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Past Questions
The hexadecimal representation of (567)8 is -
A)
1AF
B)
D77
C)
177
D)
133
To convert a number from Octal (base 8) to Hexadecimal (base 16), the most efficient method is to first convert the octal number to binary and then group the binary digits into sets of four for hexadecimal conversion.
Step 1: Convert Octal (567)₈ to Binary.
Each octal digit represents 3 binary bits:
- 5 = 101
- 6 = 110
- 7 = 111
So, (567)₈ = (101110111)₂
Step 2: Convert Binary (101110111)₂ to Hexadecimal.
Group the binary digits into sets of four, starting from the right (least significant bit). If the leftmost group is incomplete, add leading zeros:
- Group 1: 0111 (Rightmost)
- Group 2: 0111 (Middle)
- Group 3: 0001 (Leftmost, adding leading zeros to '1')
Now, convert each 4-bit group to its hexadecimal equivalent:
- 0001₂ = 1₁₆
- 0111₂ = 7₁₆
- 0111₂ = 7₁₆
Combining these, we get (177)₁₆.
Verification via Decimal:
(567)₈ = (5 × 8²) + (6 × 8¹) + (7 × 8⁰) = (5 × 64) + (6 × 8) + (7 × 1) = 320 + 48 + 7 = 375₁₀
(177)₁₆ = (1 × 16²) + (7 × 16¹) + (7 × 16⁰) = (1 × 256) + (7 × 16) + (7 × 1) = 256 + 112 + 7 = 375₁₀
The results match perfectly. Therefore, option c is correct.
Which of the following is not a dipole antenna?
A)
Yagi-Uda antenna
B)
Rhombic antenna
C)
Parabolic antenna
D)
Horn antenna
To solve this question, we must distinguish between wire-based antennas (which can be derived from or categorized as dipole-type antennas) and aperture antennas.
1. **Yagi-Uda antenna**: This is a directional antenna consisting of a driven element (which is a half-wave dipole) and several parasitic elements (reflectors and directors). Since its core radiating element is a dipole, it is categorized as a dipole-based antenna.
2. **Rhombic antenna**: This is a long-wire antenna shaped like a rhombus. It is essentially a folded dipole or a variation of a wire antenna used for HF communication. It falls under the broad category of wire/dipole antennas.
3. **Parabolic antenna**: While the dish itself is a reflector, the 'feed' used to illuminate the dish is almost always a dipole antenna (or a small horn). In many textbook contexts, the system is viewed as a dipole with a reflector.
4. **Horn antenna**: A horn antenna is an 'aperture antenna'. It is a waveguide that flares out to transition from a guided wave to a free-space wave. It does not use a dipole as its radiating element; instead, it uses the open end of the flared waveguide to radiate.
Therefore, the Horn antenna is fundamentally different in construction and operation from dipole-based antennas.
A frequency-modulated signal is given by s(t) = 10cos(2p × 106t + 3sin(2,000p t) + 4sin(4,000p t). The modulation index of given FM wave is -
A)
3
B)
4
C)
5
D)
7
Step-by-step solution:
1. **Identify the General Equation of an FM Signal**:
The general expression for a frequency-modulated signal is given by:
s(t) = A cos(2πf_c t + φ(t))
where φ(t) is the phase deviation.
2. **Analyze the Given Equation**:
The given signal is s(t) = 10 cos(2π × 10^6 t + 3sin(2,000π t) + 4sin(4,000π t)).
Comparing this to the general form, the phase deviation is:
φ(t) = 3sin(2,000π t) + 4sin(4,000π t).
3. **Understand the Modulation Index (β)**:
For a single-tone FM signal, the modulation index is the peak value of the phase deviation. For a multi-tone FM signal (composite signal), the total modulation index (β_total) is the peak value of the total phase deviation φ(t).
4. **Calculate the Peak Phase Deviation**:
φ(t) = 3sin(2,000π t) + 4sin(4,000π t).
To find the maximum value of φ(t), we look for the point where the sinusoids align.
Since the frequencies are harmonics (2,000π and 4,000π), we check for the maximum value.
The maximum value of a sum of sinusoids occurs when they reach their peaks.
Max(φ(t)) = |3| + |4| = 7.
(Specifically, at t = 1/4000 seconds, sin(2000πt) = sin(π/2) = 1 and sin(4000πt) = sin(π) = 0. However, the peak of the combined function occurs where the derivative is zero. For φ(t) = 3sin(ωt) + 4sin(2ωt), the maximum value is reached when the components constructively interfere. In this specific case, the peak value of the phase deviation is the sum of the individual modulation indices for the components: β_total = β1 + β2 = 3 + 4 = 7).
5. **Conclusion**:
The modulation index of the given FM wave is 7.
Comparing with options:
- a. 3 (Incorrect: only considers the first component)
- b. 4 (Incorrect: only considers the second component)
- c. 5 (Incorrect)
- d. 7 (Correct: sum of the modulation indices)
Aliasing in the context of programming language refers to -
A)
Multiple variables having the same memory location.
B)
Multiple variables having the same value.
C)
Multiple variables having the same identifier.
D)
Multiple uses of same variable.
Aliasing occurs when a single memory location is accessible through different symbolic names (identifiers) in a program. This is a common occurrence in languages that support pointers or references. For example, in C++, if you create a reference variable 'int &ref = x;', both 'x' and 'ref' refer to the same memory address. Any change made to 'ref' will directly affect 'x' because they are aliases for the same location.
Why other options are incorrect:
- Option (b): Multiple variables having the same value is simply called 'value equality'. Two different memory locations can hold the same value without being aliases.
- Option (c): Multiple variables cannot have the same identifier within the same scope, as this would cause a compilation error (naming collision).
- Option (d): Multiple uses of the same variable is simply standard variable usage or referencing, not aliasing.
In Frequency Division Multiplexing (FDM) system, cross talk occurs due to -
A)
Imperfect time synchronization between transmitter and receiver
B)
Imperfect filtering at the receiver front end
C)
Imperfect carrier recovery at the receiver
D)
Channel noise
In Frequency Division Multiplexing (FDM), multiple signals are transmitted simultaneously over a single channel by assigning each signal a different carrier frequency. To prevent interference, 'guard bands' (unused frequency slots) are placed between the allocated channels. At the receiver end, Band Pass Filters (BPF) are used to isolate the desired channel from the others.
1. Why 'b' is correct: Cross talk occurs when a signal from one channel leaks into another. If the filters at the receiver front end are 'imperfect' (i.e., they have a slow roll-off or insufficient selectivity), they fail to completely reject the adjacent frequency channels. This results in the overlapping of signals, which is perceived as cross talk.
2. Why 'a' is incorrect: Time synchronization is a critical requirement for Time Division Multiplexing (TDM), not FDM. In FDM, signals are separated by frequency, not time.
3. Why 'c' is incorrect: Imperfect carrier recovery leads to phase jitter or frequency offset, which affects the demodulation quality of a single signal, but it does not cause the leakage of one channel into another (cross talk).
4. Why 'd' is incorrect: Channel noise (like AWGN) adds random interference to the signal, reducing the Signal-to-Noise Ratio (SNR), but it is not the cause of cross talk, which is specifically the interference between two distinct communication channels.
Which diode is not used as a microwave mixer or detector?
A)
Schottky barrier
B)
PIN
C)
Crystal
D)
Backward
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'PIN' (Option B).
Consider DMS with two symbols X1 and X2 encoded as follows: X1 (P(X1)=0.9, Code=0), X2 (P(X2)=0.1, Code=1). The efficiency ç is
A)
80%
B)
24%
C)
22.69%
D)
46.9%
Based on established principles in the relevant subject area, the correct and most appropriate choice is '46.9%' (Option D).
If the bits 0 and 1 are transmitted using bipolar pulses, the minimum bandwidth required for the transmission is
A)
64 KHz
B)
32 KHz
C)
8 KHz
D)
4 KHz
Based on established principles in the relevant subject area, the correct and most appropriate choice is '64 KHz' (Option A).
In amplitude modulation, the modulation envelope has a peak value which is double the unmodulated carrier value. What is the value of the modulation index.
A)
25%
B)
100%
C)
75%
D)
50%
Based on established principles in the relevant subject area, the correct and most appropriate choice is '50%' (Option D).
In a delta modulation, the granular error distortion can be reduced by
A)
Decreasing the sampling rate.
B)
Increasing the sampling rate.
C)
Decreasing the step size.
D)
Increasing the step size.
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Decreasing the step size.' (Option C).
A rectangular waveguide with internal dimensions of a=4cm and b=3cm is to be operated in TE11 mode. The minimum operating frequency is
A)
6.25 GHz
B)
6.00 GHz
C)
5.00 GHz
D)
3.75 GHz
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is '5.00 GHz' (Option C).
Which of the following microwave diodes is suitable for very low power oscillator only?
A)
IMPATT
B)
TUNNEL
C)
LSA
D)
GUNN
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'GUNN' (Option D).
Operating wavelength and bandwidth of a certain antenna are 3 cm and 100 MHz respectively. The Q-factor is
A)
100
B)
200
C)
300
D)
1000
Based on established principles in the relevant subject area, the correct and most appropriate choice is '300' (Option C).
A 3m diameter circular reflector antenna operates at 10 GHz. Its length efficiency is 0.7 and its radiation efficiency is 0.9. The beam width is
A)
0.410
B)
0.610
C)
0.800
D)
0.500
Based on established principles in the relevant subject area, the correct and most appropriate choice is '0.410' (Option A).
If Z0 is the characteristics wave impedance of free space, then the characteristics wave impedance Z of a waveguide for TEmn is given by
A)
Z = Z0 (1-(λ/λc)^2)
B)
Z = Z0 / (1-(λ/λc)^2)
C)
Z = 0
D)
Z = Z0 (1-(λ/λc)^2)^2
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'Z = Z0 (1-(λ/λc)^2)' (Option A).
An air-filled rectangular waveguide has inner dimensions of 3cm × 2cm. The wave impedance of the TE10 mode of propagation in the waveguide at a frequency of 30 GHz is (free space impedance Z0 = 377 Ω).
A)
308 W
B)
355 W
C)
400 W
D)
461 W
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is '355 W' (Option B).
The output of the two arms of an E-plane Tee are
A)
In the same phase.
B)
90° out of phase.
C)
180° out of phase.
D)
45° out of phase.
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'In the same phase.' (Option A).
In a microwave test bench, why is the microwave signal amplitude modulated at 1 KHz?
A)
To increase the sensitivity of measurement.
B)
To transmit the signal to a far-off place.
C)
To study amplitude modulation.
D)
Because crystal detector fails at microwave frequencies.
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'To increase the sensitivity of measurement.' (Option A).
8085 microprocessor is a
A)
Zero address microprocessor.
B)
One address microprocessor.
C)
Two address microprocessor.
D)
Eight address microprocessor.
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'Zero address microprocessor.' (Option A).
A mast antenna consisting of a 50m long vertical conductor operates over a perfectly conducting ground plane. It is base-fed at a frequency of 600 KHz. The radiation resistance of the antenna is
A)
2π²/5 Ω
B)
π²/5 Ω
C)
4π²/5 Ω
D)
20π²/5 Ω
Based on established principles in the relevant subject area, the correct and most appropriate choice is '4π²/5 Ω' (Option C).
The dominant mode in a circular waveguide is
A)
TE10
B)
TE11
C)
TM10
D)
TM11
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'TE10' (Option A).
The radiation pattern of an antenna in spherical co-ordinates is given by F(θ)=Cos^4(θ), 0≤θ≤π/2. The directivity of the antenna is
A)
10 dB
B)
12.6 dB
C)
11.5 dB
D)
18 dB
Based on established principles in the relevant subject area, the correct and most appropriate choice is '18 dB' (Option D).
The number of memory cycles required to execute the following 8085 instructions: I. LDA 3000H, II. LXI D, F0F1H would be
A)
2 for (I) and 2 for (II).
B)
4 for (I) and 3 for (II).
C)
3 for (I) and 3 for (II).
D)
3 for (I) and 4 for (II).
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is '2 for (I) and 2 for (II).' (Option A).
The TE10 mode is to propagate through a rectangular waveguide of dimensions a=1.5cm and b=1cm. The signal frequency is 8 GHz. The waveguide is initially filled with air. In this case, TE10 mode
A)
Cannot propagate as the propagation wavelength is higher than the cut-off wavelength.
B)
Will propagate as the propagating wavelength is lower than the cut-off wavelength.
C)
Cannot propagate as the propagating wavelength is lower than the cut-off wavelength.
D)
Will propagate as the propagating wavelength is higher than the cut-off wavelength.
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'Will propagate as the propagating wavelength is lower than the cut-off wavelength.' (Option B).
Klystron operates on the
A)
Principle of velocity modulation.
B)
Principle of pulse modulation.
C)
Principle of phase modulation.
D)
Principle of amplitude modulation.
Based on established principles in Electrical / Electronics Engineering, the correct and most appropriate choice is 'Principle of velocity modulation.' (Option A).