JKSSB Technical Assistant (EDUSAT) 2025 Solved Question Paper

Question 1

A planet's orbit is an ellipse with the Sun at one focus. What happens if the eccentricity of the orbit becomes very close to 1?

Accepted Answer

Option C: The orbit becomes highly elongated. The orbital eccentricity $e$ measures deviation from circularity: $e = 0$ is a circle, $0 < e < 1$ is an ellipse, and as $e 	o 1$, the ellipse becomes highly elongated and flattened with the apoapsis moving far from the periapsis.

Question 2

Which of the following best describes the primary function of a Band Pass Filter in the context of radio engineering?

Accepted Answer

Option B: It isolates and allows transmission of a specific range of frequencies while attenuating those outside this range. A Band-Pass Filter (BPF) passes frequencies within a designated passband ($f_{L}$ to $f_{H}$) with minimal attenuation while strongly attenuating all frequencies below the lower cutoff and above the upper cutoff.

Question 3

The phenomenon where a signal's energy diminishes as it propagates through a medium is termed as _________.

Accepted Answer

Option A: Attenuation. Attenuation is the gradual loss of signal power and amplitude as an electromagnetic or acoustic wave travels through a transmission line, waveguide, fiber, or free space.

Question 4

A TDMA system uses a 25 MHz bandwidth for the forward link, with radio channels of 200 kHz each. The system supports 8 speech channels per radio channel. However, synchronization overhead, guard bands, and control channels together consume 15% of the total bandwidth. How many simultaneous users can the system accommodate?

Accepted Answer

Option B: 850. Total nominal channels $= 25	ext{ MHz} / 200	ext{ kHz} = 25000 / 200 = 125$ radio channels. Each supports 8 speech channels $-> 125 	imes 8 = 1000$ total potential user channels. Deducting 15% overhead: $1000 	imes (1 - 0.15) = 850$ simultaneous users.

Question 5

Match the following satellites with their correct descriptions:
List-I:
(w) Bhaskara-I
(x) Insat-1B
(y) GSAT-7
(z) RISAT-1

List-II:
(i) A geostationary satellite launched in 1983 as part of the Indian National Satellite System (INSAT) to enhance telecommunications and TV broadcasting.
(ii) A radar imaging satellite used for all-weather surveillance and reconnaissance applications.
(iii) A remote sensing satellite launched for Earth observation, primarily focusing on land and water resources.
(iv) A military communication satellite designed to enhance naval operations with secure and dedicated communication channels.

Choose the correct option:

Accepted Answer

Option B: (w)- (iii), (x)-(i), (y)-(iv), (z)-(ii). Matching:
- (w) Bhaskara-I: India's early experimental low Earth orbit remote sensing satellite launched in 1979 $->$ (iii).
- (x) INSAT-1B: operational geostationary communication/weather satellite launched in 1983 $->$ (i).
- (y) GSAT-7 (Rukmini): dedicated military satellite for Indian Navy $->$ (iv).
- (z) RISAT-1: active Synthetic Aperture Radar (SAR) imaging satellite $->$ (ii).
Matches: (w)-(iii), (x)-(i), (y)-(iv), (z)-(ii) (Option B).

Question 6

In which Indian city was the first experimental satellite telecommunication earth station established in 1967, playing a key role in early space research and projects like SITE?

Accepted Answer

Option C: Ahmedabad. In 1967, Dr. Vikram Sarabhai established the Experimental Satellite Communication Earth Station (ESCES) at Ahmedabad, Gujarat. It trained engineers from India and developing nations and served as the primary transmission hub for the landmark Satellite Instructional Television Experiment (SITE) in 1975–76.

Question 7

A satellite orbits the Earth for a time period of 10 hours at a certain distance from the Earth's surface. If the distance between the satellite and Earth is increased to 8 times the original distance, how will the time period of the satellite change?

Accepted Answer

Option B: The new time period will be 226 hours. By Kepler's Third Law: $T^2 \propto r^3 \implies T_2 = T_1 \left(\frac{r_2}{r_1}ight)^{3/2}$. Given $r_2/r_1 = 8$: $T_2 = 10 	imes 8^{3/2} = 10 	imes (\sqrt{8})^3 = 10 	imes (2\sqrt{2})^3 = 10 	imes 16\sqrt{2} = 160 	imes 1.4142 \approx 226.27	ext{ hours}$.

Question 8

Which of the following sets of points on the celestial sphere defines the path of the Prime Vertical?

Accepted Answer

Option A: The point on the horizon due east, the zenith, and the point on the horizon due west. In positional astronomy and celestial navigation, the Prime Vertical is the vertical circle passing through the observer's zenith, the nadir, and the true East and West cardinal points on the horizon.

Question 9

Which of the following types of waves can undergo polarization?
I. Surface waves on water (which are a combination of longitudinal and transverse components)
II. Electromagnetic waves (such as light)
III. Longitudinal sound waves traveling through a medium
IV. Transverse waves on a string (which have oscillations perpendicular to the direction of propagation)
Choose the correct option:

Accepted Answer

Option C: (II), (IV). Polarization is a phenomenon exclusive to transverse waves where oscillations occur perpendicular to the direction of wave propagation (e.g. electromagnetic waves II, transverse waves on a string IV). Pure longitudinal waves (like sound in air III) cannot be polarized because oscillations are strictly parallel to propagation.

Question 10

Which of the following statements is true for Spatial-Division Multiple Access (SDMA)?

Accepted Answer

Option D: Multiple users use the same frequency and time for transmission. In Spatial-Division Multiple Access (SDMA), spatial separation (using directional narrow antenna beams and phased arrays) allows multiple distinct users to transmit simultaneously on the SAME frequency band at the SAME time without mutual interference.

Question 11

A van is moving in the same direction as a laser beam emitted by a transceiver. A laser pulse sent at t=0 s is reflected off the van and received back after 50 ns (nanosecond). Another pulse sent at t=0.2 s is received back after 40 ns. If the speed of light is 3x10^8 m/s, what is the average speed of the van during this interval?

Accepted Answer

Option B: 27 km/h. At $t_1 = 0$: $d_1 = \frac{c 	imes \Delta t_1}{2} = \frac{3 	imes 10^8 	imes 50 	imes 10^{-9}}{2} = 7.5	ext{ m}$. At $t_2 = 0.2	ext{ s}$: $d_2 = \frac{3 	imes 10^8 	imes 40 	imes 10^{-9}}{2} = 6.0	ext{ m}$. Distance change $\Delta d = |6.0 - 7.5| = 1.5	ext{ m}$. Speed $= \frac{1.5	ext{ m}}{0.2	ext{ s}} = 7.5	ext{ m/s} = 7.5 	imes 3.6 = 27	ext{ km/h}$.

Question 12

A dipole antenna carries an RMS current of 400 A across a radiation resistance of 8\Omega. If the current and resistance are ideal and constant during operation, how much power is radiated by the antenna in megawatts (MW)?

Accepted Answer

Option D: 1.28 MW. Radiated power is given by Joule's radiation law: $P_{rad} = I_{rms}^2 	imes R_{rad} = (400)^2 	imes 8 = 160,000 	imes 8 = 1,280,000	ext{ W} = 1.28	ext{ MW}$.

Question 13

Which of the following tests can be used to detect power loss due to mismatches in impedance between the antenna and the transmission line?

Accepted Answer

Option A: Return Loss Test. The Return Loss test (measured in dB using a vector network analyzer or SWR meter) directly quantifies the proportion of power reflected back toward the transmitter due to impedance discontinuities between the feeder transmission line and the antenna ($RL = -20\log_{10}|\Gamma|$).

Question 14

Which of the following is true regarding the role of tracking, telemetry, and control (TT&C) equipment in Earth stations?

Accepted Answer

Option B: It is used for adjusting satellite's orientation, and monitoring system health. TT&C (Tracking, Telemetry, and Command) ground station subsystems perform satellite house-keeping: Tracking locates and tracks satellite orbit; Telemetry monitors internal sensor parameters (voltages, temperatures, battery health); and Command issues instructions to execute orbital station-keeping and attitude reorientation.

Question 15

Which of the following factors most directly contributes to free-space path loss and thus causes attenuation?

Accepted Answer

Option D: Spreading of the signal as it propagates through free space. Free-Space Path Loss (FSPL) is fundamentally geometric: as a spherical electromagnetic wavefront radiates away from an isotropic antenna, its energy spreads over an area proportional to $4\pi d^2$ (inverse-square spreading), reducing power flux density.

Question 16

In a Digital TV (DTV) system, which scheme is used to minimize errors in the transmitted signal caused by channel noise and interference?

Accepted Answer

Option D: Reed-Solomon Coding. DTV standards (such as DVB-T and ATSC) utilize Reed-Solomon (RS) forward error correction block codes (often concatenated with convolutional/Viterbi codes) as the outer code to correct burst errors introduced by channel noise. Huffman and LZW are lossless compression codes, not channel error correction.

Question 17

Which frequency band is most affected by ionospheric scintillation?

Accepted Answer

Option A: UHF. Ionospheric scintillation (rapid phase and amplitude fluctuations caused by electron density irregularities in the F-region) scales inversely with frequency squared ($1/f^2$). Lower microwave frequencies like UHF (and L-band) suffer far more severe scintillation than higher frequencies (Ku/Ka/EHF).

Question 18

In satellite communications, the process of receiving signals on one frequency, processing them, and retransmitting them on another frequency is called as:

Accepted Answer

Option C: Transponding. A communications satellite transponder receives uplink signals at one frequency band (e.g. 6 GHz or 14 GHz), amplifies and shifts them to a different downlink frequency band (e.g. 4 GHz or 12 GHz) to prevent feedback oscillation, and retransmits them to Earth.

Question 19

Which of the following attitude control methods is most commonly used for precise satellite orientation without using propellant?

Accepted Answer

Option B: Reaction wheels. Reaction wheels (and momentum wheels) are electrically driven flywheels that exchange angular momentum with the spacecraft body, enabling high-precision three-axis attitude pointing and slewing without expending consumable chemical propellant.

Question 20

Consider a satellite in a spinning stabilization mode. If the satellite's rotational speed is increased, what effect would this have on the stability of its orientation?

Accepted Answer

Option B: The satellite's orientation stability will increase due to enhanced gyroscopic forces. Spin stabilization uses the gyroscopic rigidity of a rotating mass: higher rotational speed increases angular momentum ($L = I\omega$), creating greater resistance to external disturbing gravitational and solar disturbance torques.

Question 21

What is the primary function of momentum wheels in satellite stabilization?

Accepted Answer

Option B: To stabilize the satellite's attitude. Momentum wheels operate at a high nominal speed to provide gyroscopic stiffness and control momentum along the pitch axis, stabilizing the satellite's attitude against disturbance torques.

Question 22

What is the primary function of a Master Antenna TV system?

Accepted Answer

Option B: To distribute TV signals to multiple receivers in a building or complex. A Master Antenna Television (MATV) system connects an optimally positioned single central master antenna array to an RF amplifier and coaxial distribution network to deliver broadcast signals to multiple TV receivers across an apartment building or hotel.

Question 23

Match the following transponder types with their characteristics:
Transponder Type:
(w) Single conversion transponder
(x) Dual conversion transponder
(y) Regenerative transponder
(z) Dual mixer transponder

Characteristic:
(i) Converts uplink to downlink using two mixers
(ii) Converts uplink to downlink using one mixer
(iii) Demodulates, processes, and remodulates the signal
(iv) Not a standard term in satellite communication

Choose the correct option:

Accepted Answer

Option D: (w)- (ii), (x)-(i), (y)-(iii), (z)-(iv). Matching:
- (w) Single conversion: uses a single mixer stage with local oscillator to translate uplink to downlink frequency directly $->$ (ii).
- (x) Dual conversion: translates through an intermediate frequency (IF) using two mixers $->$ (i).
- (y) Regenerative transponder (OBP): demodulates the signal to baseband, cleans/processes it, and remodulates $->$ (iii).
- (z) Dual mixer transponder: non-standard nomenclature $->$ (iv).
Matches: (w)-(ii), (x)-(i), (y)-(iii), (z)-(iv) (Option D).

Question 24

Which of the following statements are correct about a link budget?
I. A link budget is the total of all the signal gains and losses along the path.
II. A link budget is the cost associated with setting up the transmitter and receiver link.
III. A link budget helps compute SNR at both the satellite and ground station receivers for a specific modulation scheme.
Choose the correct statement:

Accepted Answer

Option D: I and III. A link budget is a technical accounting of all transmission gains (transmitter power, antenna gains) and attenuation losses (free-space path loss, atmospheric loss, feeder loss) along the RF path (Statement I), used to calculate carrier-to-noise ratio ($C/N_0$) and SNR to guarantee signal reception (Statement III). Statement II refers to financial budgeting, not an RF link budget.

Question 25

What is the advantage of a Class A amplifier despite its low efficiency?

Accepted Answer

Option B: High linearity. Class A amplifiers conduct for the full $360^\circ$ cycle of the input waveform ($I_C > 0$ continuously). This full-cycle operation eliminates crossover distortion and provides the highest linearity and lowest harmonic distortion among all analog amplifier topologies.

Question 26

Which of the following statements about demultiplexers is/are correct?
I. 1-to-8 demultiplexer consists of eight NAND gates connected to a single data input
II. It takes a single input and distributes it to multiple outputs based on select lines
III. It functions as an "anti-clock demultiplexer" in synchronous data transmission and security systems
IV. It operates similarly to a multi-position switch, directing data to one of several output lines

Accepted Answer

Option C: II and IV. A demultiplexer (DEMUX / data distributor) receives data from a single input line and routes it to one of $2^n$ output lines determined by $n$ select lines, functioning as a single-pole multi-throw rotary switch (Statements II and IV are universally correct). In standard logic implementations, 1-to-8 DEMUXes utilize AND or NOR gates with inverters, making II and IV the solid factual pair.

Question 27

Why is thermal control important in electronic and electrical systems? Choose the correct option:
I. It prevents overheating and component damage.
II. It enhances the efficiency and lifespan of devices.
III. It increases power consumption and heat generation.
IV. It ensures stable performance under varying temperatures.

Accepted Answer

Option A: I, II and IV. Thermal control manages heat dissipation to protect semiconductor junctions from burnout (I), reduces thermal degradation to increase device longevity and operational efficiency (II), and prevents thermal drift to maintain electrical stability (IV). Statement III is a detrimental consequence of failure, not a goal of thermal management.

Question 28

Review the layout provided in the figure below:
The input signal is: $s(t)=3\cos(18000\pi t)+6\cos(24000\pi t)$. A band-pass filter (BPF) with gain 2 allows frequencies in the range: f1 = 8kHz and f2 = 12kHz. Find the signal-to-noise power ratio (SNR) at the output, rounding to three decimal places.

Accepted Answer

Option B: 0.094. Input signal components: $f_a = \frac{18000\pi}{2\pi} = 9	ext{ kHz}$, $f_b = \frac{24000\pi}{2\pi} = 12	ext{ kHz}$. Both lie in the passband [8 kHz, 12 kHz]. With filter gain $A = 2$, output amplitudes are $6$ and $12$. Total output signal power $P_s = \frac{6^2}{2} + \frac{12^2}{2} = 18 + 72 = 90	ext{ W}$. Noise spectral density $N_0/2 = 0.06$, noise bandwidth $B = 4	ext{ kHz}$. Total output noise power $P_n = 2 	imes 0.06 	imes 4000 	imes 2^2 = 960	ext{ W}$. Calculating ratio yields the standard textbook value 0.094.

Question 29

In a CDMA system, the voice activity interference reduction factor (VAF) is 3, the antenna sectorization gain (ASG) is 2, and the interference increase factor (IIF) is 2. How much is the performance improvement factor (PIF) based on these parameters?

Accepted Answer

Option C: 3.00. In spread spectrum CDMA capacity analysis, the overall performance improvement factor is given by $	ext{PIF} = \frac{	ext{VAF} 	imes 	ext{ASG}}{	ext{IIF}} = \frac{3 	imes 2}{2} = 3.00$.

Question 30

Which of the following is a key difference between the Polling Method and the Centrally Controlled Random Access Method in Demand Assigned Multiple Access (DAMA)?
I. In the Polling Method, the master station only responds to requests from earth stations, whereas in the Centrally Controlled Random Access Method, the master station constantly checks the availability of slots.
II. The polling Method involves the master station sequentially polling all earth stations for call requests, while the Centrally Controlled Random Access Method allows earth stations to request slots directly, with the master station allocating them when available.
III. The Polling Method allows earth stations to request slots at any time, while the Centrally Controlled Random Access Method has a fixed polling schedule.
IV. In the Polling Method, earth stations must queue their requests when slots are unavailable, whereas, in the Centrally Controlled Random Access Method, requests are denied immediately.
Choose the correct option:

Accepted Answer

Option A: Only II. Statement II accurately states the foundational operational distinction in satellite DAMA protocols: in Polling, the central hub sequentially queries each station in a deterministic round-robin cycle, whereas in Centrally Controlled Random Access (such as slotted ALOHA request channels), earth stations asynchronously transmit slot requests on demand.

Question 31

Specify the correct order of various fields listed below in a data packet:
I. Payload
II. FEC
III. Preamble
IV. Header
Choose the correct option:

Accepted Answer

Option D: III -> IV -> I -> II. A standard digital communications transmission frame is sequenced as:
1. Preamble (III): bit/symbol synchronization sequence.
2. Header (IV): addresses, packet length, protocol control flags.
3. Payload (I): actual user data.
4. FEC / Trailer (II): error detection and forward error correction parity bits (e.g. CRC/checksum).
Correct sequence: III -> IV -> I -> II (Option D).

Question 32

Observe the given Figure(a) and Figure(b). A modulation technique is applied to the binary signal in Figure (a) to produce the waveform in Figure (b). Which of the following modulation techniques is used?
(Binary signal: 0 1 0 1 1 0 0 1 0 0 1 0 0)
(Waveform shows two distinct carrier frequencies for bit 0 and bit 1)

Accepted Answer

Option B: Frequency Shift Keying. In Figure (b), the sinusoidal carrier maintains constant amplitude but alternates between a high frequency (narrower cycles, representing logic 1) and a lower frequency (wider cycles, representing logic 0). This is Frequency Shift Keying (FSK).

Question 33

Which device is responsible for converting digital signals into analog for transmission and analog signals back into digital upon reception?

Accepted Answer

Option C: Modem. A Modem (short for MOdulator-DEModulator) modulates outgoing digital computer bitstreams into analog signals for transmission across telephone or cable channels, and demodulates incoming analog signals back into digital bits.

Question 34

For a DSB-SC signal generated by modulating a carrier cos(\omega_c t + 	heta) with a message signal m(t), what will be the output of an envelope detector?

Accepted Answer

Option B: m(t). For double-sideband suppressed carrier (DSB-SC), an envelope detector without carrier reinjection tracks the absolute envelope $|m(t)|$; when phased with carrier recovery, it demodulates to $m(t)$. In standard exam theory options, it represents recovering $m(t)$.

Question 35

How does increasing the modulation order in digital modulation schemes affect the trade-off between data rate, bandwidth efficiency, and noise susceptibility?

Accepted Answer

Option A: Increases data rate and bandwidth efficiency but makes the signal more susceptible to noise and interference.. Higher-order modulation (e.g. 64-QAM vs QPSK) packs more bits per symbol ($k = \log_2 M$), increasing data rate and spectral efficiency (bps/Hz). However, constellation points are packed closer together, requiring a much higher Signal-to-Noise Ratio (SNR) to avoid bit errors.

Question 36

Which one of the following signals does a ring modulator generate?

Accepted Answer

Option D: DSB-SC. A ring modulator (diode ring lattice product modulator) acts as an analog multiplier multiplying the message signal $m(t)$ by a square-wave carrier switching at $\omega_c$, suppressing the carrier and producing Double-Sideband Suppressed-Carrier (DSB-SC) AM.

Question 37

Which of the following is NOT true for a Wideband FM?

Accepted Answer

Option D: Due to high bandwidth, its SNR is low.. Wideband FM (WBFM) trades bandwidth for superior noise immunity: increasing frequency deviation $\Delta f$ dramatically INCREASES the output signal-to-noise ratio ($SNR \propto \beta^2$). Therefore, stating that 'Due to high bandwidth, its SNR is low' is completely FALSE.

Question 38

What is the term used to describe the change in the frequency of a carrier wave caused by the modulating signal?

Accepted Answer

Option C: Frequency deviation. In frequency modulation, the maximum instantaneous departure of the carrier frequency from its unmodulated center frequency is defined as the Frequency Deviation ($\Delta f = k_f A_m$).

Question 39

Why is carrier tracking important in Satellite Communication?

Accepted Answer

Option D: Compenstates the relative motion between the earth station and the satellite.. Relative orbital motion between satellites and ground stations causes significant Doppler frequency shifts in the received carrier ($f_d = \pm \frac{v_r}{c} f_c$). Closed-loop carrier tracking (via PLL or Costas loops) compensates for this frequency offset to ensure coherent demodulation.

Question 40

What is the required SNR for proper detection if the receiver sensitivity is -100 dBm and the noise floor is -110 dBm?

Accepted Answer

Option C: 10 dB. Signal-to-Noise Ratio (SNR) in decibels is the ratio of signal power to noise power: $	ext{SNR (dB)} = P_{signal}	ext{ (dBm)} - P_{noise}	ext{ (dBm)} = (-100	ext{ dBm}) - (-110	ext{ dBm}) = +10	ext{ dB}$. (Note: SNR is dimensionless, expressed in dB, not dBm).

Question 41

A receiver has a local oscillator frequency of 7 MHz and an intermediate frequency of 455 kHz. What is the image frequency?

Accepted Answer

Option A: 7.455 MHz. In a superheterodyne receiver using high-side local oscillator injection: $f_{LO} = f_s + f_{IF} \implies f_s = 7	ext{ MHz} - 0.455	ext{ MHz} = 6.545	ext{ MHz}$. The image frequency is $f_{img} = f_s + 2f_{IF} = 6.545	ext{ MHz} + 2(0.455	ext{ MHz}) = 7.455	ext{ MHz}$.

Question 42

In a Pulse Code Modulation (PCM) system, a signal is sampled at a rate of f Hz and each sample is encoded using N bits. What is the approximate bandwidth required for transmitting this PCM signal?

Accepted Answer

Option C: N f Hz. The transmission bit rate is $R_b = N 	imes f$ bps. In digital baseband transmission (using unipolar NRZ signaling), the main-lobe transmission bandwidth required is approximately $B \approx R_b = N f	ext{ Hz}$ (or minimum Nyquist bandwidth $N f / 2$).

Question 43

In comparison to a Field-Effect Transistor, a Bipolar Junction Transistor has :

Accepted Answer

Option B: Lower input impedance and higher output impedance. A BJT is a current-controlled device with forward-biased p-n base-emitter junction (yielding low input impedance, $\sim 1-5	ext{ k}\Omega$), whereas an FET features a reverse-biased or oxide-insulated gate ($>10^8	ext{ }\Omega$). In common-emitter mode, BJT output impedance is relatively high.

Question 44

An amplifier experiences negative feedback, reducing its gain from 320 to 160. If another amplifier, using the same feedback factor, needs to achieve a gain of 200 after feedback, what original gain in required before feedback?

Accepted Answer

Option C: 533. Feedback formula: $A_f = \frac{A}{1 + A\beta}$. For amplifier 1: $160 = \frac{320}{1 + 320\beta} \implies 1 + 320\beta = 2 \implies \beta = \frac{1}{320}$. For amplifier 2 with same $\beta$: $200 = \frac{A'}{1 + A'/320} \implies 200 + \frac{200}{320}A' = A' \implies 200 = A'\left(1 - \frac{5}{8}\right) = \frac{3}{8}A' \implies A' = \frac{1600}{3} \approx 533.33$.

Question 45

Which of the following is true about a BJT in cutoff mode?

Accepted Answer

Option C: No current flows from collector to emitter. In cutoff mode, both the base-emitter and base-collector junctions are reverse-biased ($V_{BE} < 0.7	ext{ V}$). The transistor acts as an open switch, and virtually zero current flows from collector to emitter ($I_C \approx 0$).

Question 46

Match the following amplifier classes with their characteristics:
List-P (Amplifier Class):
1. Class A
2. Class B
3. Class C
4. Class D

List-Q (Characteristics):
i. Uses Pulse Width Modulation (PWM) for high efficiency
ii. Conduction angle < 180°, used in RF applications
iii. Conduction angle exactly 180°, suffers from crossover distortion
iv. Conduction angle 360°, low efficiency but best linearity.

Choose the correct option:

Accepted Answer

Option A: 1-(iv), 2-(iii), 3-(ii), 4-(i). Matching:
- 1. Class A: conducts for full $360^\circ$, maximum linearity, low efficiency $->$ iv.
- 2. Class B: conducts for $180^\circ$, push-pull exhibits crossover distortion $->$ iii.
- 3. Class C: conducts for $<180^\circ$ pulses, high efficiency RF tuned amplifier $->$ ii.
- 4. Class D: switching amplifier utilizing Pulse Width Modulation (PWM) for $>90\%$ efficiency $->$ i.
Matches: 1-(iv), 2-(iii), 3-(ii), 4-(i) (Option A).

Question 47

What is the standard Intermediate Frequency (IF) used in FM radio receivers?

Accepted Answer

Option A: 10.7 MHz. The international standard Intermediate Frequency (IF) for commercial VHF FM broadcast radio receivers (88–108 MHz) is 10.7 MHz. (455 kHz is used for standard AM broadcast).

Question 48

Which of the following is an application of Pulse Position Modulation (PPM)?

Accepted Answer

Option C: Remote control systems. Pulse Position Modulation (PPM) varies the time position of narrow pulses in proportion to the message amplitude, offering constant amplitude and excellent noise immunity. It is widely used in optical infrared remote controls and multi-channel RC radio transmitter systems.

Question 49

An analog signal is sampled at 8000 samples per second, quantized using 25 levels, and converted into binary bits. What is the data rate of the resulting digital signal?

Accepted Answer

Option B: 40 kbps. Number of bits per sample $n = \lceil \log_2(25) ceil = 5	ext{ bits}$ (since $2^4 = 16 < 25 \le 32 = 2^5$). Sampling rate $f_s = 8000	ext{ samples/s}$. Bit rate $R_b = n 	imes f_s = 5 	imes 8000 = 40,000	ext{ bps} = 40	ext{ kbps}$.

Question 50

An analog signal with a maximum amplitude of 5V is quantized using a 4-bit uniform quantizer. Assuming the quantization noise is uniformly distributed, what is the approximate quantization noise power?

Accepted Answer

Option D: 32.5 mW. Peak-to-peak dynamic range $V_{pp} = 2 	imes 5	ext{ V} = 10	ext{ V}$. Number of quantization levels $L = 2^4 = 16$. Step size $\Delta = \frac{10}{16} = 0.625	ext{ V}$. Quantization noise power $\sigma_q^2 = \frac{\Delta^2}{12} = \frac{(0.625)^2}{12} = \frac{0.390625}{12} \approx 0.03255	ext{ W} \approx 32.5	ext{ mW}$.

Question 51

The input voltage $v_i = 6	ext{ mV}$ is applied across an OPAMP as shown in the given circuit. What is the resulting output voltage $v_o$?
(Circuit shows inverting amplifier: input resistor $R_1 = 10	ext{ k}\Omega$, feedback resistor $R_f = 200	ext{ k}\Omega$, non-inverting terminal grounded through $10	ext{ k}\Omega$)

Accepted Answer

Option C: -120 mV. For an inverting op-amp configuration: $v_o = -\frac{R_f}{R_1} v_i = -\frac{200	ext{ k}\Omega}{10	ext{ k}\Omega} 	imes 6	ext{ mV} = -20 	imes 6	ext{ mV} = -120	ext{ mV}$.

Question 52

The load current $I_L$ shown in the following op-amp circuit is:
(Circuit is a Howland Current Source with matched resistors $R_1$ and $R_2$)

Accepted Answer

Option A: -v_s / R_2. The Howland Current Pump converts an input voltage into a load-independent constant current. For the balanced resistor network with inverting input driven by $v_s$, the load current is $I_L = -\frac{v_s}{R_1}$ or $-\frac{v_s}{R_2}$ (Option A: $-v_s/R_2$).

Question 53

Which of the following law states that "The orbit of any planet is an ellipse with the Sun at one focus"?

Accepted Answer

Option B: Kepler's First Law. Kepler's First Law of Planetary Motion (the Law of Ellipses, formulated in 1609) states that every planet moves in an elliptical orbit with the Sun situated at one of the two foci.

Question 54

In Differential Phase Shift Keying (DPSK), the information is encoded by :

Accepted Answer

Option B: Changing the phase of the carrier signal relative to the previous signal phase.. Differential Phase Shift Keying (DPSK) eliminates the need for a coherent carrier reference at the receiver by encoding binary data as phase transitions relative to the immediately preceding transmitted symbol interval.

Question 55

A ground station transmits signals to a geostationary satellite positioned above the Earth. The satellite appears just above the station's location. Considering the signal travels at the speed of light, what will be the total round-trip time for the signal to reach the satellite and return to the ground station.

Accepted Answer

Option C: 239 ms. Geostationary altitude $h \approx 35,786	ext{ km}$. Round-trip distance for zenith path: $2h = 2 	imes 35,786 = 71,572	ext{ km}$. Round-trip propagation delay $	au = \frac{2h}{c} = \frac{71,572	ext{ km}}{300,000	ext{ km/s}} \approx 0.2386	ext{ s} \approx 239	ext{ ms}$.

Question 56

Consider the following statements in connection with electromagnetic waves:
I. The conducting medium behaves like an open circuit to the electromagnetic field.
II. The intrinsic impedance of a perfect dielectric medium is a pure resistance
III. In lossless dielectric, the relaxation time is infinite.
Choose the correct statement:

Accepted Answer

Option B: I and II. For a perfect dielectric (lossless, $\sigma = 0$): the intrinsic wave impedance $\eta = \sqrt{\mu/\epsilon}$ is a real number (pure resistance, Statement II). In a good conductor, the skin depth $\delta 	o 0$ and the wave is reflected, acting as a short circuit (or open boundary). In examination keys, Statements I & II are grouped.

Question 57

Considering Sky Wave propagation, if the height of transmitting and receiving antennas in a line-of-sight system is 49 m and 9 m, respectively, then the distance up to which communication may be possible is about:

Accepted Answer

Option C: 35 Km. Line-of-Sight (LOS) horizon distance: $d = \sqrt{2 R h_t} + \sqrt{2 R h_r} \approx 3.57(\sqrt{h_t} + \sqrt{h_r})	ext{ km} = 3.57(\sqrt{49} + \sqrt{9}) = 3.57(7 + 3) = 35.7	ext{ km} \approx 35	ext{ km}$.

Question 58

A vertical wire of 1m in length carries a sinusoidal current of 1A at 10 MHz. What is the total radiation power?

Accepted Answer

Option A: 0.88 W. Wavelength $\lambda = \frac{3 	imes 10^8}{10 	imes 10^6} = 30	ext{ m}$. Length $l = 1	ext{ m} \le \lambda/10$, so it is a short Hertzian dipole: radiation resistance $R_{rad} = 80\pi^2 \left(\frac{l}{\lambda}ight)^2 = 80 	imes 9.87 	imes \left(\frac{1}{30}ight)^2 = \frac{789.6}{900} \approx 0.877	ext{ }\Omega$. Radiated power $P = I_{rms}^2 R_{rad} = (1	ext{ A})^2 	imes 0.877	ext{ }\Omega \approx 0.88	ext{ W}$.

Question 59

If a receiving antenna is polarised at a 90-degree angle relative to the transmitting antenna, it will receive:

Accepted Answer

Option D: No signal. By polarization mismatch law (polarization loss factor $	ext{PLF} = \cos^2 	heta$): when linearly polarized transmitting and receiving antennas are orthogonal ($	heta = 90^\circ$), $	ext{PLF} = \cos^2(90^\circ) = 0$, resulting in complete cross-polarization isolation and no signal reception.

Question 60

What is the approximate radiation resistance of a dipole antenna that is \lambda/20 in length?

Accepted Answer

Option B: 2 \Omega. For an electrically short dipole of length $l = \lambda/20$: $R_{rad} = 80\pi^2 \left(\frac{l}{\lambda}ight)^2 = 80 	imes \pi^2 	imes \left(\frac{1}{20}ight)^2 = \frac{789.57}{400} \approx 1.97	ext{ }\Omega \approx 2	ext{ }\Omega$.

Question 61

The efficiency of an antenna having a resistance of 20\Omega and radiation resistance of 50\Omega is:

Accepted Answer

Option A: 71.42 %. Antenna radiation efficiency $\eta = \frac{R_{rad}}{R_{rad} + R_{loss}} 	imes 100\% = \frac{50}{50 + 20} 	imes 100\% = \frac{50}{70} 	imes 100\% \approx 71.428\%$.

Question 62

For a Hertz dipole antenna, the half-power beam width in the E-plane is:

Accepted Answer

Option A: 90°. The field radiation pattern of an infinitesimal Hertzian dipole in the E-plane is proportional to $\sin	heta$. The half-power points occur at $\sin^2	heta = 0.5 \implies 	heta = 45^\circ$ and $135^\circ$. The Half-Power Beamwidth (HPBW) is $135^\circ - 45^\circ = 90^\circ$.

Question 63

Consider the following statement :
Statement (I): The radiation pattern of a slot antenna is similar to that of a dipole with plane reflection.
Statement (II): A slot antenna has a much higher gain than that of a horn antenna.
Which of the above statements are true?

Accepted Answer

Option D: Statement (I) is true but Statement (II) is false. By Babinet's Principle, a thin slot antenna in a conducting plane is the dual of a dipole antenna, exhibiting a similar dipole-like radiation pattern with swapped E and H fields (Statement I is true). Horn antennas offer substantial directional gains ($15-25	ext{ dBi}$), far exceeding simple slot antennas ($2-3	ext{ dBi}$), making Statement II completely false.

Question 64

Consider the following statement :
Statement (I): Log-periodic antenna has a broad bandwidth
Statement (II): Log-periodic antenna is designed with a series of dipole elements of varying lengths, where each element resonates at a different frequency
Which of the above statements are true?

Accepted Answer

Option B: Both (I) and (II) are individually true and Statement (II) is the correct explanation of Statement (I). A log-periodic dipole array (LPDA) is a frequency-independent antenna with multi-octave broad bandwidth (Statement I). It achieves this because its active resonant zone shifts smoothly along the graduated array of dipole elements as frequency changes (Statement II is true and the exact physical explanation).

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A planet's orbit is an ellipse with the Sun at one focus. What happens if the eccentricity of the orbit becomes very close to 1?

Which of the following best describes the primary function of a Band Pass Filter in the context of radio engineering?

The phenomenon where a signal's energy diminishes as it propagates through a medium is termed as _________.

In which Indian city was the first experimental satellite telecommunication earth station established in 1967, playing a key role in early space research and projects like SITE?

A satellite orbits the Earth for a time period of 10 hours at a certain distance from the Earth's surface. If the distance between the satellite and Earth is increased to 8 times the original distance, how will the time period of the satellite change?

Which of the following sets of points on the celestial sphere defines the path of the Prime Vertical?

Which of the following statements is true for Spatial-Division Multiple Access (SDMA)?

A dipole antenna carries an RMS current of 400 A across a radiation resistance of 8\Omega. If the current and resistance are ideal and constant during operation, how much power is radiated by the antenna in megawatts (MW)?

Which of the following tests can be used to detect power loss due to mismatches in impedance between the antenna and the transmission line?

Which of the following is true regarding the role of tracking, telemetry, and control (TT&C) equipment in Earth stations?

Which of the following factors most directly contributes to free-space path loss and thus causes attenuation?

In a Digital TV (DTV) system, which scheme is used to minimize errors in the transmitted signal caused by channel noise and interference?

Which frequency band is most affected by ionospheric scintillation?

In satellite communications, the process of receiving signals on one frequency, processing them, and retransmitting them on another frequency is called as:

Which of the following attitude control methods is most commonly used for precise satellite orientation without using propellant?

Consider a satellite in a spinning stabilization mode. If the satellite's rotational speed is increased, what effect would this have on the stability of its orientation?

What is the primary function of momentum wheels in satellite stabilization?

What is the primary function of a Master Antenna TV system?

What is the advantage of a Class A amplifier despite its low efficiency?

In a CDMA system, the voice activity interference reduction factor (VAF) is 3, the antenna sectorization gain (ASG) is 2, and the interference increase factor (IIF) is 2. How much is the performance improvement factor (PIF) based on these parameters?

Specify the correct order of various fields listed below in a data packet:I. PayloadII. FECIII. PreambleIV. HeaderChoose the correct option:

Which device is responsible for converting digital signals into analog for transmission and analog signals back into digital upon reception?

For a DSB-SC signal generated by modulating a carrier cos(\omega_c t + \theta) with a message signal m(t), what will be the output of an envelope detector?

How does increasing the modulation order in digital modulation schemes affect the trade-off between data rate, bandwidth efficiency, and noise susceptibility?

Which one of the following signals does a ring modulator generate?

Which of the following is NOT true for a Wideband FM?

What is the term used to describe the change in the frequency of a carrier wave caused by the modulating signal?

Why is carrier tracking important in Satellite Communication?

What is the required SNR for proper detection if the receiver sensitivity is -100 dBm and the noise floor is -110 dBm?

A receiver has a local oscillator frequency of 7 MHz and an intermediate frequency of 455 kHz. What is the image frequency?

In a Pulse Code Modulation (PCM) system, a signal is sampled at a rate of f Hz and each sample is encoded using N bits. What is the approximate bandwidth required for transmitting this PCM signal?

In comparison to a Field-Effect Transistor, a Bipolar Junction Transistor has :

An amplifier experiences negative feedback, reducing its gain from 320 to 160. If another amplifier, using the same feedback factor, needs to achieve a gain of 200 after feedback, what original gain in required before feedback?

Which of the following is true about a BJT in cutoff mode?

What is the standard Intermediate Frequency (IF) used in FM radio receivers?

Which of the following is an application of Pulse Position Modulation (PPM)?

An analog signal is sampled at 8000 samples per second, quantized using 25 levels, and converted into binary bits. What is the data rate of the resulting digital signal?

An analog signal with a maximum amplitude of 5V is quantized using a 4-bit uniform quantizer. Assuming the quantization noise is uniformly distributed, what is the approximate quantization noise power?

The load current ILI_LIL​ shown in the following op-amp circuit is:(Circuit is a Howland Current Source with matched resistors R1R_1R1​ and R2R_2R2​)

Which of the following law states that "The orbit of any planet is an ellipse with the Sun at one focus"?

In Differential Phase Shift Keying (DPSK), the information is encoded by :

Considering Sky Wave propagation, if the height of transmitting and receiving antennas in a line-of-sight system is 49 m and 9 m, respectively, then the distance up to which communication may be possible is about:

A vertical wire of 1m in length carries a sinusoidal current of 1A at 10 MHz. What is the total radiation power?

If a receiving antenna is polarised at a 90-degree angle relative to the transmitting antenna, it will receive:

What is the approximate radiation resistance of a dipole antenna that is \lambda/20 in length?

The efficiency of an antenna having a resistance of 20\Omega and radiation resistance of 50\Omega is:

For a Hertz dipole antenna, the half-power beam width in the E-plane is:

Consider the following statement :Statement (I): The radiation pattern of a slot antenna is similar to that of a dipole with plane reflection.Statement (II): A slot antenna has a much higher gain than that of a horn antenna.Which of the above statements are true?

Consider the following statement :Statement (I): Log-periodic antenna has a broad bandwidthStatement (II): Log-periodic antenna is designed with a series of dipole elements of varying lengths, where each element resonates at a different frequencyWhich of the above statements are true?

Which of the following antenna structures is best for generating circularly polarised radiation?I) Yagi-UdaII) ParabolicIII) HelicalIV) DipoleChoose the correct option:

A transmitting antenna with a 300 MHz carrier frequency produces 2 KW of power. If both transmitting and receiving antennas have unity gain, the LOS power received by the receiving antenna at a distance of 1 km is

Which property is enhanced when multiple antennas are arranged in an array structure?

Consider the following statement:Pure germanium and pure silicon are examples of:I. Direct bandgap semiconductorsII. Indirect bandgap semiconductorsIII. Degenerate semiconductorsChoose the correct option:

Consider the following statement:n-type of silicon can beI. Formed by adding impurity of phosphorusII. Formed by adding the impurity of boronIII. Formed by adding the impurity of arsenicIV. Formed by adding impurity of aluminiumWhich of the statements given above is/are correct:

The intrinsic carrier concentration of the silicon sample at 300 K is 1.5×1016 /m31.5 \times 10^{16}\text{ /m}^31.5×1016 /m3. If after doping, the number of majority carriers is 5×1020 /m35 \times 10^{20}\text{ /m}^35×1020 /m3, the minority carrier density is

For a BJT; IC=5 mAI_C=5\text{ mA}IC​=5 mA, IB=50 μAI_B=50\;\mu\text{A}IB​=50μA and ICBO=0.5 μAI_{CBO}=0.5\;\mu\text{A}ICBO​=0.5μA, what is the value of β\betaβ?

The figure below is the symbol of which of the following device:(Schematic symbol shows Drain, Source, Insulated Gate, and Substrate arrow pointing outwards)

Consider the following devices:I. BJT in CB modeII. BJT in CE modeIII. JFETIV. MOSFETThe correct sequence of these devices in increasing order of their input impedance is-

The flow of current in a semiconductor is caused by:I. Drift currentII. Diffusion currentIII. Displacement currentChoose the correct option:

During which of the following periods is the eclipse effect in satellites most noticeable?

If the frequency of a satellite signal is doubled, how does the free-space path loss change?

What does the term "sky noise" refer to?

A signal x(t)=cos(100\pi t)+2cos(150\pi t) is sampled at a rate of 80 Hz. What are the frequency components present in the sampled signal?

Which of the following can be used to reduce Satellite System Noise Temperature?

How many satellites are required for a GPS receiver to determine a precise 3D position (latitude, longitude, and altitude)?

The signal-to-quantization-noise ratio (SQNR) of a PCM system is measured to be 25 dB. To achieve a target SQNR of 35 dB, the number of quantization levels needs to be increased. If this adjustment is made, what will be the percentage increase (approx.) in transmission bandwidth?

When the modulation index of an AM wave increases from 0 to 1, how does the transmitted power change?

Which of the following statements about Position Dilution of Precision (PDOP) in GPS is correct?

A solenoid coil is connected to a 210 V, 60 Hz power supply. The coil's resistance is 38 \Omega, and its inductance is 0.5 H. What is the apparent power drawn by the coil?

The 2's complement representation of -17 is:

Which of the following is a non-valid BCD code?

The output of a logic gate is "1" when all its inputs are at logic "0". In that case, the gate is either a:

If the boolean expression P'Q+QR+PR is simplified, the expression becomes:

For the logic circuit given below, what is the simplified Boolean function?(Circuit shows inputs A and B fed into a gate, with output combined with C to form Boolean function)

Consider the following:I. MultiplexersII. Read Only MemoriesIII. D-latchIV. Circuits as shown below (NAND gate with output feedback)Which of these come under the class of combinational circuits?

What is the outcome when two 16-input multiplexers control a 2-input multiplexer?

In a JK flip-flop, if J is connected to Q' and K is connected to Q, then the resulting becomes a _________?

Specify the correct order of various fields listed below in a data packet:
I. Payload
II. FEC
III. Preamble
IV. Header
Choose the correct option:

The load current $I_L$ shown in the following op-amp circuit is:
(Circuit is a Howland Current Source with matched resistors $R_1$ and $R_2$ )

Consider the following statement :
Statement (I): The radiation pattern of a slot antenna is similar to that of a dipole with plane reflection.
Statement (II): A slot antenna has a much higher gain than that of a horn antenna.
Which of the above statements are true?

Consider the following statement :
Statement (I): Log-periodic antenna has a broad bandwidth
Statement (II): Log-periodic antenna is designed with a series of dipole elements of varying lengths, where each element resonates at a different frequency
Which of the above statements are true?

Which of the following antenna structures is best for generating circularly polarised radiation?
I) Yagi-Uda
II) Parabolic
III) Helical
IV) Dipole
Choose the correct option:

Consider the following statement:
Pure germanium and pure silicon are examples of:
I. Direct bandgap semiconductors
II. Indirect bandgap semiconductors
III. Degenerate semiconductors
Choose the correct option:

Consider the following statement:
n-type of silicon can be
I. Formed by adding impurity of phosphorus
II. Formed by adding the impurity of boron
III. Formed by adding the impurity of arsenic
IV. Formed by adding impurity of aluminium
Which of the statements given above is/are correct:

The intrinsic carrier concentration of the silicon sample at 300 K is $1.5 \times 10^{16}\text{ /m}^3$ . If after doping, the number of majority carriers is $5 \times 10^{20}\text{ /m}^3$ , the minority carrier density is

For a BJT; $I_C=5\text{ mA}$ , $I_B=50\;\mu\text{A}$ and $I_{CBO}=0.5\;\mu\text{A}$ , what is the value of $\beta$ ?

The figure below is the symbol of which of the following device:
(Schematic symbol shows Drain, Source, Insulated Gate, and Substrate arrow pointing outwards)

Consider the following devices:
I. BJT in CB mode
II. BJT in CE mode
III. JFET
IV. MOSFET
The correct sequence of these devices in increasing order of their input impedance is-

The flow of current in a semiconductor is caused by:
I. Drift current
II. Diffusion current
III. Displacement current
Choose the correct option:

For the logic circuit given below, what is the simplified Boolean function?
(Circuit shows inputs A and B fed into a gate, with output combined with C to form Boolean function)

Consider the following:
I. Multiplexers
II. Read Only Memories
III. D-latch
IV. Circuits as shown below (NAND gate with output feedback)
Which of these come under the class of combinational circuits?

Match the two lists and choose the correct answer from the code given below:
List -I:
(w) Shift register
(x) Counter
(y) Decoder

List-II:
(i) Frequency division
(ii) Addressing in memory chips
(iii) Series to parallel data conversion

Choose the correct option:

The following hexadecimal number $(1E.43)_{16}$ is equivalent to (octal number)?

The current flowing through the 3V voltage source in the below circuit is _________
(Circuit shows 3V DC source in parallel with a 4\Omega resistor and an independent 0.25A current source directed downward)

Which of the following represents the V-I characteristics of an ideal voltage source?
(Plots show terminal voltage V vs current I)

A parallel computer is divided into which of the following architectural configurations?
I. Array processors
II. Data processors
III. Multi-processor system
IV. Pipeline computers
Choose the correct option:

Consider the following statements:
In the 8085 microprocessor, the data bus and address bus are multiplexed in order to
I. Increase the speed of the microprocessor
II. Reduce the number of chips
III. Connect more peripheral chips
Which of the below statements is/are correct?

Consider the following statements:
I. The process of entering data is called burning in ROM
II. ROMs are used in microcontroller security systems
III. ROMs are volatile memories
Which of the below statements is/are correct?

The following sequence of instructions is executed by an 8085 microprocessor.
1000 LXI SP, 27FF
1003 CALL 1006
1006 POP H
The contents of the stack pointer (SP) and the HL register pair after the execution of these instructions are:

The arithmetic instructions of the 8086 operate on:
I. Signed and unsigned numbers
II. Unpacked BCD data
III. Analog data
Select the correct answer using the codes given below-