Model Question Paper

Exam : B.E Branch: E and CE Semester : IV

Subject : Analog and Digital Communication Subject Code : 21UEC404C
Duration of paper : 3 Hours Max. Marks : 100

Instructions to candidates: PART-A: All questions are compulsory

PART-B: Answer any one full question from each unit

Q. No. Question Marks BLL CO PI

PART-A
1 i) The maximum power in AM, when modulation index is
01 L1 1 1.3.1
a. 0 b. 0.5 c. 0.7 d. 1
ii) In a double side-band (DSB) full carrier AM transmission system,
if the modulation index is doubled, then the ratio of total
sideband power to the carrier power increases by a factor of 02 L2 1 1.4.1
____________
a. 2 b. 4 c. 1 d. None of these
iii) A 1000 KHz carrier is simultaneously amplitude modulated with
300 Hz and 2 KHz audio sine waves. The frequency which will not
02 L2 1 2.1.3
present in output is
a. 700 KHz b. 998 KHz c. 999.7 KHz d. 1000.3 KHz
iv) Consider an angle modulated signal s(𝑡) = 6
𝑐𝑜𝑠[2𝜋×103t+2sin(8000𝜋𝑡)+4cos(8000𝜋𝑡)]𝑉. The average power
02 L2 2 1.4.1
of s(𝑡) is
a. 10 W b. 18 W c. 20 W d. 28 W
v) A 10 MHz carrier is frequency modulated by a sinusoidal signal of
500 Hz, the maximum frequency deviation being 50 KHz. The
02 L2 2 2.1.3
bandwidth required as given by the Carson’s rule is ___________
a. 100 KHz b. 101 MHz c. 101 KHz d. 10 MHz
vi) De emphasis in FM system involves
a. expansion of m(t)
b. Attenuation of high frequency components of m(t) 01 L1 2 1.4.1
c. compression of m(t)
d. Attenuation of low frequency components of m(t)
vii) A band limited signal is sampled at the Nyquist rate. The signal
can be recovered by passing the samples through
01 L2 2 2.1.3
a. an RC filter b. an envelope detector c. PLL
d. an ideal low-pass filter with the appropriate bandwidth
viii) The bandwidth required to transmit VSB signal is
01 L1 2 1.4.1
a. fm Hz b. 2 fm Hz c. fm < BW <2 fm Hz d. All of these
ix) Write the advantages of digital communication over analog 02 L2 1 2.2.4
communication.
x) Represent 101011100 using following digital data format 02 L3 1 1.4.1
a. UNIPOLAR NRZ
b. POLAR NRZ
xi) What is ASK and FSK? Explain 02 L2 2 4.1.1
xii) Determine the Nyquist rate and Nyquist sampling interval for the 02 L3 1 1.4.1
following signals
i) Sinc(100πt) ii) Sinc(100πt)+Sinc(50πt)

Note: BLL (Blooms Learning Level), CO (Course Outcome), PI (Performance Indicator)

 PART-B
UNIT – I
2 a) Define Modulation. Explain need for modulation in detail. 08 L2 1 2.3.1
b) How to generate DSB-SC signal using diode as switch. 07 L4 1 2.1.3
c) A certain AM transmitter radiates 10 KW with the carrier
unmodulated and 11.8KW when the carrier is sinusoidally
modulated. Calculate the modulation index. If another sine wave 05 L3 1 2.1.3
corresponding to 30% modulation is transmitted simultaneously
determine the total radiated power.
3 a) If m(t) = cos 1000t and c(t)=cos 10000t, find DSB-SC signal and 07 L3 1 2.1.3
sketch its spectrum. Identify USB and LSB. Verify that the
modulated signal can be demodulated using synchronous
detector.
b) Derive the equation for time domain representation of SSB signal. 08 L3 1 2.1.2
c) Explain Superheterodyne receiver with neat block diagram. 05 L4 1 2.1.3
UNIT – II
4 a) Explain the basic concept of Angle modulation. 07 L2 2 2.2.3
b) Explain direct generation of FM. 08 L4 2 2.2.3
c) Calculate the carrier swing, carrier frequency, frequency
deviation and modulation index for an FM signal which reaches a
05 L3 2 2.1.3
maximum frequency of 99.047 MHz and a minimum frequency of
99.023 MHz. The frequency of the modulating signal is 7 KHz.
5 a) What is the effect of interference in FM and PM? Explain the
10 L4 2 2.1.2
circuits used to reduce interference in FM broadcasting.
b) Explain FM demodulation using PLL. 10 L4 2 2.1.2
UNIT – III
6 a) With neat diagram, explain model of digital communication 10 L2 3 2.2.4
system
b) With neat diagram explain flat top sampling 10 L4 3 4.1.1

7 a) Explain the following line codes and their power spectral 10 L2 3

densities
i. Polar NRZ 1.4.1
ii. Bipolar RZ
iii. Manchester encoding
iv. Bipolar NRZ
v. Unipolar RZ
b) With the neat diagram explain the term quadrature sampling of 10 L2 3 1.4.1
band pass signal.
UNIT-IV
8 a) With neat diagram explain the transmitter and receiver of ASK 10 L2 4 4.1.1
(Amplitude Shift Keying) system also find the distance between
two symbols.
b) What is BPSK system? Derive the probability of error (Pe) for 10 L3 4 4.1.1
BPSK System.
9 a) With neat block diagram, explain the DPSK transmitter & 10 L4 4 1.4.1
receiver. Determine the encoded sequence & transmitted
phase sequence for the given bit stream 101101100.
b) With neat diagram explain minimum shift keying(MSK) 10 L2 4 1.4.1

Note: BLL (Blooms Learning Level), CO (Course Outcome), PI (Performance Indicator)