Electronics and Communication Engineering - Exam Questions Papers

21.
In a radar system, the range of R1 is achieved at a frequency f1. Then the range R2 at frequency R2 = 8f1 would be __________ [Neglect effect of 1 on the Beam width.]
R2 = R1
R2 = 4R1
R2 = 2R1
R2 =
Answer: Option
Explanation:

The range of the radar is directly proportional to the square root of the frequency.

R ∝

R1

and R2

.


22.
With a line charge along z-axis the field intensity is E = ; which of the following figure shows an exact field distribution?
Answer: Option
Explanation:

The given figure fails to show the symmetry with respect to Φ.

The figure shows symmetry with respect to f, also the length of arrow is decreasing away from the charge shows that magnitude E is decreasing away from line charge.

But problem with this figure is longest lines must be shown in most crowded region.

Here we use lines of fixed segments but different thickness. But this attempt also makes the region crowded near origin.

This figure shows compromise. A symmetrical distribution of lines (at every 45°) shows azimuthal symmetry and arrowheads show direction.


23.
The logic function f(A, B, C) = m(0, 2, 4, 5, 6) can be represented by :
1 only
1, 2 only
1, 3 only
1, 2 and 3
Answer: Option
Explanation:

Now the Variable Entered Map (VEM) is:


24.
In amplitude modulation, carrier signals A cos ωt has its amplitude A modulated in proportion with message bearing (low frequency) signal m(t). The magnitude of m(t) is chosen to be __________ .
less than 1
less than or equal to 1
more than 1
none of these
Answer: Option
Explanation:

For proper recovery of signal |m(t)| ≤ 1.


25.
For real values of x, the minimum value of the function f(x) exp (x) + exp (- x) is
2
1
0.5
0
Answer: Option
Explanation:

f(x) = ex + e-x

f(x) = ex - ex

f(x) = 0 ⇒ ex - e-x = 0

f'(x) = ex + e-x ⇒ +ve for x = 0

Thus minimum.

Minimum f(x) = e0 + e0 = 2.