334 + Interview Questions in Communication Systems in Electronics and Communication Engineering Page 4 InterviewSolution

151.	In a two stage cascade amplifier, each stage has a gain of 10 dB and noise figure of 10 dB. The overall noise factor is
Answer» .

Discussion

152.	If is dielectric constant of a medium, the velocity factor in that medium is
Answer» .

Discussion

153.	Some possible disadvantages of high level modulation in TV transmitters are Out of above which are true?
Answer» All these are true.

Discussion

154.	Full duplex operation
Answer» Full duplex system has all these features.

Discussion

155.	In a tape recorder the erase head is
Answer» It is engaged during recording to erase the previous matter.

Discussion

156.	Some desirable features of a computer communication network are Which of the above are true?
Answer» All the three features are necessary.

Discussion

157.	Television transmission is by
Answer» The reception of signals by space waves is governed by line of sight range limited to about 75 kms or so. For frequencies above 30 MHz (generally used for television) communication is through space waves.

Discussion

158.	Beam width of an antenna is expressed in
Answer» Beam width is the angular separation between the two half power points on the power density radiation pattern. It is expressed in degrees.

Discussion

159.	In broadcast television, the number of lines per frame is chosen to be odd number to
Answer» Odd number of lines per frame makes interlacing easier.

Discussion

160.	In a picture tube, the video signal is applied to
Answer» Video signal is applied to cathode.

Discussion

161.	If frames are repeated at 60 Hz and each frame has 525 lines, the time for scanning one horizontal line (for progressive scanning and no interlacing) is about
Answer» .

Discussion

162.	The F.T. of { ∪()} is equal to . Therefore is
Answer» Apply duality property. j F[g(t)] G(f) F[G(t)] G(-f).

Discussion

163.	Sound waves are electromagnetic waves.
Answer» Sound waves are not electromagnetic in nature.

Discussion

164.	In major diatonic musical scale, an octave is divided into
Answer» A major diatomic scale has 7 intervals between one octave.

Discussion

165.	The bandwidth of DSB suppressed carrier modulation system when the modulating frequency varies between 500 Hz and 5 kHz is
Answer» fm = 5 kHz - 500 Hz 4.5 kHz Bandwidth = 2 fm 2 x 4.5 kHz = 9 kHz.

Discussion

166.	The filter circuit for feeding a wooffer has
Answer» Series inductance and shunt capacitance is a low pass circuit.

Discussion

167.	The power to the portable unit of a cordless telephone is provided by
Answer» Rechargeable cells feed the portable unit.

Discussion

168.	In a AM wave the carrier and one of the side bands is suppressed. If = 0.5, the percentage saving in power is
Answer» .

Discussion

169.	Computer communication networks have
Answer» All the three configurations are used.

Discussion

170.	In the television system in India, the aspect ratio is
Answer» Aspect ratio is the width/height ratio of TV receiver. It is .

Discussion

171.	A remote control for TV uses
Answer» Infrared LED transmits the pulse. At receiver photo diode converts infrared signals into electrical signals.

Discussion

172.	In the FM wave described by equation = 15 sin (4 x 10 + 3 sin 1100 ), the carrier frequency and signal frequency respectively are
Answer» .

Discussion

173.	A sequence () with the transform X() = + - 2 + 2 - 3 - 4 is applied as an input to a linear, time invariant system with the impulse response () = 2δ( - 3) where The output at = 4 is
Answer» Y(Z) = X(Z) x H(Z) = 2 x (Z4 + Z2 - 2Z + 2) x Z-3 Y(n) = 2[δ(n + 1) - δ(n - 1) - 2(n - 2) + 2δ(n - 3) - 3δ(n - 7)] at n = 4, Y(4) = 0.

Discussion

174.	If a signal voltage V is accompanied by a noise voltage V the signal to noise ratio is
Answer» Power is proportional to V2.

Discussion

175.	Video signals are transmitted through
Answer» Because of large bandwidth requirement, modulation of video signals is possible only by amplitude modulation.

Discussion

176.	A TV receiver has 20 kV EHT supply and total beam current (for 3 electron guns) of 1500 μA. The power handled by IHVT is
Answer» P = 20 x 103 x 1500 x 10-6 = 30 W.

Discussion

177.	The Hilbert transform of cos ω + sin ω is
Answer» J[s(t)] = s(t + 90°).

Discussion

178.	In ionosphere incidence angle is 60°. The maximum usable frequency is equal to
Answer» .

Discussion

179.	The generally used value of EHV supply in TV receivers is
Answer» It is 1 kV per diagonal inch.

Discussion

180.	The number of channels available in MF band (300 kHz - 3 MHz) for AM modulating signal of 20 kHz is
Answer» In MF band, frequency space available = 3000 - 300 2700 kHz when AM is used Bandwidth of each channel. = 2 x 20 kHz = 40 kHz .

Discussion

181.	The function of blend control in stereo system is
Answer» Dilution of the effect of any channel to give balanced output from left and right channels is called blind control.

Discussion

182.	E and H fields are perpendicular to each other.
Answer» Radio waves have very high speed equal to that of light but speed of sound waves is very low.

Discussion

183.	If transmission bandwidth is doubled in FM, SNR is
Answer» SNR changes in the ratio of square of change in bandwidth.

Discussion

184.	Directivity means
Answer» Directivity means maximum directive gain.

Discussion

185.	In a superheterodyne receiver, having no RF amplifier, the IF is 455 kHz. The image frequency at 1000 kHz is
Answer» Image frequency = 1000 - 455 = 545 kHz.

Discussion

186.	Audio tapes have two tracks each 2.5 mm wide.
Answer» Deck is much superior to tape recorder.

Discussion

187.	In the television system in India, the odd and even fields are scanned
Answer» Each field is scanned 25 times but alternately.

Discussion

188.	A sinusoidal signal with peak to peak amplitude of 1.536 volt is quantized into 128 levels using a mid-rise uniform quantizer. The quantization noise power is
Answer» .

Discussion

189.	An FM wave is made to pass through a frequency tripler. If original modulation index is , the output of tripler has a modulation index equal to
Answer» Frequency tripler makes modulation index three times.

Discussion

190.	Consider the draw backs Which of these draw backs does Delta modulation have?
Answer» In delta modulation the, recovered waveform may be dc whereas the original signal is not dc. This noise is called granular noise.

Discussion

191.	It is required to increase the maximum range of a radar by a factor of two. The peak power transmitted in the radar system has to be increased by a factor of
Answer» Range μ (Power)0.25

Discussion

192.	Armstrong F.M. transmitter performs frequency multiplication in stages
Answer» where (Δf) is the frequency deviation.

Discussion

193.	A source generates three symbols with probabilities 0.25, 0.25, 0.50 at a rate of 3000 symbols per second. Assuming independent generation of symbols, the most efficient source encoder would have average bit rate is as
Answer» Use Shannon Fano coding. (0.25) is encoded as 01 Number of bits/sec = 0.25 x 3000 x 2 + 0.25 x 3000 x 2 + 0.5 x 3000 45000 bits/sec.

Discussion

194.	The filter circuit for feeding tweeter has
Answer» Series capacitance and shunt inductance is high pass circuit.

Discussion

195.	A balun provides an impedance transformation of
Answer» Balun has turn ratio of 2 : 1. Therefore, impedance transformation is 4 : 1.

Discussion

196.	A signal () with bandwidth 500 Hz is first multiplied by a signal () where . The resulting signal is then passes through an ideal low pass filter with bandwidth 1 kHz the output of the low pass filter would be
Answer» Multiplication in time domain is equivalent to convolution. According to the property of impulse signal, convolution of a signal m(t) with δ(t) is signal itself. m(t) x g(t) m(t).

Discussion

197.	If γ = (S/N)/(S/N) where S and S are signal power output and signal power input and N and N are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are
Answer» SSB - SC and SSB - DB have γ = 1 and are similar from noise point.

Discussion

198.	Vidicon and plumbicon operate on the principle of
Answer» Photo conduction uses the fact that resistivity of some materials depends on intensity of light falling on their surface.

Discussion

199.	A TV receiver has a width of 60 cm. The aspect ratio is 4/3. The required EHT supply is about
Answer» EHT supply is 1 kV per diagonal inch. Height = 60 x = 45 cm. Diagonal = .

Discussion

200.	The typical squelch circuit
Answer» To suppress noise when carrier is absent, squelch circuit cuts off audio amplifier.

Discussion

Explore topic-wise InterviewSolutions in .

In a two stage cascade amplifier, each stage has a gain of 10 dB and noise figure of 10 dB. The overall noise factor is

If is dielectric constant of a medium, the velocity factor in that medium is

Some possible disadvantages of high level modulation in TV transmitters are Out of above which are true?

Full duplex operation

In a tape recorder the erase head is

Some desirable features of a computer communication network are Which of the above are true?

Television transmission is by

Beam width of an antenna is expressed in

In broadcast television, the number of lines per frame is chosen to be odd number to

In a picture tube, the video signal is applied to

If frames are repeated at 60 Hz and each frame has 525 lines, the time for scanning one horizontal line (for progressive scanning and no interlacing) is about

The F.T. of { ∪()} is equal to . Therefore is

Sound waves are electromagnetic waves.

In major diatonic musical scale, an octave is divided into

The bandwidth of DSB suppressed carrier modulation system when the modulating frequency varies between 500 Hz and 5 kHz is

The filter circuit for feeding a wooffer has

The power to the portable unit of a cordless telephone is provided by

In a AM wave the carrier and one of the side bands is suppressed. If = 0.5, the percentage saving in power is

Computer communication networks have

In the television system in India, the aspect ratio is

A remote control for TV uses

In the FM wave described by equation = 15 sin (4 x 10 + 3 sin 1100 ), the carrier frequency and signal frequency respectively are

A sequence () with the transform X() = + - 2 + 2 - 3 - 4 is applied as an input to a linear, time invariant system with the impulse response () = 2δ( - 3) where The output at = 4 is

If a signal voltage V is accompanied by a noise voltage V the signal to noise ratio is

Video signals are transmitted through

A TV receiver has 20 kV EHT supply and total beam current (for 3 electron guns) of 1500 μA. The power handled by IHVT is

The Hilbert transform of cos ω + sin ω is

In ionosphere incidence angle is 60°. The maximum usable frequency is equal to

The generally used value of EHV supply in TV receivers is

The number of channels available in MF band (300 kHz - 3 MHz) for AM modulating signal of 20 kHz is

The function of blend control in stereo system is

E and H fields are perpendicular to each other.

If transmission bandwidth is doubled in FM, SNR is

Directivity means

In a superheterodyne receiver, having no RF amplifier, the IF is 455 kHz. The image frequency at 1000 kHz is

Audio tapes have two tracks each 2.5 mm wide.

In the television system in India, the odd and even fields are scanned

A sinusoidal signal with peak to peak amplitude of 1.536 volt is quantized into 128 levels using a mid-rise uniform quantizer. The quantization noise power is

An FM wave is made to pass through a frequency tripler. If original modulation index is , the output of tripler has a modulation index equal to

Consider the draw backs Which of these draw backs does Delta modulation have?

It is required to increase the maximum range of a radar by a factor of two. The peak power transmitted in the radar system has to be increased by a factor of

Armstrong F.M. transmitter performs frequency multiplication in stages

A source generates three symbols with probabilities 0.25, 0.25, 0.50 at a rate of 3000 symbols per second. Assuming independent generation of symbols, the most efficient source encoder would have average bit rate is as

The filter circuit for feeding tweeter has

A balun provides an impedance transformation of

A signal () with bandwidth 500 Hz is first multiplied by a signal () where . The resulting signal is then passes through an ideal low pass filter with bandwidth 1 kHz the output of the low pass filter would be

If γ = (S/N)/(S/N) where S and S are signal power output and signal power input and N and N are noise power output and noise power input, the value of γ for SSB-SC and DSB-SC amplitude modulated system respectively are

Vidicon and plumbicon operate on the principle of

A TV receiver has a width of 60 cm. The aspect ratio is 4/3. The required EHT supply is about

The typical squelch circuit