(2nf_s \)

B

\(nf_s \)

C

\(nf_s / 2 \)

D

\(f_s \)

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3

2013 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2013 [Session 1]

Signals from fifteen thermocouples are multiplexed and each one is sampled once per second with a 16-bit ADC. The digital samples are converted by a parallel to serial converter to generate a serial PCM signal. This PCM signal is frequency modulated with FSK modulator with 1200 Hz as 1 and 960 Hz as 0. The minimum band allocation required for faithful reproduction of the signal by the FSK receiver without considering noise is

A

840 Hz to 1320 Hz

B

960 Hz to 1200 Hz

C

1080 Hz to 1320 Hz

D

720 Hz to 1440 Hz

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4

2014 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2014

A full duplex binary FSK transmission is made through a channel of bandwidth 10 kHz. In each direction of transmission the two carriers used for the two states are separated by 2 kHz. The maximum baud rate for this transmission is:

A

2000 bps

B

3000 bps

C

5000 bps

D

10000 bps

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5

2016 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2016

The signal m(t) = cos(ω_mt) is SSB (single side-band) modulated with a carrier cos(ω_ct) to get s(t). The signal obtained by passing s(t) through an ideal envelope detector is

A

cos(ω_mt)

B

sin(ω_mt)

C

cos(ω_mt) + sin(ω_mt)

D

1

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6

2016 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2016

The signal \( m(t) = \frac{\sin(100 \pi t)}{100 \pi t} \) is frequency modulated (FM) with an FM modulator of frequency deviation constant of 30 kHz/V. Using Carson's rule, the approximate bandwidth of the modulated wave in kilohertz is ______.

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7

2024 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2024

Consider an ultrasonic measurement system shown in the figure. The ultrasonic transmitter (T) sends a continuous wave signal \( x(t) = \cos(2\pi f_1 t) \) volts towards an object whose vibration is modeled as \( m(t) = 0.5 \sin(2\pi f_2 t) \) volts. Neglecting the phase shift due to any other effect, the received signal at the receiver (R) is \( y(t) = \cos(2\pi f_1 t + \beta \cos(2\pi f_2 t)) \) volts. Assuming the frequency sensitivity factor as 500 Hz/volt, \( f_1 = 40 \) kHz, \( f_2 = 1 \) kHz, the modulation index (\( \beta \)) and the frequency deviation in \( y(t) \), respectively, are

A

0.25 and \(\pm 250 \) Hz

B

0.5 and \(\pm 500 \) Hz

C

1 and \(\pm 1000 \) Hz

D

0.75 and \(\pm 1000 \) Hz

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8

2008 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2008

Consider the AM signal \(s(t) = [1 + m(t)]\cos(2\pi f_c t)\). It is given that the bandwidth of the real, low-pass message signal \(m(t)\) is 2 kHz. If \(f_c = 2\,MHz\), the bandwidth of the band-pass signal \(s(t)\) will be

A

2.004 MHz

B

2 MHz

C

4 kHz

D

2 kHz

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9

2008 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2008

Ten real, band-pass message signals, each of bandwidth 3 kHz, are to be frequency division multiplexed over a band-pass channel with bandwidth \(B\,kHz\). If the guard band in between any two adjacent signals should be of 500 Hz width and there is no need to provide any guard band at the edges of the band-pass channel, the value of \(B\) should be at least

A

30

B

34.5

C

35

D

35.5

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10

2017 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2017

The figure shows a phase locked loop. The output frequency is locked at \(f_0 = 5\) kHz. The value of \(f_i\) in kHz is __________.

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11

2017 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2017

In a sinusoidal amplitude modulation scheme (with carrier) the modulated signal is given by \(A_m(t) = 100 \cos(\omega_c t) + 50 \cos(\omega_m t) \cos(\omega_c t)\), where \(\omega_c\) is the carrier frequency and \(\omega_m\) is the modulation frequency. The power carried by the sidebands in % of total power is __________%.

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12

2017 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2017

An angle modulated signal with carrier frequency \(\omega_c = 2\pi \times 10^6 \text{ rad/s}\) is given by \(\phi_m(t) = \cos(\omega_c t + 5 \sin(1000\pi t) + 10 \sin(2000\pi t))\). The maximum deviation of the frequency in the angle modulated signal from that of the carrier is __________ kHz.

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13

2018 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2018

An amplitude modulated signal is shown in the figure. The modulation index is (up to one decimal place) ____.

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14

2019 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2019

A signal \(\cos(2\pi f_m t)\) modulates a carrier \(\cos(2\pi f_c t)\) using the double-sideband-with-carrier (DSBWC) scheme to yield a modulated signal \(\cos(2\pi f_c t) + 0.3\cos(2\pi f_m t)\cos(2\pi f_c t)\). The modulation index is _____. (Answer should be rounded off to one decimal place)

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15

2021 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2021

An amplitude modulation (AM) scheme uses tone modulation, with modulation index of 0.6. The power efficiency of the AM scheme is ____% (rounded off to one decimal place).

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16

2022 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2022

A sinusoidal carrier wave with amplitude $A_c$ and frequency $f_c$ is amplitude modulated with a message signal $m(t)$ having frequency $0 < f_m \ll f_c$ to generate the modulated wave $s(t)$ given by \[s(t)=A_c[1+m(t)]\cos(2\pi f_ct)\] The message signal that can be retrieved completely using envelope detection is ______

A

m(t)=0.5\cos(2\pi f_mt)

B

m(t)=1.5\sin(2\pi f_mt)

C

m(t)=2\sin(4\pi f_mt)

D

m(t)=2\cos(4\pi f_mt)

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17

2022 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2022

Consider 24 voice signals being transmitted without latency using time-division multiplexing. If each signal is sampled at 12 kHz and represented by an 8-bit word, the bit-duration (in microseconds) is ______ (round off to two decimal places)

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18

2026 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2026

An analog speech signal contains signals from 200 Hz to 2400 Hz. It is sampled at 6 kHz and quantized with 512 levels for pulse code modulation (PCM). The bit rate will be ______ kbps.

A

16

B

48

C

19.2

D

54

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19

2026 · Instrumentation Engineering · Communication and Optical Instrumentation · Modulation, Multiplexing and Sensor Networks

Instrumentation Engineering (IN) 2026

An amplitude modulated voltage signal \(x(t)\) drives a load of 1 \(\Omega\).
\(x(t) = K \cos(300\pi t) + L \cos(240\pi t) + L \cos(360\pi t)\).
If the efficiency is 60% and the carrier power is 50 W, the value of \(L\) is ______ V.

A

8.66

B

1.22

C

0.81

D

17.32

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