Advanced Communication Systems mcq questions , ACS MCQ QUESTIONS AND ANSWERS
## 🟢 Unit I: Digital Modulation Techniques
### ASK, FSK, PSK, QPSK (modulation/demodulation diagrams, operation, waveforms) + Basic OFDM
1. ASK stands for:
A) Amplitude Shift Keying
B) Angle Shift Keying
C) Amplitude Side Keying
D) Angle Side Keying
**Answer: A**
2. In ASK, binary '1' is represented by:
A) High amplitude carrier
B) Low amplitude carrier
C) Frequency shift
D) Phase shift
**Answer: A**
3. ASK is also known as:
A) On‑Off Keying (OOK)
B) Phase Modulation
C) Frequency Modulation
D) Quadrature Modulation
**Answer: A**
4. FSK varies which parameter of the carrier:
A) Amplitude
B) Phase
C) Frequency
D) Power
**Answer: C**
5. In BFSK, '1' and '0' are represented by:
A) Same frequency
B) Two distinct frequencies
C) Two amplitudes
D) Phase shift
**Answer: B**
6. Binary FSK demodulation can be:
A) Coherent only
B) Non‑coherent only
C) Both coherent and non‑coherent
D) Neither
**Answer: C**
7. PSK modulates which property of the carrier:
A) Amplitude
B) Frequency
C) Phase
D) Time
**Answer: C**
8. BPSK uses:
A) Four phase states
B) Two phase states (0°, 180°)
C) Two frequencies
D) Two amplitudes
**Answer: B**
9. QPSK transmits:
A) 1 bit per symbol
B) 2 bits per symbol
C) 4 bits per symbol
D) 0 bits per symbol
**Answer: B**
10. QPSK uses which phase angles:
A) 0°, 180°
B) 0°, 90°, 180°, 270°
C) Any continuous angle
D) No phase shift
**Answer: B**
11. BPSK and QPSK have:
A) Different BER
B) Same BER under equal SNR
C) QPSK always better BER
D) BPSK always better BER
**Answer: B**
12. OFDM stands for:
A) Orthogonal Frequency Division Multiplexing
B) Ordered Frequency Direct Modulation
C) Orthogonal Frequency Direct Multiplexing
D) Off Frequency Division Multiplexing
**Answer: A**
13. OFDM divides data into parallel streams and transmits on:
A) One carrier
B) Orthogonal subcarriers
C) Random frequency
D) Phase‑shifted carriers
**Answer: B**
14. The main advantage of OFDM is:
A) Simple hardware
B) Robustness against multipath and ISI
C) Low peak-to-average power ratio
D) Single carrier efficiency
**Answer: B**
15. OFDM is used in:
A) AM radio
B) 4G/LTE, Wi‑Fi, DVB
C) FM broadcast only
D) Traditional analog systems
**Answer: B**
16. FSK is more immune to noise than ASK because:
A) Amplitude variations do not affect frequency detection
B) ASK uses frequency changes
C) FSK has variable amplitude
D) FSK uses phase changes only
**Answer: A** ([digimodstu.vercel.app][10], [Wikipedia][17], [Sanfoundry][9], [Sanfoundry][5])
17. Continuous-phase FSK avoids:
A) Bandpass filters
B) Abrupt phase changes
C) Demodulation
D) Frequency shifts
**Answer: B**
18. A coherent detector detects:
A) Amplitude only
B) Phase with reference
C) Frequency only
D) No reference
**Answer: B** 19. Which technique uses both amplitude and phase modulation:
A) ASK
B) FSK
C) PSK
D) QAM
**Answer: D**
20. OFDM uses which transform at receiver:
A) Fourier series
B) FFT
C) IFFT
D) Laplace transform
**Answer: B**
---
## 🟢 Unit II: Satellite Communication
Kepler’s laws, orbits, geostationary, Apogee/Perigee, active/passive satellites, mobile services, DTH, GPS, NavIC, TDMA/FDMA/CDMA
21. Kepler’s First Law states that orbits are:
A) Circular
B) Elliptical with Sun at one focus
C) Parabolic
D) Hyperbolic
**Answer: B**
22. Geostationary orbit means satellite appears:
A) Moving west-east
B) Stationary over equator
C) In polar orbit
D) Changing position
**Answer: B**
23. Apogee is:
A) Closest point to Earth
B) Farthest point in elliptical orbit
C) Mid‑point
D) Orbital speed reference
**Answer: B**
24. Passive satellite:
A) Amplifies and retransmits
B) Just reflects signals
C) Generates signals
D) Mobile terminal
**Answer: B**
25. Active satellite has:
A) No transponder
B) Transponder amplifying signals
C) Passive reflector only
D) User terminal
**Answer: B**
26. DTH stands for:
A) Direct To Home
B) Digital Television Hub
C) Digital Transmission House
D) Direct Television Hub
**Answer: A**
27. GPS provides:
A) 2‑D position only
B) 3‑D position and time
C) 1‑D position only
D) Only time
**Answer: B**
28. NavIC is India’s:
A) Data network
B) Regional satellite navigation system
C) Audio broadcast system
D) Satellite dish
**Answer: B**
29. TDMA divides access by:
A) Frequency
B) Code
C) Time slots
D) Space beams
**Answer: C**
30. FDMA divides access by:
A) Time
B) Frequency
C) Code
D) Space
**Answer: B**
31. CDMA spreads user data across:
A) Time slots
B) Frequency sub‑bands
C) Entire spectrum using code
D) Spatial beams
**Answer: C**
32. Which multiple access is most suitable for digital satellite communications:
A) FDMA
B) TDMA
C) CDMA
D) SDMA
**Answer: B**
33. CDMA requires:
A) Simple filters
B) Large bandwidth and complex circuitry
C) No code assignment
D) No timing sync
**Answer: B** ([mcq.electronics-club.com][20])
34. Geostationary orbit altitude is approx:
A) 300 km
B) 36,000 km
C) 3,600 km
D) 100,000 km
**Answer: B**
35. Satellite mobile services include:
A) Only TV broadcast
B) Internet, voice, emergency comms
C) Only GPS
D) Only military uses
**Answer: B**
36. Kepler’s Second Law describes:
A) Equal areas in equal times
B) Orbit periods relation
C) Circular orbits
D) Apogee and perigee
**Answer: A**
37. Kepler’s Third Law:
A) Squares of periods proportional to cubes of semi-major axis
B) Apogee and perigee distances equal
C) Orbits are circular
D) Satellite speed constant
**Answer: A**
38. Satellite transponders operate in:
A) C, Ku, Ka bands
B) VHF only
C) UHF
D) Infrared
**Answer: A** ([Reddit][21])
39. NavIC covers:
A) Global region
B) Regional coverage around Indian sub‑continent
C) US only
D) African coverage
**Answer: B**
40. Demand‑assigned multiple access (DAMA) is:
A) TDMA variant
B) FDMA variant
C) Dynamic allocation method
D) Passive satellite type
**Answer: C**
---
## 🟢 Unit III: Optical Communication
LED & LASER sources, PIN/APD detectors, connectors/splices/couplers, transmitter/receiver blocks, applications.
41. LED stands for:
A) Light Emitting Diode
B) Laser Emitting Device
C) Light Emission Driver
D) Light Energy Diode
**Answer: A**
42. LASER differs from LED by having:
A) Incoherent light
B) Coherent, monochromatic beam
C) Lower power
D) Wider spectral width
**Answer: B**
43. PIN photodiode uses:
A) PN junction only
B) Intrinsic layer between P and N
C) Avalanche region only
D) Metal-semiconductor junction
**Answer: B**
44. APD stands for:
A) Avalanche Photo Diode
B) Amplified PIN Device
C) Advanced Photodiode
D) Active Photo Detector
**Answer: A**
45. APD advantage over PIN:
A) Lower sensitivity
B) Internal gain via avalanche
C) No bias required
D) Simplicity
**Answer: B**
46. Fiber splice is used to join:
A) Electrical wires
B) Optical fibers
C) Coax cables
D) Metal pipes
**Answer: B**
47. Optical coupler function:
A) Split or combine optical signals
B) Provide mechanical support
C) Convert light to electricity
D) Clean connector ends
**Answer: A**
48. In optical transmitter block diagram, data → driver → light source → fiber. Correct?
A) Yes
B) No
**Answer: A**
49. Optical receiver includes:
A) Light source
B) Optical detector + amplifier + decision circuit
C) Multiplexer
D) Comb coupler
**Answer: B**
50. Applications of optical fibers:
A) Telephony, internet backbone, sensors
B) Only voice
C) Only mobile
D) Radiowave only
**Answer: A**
51. LED transmitter is:
A) Expensive, high-speed
B) Low-cost, lower bandwidth
C) Coherent
D) Narrow spectral width
**Answer: B**
52. Semiconductor laser has:
A) Broad linewidth
B) Narrow linewidth, high modulation speed
C) No bias need
D) Low coherence
**Answer: B**
53. PIN diode speed compared to APD:
A) Faster
B) Slower
C) Same speed
D) Zero speed
**Answer: B**
54. Fiber connector example:
A) RJ45
B) ST, SC, LC
C) BNC
D) HDMI
**Answer: B**
55. Multimode fiber is used for:
A) Short distance links
B) Long-distance comms
C) Wireless only
D) Satellite link
**Answer: A**
56. Single‑mode fiber supports:
A) Long distance, high bandwidth
B) Short distance only
C) No light propagation
D) Microwave signals
**Answer: A**
57. Coupler splits light ratio as:
A) Electrical voltage
B) 50/50, 70/30 etc.
C) Time division
D) Frequency bands
**Answer: B**
58. Optical transmitter block includes:
A) Laser, optical modulator, driver
B) Detector only
C) Multiplexer only
D) Splice
**Answer: A**
59. Receiver decision circuit converts:
A) Optical to digital data bits
B) Bits to light
C) Electric to magnetic
D) Frequency to amplitude
**Answer: A**
60. Optical communication offers:
A) Low bandwidth
B) Immune to EMI, high bandwidth
C) Low data rate only
D) Poor security
**Answer: B**
---
## 🟢 Unit IV: Microwave Communication
Propagation types, frequency ranges, transmitter/receiver/repeater blocks, horn antenna.
61. Ground wave propagation uses:
A) Sky reflected waves
B) Follows Earth's surface at low MHz
C) Ionospheric bounce
D) Satellite link
**Answer: B**
62. Sky wave propagation uses:
A) Ground reflection
B) Space wave
C) Ionosphere reflection
D) Fiber optic
**Answer: C**
63. Space wave propagation uses:
A) Fiber link
B) Microwave line-of-sight
C) Ionosphere
D) Ground bounce
**Answer: B**
64. Microwave frequency range roughly is:
A) 300 kHz–3 MHz
B) 300 MHz–300 GHz
C) 3 GHz–300 GHz
D) 30 kHz–300 kHz
**Answer: C**
65. Microwave transmitter block includes:
A) Modulator, oscillator, power amplifier, antenna
B) Detector only
C) Fiber coupler
D) Horn connector only
**Answer: A**
66. Microwave receiver includes:
A) Antenna, LNA, mixer, IF amplifier, demodulator
B) Laser source
C) Splice
D) Baseband only
**Answer: A**
67. Microwave repeater extends link by:
A) Reflecting signals passively
B) Receiving, amplifying and re-transmitting
C) Changing frequency only
D) Encrypting signals
**Answer: B**
68. Horn antenna is:
A) Omnidirectional
B) Directive, used with waveguides
C) Fiber-based
D) Used for satellite only
**Answer: B**
69. Horn antenna advantages:
A) Broad beam
B) High gain, low loss
C) Cheap plastic
D) Variable frequency operation
**Answer: B**
70. Horn antenna is used in:
A) Satellite dishes only
B) Microwave links, radar, measurement
C) Optical fiber
D) AM radio
**Answer: B**
71. In microwave link, line-of-sight distance must consider:
A) Earth's curvature and Fresnel zone clearance
B) Fiber loss only
C) Satellite orbit
D) Ionosphere delay
**Answer: A**
72. Microwave frequency band not in use:
A) Ku band
B) VHF band
C) Ka band
D) X‑band
**Answer: B**
73. Horn antenna feed type:
A) Direct waveguide feed
B) Fiber feed
C) Coax feed only
D) Dish feed
**Answer: A**
74. Microwave links often use:
A) Duplex communication
B) Only simplex
C) No antennas
D) Optical only
**Answer: A**
75. Space wave propagation is limited by:
A) Ionosphere
B) Line of sight
C) Ocean reflection
D) Underground structures
**Answer: B**
76. Ground wave useful up to:
A) GHz band
B) Low HF to MF band (\~3 MHz)
C) Optical frequencies
D) Microwave range
**Answer: B**
77. Horn antenna design shape:
A) Parabolic reflector
B) Flared metal waveguide
C) Wire whip
D) Yagi structure
**Answer: B**
78. Microwave mixer block converts:
A) Baseband to RF
B) High‑frequency to IF
C) Optical to electrical
D) Amplitude to phase
**Answer: B**
79. Microwave LNA is placed at:
A) Transmitter
B) Receiver antenna input
C) Mixer output
D) Horn mouth
**Answer: B**
80. Repeater frequency planning avoids:
A) Using same frequency for tx/rx
B) Frequency shift between uplink/downlink
C) Spatial reuse
D) Duplex spacing
**Answer: B**
---
## 🟢 Unit V: Digital Cellular Systems
GSM architecture, services, basics of GPRS.
81. GSM stands for:
A) Global System for Mobile Communications
B) General Satellite Mobile
C) Global Signal Mode
D) Government Subscriber Mobile
**Answer: A**
82. GSM services include:
A) Voice, SMS, data, location-based services
B) Only voice
C) Only SMS
D) Optical fiber
**Answer: A**
83. GSM architecture includes:
A) MS, BSC, BTS, MSC, HLR, VLR, AUC
B) Only BTS and MSC
C) Only Baseband unit
D) Only HLR
**Answer: A**
84. GPRS stands for:
A) General Packet Radio Service
B) Global Packet Radio Service
C) General Push Radio Service
D) Global PSTN Radio Service
**Answer: A**
85. GPRS adds which capability to GSM:
A) Packet-switched data
B) Only voice
C) Optical communication
D) Satellite link
**Answer: A**
86. GSM uses which multiple access:
A) FDMA + TDMA
B) CDMA only
C) FDMA only
D) TDMA only
**Answer: A**
87. GPRS supports:
A) Circuit switching only
B) Packet switching over GSM
C) Optical fiber
D) Microwave links
**Answer: B**
88. Mobile Station (MS) refers to:
A) Base station
B) Subscriber handset and SIM
C) Network controller
D) Satellite dish
**Answer: B**
89. BTS stands for:
A) Base Transceiver Station
B) Base Transfer System
C) Bandwidth Transmission Station
D) Broadband Terminal System
**Answer: A**
90. MSC manages:
A) Local cell only
B) Switching between BSCs and external networks
C) Optical fiber links
D) Horn antenna
**Answer: B**
91. HLR stores:
A) Frequencies only
B) Permanent subscriber info
C) Optical transmitter data
D) Horn parameters
**Answer: B**
92. VLR stores:
A) Permanent subscriber info
B) Temporary info for roaming MS
C) Optical coupler data
D) Mixer parameters
**Answer: B**
93. AUC provides:
A) Voice routing
B) Authentication and encryption keys
C) Horn design
D) Optical fiber status
**Answer: B**
94. SMS in GSM is:
A) Short Message Service
B) Satellite Messaging System
C) Subscriber Messaging Server
D) Spatial Message Service
**Answer: A**
95. GPRS C‑interface connects:
A) BSC to SGSN
B) MS to BTS
C) MSC to PSTN
D) None
**Answer: A**
96. SGSN is:
A) SMS server
B) Serving GPRS Support Node
C) Satellite Gateway Node
D) Subscriber GNSS Node
**Answer: B**
97. GPRS supports which IP protocol:
A) IPv6 only
B) IPv4
C) Only voice
D) Optical
**Answer: B**
98. GPRS billing is:
A) Flat rate only
B) Based on data volume/time
C) Only voice based
D) Free
**Answer: B**
99. GSM TRX carries:
A) Control channel only
B) Traffic channels
C) Fiber signals
D) Horn signals
**Answer: B**
100. GSM frequency band in India is:
A) 900 & 1800 MHz
B) 800 MHz only
C) 2.4 GHz
D) 5 GHz
**Answer: A**
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