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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 3
11.
In telephone systems the relation between load r, number of calls initiated during a specified interval λ and average duration of a call (h) is
r = λh
r = λh2
λ = rh
h = λr
Answer: Option
Explanation:

Load = (number of calls) (duration of call).

12.
In a Vidicon camera tube
grid G1 accelerates electrons
grid G2 accelerates electrons and grid G3, slows down electrons
grid G3 accelerates electrons and grid G2 slows down electrons
both grids G2 and G3 accelerate electrons
Answer: Option
Explanation:

Grid G2 accelerates the electrons. Grid G3, is focus grid and slows the electrons so that they fall perpendicularly on the target at a low speed without causing secondary emission.

13.
In a CD the sampling frequency is nearly
half the highest frequency in audio signal
equal to highest frequency in audio signal
double the highest frequency in audio signal
four times the highest frequency in audio signal
Answer: Option
Explanation:

For proper sampling and faithful reproduction sampling frequency must be at least twice the highest frequency in the signal.

14.
Consider the following statements about loop antenna
  1. It is suitable for direction finding application
  2. It is a single turn or multiturn coil carrying RF current
  3. The loop is surrounded by a magnetic field everywhere perpendicular to the loop
Which of the above statements are correct?
1 and 2 only
1 only
1, 2, 3
2 and 3 only
Answer: Option
Explanation:

All the three are correct.

15.
Which of the following is present in both TRF receiver and superheterodyne receiver?
Detector
Mixer
IF amplifier
Local oscillator
Answer: Option
Explanation:

Detection (also called demodulation) is an essential function.

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