Electronics and Communication Engineering - Communication Systems

36. 

It is desired that transmission line and load should match for a range of frequencies. The best method is

A. to use a balun
B. to use a single stub of adjustable position
C. to use a double stub
D. to use a broad band amplifier

Answer: Option C

Explanation:

When matching over a range of frequencies is desired, double stub is necessary.


37. 

Which of the following has the highest input impedance?

A. CE
B. CB
C. CC
D. Push pull

Answer: Option C

Explanation:

CC connection has very high input impedance and low output impedance.


38. 

In a fascimile reproduction time to scan one line is 2 ms. If it has 4% blanking, the visible trace time is

A. 1.92 ms
B. 2.08 ms
C. 50 ms
D. 0.08 ms

Answer: Option A

Explanation:

(2 ms) (1 - 0.04) = 1.92 ms.


39. 

Consider the following statements

  1. The amplitude of an FM wave is constant
  2. FM is more immune to noise than AM
  3. FM broadcasts operate in upper VHF and UHF frequency ranges
  4. FM transmitting and receiving equipments are simpler as compared to AM transmitting and receiving equipments
Which of the above are correct?

A. 1, 2, 3, 4
B. 1, 2, 3
C. 2, 3, 4
D. 1, 3, 4

Answer: Option B

Explanation:

FM equipments are complex as compared to AM equipments.


40. 

Signal to noise ratio of microphone is defined as the ratio of output when the sound pressure is __________ to the output in the absence of any sound signal.

A. 0.5 Pa
B. 0.2 Pa
C. 0.1 Pa
D. 0.01 Pa

Answer: Option C

Explanation:

0.1 Pa (= 0.5 x 10-4 W/m2) is taken as standard sound pressure for defining S/N ratio of microphones.