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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.
| 251. |
The efficiency of using a binary system for selection of 1 out of 13 equally probable events is |
| Answer» log2 13 = 3.7 therefore, number of bits = 4. . | |
| 252. |
The most suitable method for detecting a modulated signal () = (3 to 6 cos 2) cos 2 is |
| Answer» Because it is an AM envelope. | |
| 253. |
In VHS format each video head is tilted from azimuth by |
| Answer» Tilting of heads is done to reduce cross-talk. | |
| 254. |
The number of possible colours with a 4 line digital input monitor are |
| Answer» 24 = 16. | |
| 255. |
Convolution of ( + 5) with impulse function δ( - 7) is equal to |
| Answer» Convolution of | x(t + s) with d(t - 7) x(t - 7 + 5) x(t - 2). | |
| 256. |
An angle modulated signal is given by () = cos 2 (2 x 10 + 30 sin 150 + 40 cos 150). The maximum frequency and phase deviations of () are |
| Answer» s(t) = cos 2p(2 x 10+16t + 30 sin 150t + 40 cos 150t) Phase deviation = 100 p Frequency deviation = 7.5 kHz. | |
| 257. |
If velocity of sound waves in air at 0°C is 330 m/s, the velocity at 40°C is about |
| Answer» or v = 353 m/s. | |
| 258. |
A 5000 W signal is attenuated by - 196 dB. The resultant signal strength is |
| Answer» or P = 1.26 x 10-16 W. | |
| 259. |
A 400 W carrier is amplitude modulated with = 0.75. If single side band suppressed carrier is used the total power in modulated wave is |
| Answer» . | |
| 260. |
In TV transmitter, the function of duplexer is |
| Answer» Duplexer combines video and audio signals so that they can be sent out by a common antenna. | |
| 261. |
In single tone AM modulation, the transmission efficiency for = 1 is |
| Answer» Since signal power = 0.5 PC and total power is 1.5 PC efficiency is 33.3%. | |
| 262. |
An antenna has a resistance of 50 Ω and an equivalent noise resistance of 30 Ω The noise figure in decibels is |
| Answer» . | |
| 263. |
An MTI radar operating at 5 GHz has a PRF of 800 pps. The lowest blind speed is |
| Answer» Lowest blind speed = 800 x 0.06 = 48 m/s. | |
| 264. |
For maximum output the width of air gap of audio head should be |
| Answer» When width of air gap is 0.5 1, output is maximum. | |
| 265. |
The simplest mixer circuit for public address system uses |
| Answer» A mixer circuit has variable resistance in series with each microphone to control intensity of sound. | |
| 266. |
PAM stands for |
| Answer» PAM or pulse amplitude modulation is a system in which signal is sampled at regular intervals and each sample is made proportional to amplitude of the signal at the instant of sampling. | |
| 267. |
Microwave link repeaters are typically 50 km apart in TV transmission due to |
| Answer» Earth's curvature limits line of sight distance. Therefore, repeaters are needed. | |
| 268. |
The tape recorders used in homes have |
| Answer» Common head and common amplifier is used. | |
| 269. |
To separate channels in FDM receiver we have to use |
| Answer» Band pass filter allows a band of frequencies to pass through and attenuates other frequencies. | |
| 270. |
A device with input () and () is characterized by () = (). An FM signal with frequency deviation of 90 kHz and modulating signal bandwidth of 5 kHz is applied to this device. The bandwidth of the output signal is |
| Answer» If we square the signal, bandwidth will becomes double. B.W. for x(t) = 2(90 + 5) = 190 kHz for x2(t) = 2 x 190 380 kHz. | |
| 271. |
Each frequency in the modulating wave gives rise to four side bands. |
| Answer» Each frequency gives two side bands. | |
| 272. |
In the television system in India, each channel is allowed a bandwidth of |
| Answer» Each channel is allowed a bandwidth of 7 MHz. | |
| 273. |
A diode detector load consists of 0.01 μF capacitor in parallel with a 5 k ohms resistor. The maximum depth of modulation without diagonal clipping at modulating frequency of 1000 Hz and 10 kHz is |
| Answer» . | |
| 274. |
Fourier series expansion of a real periodic signal with fundamental frequency is given by It is given that = 3 + 5. then is |
| Answer» For real signal ck = c*-k 3 - i5. | |
| 275. |
Loudness control gives |
| Answer» For depth in sound the low frequency notes, (i.e., bass) need more amplification. | |
| 276. |
A mobile telephone has a range of about |
| Answer» Mobile telephone has about 50 km range. | |
| 277. |
If transmitted power is 75 kW, the field strength at 30 km distance will be about |
| Answer» Using the derivation, . | |
| 278. |
In a perfect conductor the resistor noise is |
| Answer» A perfect conductor does not generate noise. | |
| 279. |
An RF carrier of 12 kV at 1 MHz is amplitude modulated by 1 kHz signal having peak value of 6 kV. The modulation pattern is seen on CRO screen. The voltage indicated will be |
| Answer» Modulation pattern on CRO will show peak to peak value = 2 (12 + 6) = 36 kV. | |
| 280. |
In push pull amplifier, each transistor conducts for |
| Answer» In push pull circuit each transistor conducts for 180° so that complete conduction for 360° occurs. Hence minimum distortion and maximum efficiency. | |
| 281. |
When energy is fed into open wire transmission line the energy may get dissipated due to |
| Answer» All the three cause dissipation of energy as heat. | |
| 282. |
A TV remote control works on the principle of |
| Answer» Infrared light is used in TV remote control. | |
| 283. |
As the magnitude of reverse bias is increased, the capacitance of varactor diode |
| Answer» When magnitude of reverse bias is increased, thickness of depletion layer increases. Capacitance is inversely proportional to thickness. | |
| 284. |
To prevent overloading in the last IF amplifier one should use |
| Answer» Variable sensitivity prevents overloading. | |
| 285. |
In a two tone AM system the two modulating frequencies are 2000 and 4000 rad/sec. If carrier frequency is 2 x 10 rad/sec the frequencies of upper sidebands are |
| Answer» . | |
| 286. |
For a system to be designated as hi-fi, the signal to noise ratio should be at least |
| Answer» Hi-Fi system has a ratio at least equal to 50 dB. | |
| 287. |
Dolby system of noise reduction divides the total audio spectrum into |
| Answer» Dolby A system divides the frequency in 4 bands viz.f < 80 Hz, 80 Hz < f < 2999 Hz, f > 3000 Hz, f > 9000 Hz. | |
| 288. |
In a system an input resistance of 20 kΩ causes a noise voltage of 15μV. If two such input resistances each of 20 kΩ are used in parallel, the total noise voltage will be about |
| Answer» Overall resistance = 10 kW. Noise voltage = (15) = 10.6 μV. | |
| 289. |
For an ideal 3000 Hz channel, S/N ratio is |
| Answer» FALSE | |
| 290. |
In transistor radio receivers the number of IF amplifier stages are |
| Answer» Two IF amplifier stages are very commonly used. | |
| 291. |
To relay outdoor remotely located live programs, TV transmitter use |
| Answer» Microwave links are used. | |
| 292. |
If each short element of signal occupies 20 , the speed is |
| Answer» . | |
| 293. |
A cordless telephone using separate frequencies for transmission in base and portable units is known as |
| Answer» Separate frequencies for transmission from base and portable units allows two way transmission and is called duplex arrangement. | |
| 294. |
For attenuation of high frequencies we should use |
| Answer» Since Xc for high frequencies is low, the high frequencies are shunted to ground and are not transmitted. | |
| 295. |
A modem is classified as low speed if data rate handled is |
| Answer» When data rate in bits per second is upto 600, modem is low speed. | |
| 296. |
VSB modulation is preferred in TV because |
| Answer» VSB (vestigial side band) transmission transmits one side band fully and the other side band partially thus, reducing the bandwidth requirement. | |
| 297. |
A woofer should be fed from the input through a |
| Answer» Woofer is a low frequency loud speaker covering the range 16 Hz to 500 Hz. | |
| 298. |
A 400 W carrier is amplitude modulated with = 0.75. The total power in AM is |
| Answer» . | |
| 299. |
A generator is feeding power to a transmission line of characteristic impedance Z. The line is terminated in impedance Z. Standing waves will be set up if |
| Answer» Both the case, i.e., ZL > Z0 and ZL < Z0 give rise to standing waves. | |
| 300. |
In sound recording the degree of pre-emphasis is about 6 dB/ octave. |
| Answer» It erases the matter already existing on the tape. | |