Q: A certain 8 bit uniform quantization PCM system can accommodate a signal ranging from - 1 V to + V. The rms value of the signal is V . The signal to quantization noise ratio is:

(SNR)dB = 1.76 + 6.02n n = 8 Thus (SNR)dB = 1.76 + 6.02 x 8 = 49.92 dB.

Question 1

For a given voltage, four heating coils will produce maximum heat when connected

Accepted Answer

.

Question 2

A radar receiver has a noise figure of 10 dB at 300 K having a bandwidth of 2.5 MHz. The minimum power it can receive is

Accepted Answer

Pm = kT0Δf(F - 1) = 93.15 x 10-15 W.

Question 3

Consider the probability density f(x) = ae-b|x| where x is a random variable whose allowable values range from x = - ∞ to x = + ∞. P(1 ≤ x ≤ 2)

Accepted Answer

P(x) = ae-b|x|dx to get apply aebxdx + ae-bxdx, we get = .

Question 4

Find 'X' in the circuit below : f1(A, B, C, D) = Σ(6, 7, 13, 14); f2(A, B, C, D) = Σ(3, 6, 7); f3(A, B, C, D) = Σ(5, 6, 7, 14, 15)

Accepted Answer

f1(A, B, C, D) = ∑(6, 7, 13, 14) f2(A, B, C, D) = ∑(3, 6, 7) f1 ⊕ f2 = ∑(3, 13, 14) f3 x (f1 ⊕ f2) = ∑(14) = y X = f1 x y ⇒ ∑14.

Question 5

The gradient of any scalar field always yields __________ .

Accepted Answer

Dot product is conservative. Gradient is nothing but dot product.

Question 6

The antenna current of an AM transmitter is 8 A, when only the carrier is sent, but it increases to 8.93 A when the carrier is modulated by a single sine wave. Determine the antenna current when the percent of modulation changes to 0.8

Accepted Answer

Ic = 8 A m = 0.8 = 8 x 1.149 = 9.19 A.

Question 7

Consider the signal flow graph shown in figure below. The gain is :

Accepted Answer

P1 = abcd L1 = be, L2 = cf, L3 = dg Δ1 = 1 .

Question 8

In the following non planar graph number of independent loop equations are

Accepted Answer

Number of independent loop equations are given by, L = B - N + 1 where L : No. of loop equations B : No. of branches = 12 N : No. of nodes = 8 L = 12 - 8 + 1 = 5.

Question 9

The amplifier circuit shown below uses a silicon transistor. The capacitors Cc and CE can be assumed to be short at signal frequency and the effect of output resistance r0 can be ignored. If CE is disconnected from the circuit, which one of the foll…

Accepted Answer

Given circuit after removing CE will behave as current-series feedback. Overall voltage gain will decrease as feedback signal comes into picture and since it is current-series feedback, input impedance increases.

Question 10

Consider the amplitude modulated (AM) signal Ac cos ωct + 2 cos ωmt cos ωct For demodulating the signal using envelope detector, the minimum value of Ac should be

Accepted Answer

AC cos ωct + 2 cos ωmt cos ωct AC cosωct for envelope detection μ < 1 ⇒ < 1 ⇒ Ac should be at least-2.

Question 11

A unity-feedback control system has the open loop transfer function . If the input system is a unit ramp, the steady state error will be

Accepted Answer

.

Question 12

A certain 8 bit uniform quantization PCM system can accommodate a signal ranging from - 1 V to + V. The rms value of the signal is V . The signal to quantization noise ratio is:

Accepted Answer

(SNR)dB = 1.76 + 6.02n n = 8 Thus (SNR)dB = 1.76 + 6.02 x 8 = 49.92 dB.

Question 13

In a semiconductor material. The hole concentration is found to be 2 x 2.5 x 1015 cm-3. If mobility of carriers is 0.13 m2/ v-s. Then find the current density if electric field intensity is 3.62 x 10-19

Accepted Answer

Current density J = σE Where σ = conductivity Given -> μ = 0.13 m2/v-s = 0.13 x 104 cm2/V sec P = 2.25 x 1015/cm3 We have, ∴ ni = 1.5 x 1010 Also n.p. = ∴ n = /p = (1.6 x 10-19 x 0.13 x 104 x 2.25 x 1015) x = (0.468) (4.5 x 1015) σ = 2.106 x 1015 μ/cm J = σE ∴ Current density = 2.106 x 1015 x 3.620 x 10-19 = 7.6237 x 10-4 A/m2.

Question 14

The analog signal given below is sampled at 1200 samples per second. m(t) = 2 sin 120 pt + 3 sin 240 pt + 4 sin 360 pt + 5 sin 480 pt + 6 sin 600 pt + 7 sin 720 pt. The folding (maximum) frequency is __________ .

Accepted Answer

Folding frequency (max.) = = 600 Hz.

Question 15

A rectangular waveguide, in dominant TE mode, has dimensions 10 cm x 15 cm. The cut off frequency is

Accepted Answer

For TE10 mode

Question 16

A noiseless 3 KHz channel can transmit binary at the rate __________ .

Accepted Answer

Maximum data rate for noiseless channel is given by Nyquist Theorem = 2H log2 V bits/sec V - discrete levels (Here Binary i.e. 2) H - Bandwidth ∴ Maximum data rate = 2H log2 V = 2(3 KHz) log2 2 = 2 x 3 x 103 x 1 = 6 x 103 = 6000 bps.

Question 17

Radiation resistance of an antenna is 54 Ω and loss resistance is 6 Ω. If antenna has power gain of 10, then directivity is:

Accepted Answer

Efficiency of antenna Power gain = 10 Thus directivity .

Question 18

Consider a unity feedback control system with open-loop transfer function The steady state error of the system due to a unity step input is :

Accepted Answer

.

Question 19

When phase-lag compensation is used in a system, then gain cross over frequency, bandwidth and undamped frequency are respectively

Accepted Answer

Phase lag is delay between a correcting signal of control system and response to it.

Question 20

What is the propagation constant for air filled wave guide with dimensions a = 1.59" and b = 0.795" at 4.95 GHz?

Accepted Answer

Here, a = 1.59'' = 40.386 mm = 4.04 cm ∴ .

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