GATE EC Communications questions

An AM signal is detected using an envelope detector. The carrier frequency and modulating signal frequency are $1 \; \mathrm{MHz}$ and $2 \; \mathrm{kHz}$ respectively. An appropriate value for the time constant of the envelope detector is

An AM signal and a narrow-band FM signal with identical carriers, modulating signals and modulation indices of $0.1$ are added together. The resultant signal can be closely approximated by

In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval $t_{1} < t < t_{2}.$ This indicates that during this interval

The value of $\mathrm{C}$ required for sinusoidal oscillations of frequency $1 \; \mathrm{kHz}$ in the circuit of given figure is

A $1 \mathrm{~mW}$ video signal having a bandwidth of $100 \; \mathrm{MHz}$ is transmitted to a receiver through a cable that has $40 \mathrm{~dB}$ loss. If the effective one-sided noise spectral density at the receiver is $10^{-20}$ Watt $/ \mathrm{Hz}$, then the signal-to-noise ratio at the receiver is

A $100 \; \mathrm{MHz}$ carrier of $1 \mathrm{~V}$ amplitude and a $1 \; \mathrm{MHz}$ modulating signal of $1 \mathrm{~V}$ amplitude are fed to a balanced modulator. The output of the modulator is passed through an ideal high-pass filter with cut-off frequency of $100 \; \mathrm{MHz}$. The output of the filter is added with $100 \; \mathrm{MHz}$ …

Two sinusoidal signals of same amplitude and frequencies $10 \; \mathrm{kHz}$ and $10.1 \; \mathrm{kHz}$ are added together. The combined signal is given to an ideal frequency detector. The output of the detector is

Consider a binary digital communication system with equally likely $0$'s and $1$'s. When binary 0 is transmitted the voltage at the detector input can lie between the levels $-0.25 \mathrm{~V}$ and $+0.25 \mathrm{~V}$ with equal probability: when binary $1$ is transmitted, the voltage at the detector can have any value between $0$ and …

Choose the correct one from among the alternatives $\mathrm{A}, \mathrm{B}, \mathrm{C}, \mathrm{D}$ after matching an item from Group $1$ with the most appropriate item in Group $2.$ …

Three analog signals, having bandwidths $1200 \mathrm{~Hz}$, $600 \mathrm{~Hz}$ and $600 \mathrm{~Hz}$, are sampled at their respective Nyquist rates, encoded with $12$ bit words, and time division multiplexed. The bit rate for the multiplexed signal is

A source produces binary data at the rate of $\text{10 kbps.}$ The binary symbols are represented as shown in the figure given below. The source output is transmitted using two modulation schemes, namely Bìnary PSK (BPSK) and Quadrature PSK (QPSK). Let $\mathrm{B}_{1}$ and $\mathrm{B}_{2}$ be the bandwidth requirements of BPSK and QPSK respectively. …

In a microwave test bench, why is the microwave signal amplitude modulated at $1 \; \mathrm{kHz}$?

A signal is sampled at $8 \; \mathrm{kHz}$ and is quantized using $8$-bit uniform quantizer. Assuming $\mathrm{SNR}_q$ for a sinusoidal signal, the correct statement for $P C M$ signal with a bit rate of $R$ is

The input to a coherent detector is DSB-SC signal plus noise. The noise at the detector output is

The noise at the input to an ideal frequency detector is white. The detector is operating above threshold. The power spectral density of the noise at the output is

At a given probability of error, binary coherent $\text{FSK}$ is inferior to binary coherent $\text{PSK}$ by

A DSB-SC signal is to be generated with a carrier frequency $f_{t}=1 \; \mathrm{MHz}$ using a non-linear device with the input-output characteristic $$v_{0}=a_{0} v_{i}+a_{1} v_{i}^{3}$$ where $a_{0}$ and $a_{1}$ are constants. The output of the non-linear device can be filtered by an appropriate band-pass filter. Let …

The data for Q. 75-76 are given below. Solve the problems and choose the correct answers. Let $m(t)=\cos \left[\left(4 \pi \times 10^{3}\right) t\right]$ be the message signal and $\left.c(t)=5 \cos \left[2 \pi \times 10^{b}\right) t\right]$ be the carrier $c(t)$ and $m(t)$ are used to generate an AM signal. The modulation index of the generated AM …

The data for Q. 75-76 are given below. Solve the problems and choose the correct answers. Let $m(t)=\cos \left[\left(4 \pi \times 10^{3}\right) t\right]$ be the message signal and $\left.c(t)=5 \cos \left[2 \pi \times 10^{b}\right) t\right]$ be the carrier $c(t)$ and $m(t)$ are used to generate an $\text{FM}$ signal. If the peak frequency deviation …

Choose the correct one from among the alternative $\text{A, B, C. D}$ after matching an item in Group $1$ with the most appropriate item in Group $2.$ …