Modulasi Amplitudo Pertemuan 3
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Transcript of Modulasi Amplitudo Pertemuan 3
Modulasi AmplitudoPertemuan 3
Matakuliah : H0122 / Dasar TelekomunikasiTahun : 2008
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Mahasiswa dapat menjelaskan tujuan modulasi, proses dan jenis
modulasi amplitudo.
Learning Outcomes
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• Pengertian modulasi• Tujuan Modulasi• Proses Modulasi Amplitudo• Klasifikasi Modulasi
Amplitudo
Outline Materi
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•Modulasi ialah proses untuk mengkombinasikan suatu sinyal yang berisi informasi dengan sinyal lain.
•Persamaan matematikanya:– ec(t) = Ec(t) cos (ωct + Φ(t))
dengan•ωc = 2f c•ec = sinyal termodulasi (gelombang
carrier )•Ec(t) = envelope dari ec(t)•Φ(t) = deviasi fasa dari ec(t)• f c = frekuensi carrier
Pengertian
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Introduction
• Amplitude Modulation is the process of changing the Amplitude of a relatively high frequency carrier signal in accordance with the amplitude of the modulating signal (Information).
• AM Modulators are nonlinear devices with 2 inputs• A single, high frequency of carrier signal of
constant-amplitude carrier signal• The low frequency information signal.
• The Output of AM Modulator is called Modulated Wave and the shape of the Modulated Wave is called AM Envelope.
• It is often used for commercial broadcasting of both audio and video signals.
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AM Waveform
•Generally.• Carrier Signal => VCsin(2fct)• Modulating Signal => Vmsin(2fmt)• Modulated Wave => Vam(t)
•For Double sideband full carrier (DSBFC) AM waveform consists of:
• DC voltage• The carrier frequency fc• Lower side frequency (fc - fm)• Upper side frequency (fc + fm) Known as AM envelope
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•Indeks Modulasi :M = (modulated peak voltage-unmodulated carrier
voltage)/(unmodulated carrier voltage), dengan 0<m<1
fc-fm fc fc + fmf
E
EcmEc
2mEc
2
fc-fm fc fc + fmf
E
EcmEc
2mEc
2
Indeks Modulasi
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• The AM waveform reaches maximum value when the modulating signal amplitude is at maximum value.
• The AM waveform reaches minimum value when the modulating signal amplitude is at maximum negative.
• The repetition rate of the envelope is equal to the frequency of the modulating signal, and the shape of the envelope is identical to the shape of the modulating signal.
AM Waveform
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AM Waveform
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Frequency Spectrum
• The Frequency Spectrum of AM DBSFC is shown below:• Frequencies between fc-fcmax and fc is called lower side band
(LSB) • Frequencies between fc and fc+fmmax is called upper side band
(USB) • The Bandwidth of AM DBSFC is FB = 2fm (max)• AM signal does not contain modulating signal frequency
Am
plitu
de
Frequency
Upper side frequencies
Lower side band
Lower side frequencies
Upper side band
Carrier
fc-fm(max) fc fc+fm(max)
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Modulation Index
•Modulation index is an indicator to describe the amount of amplitude change (modulation) present in an AM waveform (depth of modulation), basically stated in form of percentage.
•It is defined mathematically as :m = Em / Ec
• m = modulation coefficient (unitless)• Em = peak change in the amplitude of the
output waveform voltage• Ec = peak change in the amplitude of the
unmodulated carrier voltage• Percent modulation:
M= m x 100%
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• Indeks modulasi dan daya sinyal :Pt = Pc [1+ {m2/2}]
• dengan– Pt = daya total – Pc = daya carrier
Indeks Modulasi
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0 < m < 1 m = 1 m > 1mod 100 % (over-modulation)
Indeks Modulasi
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• Klasifikasi modulasi amplitudo linier:– Double side band (DSB)
•ec(DSB) = emEc(t) sin ωct •Bandwidth : BT = 2 fm
e(t)
1/2T Tt
t
e(t)
fmf
LSB USBfc
fc + fmfc - fm
t
BT=2 fm
fc
Klasifikasi AM
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•Single side band (SSB)– Bandwidth : BT = fm
•Vestigial side band (VSB)– Bandwidth : BT = fm + α, where α <
fm•Bandwidth DSB, SSB, and VSB:
– BT(SSB) < BT(VSB) < BT(DSB)
=30%
ModulasiDSB
Filter VSB
SSB USB
=30% fmfw
fc
2
fc + fc + fm
=30%
ModulasiDSB
Filter VSB
SSB USB
=30% fmfw
fc
2
fc +
=30%
ModulasiDSB
Filter VSB
SSB USB
=30% fmfw
fc
2
=30%
ModulasiDSB
Filter VSB
SSB USB
=30% fmfw
=30%
ModulasiDSB
Filter VSB
SSB USB
=30% fm
ModulasiDSB
Filter VSB
ModulasiDSB
Filter VSB
ModulasiDSB
Filter VSB
SSB USB
=30% fmfw
fc
2
fc + fc + fm
Klasifikasi AM
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AM Transmitter Diagram
RF carrier oscillator
Carrier driver
Modulating signal source
AM modulator and output
power amplifier
Antenna
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AM Receiver Diagram
RF section
Bandpass Filter
Mixer/ converter section
Bandpass filter
IF section Bandpass filter
AM detector
Bandpass filter
Audio section
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• Telah dipelajari karakteristik modulasi amplitudo
• Telah dipelajari peran sidebands.
Summary