Amplitude Modulation -Power Distribution
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Transcript of Amplitude Modulation -Power Distribution
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ANALOG AND DIGITAL COMMUNICATION
Presentation by:
KARTHIKA S.
AP,ECE
SSN College of Engineering
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UNIT I
FUNDAMENTALS OF ANALOG
COMMUNICATION
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Learning Objectives
On completion of this session you will be able to:
• Understand AM power distribution
• Understand modulation by a complex waave
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AM POWER DISTRIBUTION
• The average power dissipated in a load by
unmodulated carrier is given by
Pc = (0.707 Ec )2/R = (Ec )2/2R
• The upper and lower sideband powers are expressed
mathematically as
Pusb = Plsb = (m Ec/2)2/2R
= m2 Ec2 /8R
= m2 Pc /4
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AM POWER DISTRIBUTION
• Total power in an AM DSBFC envelope is
Pt = Pc+ Pusb+ Plsb
= Pc+ (m2 Pc /4) + (m2 Pc /4)
= Pc+ (m2 Pc /2)
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AM POWER DISTRIBUTION
• Factoring Pc gives
Pt = Pc[1+ (m2 /2)]
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AM POWER DISTRIBUTION
• From the AM power analysis the following
characteristics can be noted
1. Carrier power is unaffected by the modulation
process
2. m increases, Pt increases
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AM POWER DISTRIBUTION
• For m = 0, Pt is equal to Pc
• For m = 1, total sideband power is one half of carrier
power – most of the power is wasted in carrier since
information is contained in the sideband –
disadvantage of AM DSBFC
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AM POWER DISTRIBUTION
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AM CURRENT CALCULATION
• The relationship between carrier current and the
current of the modulated wave is
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MODULATION BY COMPLEX
INFORMATION SIGNAL
• If carrier is amplitude modulated by complex wave,
the combined coefficient of modulation is given by,
mt = m12+ m2
2+ m3
2+ mn
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m1, m
2, m
3, mn @coefficient of modulation for input signals 1,2,3, and n
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MODULATION BY COMPLEX
INFORMATION SIGNAL
• The upper and lower sideband and total
transmitted power is given as,
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PROBLEMS
2. For an AM DSBFC wave with a peak unmodulated
carrier voltage Pc =10 Vp, a load resistance RL = 10Ω,
and a modulation coefficient m = 1, determine
(a) powers of the carrier and upper and lower
sidebands
(b) total sideband power
(c) total power of the modulated carrier
(d) draw the power spectrum