Code: DE12 Subject: COMMUNICATION ENGINEERING
Time: 3 Hours Max. Marks: 100
NOTE: There are 9 Questions in all.
· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.
· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.
· Any required data not explicitly given, may be suitably assumed and stated.
Q.1 Choose the correct or best alternative in the following: (2x10)
a. In a communication channel, noise is most likely to affect the signal
(A) at the transmitter. (B) in the channel.
(C) at the receiver. (D) both (B) & (C).
b. The value of resistor creating thermal noise is halved. The noise power generated is
(A) halved. (B) quadrupled.
(C) doubled. (D) unchanged.
c. The modulation index of an AM signal is decreased from 1 to 0. The carrier power
(A) remains unchanged. (B) gets half.
(C) gets doubled. (D) None of the above.
d. The percentage of modulation for 60 KHz deviation in the FM broadcast band will be
(A) 40 (B) 80
(C) 20 (D) 0
e. The S/N ratio in PCM depends on
(A) sampling rate. (B) Bandwidth.
(C) no. of quantization levels (D) None of the above
f. What type of transmission is used in TV broadcasting?
(A) VSB (B) ISB
(C) DSB (D) SSBSC
g. The output of the vertical amplifier applied to the yoke in TV receiver consists of
(A) direct current. (B) a saw tooth current.
(C) a saw tooth voltage. (D) None of the above
h. The VSWR on a transmission line lies between
(A) 0 to
1
(B) 1 to 
(C)
0 to
(D) –1 to +1
i. If a carrier in 100% modulated AM wave is suppressed, the percentage power saving will be
(A) 50 (B) 66.6
(C) 100 (D) 75
j. Which mode is not possible in rectangle wave guide
(A) TM01 (B) TE10
(C) TEM (D) None of the above
Answer any FIVE Questions out of EIGHT Questions.
Each question carries 16 marks.
Q.2 a. Explain thermal noise and noise voltage. (8)
b. For an amplifier with an output signal power of 10W and an output noise power of 0.001W. Determine the S/N power ratio. (8)
Q.3 a. What is amplitude modulation? Derive a relationship for output of AM transmitter by complex signal. (8)
b. A sinusoidal carrier voltage of frequency 1500 kHz is amplitude modulated by a sinusoidal voltage of frequency 20 kHz resulting in maximum and minimum modulated carrier amplitudes of 120V and 80V respectively. Find
(i) frequency of sidebands
(ii) the unmodulated carrier amplitude
(iii) modulation index and amplitude of each sideband (8)
Q.4 a. Draw the block diagram of an Armstrong indirect FM transmitter and describe its operation. (8)
b. Explain the working of balanced slope detector using circuit diagram. (8)
Q.5 a. What is ground wave propagation? Describe briefly. (8)
b. List out the advantages and disadvantages of optical fibre communication. (8)
Q.6 a. What is sampling theorem? Explain briefly. (8)
b. Draw the block diagram of PCM system and describe each block briefly. (8)
Q.7 a. What is transmission line impedance matching? Describe quarter wavelength transformer matching. (8)
b. What is photo detector? Describe PIN diode with the help of diagram. (8)
Q.8 a. Describe horn antenna. (8)
b. Describe the synchronizing pulses used in TV transmission. (8)
Q.9 a. Draw and explain by way of a block diagram the operation of satellite system. (8)
b. Write short note on pre-emphasis and deemphasis. (8)