334 + Interview Questions in Communication Systems in Electronics and Communication Engineering Page 3 InterviewSolution

101.	If transmitted power is 10 kW, the field strength at a distance is 50 mV/m. If transmitted power is reduced to 2.5 kW, the field strength at the same point will be
Answer» E ∝ Pt .

Discussion

102.	Some features of advanced mobile phone service are Which of the above are true?
Answer» All the three features are necessary.

Discussion

103.	The carrier frequency will be if L = 50 µH and C = 1 nF.
Answer» L = 50 µH, C = 1 nF .

Discussion

104.	In case of probability of the message is 1 to 16 then the information will be
Answer» .

Discussion

105.	The saving of power in DSB-SC modulated at 80% is
Answer» .

Discussion

106.	A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will be
Answer» Sideband frequencies will be fc ± fm.

Discussion

107.	A geostationary satellite
Answer» It orbits the earth in a 24 hour period. Thus it appears to be stationed over one spot of the globe.

Discussion

108.	In equally tampered scale, frequency of each tone equals the frequency of lower adjacent tone multiplied by
Answer» Since these are 12 intervals in one octave, hence (2)1/12.

Discussion

109.	A carrier is modulated by two modulating waves A and B having modulation indices of 0.6 and 0.8 respectively. The overall modulation index is
Answer» .

Discussion

110.	A communication channel disturbed by additive white, Gaussian noise has a bandwidth of 4 kHz and SNR of 15. The highest transmission rate that this channel can support (in k bits/sec) is
Answer» Channel capacity = 4000 log2 (1 + 15) = 16000 bits/s.

Discussion

111.	The reactance of coupling capacitor for AC signals in an amplifier, should be
Answer» XC for ac signal should be low so that the attenuation is minimum.

Discussion

112.	In a circuit the value of resistor is made four times. The noise voltage generated by this resistance will
Answer» Noise voltage ∝ R.

Discussion

113.	A resistor of 10 k&ohm; has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 k&ohm; under the same conditions will have an rms noise voltage of
Answer» i ∝ R.

Discussion

114.	Which camera tube has highest sensitivity and very wide spectral response?
Answer» New vicon has very high sensitivity and very wide spectral response which extends well into infrared region.

Discussion

115.	A computer monitor uses 180 W in normal operation and 20 W in sleep mode. The computer is on all the 24 hours but is in sleep mode for 18 hours a days. The energy units saved in 30 days are
Answer» .

Discussion

116.	Resonant circuits are used in
Answer» RF amplifiers use resonant loads (L and C in parallel).

Discussion

117.	Linear diode detector utilizes
Answer» Detection (also called demodulation) is due to rectification property of diode.

Discussion

118.	In the equivalent circuit of a moving coil cone type loudspeaker, the mass of the moving system is represented by
Answer» Mass has inertia and is analogous to inductance.

Discussion

119.	Quantizing error occurs in
Answer» An analog number cannot be converted into an exact digital number. This is called quantizing error.

Discussion

120.	In audio cassettes the width of each recording track is
Answer» Each track is 2.5 mm wide.

Discussion

121.	The most commonly used transistor amplifier circuit is
Answer» Common emitter connection has high power gain, and good current and voltage gains.

Discussion

122.	If aspect ratio is and number of lines in each frame is 625, the number of picture elements in one frame is
Answer» Since there are 625 lines in one frame, the number of picture elements is .

Discussion

123.	In a satellite system circular polarization is to be obtained. The antenna used is
Answer» Helical antenna produces a circularly polarized radiation if its two components are at right angles and are equal. It is very commonly used in radio telemetry.

Discussion

124.	A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 μs and retrace time is 12 μs, the transistor is conducting for about
Answer» Total time for each horizontal line = . Time for trace = 64 - 12 = 52 μs. Time for which transistor is not conducting = 12 + 0.4 x 52 = 32.8 ms. Time for which transistor is conducting = 64 - 32.8 = 31 μs.

Discussion

125.	Indicate the false statement: If SWR on a transmission line is infinite, the line is terminated in
Answer» If line is OC or SC or terminated in pure reactance, SWR is 1.

Discussion

126.	In TV signals colour burst is used
Answer» Colour burst consists of a short train of about 10 cycles sent to the receiver along with synchronous signals. It ensures I and Q phase correctly.

Discussion

127.	The resonant frequency of an R amplifier is 1 MHz and its bandwidth is 10 kHz. The Q factor will be
Answer» .

Discussion

128.	It is found that in a telephone system 60 subscribers initiate calls during a 30 minute interval and the total duration of all the calls is 100 minutes. The load is
Answer» .

Discussion

129.	The name modem is a contraction of terms modulator demodulator.
Answer» Baudot code is 5 bit code.

Discussion

130.	The use of SSB
Answer» One side band is eliminated in SSB. Therefore bandwidth is halved.

Discussion

131.	In the absence of noise, if C is channel capacity in bits/s, δ is channel bandwidth in Hz and N is number of coding levels. Then
Answer» Hartley law C = 2 δf log2N.

Discussion

132.	The open loop gain of an amplifier is 50 but is likely to change by 20%. If negative feedback with β = 0.1 is used, the change in gain will be about
Answer» . Change in gain is about 4%.

Discussion

133.	Audio amplifiers need
Answer» Bass means low frequency tones and treble means high frequency tones.

Discussion

134.	Fields are said to be circularly polarised if their magnitudes are
Answer» Magnitudes should be equal and phase angle ± 90°.

Discussion

135.	Three analog signals, having bandwidths 1200 Hz, 600 Hz, 600 Hz are sampled at their Nyquist rates, encoded with 12 bit words, and time division multiplexed. The bit rate for the multiplexed signal is
Answer» The total message bandwidth = 1200 Hz + 600 Hz + 600 Hz = 2400 Hz Sampling frequency = 4800 samples/sec. Hence, Bit rate = 4800 x 12 57.6 kbps.

Discussion

136.	In a TV, studio the function of vision switcher is to
Answer» Viscon switcher has a provision to select any one or more of a large number of inputs and switching then on to outgoing circuits.

Discussion

137.	In the equation of M-ary PSK signal (where E is symbol energy), M becomes large. Then will approach
Answer» When M is large, sine term will tend to zero.

Discussion

138.	The trapezoidal pattern of figure is obtained when examining an AM wave by an oscilloscope. Modulation factor of the wave is
Answer» .

Discussion

139.	Y signal has maximum percentage of
Answer» Y = 0.3 R + 0.59 G + 0.11 B.

Discussion

140.	To ensure good transient response in audio systems the natural frequencies should be
Answer» The useful audio range is 40 Hz to 15 kHz. Therefore natural frequency should be outside this range.

Discussion

141.	In a CD player the speed of CD is
Answer» Since the circumference of outer tracks is more than that of tracks near the centre, the speed of disc is varied from 200 rpm to 500 rpm.

Discussion

142.	In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval < < . This indicates that during this interval
Answer» In delta modulator, when consecutive pulses of polarity are opposite then signal is constant.

Discussion

143.	A fascimile reproduction has a specification of 200 lines per frame, progressive scanning and 5 frames per second. The time to scan one line is
Answer» .

Discussion

144.	In an FM system, when the AF is 500 Hz and the AF voltage is 2.4 V, the deviation is 4.8 kHz. If the AF voltage is now increased to 7.2 V, the new deviation will be
Answer» Δf' = 2 x 7.2 14.4 kHz New frequency donation will be 14.4 kHz.

Discussion

145.	An AM signal and a narrowband FM signal with identical carriers, modulating signals and modulation index of 0.1 are added together. The resultant signal can be closely approximated by
Answer» s(t)AM + s(t)NBFM = A1 sin ωct + A2 cos ωct + (A - B) m m(t) sin ωct it will not be NBFM because μ = 0.1, and SSB with carrier.

Discussion

146.	The equation () = A cos [ω + φ()] where A and ω are constant and φ() is a function of base signal represents Which of the above are true?
Answer» This equation can represent frequency, angle and phase modulation.

Discussion

147.	An FM signal with deviation δ is passed through mixer. Its frequency is reduced five fold. The deviation in output of mixer is
Answer» Deviation is not affected by mixer.

Discussion

148.	The total number of channels allotted for cellular telephone is
Answer» Cellular telephones have been assigned 666 channels (826 to 845 MHz and 870 to 890 MHz). Each channel has width of 30 kHz.

Discussion

149.	Modulation is also called detection.
Answer» Demodulation is called detection.

Discussion

150.	The maximum range of a transmitter depends on
Answer» Both power and frequency determine the maximum range.

Discussion

Explore topic-wise InterviewSolutions in .

If transmitted power is 10 kW, the field strength at a distance is 50 mV/m. If transmitted power is reduced to 2.5 kW, the field strength at the same point will be

Some features of advanced mobile phone service are Which of the above are true?

The carrier frequency will be if L = 50 µH and C = 1 nF.

In case of probability of the message is 1 to 16 then the information will be

The saving of power in DSB-SC modulated at 80% is

A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will be

A geostationary satellite

In equally tampered scale, frequency of each tone equals the frequency of lower adjacent tone multiplied by

A carrier is modulated by two modulating waves A and B having modulation indices of 0.6 and 0.8 respectively. The overall modulation index is

A communication channel disturbed by additive white, Gaussian noise has a bandwidth of 4 kHz and SNR of 15. The highest transmission rate that this channel can support (in k bits/sec) is

The reactance of coupling capacitor for AC signals in an amplifier, should be

In a circuit the value of resistor is made four times. The noise voltage generated by this resistance will

A resistor of 10 k&ohm; has an rms noise voltage of 1 mV under a certain set of conditions. A resistor of 20 k&ohm; under the same conditions will have an rms noise voltage of

Which camera tube has highest sensitivity and very wide spectral response?

A computer monitor uses 180 W in normal operation and 20 W in sleep mode. The computer is on all the 24 hours but is in sleep mode for 18 hours a days. The energy units saved in 30 days are

Resonant circuits are used in

Linear diode detector utilizes

In the equivalent circuit of a moving coil cone type loudspeaker, the mass of the moving system is represented by

Quantizing error occurs in

In audio cassettes the width of each recording track is

The most commonly used transistor amplifier circuit is

If aspect ratio is and number of lines in each frame is 625, the number of picture elements in one frame is

In a satellite system circular polarization is to be obtained. The antenna used is

A horizontal output stage is cutoff for retrace and 40% of trace. If time for each horizontal line is 64 μs and retrace time is 12 μs, the transistor is conducting for about

Indicate the false statement: If SWR on a transmission line is infinite, the line is terminated in

In TV signals colour burst is used

The resonant frequency of an R amplifier is 1 MHz and its bandwidth is 10 kHz. The Q factor will be

It is found that in a telephone system 60 subscribers initiate calls during a 30 minute interval and the total duration of all the calls is 100 minutes. The load is

The name modem is a contraction of terms modulator demodulator.

The use of SSB

In the absence of noise, if C is channel capacity in bits/s, δ is channel bandwidth in Hz and N is number of coding levels. Then

The open loop gain of an amplifier is 50 but is likely to change by 20%. If negative feedback with β = 0.1 is used, the change in gain will be about

Audio amplifiers need

Fields are said to be circularly polarised if their magnitudes are

Three analog signals, having bandwidths 1200 Hz, 600 Hz, 600 Hz are sampled at their Nyquist rates, encoded with 12 bit words, and time division multiplexed. The bit rate for the multiplexed signal is

In a TV, studio the function of vision switcher is to

In the equation of M-ary PSK signal (where E is symbol energy), M becomes large. Then will approach

The trapezoidal pattern of figure is obtained when examining an AM wave by an oscilloscope. Modulation factor of the wave is

Y signal has maximum percentage of

To ensure good transient response in audio systems the natural frequencies should be

In a CD player the speed of CD is

In the output of a DM speech encoder, the consecutive pulses are of opposite polarity during time interval < < . This indicates that during this interval

A fascimile reproduction has a specification of 200 lines per frame, progressive scanning and 5 frames per second. The time to scan one line is

In an FM system, when the AF is 500 Hz and the AF voltage is 2.4 V, the deviation is 4.8 kHz. If the AF voltage is now increased to 7.2 V, the new deviation will be

An AM signal and a narrowband FM signal with identical carriers, modulating signals and modulation index of 0.1 are added together. The resultant signal can be closely approximated by

The equation () = A cos [ω + φ()] where A and ω are constant and φ() is a function of base signal represents Which of the above are true?

An FM signal with deviation δ is passed through mixer. Its frequency is reduced five fold. The deviation in output of mixer is

The total number of channels allotted for cellular telephone is

Modulation is also called detection.

The maximum range of a transmitter depends on