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This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 201. |
Where do we use amplitude limiters ? |
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Answer» The amplitude limiters are generally used in frequency modulated receivers. They remove the variation in amplitude of the modulated carrier wave caused by noise. |
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| 202. |
What is full form of AGC ? Where is it used? |
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Answer» AGC stands for automatic gain control. It is used in a receiver so that the strength of received signal is almost constant. |
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| 203. |
What are the band widths of an A.M. radio station and an FM radio station? |
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Answer» Band width used for AM radio transmission is 10 kHz and for FM radio transmission, band width is 150 kHz. |
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| 204. |
What are the band widths of an A.M. radio station? |
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Answer» For an AM radio station, band width is generally 10kHz. |
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| 205. |
What is the function of repeater in a communication system? |
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Answer» A repeater is a combination of a transmitter, an amplifier and a receiver. It picks up a signal from transmitter, amplifies it and retransmits it to the receiver sometimes with a change of carrier frequency. |
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| 206. |
What is audio frequency range? |
| Answer» The audio frequency signals range from 20 Hz to 20kHz. | |
| 207. |
Communication is the process ofA. keeping in touchB. exchange informationC. broad castingD. entertainment by electronics |
| Answer» Correct Answer - B | |
| 208. |
A repeater is a combination ofA. ReceiverB. AmplifierC. TransmitterD. All of these |
| Answer» Correct Answer - D | |
| 209. |
Audio frequency range is fromA. 100 Hz to a kHzB. 20 Hz to 20 kHzC. 3 KHz to 15 kHzD. 20 Hz to 2 kHz |
| Answer» Correct Answer - B | |
| 210. |
Which one of the following has the maximum energy ?A. Radio wavesB. Infrared raysC. Ultraviolet raysD. Micro waves |
| Answer» Correct Answer - C | |
| 211. |
The losses in transmission lines areA. radiation losses onlyB. conductor heating onlyC. dielectric heating onlyD. all of these |
| Answer» Correct Answer - D | |
| 212. |
The disturbance or distortion in the transmission and processing of message signals is calledA. NoiseB. AttenuationC. InterferenceD. None of these |
| Answer» Correct Answer - A | |
| 213. |
Decrease in signal strength due to energy losses is calledA. DistortionB. InterferenceC. AttenuationD. Noise |
| Answer» Correct Answer - C | |
| 214. |
A device which provides output in electrical form or it has input in electrical form is called aA. TransmitterB. ReceiverC. RepeaterD. Transducer |
| Answer» Correct Answer - D | |
| 215. |
Out of the following, which is not an essential element of a communication system?A. TransmitterB. TransducerC. ReceiverD. Communication channel |
| Answer» Correct Answer - B | |
| 216. |
What should be the length of the diploe antenna for a carrier wave of frequency `3 xx 10^(8) Hz`? |
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Answer» Here, `v = 3 xx 10^(8)Hz`, `c= 3xx10^(8)m//s` Length of dipole antenna `= lambda/2 = c/2v` (Hertz Antenna) ` = (3 xx 10^(8))/(2 xx 3 xx 10^(8)) = 0.5m` This antenna is not grounded. On the other hand, Marconi antenna is grounded and its length ` = lambda/4 = c/4 v = (3xx10^(8))/(4xx3xx10^(8))` `= 0.25 m` |
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| 217. |
If sky wave with a frequency of 60 MHz is incident on D- region at an angle of `30^@`, then find the angle of refractive. |
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Answer» For D-region, `N = 10^(9) m^(-3)`. Here `v = 60 xx 10^6 Hz` Refractive index of the atmospheric layer is `mu = [ 1- (81.45N)/v^2]^(1//2) = sqrt( 1- (81.45 xx 10^9)/(60 xx 10^6)^2) ~~1` Now, `mu = (sin i)/(sin r) = 1 or sin i = sin r or r = i = 30^@` . |
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| 218. |
The intensity of a light pulse travelling along a communication channel decreases exponentially with distance x according to the relation `I=I_0 e^(-alpha x)`, where `I_0` is the intensity at x = 0 and `alpha` is the attenuation constant. What is the distance travelled by the wave, when the intensity reduces by 75% of its initial intensity?A. `(log_e4)/alpha`B. `(log_e2)/alpha`C. `alpha/(log_e 4)`D. `alpha/(log_e 2)` |
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Answer» Correct Answer - A `I=I_0e^(-alpha x)` is the intensity of the light pulse. When the initial intensity is reduced by 75 % , the intensity becomes (25%) `I=I_0/4` `because I=I_0 e^(-alpha x ) therefore I_0/4 = I_0e^(-alpha x ) therefore 1/4 = e^(-alpha x )` Taking logs on both sides , we get `therefore log_e 1-log_e 4=-alphax` `therefore log_e4=alphax` `therefore x=(log_e4)/alpha` `therefore` The intensity is reduced by 75% at a distance of `(log_e 4)/alpha ` |
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| 219. |
A sinusoidal voltage is used to amplitude modulate a sinusoidal voltage of amplitude 1 KV. This results in the production of two side bands, each of amplitude 200 V. What is the modulation index ?A. 0.1B. 0.2C. 0.3D. 0.4 |
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Answer» Correct Answer - D Amplitude of the carrier wave `(A_C)` = 1 KV = 1000 V Amplitude of each side band `=(muA_C)/2` `therefore 200=(muxx1000)/2 therefore mu = (200xx2)/1000=0.4` |
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| 220. |
Identify the logic gates marked X,Y in Fig. MTP 1.1. write down the output at y, when `A=1,B=1` and `A=0` and B=0. |
| Answer» X is NOR gate and Y is NOT gate: (1,0). | |
| 221. |
ln the night, ionosphere consists ofA. E, `F_1` and `F_2` layersB. D,E,`F_1` and `F_2` layersC. E and `F_2` layersD. D,E and `F_2` layers |
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Answer» Correct Answer - C The ionosphere consists of different layers D,E,`F_1` , `F_2` . At night layers D and `F_1` disappear. Hence it consists of only E and `F_2` layers |
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| 222. |
The maximum peak-to-peak voltage of an `AM` wave is `16 mV` and the minimum peak-to-peak voltage is `4 mV`. The modulation factor is equal toA. `2/3`B. `2/5`C. `1/3`D. `3/5` |
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Answer» Correct Answer - D `E_"max"=16/2`=8 mV `E_"min" = 4/2 =2 ` mV `therefore mu=(E_"max"-E_"min")/(E_"max"+E_"min") =(8-2)/(8+2)=6/10=3/5` |
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| 223. |
In a satellite communication, what is the minimum angular spacing of two satellites using the same frequency band. |
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Answer» In satellite communication, when two satellites using the same frequency band came close enough to each other, they will interfere with each other. Due to which the signals received on ground stations will not be clear. To avoid this problem, current standards require a `4^@` spacing (angular displacement as measured from the earth) in the `4//6 GHz` band and a `3^@` spacing in `12//14 GHz`. |
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| 224. |
Identify the mathematical expression for amplitude modulated wave:A. `A_( c) sin [{ omega_(c ) + k_(1) v_(m) (t)} t + phi ]`B. `A_(c ) sin { omega_( c ) t + phi + k_(2) v_(m) (t)}`C. `{ A_(c ) + k_(2) v_(m) (t) } sin (omega_(c ) t + phi )`D. `A_(c ) v_(m) (t) sin [ omega_( c) t + phi]` |
| Answer» Correct Answer - C | |
| 225. |
In frequency modulation, the amount of frequency deviation depends on theA. Frequency of audio signalB. Amplitude of audio signalC. Both the frequency and amplitude of audio signalD. None of these |
| Answer» Correct Answer - B | |
| 226. |
The communication satellites are parked at a height of (from surface of earth)A. 36 kmB. 360 kmC. 3600 kmD. 36000 km |
| Answer» Correct Answer - D | |
| 227. |
Identify the mathematical expression for amplitude modulated wave:A. `(A_c+A_m sin omega_m t) cos (omega_c t+phi)`B. `A_c sin {omega_c t +phi + k_2v_m(t)}`C. `{A_c +k_2v_m (t)} sin (omega_c t + phi)`D. `A_cv_m (t) sin [omega_c t + phi]` |
| Answer» Correct Answer - A | |
| 228. |
The distance between consecutive maxima and minima is given by-A. `lambda//2`B. `2lambda`C. `lambda`D. `lambda//4` |
| Answer» Correct Answer - D | |
| 229. |
Long distance short-wave radio broadcasting usesA. Ground waveB. ionospheric waveC. Direct waveD. Sky wave |
| Answer» Correct Answer - B | |
| 230. |
3-30 MHz frequency range is known asA. HFB. VHFC. UHFD. MF |
| Answer» Correct Answer - A | |
| 231. |
Long distance short-wave radio broadcasting usesA. Ground waveB. Sky waveC. Dried waveD. Space wave |
| Answer» Correct Answer - B | |
| 232. |
Digital signalsA. Do not provide a continuous set of valuesB. Utilize binary systemsC. Ensures error and noise free communicationD. All of these |
| Answer» Correct Answer - D | |
| 233. |
What is the range of frequencies used in satellite communication? What is common between these waves and light waves? |
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Answer» Range of frequencies used in satellite communication is : uplink : `5.925 "to" 6.425 GHz` and down link `: 3.7 "to" 4.2 GHz`. Both, the waves used in satellite communication and light waves are electromagnetic waves and can travel through vacuum with the same speed. |
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| 234. |
What is the range of frequencies used in satellite communication? What is common between these waves and light waves?A. 1 MHzB. 1 KHzC. 20 MHzD. 20 kHz |
| Answer» Correct Answer - C | |
| 235. |
A photodetector is made from a compound semiconductor with band gap 0.73eV. The maximum wavelength it can detect isA. 12400 ÅB. 17030 ÅC. 6200 ÅD. 1703 Å |
| Answer» Correct Answer - B | |
| 236. |
the attenution in optical fibre is mainly due toA. absorptionB. scatteringC. neither absorption nor scatteringD. both (1) and (2) |
| Answer» Correct Answer - D | |
| 237. |
The space waves which are affected seriously by atmospheric condition are-A. MFB. HFC. VHFD. UHF |
| Answer» Correct Answer - D | |
| 238. |
A T.V. tower has a height 150m. What is the population density around the T.V. tower if the total population covered is 50 lakh? (Radius of earth `=6.4xx10^(6)m)`A. `82.6km^(_2)`B. `800.6km^(-2)`C. `826.6km^(-2)`D. `876.6km^(-2)` |
| Answer» Correct Answer - C | |
| 239. |
A message signal frequency `omega_(m)` is superpiosed on a carrier wave of frequency `omega_(c)` to gent an amplitude modulated wave (`AM`).The frequency of the `AM` wave will beA. `omega_(m)`B. `omega_(c )`C. `( omega_( c) + omega_( m))/( 2)`D. `( omega_( c) - omega_( m))/( 2)` |
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Answer» Correct Answer - B In amplitude modulation the frequency of modulated wave is equal to the frequency of carrier wave . Thus option (b) is correct . |
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| 240. |
When the modulation percentage is 75, an AM transmitter produces to 10kW. How much of this is carrier power? |
| Answer» Correct Answer - 7.81 kW | |
| 241. |
If `v_(r)` is velocity of red light and `v_(b)` is velocity of blue light in vaccum thenA. `v_(r) gt v_(b)`B. `v_(r) lt v_(b)`C. ` v_(r) = v_(b)`D. none of these |
| Answer» Correct Answer - C | |
| 242. |
Which of the following is not an electromagnetic wave?A. X - raysB. UV raysC. Sound wavesD. radio waves |
| Answer» Correct Answer - C | |
| 243. |
Sky wave propagation is also calledA. tropospheric wave propagationB. satellite communicationC. ionospheric wave propagationD. none of these |
| Answer» Correct Answer - C | |
| 244. |
The wavelength range of `SHF` ( super high frequency) waves isA. `1 m" to" 10 m `B. ` 1 cm "to" 10 cm`C. `1 m "to" 1 km`D. `10 m "to" 100 m ` |
| Answer» Correct Answer - B | |
| 245. |
Ground wave propagation is not suited forA. high frequency signalsB. low frequency signalsC. medium frequency signalsD. none of these |
| Answer» Correct Answer - A | |
| 246. |
Ground wave propagation is suitable forA. high frequenciesB. very short wavelengthsC. low frequenciesD. T.V. signals |
| Answer» Correct Answer - C | |
| 247. |
The correct relation between plasma frequency `v` of a radio wave and electron density `N` of the ionosphere layer isA. ` v = 10^(9) N`B. ` v = 9 N`C. `v = 9 sqrt(N)`D. `N = 9 sqrt(v)` |
| Answer» Correct Answer - C | |
| 248. |
Refractive index `mu` of a layer in sky wave propagation is given byA. ` mu = sqrt( 1 - ( 81.45 N)/(v^(2)))`B. ` mu = sqrt( 1 + ( 81.45 N)/(v^(2)))`C. ` mu = sqrt( 1 + ( 81.45 N^(2))/(v))`D. ` mu = sqrt( 1 - ( 81.45 N^(2))/(v))` |
| Answer» Correct Answer - A | |
| 249. |
Name the two regions of AM band. |
| Answer» Medium wave band and short wave band. | |
| 250. |
The audio signalA. can be sent directly over the air for large distanceB. cannot be sent directly over the air for large distanceC. possess very high frequency.D. none of these |
| Answer» Correct Answer - B | |