Communications MCQ Set 1
1. Which of the following devices is used to generate AM waves?
b) Square law modulator
Answer: a [Reason:] AM signals is generated by Square-law modulators. The input for generating AM signal should be of type (A + m(t)) instead of m(t). Square-law modulator sums carrier and information signal, then square them using a non linear device.
2. What is the full form of ASCII?
a) American Standard Character for Information Interchange
b) American Standard Class for Information Interchange
c) American Standard Code for Information Interchange
d) Alphanumeric Standard Code for Information Interchange
Answer: c [Reason:] ASCII is the most common format for text files in computers. In an ASCII file each symbol is represented by a 7 bit binary number. In this 128 possible characters are defined.
3. The transmitter and receiver are not synchronized at all, in asynchronous transmission.
Answer: b [Reason:] In Asynchronous transmission, transmitter and receiver are synchronized frame-by-frame using the start and stop bits.
4. In synchronous transmission, receiver is able to sync with the transmitter by using ________
a) Clock bits
b) Separate clock line
c) CRC bits
d) Data bits
Answer: d [Reason:] In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient. Receiver and transmitter are in sync with each other by using data bits.
5. Which chart is used for calculations of transmission lines?
a) Andre chart
b) Smith chart
c) Wilson chart
d) Federer chart
Answer: b [Reason:] Smith chart is highly used in radio frequency engineering. Because it is highly useful in solving problems related with transmission lines and matching circuits. It is highly useful for displaying multiple parameters like impedance, admittance etc simultaneously.
6. FEC stands for _________
a) Forward Error Correction
b) Fixed Error Correction
c) Forward Error Control
d) Fixed Error Control
Answer: a [Reason:] FEC is a method of obtaining error control in data transmission. It stands for Forward Error Correction.
7. Run-length encoding is used to ________
a) correct data
b) reduce the length
c) encrypt data
d) compress data
Answer: d [Reason:] Run length encoding is a very simple form of lossless data compression in which runs of data are stored as a single value data, rather than as original run.
8. The term CD in CSMA/CD stands for _________
a) Collision Detection
b) Collision Delay
c) Carrier Detection
d) Carrier Delay
Answer: a [Reason:] CSMA/CD stands for Carrier Sense Multiple Access with Collision Detection. It is mostly used in early Ethernet technology for local area networking.
9. Dumb terminals are used in token-passing networks.
Answer: b [Reason:] A dumb terminal is an output that accepts data from CPU. It has no processing capabilities. Dumb terminals are used in networks that requires central monitoring.
10. In networks, long messages are divided into “chunks” called __________
Answer: a [Reason:] For any long message to be transmitted, it is first divided into many small parts called packets. Individual packets belonging to a long message may arrive out of order at the destination.
Communications MCQ Set 2
1. Why sampling is used in communication?
a) for getting higher speed of communication
b) for getting higher efficiency
c) cheaper equipment is required
d) for a better transmission
Answer: a [Reason:] Sampling is the conversion of continuous-time signal to discrete-time signal. It is highly used in communication for getting higher speed of communication.
2. Which two noises are present in Delta Modulation (DM)?
a) Slope overload and Thermal noise
b) Granular and shot noise
c) Slope overload and granular noise
d) Thermal and shot noise
Answer: c [Reason:] Delta modulation is used for transmission of voice information where quality is not the primarily importance. Its drawback is it has two noises namely slope overload and granular noise. So for getting rid from these noises we use ADM (Adaptive Delta Modulation).
3. What is the need of doing Pre emphasis?
a) For boosting of modulating signal voltage
b) For restoring of original signal power
c) For removing amplitude variations due to noise
d) For removing frequency variations
Answer: a [Reason:] It is use for boosting. It boosts the modulating voltages at higher frequencies.
4. Varacter is used for generation of ________
a) PM signals only
b) FM signals only
c) AM signals only
d) PM and FM signals
Answer: b [Reason:] Varacter diode or tuning diode that has a variable capacitance. It is operated as reverse-biased and therefore no current flows. It is mainly used for generation of FM signals only.
5. What will happen in amplitude modulation, if modulation index is more than 1?
a) bandwidth will increase
b) bandwidth will decrease
c) there will be chances of interference
d) waves will get distorted
Answer: d [Reason:] Modulation index tells us the amount by how much the modulated variable of carrier varies. If modulation index is greater than 1 then the wave gets distorted.
6. The adverse effect of noise in communication system can be seen in ________
Answer: d [Reason:] Noise is a sound that is very much unpleasant that causes disturbance. Its adverse effect is highly seen on channel.
7. Which among the following is not an advantage of FM over AM?
a) modulating power required is less
b) low bandwidth is required
c) better noise immunity
d) transmitted power is more useful
Answer: b [Reason:] In frequency modulation, frequency of carrier varies with the modulated wave. It has many advantages over AM but requirement of low bandwidth is not the one.
8. Which of the following is the advantage of base modulation over collector modulation of a class C amplifier?
a) lower modulation power is required
b) higher power output per transistor
c) better efficiency
d) better linearity of modulation
Answer: a [Reason:] Base modulation has many advantage over collector modulation. Its most important use is its requirement of low modulation power.
9. What is the radio frequency range of a frequency modulated signal?
a) 20-80 MHz
b) 100-200 MHz
c) 200-350 MHz
d) 90-105 MHz
Answer: d [Reason:] The standard frequency range of a frequency modulated signal is between 90-105 MHz.
10. Vestigial side band (VSB) is most commonly used in ________
a) Television Transmission
d) Laser Equipments
Answer: a [Reason:] Vestigial side band is highly used in transmission because it requires low bandwidth. It is a type of amplitude modulation technique that encodes data by vary amplitude of a single carrier frequency.
Communications MCQ Set 3
1. In pulse code modulation bandwidth required is low.
Answer: b [Reason:] PCM stands for pulse code modulation. It is a digital technique. In PCM usually a large bandwidth is required.
2. How do we eliminate the ghosts in the picture?
a) by using a long transmission line
b) by using a booster
c) by changing the orientation of antenna
d) by twisting the transmission line
Answer: c [Reason:] Change in antenna orientation helps in improving the reception of signals which further removes ghosts in the picture.
3. For getting maximum undistorted transmitted power in a carrier wave, the value of modulation should be _________
Answer: a [Reason:] The possible maximum value of modulation can be one. At this value we have maximum undistorted transmitted power.
4. To avoid fading in communication, broad band antenna is used.
Answer: b [Reason:] It is generally observed that a ship to ship communication suffers from fading. This problem can be avoided by using diverse frequency.
5. What is the commercial channel bandwidth in frequency modulated system?
a) 150 KHz
b) 250 KHz
c) 500 KHz
d) 900 KHz
Answer: a [Reason:] The standard commercial channel bandwidth for frequency modulated system is about 150 KHz.
6. A buffer amplifier is a ________
a) double tuned amplifier
b) tuned amplifier
c) high gain DC amplifier
d) cathode amplifier
Answer: c [Reason:] A buffer amplifier is basically a high gain DC amplifier. It is basically used for transferring voltage from a high output impedance level to a low input impedance level circuit.
7. The direction of rotation of a CD is clockwise.
Answer: b [Reason:] CD stands for compact disk. The direction of rotation of Compact Disk is anticlockwise.
8. If the length of antenna is equal to whole wavelength the radiation is zero in all direction?
Answer: b [Reason:] If the length of antenna is equal to whole wavelength only the radiations which is at right angles is zero.
9. What is the full form of PAM?
a) Pulse Analogue Modulation
b) Phase Analogue Modulation
c) Pulse Amplitude Modulation
d) Phase Amplitude Modulation
Answer: c [Reason:] In communication, PAM stands for Pulse Amplitude Modulation. In PAM, message signal is encoded in the amplitude of a series of signal pulse.
10. In a TV receiver antenna the length of reflector rod is _________
a) same as that of dipole
b) less than that of dipole
c) more than that of dipole
d) may be equal, more or less than that of dipole
Answer: c [Reason:] The length of receiving antenna must be more than that of dipole to get a better reception of signals.
Communications MCQ Set 4
1. What is the full form of PSTN?
a) Public Switched Telephone Network
b) Primary Switched Telephone Network
c) Private Switched Telephone Network
d) Public Service Telephone Network
Answer: a [Reason:] PSTN stands for Public Switched Telephone Network. It is the aggregate of the world’s circuit-switched telephone network.. It helps in providing services for public telecommunication.
2. Which statement is true about Huffman code?
a) allow errors to be detected but not corrected
b) allow only alphanumeric data to be corrected
c) allow errors to be detected and corrected
d) allow alphanumeric data to be compressed
Answer: d [Reason:] Huffman is generally used to convert fixed length codes into variable length codes. It results in lossless compression. It allows alphanumeric data to be compressed.
3. What is the another name for VRC?
Answer: c [Reason:] VRC is generally used in communication. It is same as parity.
4. What is required in SDLC to use flags?
a) Different flags at either end of a frame
c) Complex data bits
d) Bit stuffing
Answer: d [Reason:] SDLC stands for Software Development Life Cycle. It consists of a detailed plan describing how to develop and maintain software. Bit stuffing is required in it, if we want to use flags.
5. Thermal noise, shot noise and transit time noise is part of internal noise in communication.
Answer: a [Reason:] Internal noise in communication is the noise that gets generated within the receiver or communication system. It may be put into the following categories: thermal noise, shot noise, transit time noise.
6. In amplitude modulation, magnitude of side bands is 2ma times the carrier amplitude.
Answer: b [Reason:] In amplitude modulation, amplitude of carrier is varied with respect to wave being propagate. In amplitude modulation, magnitude of side bands is 4ma times the carrier amplitude.
7. Synchronous transmission is more efficient than asynchronous transmission because _________
a) it has no start and stop bits
b) it has start and stop bits
c) it has more data bits than asynchronous transmission
d) it has alphanumeric data bits
Answer: a [Reason:] In synchronous transmission both sender and receiver access the data according to same clock. It has no start and stop bits and thus it has more efficient.
8. In data transmission, character code only includes alphanumeric characters.
Answer: b [Reason:] Character code not only includes alphanumeric characters. But it also includes data link control characters and graphic control chatacters.
9. If a digital data is not used to carry characters, then it is called as ________
a) numerical data
b) binary data
c) character data
d) floating data
Answer: b [Reason:] In a binary data user can take only two values 0’s and 1’s. So it is binary data which can’t be used for carrying characters.
10. What is the full form of POTS?
a) Private Office Telephone System
b) Public Office Telephone System
c) Primary Office Telephone System
d) Plain Old Telephone Service
Answer: d [Reason:] POTS is an analog telephone service. It is implemented over copper twisted pair wires. It is based on Bell Telephone System. POTS is used more widely due to its reliability.
Communications MCQ Set 5
1. Calculate power in each sideband, if power of carrier wave is 176W and there is 60% modulation in amplitude modulated signal?
Answer: d [Reason:] Modulation index = 0.6 and Pc = 176W. Power in sidebands may be calculated as
2. What is the full form of SDLC?
a) Synchronous Data Link Character
b) Synchronous Data Line Control
c) Synchronous Data Line Character
d) Synchronous Data Link Control
Answer: d [Reason:] SDLS stands for Synchronous Data Link Control. It is a layer 2 protocol for IBM’s Systems Network Architecture. It supports multipoint links as well as error-correction.
3. Mostly LANs are based on Ethernet.
Answer: a [Reason:] LAN is a computer network that interconnects computers within a limited area. Most LANs are based on Ethernet only.
4. CSMA stands for _________
a) Carrier Sense Multiple Access
b) Carrier Sense Multiple Access
c) Carrier Server Multiple Access
d) Client Server Multiple Access
Answer: a [Reason:] CSMA stands for Carrier Sense Multiple Access. It is a media access control protocol. In it a node verifies the absence of other traffic before transmission.
5. What we called each computer in a network?
Answer: a [Reason:] In networks, each connected computer is seen as a node.
6. Which network never experienced a collision?
d) all networks have collision at some point
Answer: b [Reason:] Token passing is a channel access method. In it, a signal which is seen as a token is passed between nodes to authorize that node to communicate. Token passing never experiences any type of collisions.
7. What is the effect of too many collisions in any network?
a) network slows down
b) network goes down
c) cable overheats
d) data gets lost
Answer: a [Reason:] If a network receives too many collisions, it directly affects its connected nodes. Due to which the network finally slows down.
(Q.8 – Q.11) An AM signal is represented by x(t) = (30 + 2Sin(700πt)) Cos(2πt x 10²t)V.
8. The modulation index is
Answer: b [Reason:] Given equation can be written as 30(1 + 0.066 Sin(700πt)). So modulation index is 0.066.
9. Carrier power of the wave is?
Answer: c [Reason:]
10. Find the total power of amplitude modulated wave?
Answer: d [Reason:] Total power,
11. What is its sideband power?
Answer: b [Reason:] Sideband power is (Pt – Pc) i.e. 451 – 450 = 1W.