An AM modulation has output xc(t) = A cos 400πt + B cos

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An AM modulation has output x_c(t) = A cos 400πt + B cos 380πt + B cos 400πt
The carrier power is 100 W and the efficiency is 40%. The value of A and B are—

1. 14.14, 16.33
2. 50, 10
3. 22.36,13.46
4. None of these

Correct Option: A

Given modulator output
x_c(t) = A cos 400 πt + B cos 380 πt + B cos 420 πt …(i)
Carrier power = 100 W
Efficiency = 40%
Equation (i) can be represented in standard equation as

x_ct = A		1 +	B	cos 20 πt		cos 400 πt
			A

...(ii)
Given that

P_c = 100 =	A_c²
	2

(here A_c = A)

μ =	B
	A

A² = 200
or
A = √200 = 14.14

Efficiency =	μ²
	2 + μ²

0.4 =	(B/A)²
	2 +(B/A)²

0.4 =	B²
	2A² + B²

or
0.8A² + 0.4B² = B²
or

B² =	0.8A²	=	4A²	=	4	× 200	=	800
	0.6		3		3			3

B =	√	800	=	√266.67	= 16.33
		3