MODULATION AND DEMODULATION | NCERTBOOKSPDF.COM

Objective Questions

Short notes

Objective questions (Answers are given below)

The main purpose of modulation is to
(a) combine two waves of different fre- quencies
(b) achieve wave-shaping of the carrier wave
(c) transmit low-frequency information over
long distances efficiently
(d) produce sidebands.
Demodulation
(a) is performed at the transmitting station
(b) removes side-bands
(c) rectifies modulated signal
(d) is opposite of modulation.
In amplitude modulation
(a) carrier frequency is changed
(b) carrier amplitude is changed
(c) three sidebands are produced
(d) fidelity is improved.
100% modulation is produced in AM when carrier
(a) frequency equals signal frequency
(b) frequency exceeds signal frequency
(c) amplitude equals signal amplitude
(d) amplitude exceeds signal amplitude.
For a given carrier wave, maximum undistorted
power is transmitted when value of modulation
is
(a) 1 (b) 0.8
(c) 0.5 (d) 0.
In an AM wave with 100 percent modulation,
each sideband carries — of the total transmitted
power.
(a) one-half (b) one-sixth
(c) one-third (d) two-third
Given a carrier frequency of 100 kHz and
a modulating frequency of 5 kHz, the bandwidth
of AM transmission is____ kHz.
(a) 5 (b) 200
(c) 10 (d) 20
When modulation of an AM wave is decreased
(a) percentage carrier power is decreased
(b) percentage carrier power is increased
(c) total transmitted power is increased
(d) percentage sideband power is unaffe cted.
In AM transmission, power content of the carrier
is maximum when m equals
(a) 0 (b) 1
(c) 0.8 (d) 0.5.
In AM transmission with m = 1, suppression
of carrier cuts power dissipation by a factor of
(a) 6 (b) 2
(c) 3 (d) 4
As compared to DSB-FC 100% modulated
transmission, power saving in SSB-SC system
is __ per cent.
(a) 94.4 (b) 50
(c) 100 (d) 83.3
In an AM transmission with 100% modulation,
66.7% of power is saved when _
is/are suppressed.
(a) carrier (b) carrier and USB
(c) carrier and LSB (d) USB and LSB
In an AM system, full information can be conveyed
by transmitting only
(a) the carrier (b) the upper sideband
(c) the lower sideband (d) any one sideband.

A 10 M Hz carrier of peak value 10 V is
amplifide modulated by a 10 kHz signal of amplitude
6 V. The amplitude of each side band
frequency is
(a)3 V (b) 4 V
(c)5 V (d) 6 V

The block diagram of an AM receiver is shown
in Fig. 66.32. The missing block and its location
are respectively
(a) Band – pass filter at A
(b) High-pass filter at B
(c) Band – pass filter at C
(d) Low-pass filter (audio amplifier) at D.
In FM transmission, amplitude of the modulating
signal determines
(a) rate of frequency variations
(b) amount of frequency shift
(c) tonal balance of transmission
(d) distance of broadcast.
In FM, when frequency deviation is doubled
(a) modulation is doubled
(b) modulation is halved
(c) carrier swing is halved
(d) modulation index is decreased.
In an FM broadcast in VHF band, channel width
is __
(a) 75 (b) 25
(c) 88 (d) 200
Modern FM receivers use de-emphasis circuit
for
(a) reducing high frequency noise
(b) reducing the amplitude of high fre- quencies
in the audio signal
(c) increasing the amplitude of higher modulating
frequencies
(d) making demodulation easy
One of the serious disadvantages of FM transmission
is its
(a) high static noise
(b) limited line-of-sight range
(c) expensive equipment
(d) adjacent channel interference.
In India, the maximum frequency deviation is
commercial FM broadcasting signals is about,
(a) 5 kHz (b) 15 kHz
(c) 7.5 kHz (d) 200 kHz
The correct sequence of subsystems in an FM
receiver is
(a) mixer, RF amplifier, limiter, IF amplifier,
discriminator, audio amplifier
(b) RF amplifier, mixer, IF amplifier, limiter,
discriminator, audio amplifier
(c) RF amplifier, mixer, limiter, discriminator,
IF amplifier, audio amplifier
(d) mixer, IF amplifier, limiter, audio amplifier,
discriminator.

(c) 2. (d) 3. (b) 4. (c) 5. (a) 6. (b) 7. (c) 8. (b) 9. (a) 10. (c) 11. (d) 12.(a) 13. (d) 14. (a) 15. (d) 16. (b) 17. (a) 18. (d) 19. (b) 20. (b) 21. (d) 22. (b)

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