Download - Sistem Komunikasi Analog 3
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Selamat Pagi
Good Morning, How Are You today
?
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Modulator
Demodulator
Transmission Channel
Input transducer
Transmitter
Receiver
Output transducer
Carrier
EM waves (modulated signal)
Baseband signal (electrical signal)
Baseband signal (electrical signal)
Basic analog communications system
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3. Modulasi Amplitudo Modulasi amplitudo ( AM = Amplitudo Modulation) : Suatu teknik modulasi, dimana amplitudo sesaat gelombang sinyal pembawa (carrier), diubah-ubah sesuai dengan amplitudo sesaat gelombang sinyal informasi.
Amplitude Modulation is a process where the amplitude of a carrier signal is altered according to information in a message signal.
The frequency of the carrier signal is usually much greater than the highest frequency of the input message signal.
Gelombang sinyal pembawa berfrekuensi tinggi, gelombang sinyal informasi berfrekuensi rendah.
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Beberapa jenis /macam teknik modulasi amplitudo :
1) AM-DSB-FC: Amplitudo Modulation Double Side Band Full Carrier2) AM-DSB-SC: Amplitudo Modulation Double Side Band Suppressed Carrier3) AM-SSB-FC: Amplitudo Modulation Single Side Band Full Carrier4) AM-SSB-SC: Amplitudo Modulation Single Side Band Suppressed Carrier5) AM-VSB : Amplitudo Modulation Vestigial Side Band, yang digunakan
AM-DSB-FC : Modulator AM merupakan perangkat nonlinier. Modulator memiliki dua input dan satu output. Input pertama sinyal gelombang informasi Vm(t). Input kedua gelombang sinyal pembawa Vc(t). Output gelombang sinyal termodulasi VAM(t). Vm(t) = VmSinωmt.
Vc(t) = VcSinωct.
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Persamaan Gel AM-DSB-FC :
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Gelombang Sinyal Informasi
Gelombang Sinyal Pembawa (Carrier)
Gelombang Sinyal AM (termodulasi)
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tfVtVFor ccc 2cos)( tfVtV mmm 2cos)(
tfftffmVc
tfVtV
givesWhich
tftfmVtfVtVgetWe
YXYXYXGiven
tftfmVtV
tftfVVtVSignalModulated
mcmcccAM
mccccAM
cmcAM
cmmcAM
)(2cos)(2cos2
2cos)(
:
2cos2cos2cos)(:
)cos(2
1)cos(
2
1))(cos(cos:
2cos2cos1)(
2cos2cos)(:
Dimana m = Indeks modulasi,
c
m
V
Vm =
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Persamaan Matematis Gelombang AM-DSB-FC
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c
m
V
Vm =
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%
%
X 100 %
X 100 %
Untuk Modulasi AM, indeks modulasi maksimum sebesar 1 atau 100 %, jika indeks modulasi lebih besar dari 1 atau lebih besar dari 100 %, maka akan terjadi over modulasi.
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AM – Percentage Modulation
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Under modulated (<100%) 100% modulated
Envelope Detector
Can be used
Envelope Detector
Gives Distorted signal
Over Modulated (>100%)
AM – Percentage Modulation
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Spektrum, Bandwidth dan Daya AM-DSB-FC
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Spektrum AM-DSB-FC
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Banwidth, Bw = 2 fm
Daya pancar totalAM-DSB-FC :
21
2mPP ct
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DSB-FC EXAMPLE1. FOR AN AM DSB-FC MODULATOR, WITH CARRIER FREQUENCY OF 100 kHz, AND A MAXIMUM MODULATING SIGNAL OF 5 kHz, DETERMINE:
a) FREQUENCY LIMITS FOR THE UPPER AND LOWER SIDEBANDS
Jawab : (100 - 5) kHz TO 100 kHz = 95 kHz TO 100 kHz = LSB 100 kHz TO (100 + 5) kHz = 100 kHz TO 105 kHz = USB
b) BANDWITH OF THE MODULATED SIGNAL
Jawab : B = 2 fm = 2 x 5 kHz = 10 kHz
Jawab : (100 - 3) kHz = 97 kHz = LSF (100 + 3) kHz = 103 kHz = USF
c) UPPER AND LOWER SIDE FREQUENCIES WHEN MODULATING SIGNAL IS A 3 kHz TONE
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2. FOR THE AM WAVEFORM BELOW:
DETERMINE:
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a) PEAK AMPLITUDE OF THE UPPER AND LOWER SIDE FREQUENCIES
)(4
1
2minmax VV
VVV
mlsfusf
VoltVV lsfusf 4)218(4
1
b) PEAK AMPLITUDE OF THE UNMODULATED CARRIER
VoltVVVc 10)218(2
1)(
2
1minmax
c) PEAK CHANGE IN THE AMPLITUDE OF THE ENVELOPE
VoltVVVm 8)218(2
1)(
2
1minmax
Jawab :
Jawab :
Jawab :
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d) COEFFICIENT INDEX
8.010
8
minmax
minmax
VV
VV
V
V
c
m
e) PERCENT MODULATION
%80%1008.0%100 xxV
Vm
c
m
%80%100218
218%100
minmax
minmax
xxVV
VVM
Jawab :
Jawab :
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3. ONE INPUT TO A CONVENTIONAL MODULATOR IS A 500 kHz CARRIER WITH AN AMPLITUDE OF 20 Vp. THE SECOND INPUT IS A 10 kHz MODULATING SIGNAL THAT IS OF SUFFICIENT AMPLITUDE TO CAUSE A CHANGE IN THE OUTPUT WAVE OF .
DETERMINE:a) UPPER AND LOWER SIDE FREQUENCIES
b) MODULATION COEFFICIENT AND PERCENT MODULATION
(500 + 10) kHz = 510 kHz = USF(500 - 10) kHz = 490 kHz = LSF
Vp5.7
375.020
5.7m
%5.37%10020
5.7 xm
Jawab :
Jawab :
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C) PEAK AMPLITUDE OF THE MODULATED CARRIER
d) UPPER AND LOWER SIDE FREQUENCY VOLTAGES
Vc (MODULATED) = Vc (UNMODULATED) = 20 Vp
VpmVV
VVcm
lsfusf 75.32
)20(375.0
22
e) MAXIMUM AND MINIMUM AMPLITUDES OF THE ENVELOPE
mcmc VVVVVV minmax ;
VpV 5.275.720max
VpV 5.125.720min
Jawab :
Jawab :
Jawab :
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4. FOR AN AM DSB-FC WAVE WITH A PEAK UNMODULATED CARRIER VOLTAGE Vc = 10 Vp, A LOAD RESISTANCE OF RL = 10 Ohms, AND A MODULATION INDEX OF 1,
DETERMINE:
a) CARRIER POWER
b) UPPER AND LOWER SIDEBAND POWER
WR
VP
cc 5
)10(2
10
2
22
WPm
PP clsbusb 25.14
)5(1
4
2
c) TOTAL SIDEBAND POWER
WPm
PP clsbusb 5.22
)5(1
2
2
Jawab :
Jawab :
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d) TOTAL POWER IN THE MODULATED WAVE
Wm
PP ct 5.7)2
11(5)
21(
22
POWER SPECTRUM:
Jawab :
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Thankyou, see you next
week, ok
Bye-bye