Numerical - Power saving in AM when carrier and side band are suppressed

Q.  Calculate the power saved in an Amplitude Modulated wave when it is transmitted with 45% modulation
- Without carrier
- Without carrier and a sideband
- Published on 13 Oct 15

a. 90%, 95%
b. 82%, 91%
c. 82%, 18%
d. 68%, 16%

ANSWER: 90%, 95%
 
i) The total power in an AM is given by
Pt = Pc ( 1 + m2/2)

Given: m = 0.45
Therefore Pt = Pc ( 1 + 0.452/2 )
Pt= Pc *1.10125
Pc/ Pt = 1/1.10125
= 0.908
= 90%

This shows that the carrier occupies 90% of total power. So 90% of total power may be saved if carrier is suppressed in the AM signal.

(ii) If one of the sidebands is also suppressed, half of the remaining power will be saved
i.e., 10/2 = 5 %. So a total of 95% (90% + 5% ) will be saved when carrier and a side band are suppressed.

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