DipIETE – ET (OLD SCHEME)

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 the best alternative in the following: (210)

a. The Very High Frequency (VHF) range extends from _________.

(A) 3-30 MHz (B) 30-300 MHz

(C) 300-3000 MHz (D) 3000-30000 MHz

b. Pre-emphasis is used to improve noise immunity ______________.

(A) at higher baseband frequencies

(B) at lower baseband frequencies

(C) over the entire baseband

(D) for AM

c. In commercial FM broadcasting, the maximum frequency deviation is normally ________.

(A) 5 kHz (B) 15 kHz

(C) 75 kHz (D) 200 kHz

d. Picture information is transmitted in T.V. signals by _____________.

(A) AM (B) FM

(C) PAM (D) None of these

e. In a PCM system, the quantization noise depends upon ___________.

(A) The number of quantization level only

(B) The sampling rate only

(C) Both the sampling rate and the number of quantization levels

(D) None of the above is correct

f. The dominant mode in a rectangular waveguide is____________.

(A) (B)

(C) (D) TEM

g. Frequencies in the UHF range normally propagate by means of _________.

(A) ground waves (B) sky waves

(C) surface waves (D) space waves

h. Indicate which of the following systems is digital?

(A) Pulse-position modulation (B) Pulse-code modulation.

(C) Pulse-width modulation. (D) Pulse-frequency modulation.

i. In commercial T.V. transmission in India, picture and speech signal are modulated respectively as:

(A) VSB and VSB. (B) VSB and SSB.

(C) VSB and FM. (D) FM and VSB.

j. Thermal noise power is proportional to __________.

(A) (B)

(C) (D) BT

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2 a. What is noise? Explain various sources of noise. (8)

b. What is bandwidth of information signals? Explain the relationship between bandwidth and channel capacity. (8)

Q.3 a. What is amplitude modulation? Derive an expression for amplitude modulated wave. (8)

b. A transmitter with 20 kW carrier transmits 22.4 kW when modulated with a single sine wave. Calculate the modulation index, if the carrier is simultaneously modulated with another sine wave at 50% modulation. Find the total transmitted power. (8)

Q.4 a. Explain following terms: (8)

(i) Ratio.

(ii) Noise figure.

b. State advantages and disadvantages of SSB transmission over DSB transmission. (8)

Q.5 a. Estimate the Bandwidth and Power of an FM signal given by (8)

b. Compare PAM, PWM and PPM. (8)

Q.6 a. Draw the block diagram of PLL and briefly explain its working. (8)

b. What are different modes of radio wave propagation? Describe ground wave propagation briefly. (8)

Q.7 a. Describe briefly different sources of losses in optical fibres. (8)

b. Describe following terms for antenna: (8)

(i) Polarisation.

(ii) Bandwidth.

(iii) Antenna Gain.

Q.8 a. State the advantages and disadvantages of satellite communication. (8)

b. Explain the working of a balanced slope detector using suitable diagram. (8)

Q.9 a. Describe briefly the use of blanking and synchronizing pulses in T.V. signals. (8)

b. What is sampling theorem for low pass signal? Explain it briefly (8)