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Communication and Optical Instrumentation

15 Questions
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q1
MCQ[1 Mark]
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.
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q2
MCQ[1 Mark]
The slope efficiency of a laser diode is 0.5 W/A, and the output optical power at a current of 100 mA is 30 mW. Assuming piece-wise linear characteristics of the laser diode, the threshold current of the laser is _____ mA.
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q3
MCQ[2 Marks]
An amplitude modulated voltage signal x(t)x(t) drives a load of 1 \Omega. x(t)=Kcos⁡(300πt)+Lcos⁡(240πt)+Lcos⁡(360πt)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.
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q4
NAT[2 Marks]
In the phase-locked-loop circuit shown below, the output of the VCO is a digital square wave. If the input is a square wave at 10 kHz, the steady state frequency of the output is kHz. (rounded off to the nearest integer)
Figure for Question 4
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q5
NAT[2 Marks]
For a fiber Bragg grating-based sensor, the shift in the Bragg wavelength gives information about the value of the measurand. For a Bragg wavelength of 1550 nm and effective index of 1.44, the grating period is nm. (rounded off to two decimal places)
GATE→2026→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q6
NAT[2 Marks]
A photodiode has a responsivity 0.8 A/W. If the input optical power to the photodiode is 2 mW, the power delivered to a 50 \Omega load is \mu W. (rounded off to the nearest integer)
GATE→2025→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q7
NAT[2 Marks]
A schematic of a Michelson interferometer... If a 532 nm laser beam produces 30 interference fringes on the screen, then the number of fringes produced by a 632.8 nm laser beam will be (rounded off to one decimal place).
Figure for Question 7
GATE→2024→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q8
MCQ[2 Marks]
Consider an ultrasonic measurement system shown in the figure... the modulation index (\beta) and the frequency deviation in y(t)y(t), respectively, are
Figure for Question 8
GATE→2024→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q9
NAT[2 Marks]
An ADC has a full scale voltage of 1.4 V, resolution of 200 mV... The data rate at the output of the parallel-to-serial converter is Gbps (rounded off to nearest integer).
GATE→2023→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q10
MCQ[2 Marks]
In a p-i-n photodiode, a pulse of light containing 8×10128 \times 10^{12} incident photons... The quantum efficiency of the photodiode at this wavelength is
GATE→2023→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q11
NAT[2 Marks]
A silica-glass fiber has a core refractive index of 1.47 and a cladding refractive index of 1.44. If the cladding is completely stripped out and the core is dipped in water having a refractive index of 1.33, the numerical aperture of the modified fiber is (rounded off to three decimal places).
GATE→2022→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q12
MCQ[1 Mark]
A sinusoidal carrier wave with amplitude AcA_{c} and frequency fcf_{c} is amplitude modulated... The message signal that can be retrieved completely using envelope detection is
GATE→2022→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q13
NAT[1 Mark]
Consider 24 voice signals being transmitted without latency using time-division multiplexing... the bit-duration (in microseconds) is (round off to two decimal places).
GATE→2022→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q14
NAT[1 Mark]
A photodiode is made of a semiconductor with a bandgap of 1.42 eV... the cut-off wavelength (in nanometers) of the photodiode is (round off to one decimal place).
GATE→2022→Communication and Optical Instrumentation→Communication and Optical Instrumentation
Q15
MCQ[2 Marks]
A car is moving collinearly with a laser beam emitted by a transceiver... the average speed of the car in this interval is