First slide

Modulation

Question

The antenna current of an AM transmitter is 8 A when only the carrier wave is sent but it increases to 9.19 A when carrier is modulated. Find the modulation.

Difficult

A

0.7
B

0.95
C

0.5
D

0.8

Solution

$T o t a l p o w e r c a r r i e d b y A M w a v e P_{T} = P_{c} [1 + \frac{m^{2}}{2}] I f R i s l o a d r e s i s \tan c e I_{m} \to i s c u r r e n t w h e n c a r r i e r i s m o d u l a t e d I_{C} \to i s c u r r e n t w h e n d e m o d u l a t e d, t h e n \frac{P_{t}}{P_{c}} = \frac{I_{m}^{2} R}{I_{C}^{2} R} \Rightarrow 1 + \frac{m^{2}}{2} = \frac{I_{m}^{2} R}{I_{c}^{2} R} Given : I_{m} = 9.19 A, I_{C} = 8 A ∴ m^{2} = 2 [{(\frac{9.19}{8.0})}^{2} - 1] ∴ m = 0.8$

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