GATE EC Communications questions

The peak-to-peak input to an $8$-bit $\text{PCM}$ coder is $2$ volts. The signal power-to-quantization noise power ratio (in $d\text{B}$) for an input of $0.5 \cos \left(\omega_{m} t\right)$ is

The maximum usable frequency of an ionospheric layer at $60^{\circ}$ incidence and with $8 \; \mathrm{mHz}$ critical frequency is

The spectral density of a real valued random process has

For a given data rate, the bandwidth $\mathrm{B}_{p}$ of a $\text{BPSK}$ signal and the bandwidth $\text{B}_{0}$ of the $\mathrm{OOK}$ signal are related as

Compression in $\text{PCM}$ refers to relative compression of

Quadrature multiplexing is

A $\text{DSB-SC}$ signal is generated using the carrier $\cos \left(\omega_{c}, t+\theta\right)$ and modulating signal $x(t)$. The envelope of the $\text{DSB-SC}$ signal is

In a $\text{PCM}$ system with uniform quantisation, increasing the number of bits from $8$ to $9$ will reduce the quantisation noise power by a factor of

The image channel selectivity of superheterodyne receiver depends upon

The line code that has zero $\text{dc}$ component for pulse transmission of random binary data is

A parabolic dish antenna has a conical beam $2^{\circ}$ wide, the directivity of the antenna is approximately

An amplifier A has $6 \; d \mathrm{B}$ gain and $50 \; \Omega$ input and output impedances. The noise figure of this amplifier as shown in the figure is $(a)$ is $3 \; d \mathrm{B}$. A cascade of two such amplifiers as in the figure is will have a noise figure of

The power spectral density of a deterministic signal is given by $\left[\sin (f) / f^{2}\right]$ where $f$ is frequency. The autocorrelation function of this signal in the time domain is

A communication channel has first-order low pass transfer function. The channel is used to transmit pulses at a symbol rate greater than the half-power frequency of the low pass function. Which of the network shown in the figure is can be used to equalise the received pulses?

The image channel rejection in a superheterodyne receiver comes from

A $1 \mathrm{~km}$ long microwave link uses two antennas each having $30 \mathrm{~dB}$ gain. If the power transmitted by one antenna is $1 \mathrm{~W}$ at $3 \; \mathrm{GHz}$, the power received by the other antenna is approximately

The critical frequency of an ionospheric layer is $10 \; \mathrm{MHz}$. What is the maximum launching angle from the horizon for which $20 \; \mathrm{MHz}$ wave will be reflected by the layer?

An $\text{FM}$ signal with a modulation index $9$ is applied to a frequency tripler. The modulation index in the output signal will be

The number of bits in a binary $\mathrm{PCM}$ system is increased from $n$ to $n+1$. As a result, the signal to quantization noise ratio will improve by a factor

A $\text{PAM}$ signal can be detected by using