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May 2008 Cables-Engl - 1 © P. Nicoletti: see note pag. 2 Copper and Fiber Optic Cables Pietro Nicoletti piero[at]studioreti.it
May 2008
Cables-Engl - 1 © P. Nicoletti: see note pag. 2
Copper and Fiber Optic Cables
Pietro Nicolettipiero[at]studioreti.it
May 2008
Cables-Engl - 2 © P. Nicoletti: see note pag. 2
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May 2008
Cables-Engl - 3 © P. Nicoletti: see note pag. 2
Copper cables main characteristics
The main characteristics of a transmission media are:
Vp: Velocity of propagation of the signal expressed as c fraction (speed of the light in the empty space):
values included between 0.5 and 0.8 c
Z = r+jI impedance of the line
conductors' dimension
american AWG unit of measurement
Diameter, electrical resistance
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AWG: American Wire Gage
Scale to measure the copper wire dimension
It is a geometrical regression
with 39 values in the interval 000 gage (0.460 diameter inch) and 36 gage (0.005 diameter inch)
Every increase of a gage corresponds to a diameter relationship of:
0.460
0.005( )
1/39
= 92 = 1.2293221/39
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Copper cables AWG
AWG mm (Ø) mm2 Kg/Km Ω/Km
22 0.6438 0.3255 2.894 52.96
23 0.5733 0.2582 1.820 84.21
24 0.5106 0.2047 1.746 87.82
25 0.4547 0.1624 1.414 108.4
26 0.4049 0.1288 1.145 133.9
24 or 22 AWG for structured cabling system
26 AWG for patch cord
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Copper cable attenuation
The attenuation is the output signal reduction with respect to the entry signal in the cable:
attenuation linearly grows in dB with the length of the cable and the frequency square root
to reduce the cable attenuation expanded insulators are used because improve the capacity
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Attenuation
V1 V2
αdB = 20 log10 (V1 / V2)
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Copper pair Cross-Talk
Signal energy part induction on the near conductors, where a disturb becomes
The phenomenon increases with increasing it by frequency
It can be measured in several manners
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NEXT: Near End Cross-Talk
Cross-Talk measured at the transmitter side
V1
V3
NEXTdB = 20 log10 (V1 / V3)
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NEXT: Near End Cross-Talk
The attenuation only makes the NEXT measure significant by the first 20-30 mt of cable
The measurement is necessary to both ends:
dual NEXT
V1
V3
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FEXT: Far End Cross-Talk
Cross-Talk measured at the receiver side
V1
V4
FEXTdB = 20 log10 (V1 / V4)
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ACR
ACR (Attenuation to Cross-Talk Ratio)
Combination of attenuation and NEXT
signal to noise ratio
noise caused by Cross-Talk
Required only by ISO and EN normative
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ELFEXT: Equal Level FEXT
~~
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PSELFEXT (Power Sum ELFEXT)
~~
~~
~~
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Velocity of propagation (Vp)
The propagation velocity of the signals on the transmission means is high, but not infinite, so the propagation time is little but not null
It is necessary to ensure that delays do not exceed certain maximum values to ensure the protocol working
VP ≅ 2/3 c(c is speed of the light in the empty
space≅ 3 • 108 m/s)
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Delay skew
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Return loss Il return loss = reflections measurements
Z1 Z3Z2Impedance variations
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Shielded cable
The shield presence can involve:
bigger immunity to the electromagnetic disturb
disturb radio emission reduction
bigger constancy of the impedance
if applied to single pair reduces the crosstalk
It is necessary to make a correct screen grounding:
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Twisted pair cable
Constituted by one or more twisted pair of copper conductors
Used for voice, local nets, structured cabling system
the electrical characteristic required for LAN are definitely higher than those for voice
Lower bandwith than the coaxial one
Reduced costs and simple installation
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Twisted Pair cable types
UTP (Unshielded Twisted Pair):
(Z = 100 Ω)
FTP (Foiled Twisted Pair):
(Z = 100 Ω)
S-UTP o S-FTP:
(Z = 100 Ω)
STP (Shielded Twisted Pair):
(Z = 150 Ω)
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UTP 100 Ω
pair 1
pair 2
pair 3
pair 4
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FTP 100 Ω
pair 1
pair 2
pair 3
pair 4
Drain wire for shield continuity
Foil shield
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S-UTP or S-FTP 100 Ω
pair 1
pair 2
pair 3
pair 4
Copper braid
Single foil shielded pair
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STP 150 Ω
Know as Type 1 IBM
22 AWG
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GLASS FIBER OPTIC
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Glass Fiber Optic
It is a tiny and flexible glass material thread:
an internal part called core
an outside part called cladding
core and cladding have different refraction indexes to border the light inside core
CORE
CLADDING
PRIMARY COATING
SECONDARY COATING
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Glass Fiber Optic characteristics
The optic fibers are just suitable for point point links
Total immunity to the electromagnetic troubles
Characterized by two numbers n/m where:
diameter n of the leading internal light part
diameter m of the outside part
Typical values in micron
multimode 50/125, 62.5/125, 100/140
singlemode 8-10/125
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Step-index multimode fiber
Characteristics
High modal dispersion
Low bandwith
M1
M4M3
M2
M1
M2
M3
M4
T1 T2
Input signal Output signal
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Graded-index multimode fiber
Graded-index fiber have a bandwith higher than step-index
work in 1st and 2nd window (850 and 1300 nm)
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Singlemode fiber
The fiber behaves like a wave guide admitting a single propagation mode:
does not have modal dispersion
the bandwith is very high, of the order of hundreds of GHz*Km
work in 2nd and 3th window (1300 and 1500 nm)
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Wavelenght and optical componentsA
ttenuation
(dB
X K
m)
100
1
5
10
500 600 700 850 900 1000 1100 1200 1300
13101400 1550
LED\VCSEL
LASER DIODEVCSEL
LASER DIODE
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Fiber optic cable types
Tight
Break-out
dual fiber patch cord
Light-duty
Loose
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Break-Out tight fiber optic cable
Fiber opticExternal diameter 250 µm
250 µm = 125 µm + primary coating
CentralDielectric element
SheathToxfree or Low-smoke-fume
Kevlar
Secondary coatingExternal diameter 0.9 mm
External diameter 2 ÷ 3 mm
Indoor installation
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Dual fiber patch cord
Fiber opticExternal diameter 250 µm
250 µm = 125 µm + primary coating
SheathToxfree o Low-smoke-fume
Kevlar
Secondary coating
External diameter 0.9 mm External diameter 2 ÷ 3 mm
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Light-duty tight fiber optic cable
Central
Dielectric element
Kevlar
Secondary coating
External diameter 0.9 mm
Fiber optic
External diameter 250 µm250 µm = 125 µm + primary coating
Roditor resistant protection
SheathToxfree o Low-smoke-fume
Indoor/Outdoor installation
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Loose fiber optic cable
Fiber optic
External diameter 250 µm250 µm = 125 µm + primary coating
Central
Dielectric elementKevlar
Roditor resistant protection
TubeJelly filled
Sheath
Sheath
Outdoor installation
