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## Communications MCQ Set 1

1. If the modulating frequency of a carrier wave varies between 700Hz and 7KHz, find it’s bandwidth?
a) 10 KHz
b) 23 KHz
c) 17.3 KHz
d) 12.6 KHz

Answer: d [Reason:] fm= 7KHz – 700Hz =6.3KHz and Bandwidth = 2fm= 2 x 6.3 = 12.6 KHz.

2. A 400W carrier wave is modulated to a depth of 65%. Find the total power of modulated wave?
a) 512.5W
b) 493W
c) 484.5W
d) 609.6W

Answer: c [Reason:] Pt = Pc (1 + m22). By putting values in the equation we have Pt = 400 (1 +0.6522) = 484.5W.

3. Inductance and capacitance of a line is 0.8 μHm and 32 pFm . Find Z0 )?
a) 158
b) 166
c) 143
d) 127

4. Find VSWR of a line having maximum and minimum value equals to 120mV and 40mV respectively?
a) 3
b) 2
c) 1
d) 4

5. A 1000 KHz carrier is modulated with 300 Hz, 8000 Hz and 2 KHz waves. Determine the frequencies whose chances of occurring in output is least?
a) 1000 KHz
b) 1002 KHz
c) 998 KHz
d) 999.2 KHz

Answer: a [Reason:] Frequencies present in output are of the form fc ± fm, fc ± 2fm, fc ± 3fm.

6. If average power of a transmitter is 4kW and maximum power is 20000KW. What is its duty cycle?
a) 2 x 10-3
b) 2 x 10-4
c) 3 x 10-3
d) 0.05

7. The voltage and electric current of a line are respectively 5kV and 1000μA. Find its power?
a) 12W
b) 13W
c) 5W
d) 10W

Answer: c [Reason:] Power, P =V x I. By substituting the values of voltage(V) and current(I), we have P = (5×103)(1000×10-6) = 5W

8. ________ microphones works on piezoelectric effect?
a) Crystal
b) Carbon
c) Moving coil
d) Condenser

Answer: a [Reason:] Piezoelectric effect is the ability of materials to generate an electric charge in response to applied mechanical stress. Crystal microphones works on the piezoelectric effect.

9. If modulation index of an AM wave is increased from 1.5 to 2, then the transitted power ________
a) remains same
b) increases by 20%
c) increases by 41%
d) increases by 50%

Answer: c [Reason:] When m=1.5, transmitted power .

## Communications MCQ Set 2

1. A Marconi antenna has length equal to ________
a) ʎ4
b) ʎ2
c) 1
d) ʎ8

Answer: a [Reason:] Marconi antenna is like a vertical wire having length one fourth of the working wavelength. It requires a ground plane with very good conductivity.

2. In a Vidicon camera tube, both sides of the target plate have the coating of antimony tri-sulphide.
a) True
b) False

Answer: b [Reason:] In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

3. A trigonometric function is a synonym of ________
a) triangular function
b) orthogonal function
c) singular function
d) rectangular function

Answer: a [Reason:] Trigonometric function is the angle expressed as the ratio of two sides of a triangle that contains the angle. It can also be seen as a synonym of triangular function.

4. White noise is a synonym of ________
a) Atmospheric noise
b) shot noise
c) johnson noise
d) transit time noise

Answer: c [Reason:] White noise is a type of internal noise in communication. It can also be called thermal noise or johnson noise.

5. Local programmes in a cable TV can be telecast at any frequency.
a) True
b) False

Answer: a [Reason:] There is not a fixed frequency range for broadcasting of local programmes in a cable TV. It can be telecast at any frequency.

6. Minimum viewing angle of resolution of human eye is ________

Answer: b [Reason:] Minimum resolution of human eye for clear observation is generally . The diameter of human eye is about 25mm.

7. Power density spectrum of a resistor R can be expressed as ________
a) 2 kTR
b) 1 kTR
c) 0.75 kTR
d) 3 kTR

Answer: a [Reason:] The Power density spectrum of a resistor R can be expressed as 2 kTR where k is Boltzmann’s constant, T is Temperature and R is given resistance.

8. VSB is generally used in ________
a) television production
c) telephonic conversations
d) long distance conversations

Answer: a [Reason:] Vestigial Side Band (VSB) is generally used in television production because it reduces the required bandwidth to half.

9. A helical antenna is used for satellite tracking due to its __________
b) circular polarization
c) linear polarization
d) good front to back ratio

Answer: d [Reason:] Helical antenna consists conducting wire. These conducting wire is wound around it in the form of helix. It is mainly used for satellite tracking due to its good front to back ratio.

10. What is the typical bandwidth of a 2-wire telephone line?
a) 20 Hz to 6 KHz
b) 300 Hz to 3.4 KHz
c) 20 Hz to 20 KHz
d) 200 Hz to 6.5 KHz

Answer: b [Reason:] The bandwidth of a 2-wire telephone line is fixed in a particular range. Its range generally varies between 300 Hz to 3.4 KHz.

## Communications MCQ Set 3

1. What is the full form of SONET?
a) Synchronous Optical Network
b) Standard Optical Network
c) Simple Optical Network
d) Service Optical Network

Answer: a [Reason:] SONET stands for Synchronous Optical Network. SONET transfers multiple digital bit streams in a synchronized way over optical fiber using lasers.

2. VFO stands for ________
a) Voltage Feedback Oscillator
b) Variable Feedback Oscillator
c) Voltage Frequency Oscillator
d) Variable Frequency Oscillator

Answer: d [Reason:] VFO stands for Variable Frequency Oscillator. VFO is an oscillator whose frequency can be tuned over some range. It is a necessary component in any tunable radio.

3. What is used in Hartley oscillator?
a) a piezoelectric crystal
b) an RC time constant
c) a two-capacitor divider
d) a tapped inductor

Answer: d [Reason:] In Hartley oscillator. The oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors. Hartley oscillator was invented in 1915.

4. The conditions for sinusoidal oscillation from an amplifier are called _________
a) Loop-gain criteria
b) Hartley criteria
c) Bode criteria
d) Barkhausen criteria

Answer: d [Reason:] The conditions for sinusoidal oscillation from an amplifier are called Barkhausen criteria. It was invented in 1921.

5. Which parts of a sinusoidal carrier can be modulated?
a) its amplitude
b) its frequency
c) its amplitude, frequency and direction
d) its amplitude, frequency and phase angle

Answer: d [Reason:] If the carrier wave is sinusoidal, then we can vary its amplitude, frequency, and phase in proportion with the wave which is transmitted.

6. The power density of a flicker noise is _________
a) low at high frequencies
b) greater at low frequencies
c) greater at high frequencies
d) low at low frequencies

Answer: b [Reason:] Flicker noise is a form of noise that exhibits an inverse frequency power density curve. Its power density is greater at low frequencies.

7. Power above the minimum required by an optical receiver is called ________
a) overdrive
b) system margin
c) excess gain
d) gain margin

Answer: b [Reason:] System margin is the term used when the applied power is above the minimum required power by an optical receiver.

8. What is the full form of DWDM?
a) Dense Wavelength Division Multiplexing
b) Dense Wavelength Division Modulation
c) Double Wavelength Division Multiplexing
d) Double Wavelength Division Modulation

Answer: a [Reason:] DWDM stands for Dense Wavelength Division Multiplexing. In DWDM, each signal has its own separated wavelength.

9. For signal, m(t) = 50cos(10 × 90t + 30 sin100t), the power dissipated by the 20Ω resistor is ________
a) 100W
b) 65W
c) 74.7W
d) 62.5W

Answer: d [Reason:] On Comparing with the equation, m(t) = Acos(ωct + mf sinωmt). We have A = 50, dissipated power,

10. FTTC stands for ________
a) Fiber To The Curb
b) Fiber Telephone Transmission Cable
c) Fiber Transmission Timing Cable
d) Fiber Transmission Timing Constraint

Answer: a [Reason:] FTTC stands for Fiber To The Curb. It is a replacement of Plain Old Telephone Service (POTS) that we see in our neighborhood.

## Communications MCQ Set 4

1. The output stage in a television transmitter is likely to be ________
a) screen modulated
b) plate modulated
c) rectangular modulated
d) grid modulated

Answer: d [Reason:] We generally use vestigial sideband for television production. VSB is used because it reduces the required bandwidth. The output stage in a television transmitter is generally grid modulated.

2. The advantage of using mechanical filter in filter system of sideband suppression is good band pass.
a) True
b) False

Answer: a [Reason:] The advantage of using mechanical filter in filter system of sideband suppression is smaller size, good band pass, good attenuation characteristics.

3. Television transmission is possible through ________
a) DSB-SC
b) SSB
c) VSB
d) PM

Answer: c [Reason:] We generally use vestigial sideband (VSB) for television production. VSB is used because it reduces the required bandwidth to half.

4. The rms value of a thermal noise voltage is proportional to (where k is Boltzmann’s constant) _______
a) √k
b) k
c) k2
d) k13

Answer: a [Reason:] The root means square value of thermal or white noise is proportional to root k times, where k represents Boltzmann’s constant.

5. For a human eye the minimum viewing angle of resolution should be ʎD where D is iris opening and ʎ is wavelength of light.
a) True
b) False

Answer: b [Reason:] For a human eye the minimum viewing angle of resolution should be 1.22ʎ/D. The diameter of human eye is about 25mm.

6. In amplitude modulation, magnitude of side bands is ________ times the carrier amplitude.
a) ma2
b) 4ma
c) ma
d) 2ma

Answer: b [Reason:] In amplitude modulation, for a good transmission and reception the magnitude of side bands must be 4ma times the amplitude of carrier wave.

7. Noises which get generated within the receiver is called ________
a) Internal noise
b) External noise
d) Default noise

Answer: a [Reason:] Internal noise in communication is the noise that gets generated within the receiver or communication system.

8. Autocorrelation function of white noise is ________
a) an impulse function
b) a step function
c) a constant
d) a variable

Answer: c [Reason:] White noise or thermal noise or Johnson noise is an interior type of noise in communication system. It is a random signal having equal intensities at different frequencies which gives it a constant power and autocorrelation function.

9. In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 (tin oxide) and the side facing electron gun has a coating of antimony trisulphide.
a) True
b) False

Answer: a [Reason:] In a Vidicon camera tube, the side of target plate facing the light has a coating of Sno2 and the side facing electron gun has a coating of antimony trisulphide.

10. Marconi antenna ________
a) is a grounded antenna
b) is an ungrounded antenna
c) can either be grounded or ungrounded antenna
d) can neither be grounded nor ungrounded antenna

Answer: a [Reason:] Marconi antenna is like a vertical wire having length one fourth of the working wavelength. It requires a ground plane with very good conductivity. Hence it is also called as a grounded antenna.

## Communications MCQ Set 5

1. A 1000KHz carrier is modulated by 100Hz and 200Hz waves, then which of the following frequencies cannot be present at the output?
a) 1000.1KHz
b) 999.9KHz
c) 1000.2KHz
d) 999.7KHz

Answer: d [Reason:] Frequencies present at output will be 1000 ± 0.1 and 1000 ± 0.2.

2. A Bluetooth “piconet” has ________
a) 1 node
b) 2 nodes
c) 2 to 8 nodes
d) 2 to 16 nodes

Answer: c [Reason:] Bluetooth is a wireless technology. It is used for exchanging data over short distances. It usually uses frequency hopping. A Bluetooth piconet has 2 to 8 nodes.

3. POCSAG stands for ________
a) Post Office Code Standardization Advisory Group
b) Post Office Common Standardization Advisory Group
c) Pager Office Code Standardization Advisory Group
d) Pager Office Common Standardization Advisory Group

Answer: a [Reason:] POCSAG stands for Post Office Code Standardization Advisory Group. It formulates a paging protocol, known as POCSAG protocol.

4. Who invented the technology CDMA?
a) Qualcomm
b) Bell Labs
c) SAP Labs
d) AT&T

Answer: a [Reason:] CDMA was invented by Qualcomm. CDMA is a channel access method used by various radio communication technologies. CDMA stands for Code Division Multiple Access.

5. AMPS was designed for POTS only.
a) True
b) False

Answer: b [Reason:] AMPS was designed for POTS as well as for voice. It was also designed for the use built into an automobile.

6. What is the full form of MTSO?
a) Minimum Transmitted Signal Output
b) Maximum Transmitted Signal Output
c) Mobile Telephone Switching Office
d) Mobile Telephone Signal Office

Answer: c [Reason:] MTSO stands for Mobile Telephone Switching Office. It contains the switching equipment for routing mobile phone calls.

7. AMPS stands for ________
a) American Mobile Phone System
c) Analog Mobile Phone Service

Answer: b [Reason:] AMPS stands for Advanced Mobile Phone Service. It is a standard system for analog signal cellular telephone service in United States and in other countries.

8. What is number of possible outputs if there is 6 line digital input?
a) 64
b) 32
c) 16
d) 128

Answer: a [Reason:] Total possible outputs will be 26 which is equal to 64.

9. “Station-keeping” refers to ___________
a) antenna maintenance
d) range of frequencies