Modul – 3
Sistem Transmisi
TE-09-1313
2 sks
Tim Bidang Studi
Telekomunikasi Multimedia
(Achmad Ansori, Devy Kuswidiastuti, Gatot Kusrahardjo, M Aries Purnomo)
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The use of the decibel and
of relative levels
in speechband telecommunications
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In transmission engineering, most often it would be rather
impractical to characterize the magnitude of signals directly by
a numerical value in volts or watts.
Instead, a logarithmic measure is used, expressed in "dB", to
characterize the signal magnitude in relation to some chosen
reference value.
Designations commonly used are "power level difference",
"voltage level difference", etc., all expressed in "dB".
A level difference from a standard situation is described simply
as "level".
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Fundamentals about dB
Alexander Graham Bell
The bel (symbol B) expresses the ratio of two powers by the
decimal logarithm of this ratio.
This unit is not often used, having been replaced by the decibel
(symbol dB) which is one-tenth of a bel.
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Bel
• Unit dari ukuran perubahan daya
• Bel = Log (P1/P2)
• P1 dan P2 dalam satuan yang sama
( Watt, mWat, kWatt )
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Daya, Tegangan dan Arus
• Daya = Tegangan x Arus
• Satuan :
Daya : Watt , Tegangan : Volt , Arus : Ampere (Amp)
• P=VxI
• V=IxR
dimana R : tahanan, Ohm ()
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Bel dan Perubahan Tegangan
• P = V x I = V²/R , dimana V : tegangan (Volt),
I : arus (Amp), R : tahanan (Ohm, )
• Bel = Log P1/P2 = Log (V1²/R1) / (V2²/R2) =
Log (V1/V2)².(R2/R1) = Log (V1/V2)² +
Log(R2/R1) = 2 Log(V1/V2) + Log(R2/R1)
• Bel = 2 Log (V1/V2), jika R1 = R2
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Bel dan Perubahan Arus
• P = V²/R = (I x R)²/R = I²/R
• Bel = Log P1/P2 = Log(I1²/R1)/(I2²/R2) =
Log(I1²/I2²)(R1/R2) = Log(I1/I2)² +
Log(R1/R2)
• Bel = 2 Log I1/I2 + Log R1/R2
• Bel = 2 Log I1/I2 , jika R1 = R2
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Ringkasan (1)
• Bel = Log P1/P2
• Bel = 2 Log V1/V2 , jika R1 = R2
• Bel = 2 Log V1/V2 + Log R2/R1 ,
jika R1  R2
• Bel = 2 Log(V1R2)/V2R1) ,
jika R1  R2
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Ringkasan (2)
• Bel = 2 Log I1/I2 , jika R1 = R2
• Bel = 2 Log I1/I2 + Log R1/R2 ,
jika R1  R2
• Bel = 2 Log (I1R1)/(I2R2) ,
jika R1  R2
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DECIBEL (1)
• Unit yang menyatakan ratio
• Bentuk logaritma dengan dasar 10
• Decibel ( dB ) = 10 Log ( power ratio )
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Decibel (2)
• Decibel ( dB) = 10 x Bel
• dB = 10 Log P1/P2
• Jika R1 = R2
dB = 20 Log V1/V2
dB = 20 Log I1/I2
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Decibel (3)
• Jika R1  R2
dB = 20 Log V1/V2 + 10 Log R2/R1
dB = 20 Log I1/I2 + 10 Log R1/R2
dB = 20 Log (V1R2)/(V2R1)
dB = 20 Log (I1R1)/(I2R2)
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Power Ratio & Voltage Ratio (1)
dB
0
1
2
3
4
5
6
7
8
9
10
20
30
40
Gain
Power Ratio Voltage Ratio
1.00
1.26
1.58
2.00
2.51
3.16
3.98
5.01
6.31
7.94
10.00
100.00
1000.00
10000.00
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1.00
1.12
1.26
1.41
1.58
1.78
2.00
2.24
2.51
2.82
3.16
10.00
31.62
100.00
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Power Ratio & Voltage Ratio (2)
dB
0
1
2
3
4
5
6
7
8
9
10
20
30
40
Loss
Power Ratio Voltage Ratio
1.0000
0.7943
0.6310
0.5012
0.3981
0.3162
0.2512
0.1995
0.1585
0.1259
0.1000
0.0100
0.0010
0.0001
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1.0000
0.8913
0.7943
0.7079
0.6310
0.5623
0.5012
0.4467
0.3981
0.3548
0.3162
0.1000
0.0316
0.0100
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Power Ratio & Voltage Ratio (3)
dB
Ratio
Power
Voltage
1
2
4
8
10
16
32
64
100
128
256
512
1000
0.00
3.01
6.02
9.03
10.00
12.04
15.05
18.06
20.00
21.07
24.08
27.09
30.00
0.00
6.02
12.04
18.06
20.00
24.08
30.10
36.12
40.00
42.14
48.16
54.19
60.00
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Pengembangan Unit dB
• dBm = 10 Log ( power ratio ) dg ref. 1 mW
• dBm = 10 Log ( power / 1mW )
• dBW = 10 Log ( power ratio ) dg ref. 1 W
• dBW = 10 Log ( power / 1W )
• power output = 20 W
= 10 Log (20W/1mW)
= 10 Log (20.000mW/1mW) = 43 dBm
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dBm, dBW, Watt & milliWatt
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Voltage & Current Ratio
• dB(Voltage) = 20 Log ( ratio voltage )
• dB(Current) = 20 Log ( ratio current )
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dBmV
• Digunakan pada transmisi video
• Tegangan ( Voltage ) referensi = 1 mVolt
pada beban 75 Ohm
• dBmV = 20 Log ( tegangan/1 mVolt )
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dBmV
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dBµV/m
• Pengukuran kuat medan listrik
• Referensi 1µV/m  dBµV/m = 20 Log (µV/m)
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KONSEP SISTEM TRANSMISI
Loss & Gain
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attenuation, loss :
1. A decrease between two points of an electric, electromagnetic
or acoustic power.
2. The quantitative expression of a power decrease, by the ratio
of the values at two points of a power or of a quantity related to
power in a well-defined manner.
NOTE 1 : By extension, the words “attenuation” or “loss” may represent the
ratio of powers in a given situation and in a reference condition;
for example “insertion loss”.
NOTE 2 : Although the term “loss” is not synonymous in English with
“attenuation” in every context, it is used to express the ratio of two
powers in certain specified conditions as for example in “insertion
loss” and “return loss” equivalent in French to
“affaiblissement d'insertion” and “facteur d'adaptation”.
NOTE 3 : Attenuation is generally expressed in logarithmic units by a positive
value.
In some cases, attenuation could be used instead of gain, when
the logarithmic unit value of a gain is negative.
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Gain :
1. An increase between two points of an electric, electromagnetic,
or acoustic power.
2. The quantitative expression of a power increase, by the ratio of
the values at two points of a power or of a quantity related to
power in a well-defined manner.
NOTE 1 : By extension, the word “gain” may represent the ratio of
powers in a given situation and in a reference condition;
for example the “gain of an antenna”.
NOTE 2 : Gain is generally expressed in logarithmic units by a positive
or negative value. When a gain has a negative value in
logarithmic units, attenuation may be used instead of gain.
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LOSS
1000 Watt
1 Watt
Kabel
Input
Output
• Loss (dB ) = 10 Log(power ratio) =
= 10 Log(output/input) =
= 10 Log ( 1 / 1.000 ) =
= 10x(-3) = -30 dB
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LOSS
1000 Watt
Kabel
Input
Output = ?
Loss = 10 dB = 10 x
Power Output = Power Input : Loss
= 1.000 Watt : 10 = 100 Watt
Power Output = Power Input - Loss
= 30 dBW - 10 = 20 dBW
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GAIN (PENGUATAN)
1 Watt
2 Watt
Amplifier
Input
Output
• Gain (dB ) = 10 Log(power ratio) =
= 10 Log(output/input) =
= 10 Log ( 2 / 1 ) = 10 x 0,3013
= 3,013 dB = 3 dB
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GAIN (PENGUATAN)
1 Watt
Amplifier
Input
Output =?
Gain = 6 dB = 4 x
Power Output = Power Input x Gain
Power Input = 1 Watt = 30 dBm
Power Output = 1 Watt x 4 = 4 Watt
Power Output = 30 + 6 = 36 dBm
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Model Sistem Komunikasi Listrik
PowerOutput :
1 mW =
0 dBm
Pemancar
Loss
10 dB
Power Input :
- 10 dBm
Media
Transmisi
Penerima
Wire / Kawat / Kabel
Wireless / Radio
Fiber Optik
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Model Sistem Pemancar
Power Output
1 kW = 30 dBW
Power Input
27 dBW
Gain = 10 dB
Loss = 3 dB
Antena
Pemancar
Wire / Kawat /Kabel /
Kabel Koaxial
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Effective
Radiated
Power
(ERP) :
37 dBW
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effective radiated power (e.r.p.) (in a given direction )
The product of the power supplied to the antenna and its gain
relative to a half-wave dipole in a given direction.
Note :
The reference antenna, when fed with a power of 1 kW,
is considered to radiate an e.r.p. of 1 kW in any direction in
the equatorial plane and produces a field strength of 222 mV/m
at 1 km distance.
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equivalent isotropically radiated power (e.i.r.p.) :
The product of the power supplied to the antenna and
the antenna gain in a given direction relative to an isotropic
antenna (absolute or isotropic gain).
Note :
The isotropic antenna, when fed with a power of 1 kW, is
considered to provide an e.i.r.p. of 1 kW in all directions and
to produce a field strength of 173 mV/m at 1 km distance.
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Model Sistem Pemancar & Penerima
ERP : 68 dBm
-32 dBm
Loss = 100 dB
Gain
10 dB
Wireless / Radio
Loss = 3 dB
Loss = 2 dB
Pemancar
Gain
10 dB
Power
Input =
-25 dBm
Penerima
Power Output
1 kW = 60 dBm
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Series Network
S
G
3 dB
L
5 dB
G
3 dB
N1
N2
N3
T
10dBm
13
dBm
8
dBm
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dBm
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Noise Figure (1)
Spot noise factor, spot noise figure
(of a linear two-port network) :
Symbol: F( f ), NF
The ratio of the exchangeable power spectral density of the
noise appearing at a given frequency at the output of a given
linear two-port electrical network, to the spectral density which
would be present at the output if the only source of noise were
the thermal noise due to a one-port electrical network connected
to the input and which is assumed to have at all frequencies a
noise temperature equal to the reference thermodynamic
temperature fixed, by convention, around 290 K.
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Noise Figure (2)
Noise Figure ( NF ) = SNRin - SNRout (dB)
NF = 1 ( 0 dB )  Noiseless
SNRin
Network
40 dB
SNRout
30 dB
Noise Figure ( NF ) = 40 – 30 = 10 dB
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Noise Figure (3)
NF = NF1 + (NF2 – 1)/G1 + (NF3 -1)/G1G2 + ….
antena
NF2=3dB
Loss=3dB
kabel
NF3=16dB
G3=60dB
Penerima
NF2 = 3 dB = 2 ; Loss = 3 dB = 2 = G2 = 0,5 ;
NF3 = 16 dB = 40 ; G3 = 60 dB = 1.000.000
NF = NF2 + (NF3-1)/G2
= 2 + (40-1)/0,5 = 80 = 19 dB
Gain = -3 +60 = 57 dB
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Noise Figure (4)
antena
NF1=6dB
G1=20dB
NF2=3dB
Loss=3dB
NF3=16dB
G3=60dB
preamp
kabel
Penerima
NF1 = 6 dB = 4 ; G1 = 20 dB = 100 ; NF2 = 3 dB = 2
Loss = 3 dB = 2 = G2 = 0,5 ;
NF3 = 16 dB = 40 ; G3 = 60 dB = 1.000.000
NF = 4 + (2-1)/100 + (40-1)/(100).0,5 = 4,79 = 6,8 dB
Gain = 20 – 3 + 60 = 77 dB
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Noise Figure (5)
antena
NF1=3dB
Loss=3dB
kabel
NF2=6dB
G2=20dB
preamp
NF3=16dB
G3=60dB
Penerima
NF1 = 3 dB = 2 ; Loss = 3 dB = 2 = G1 = 0,5 ;
NF2 = 6 dB = 4 ; G2 = 20 dB = 100 ;
NF3 = 16 dB = 40 ; G3 = 60 dB = 1.000.000
NF = 2 + (4-1)/0,5 + (40-1)/(100).0,5 = 8,78 = 9,4 dB
Gain = -3 + 20 +60 = 77 dB
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