fibre optics-theory

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MOBILE PHONES OFF PLEASE

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FIBER OPTICS Optical Fiber Theory

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5.0 Fiber Optic Theory

5.1 Optical Fiber Theory 5.1.1 - What is Fiber Optics 5.1.2 - Construction of Optical Fiber 5.1.3 - Types of Optical Fiber 5.1.4 - Fiber Transmission Factors 5.1.5 - Different cable constructions 5.1.6 - Choosing a cable type

5.2 Fiber cable Installation 5.2.1 - Installation procedures guidelines and practices 5.2.2 - Pulling Fiber Cables 5.2.3 - Bending Radius/Hauling Tension 5.2.4 - General Guidelines 5.2.4 - Design

5.3 Practical 5.3.1 - Stripping preparing and splicing fiber

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FIBER OPTICS

5.0 OPTICAL FIBER THEORY

- CONSTRUCTION OF FIBER

- TYPES OF OPTICAL FIBER - DIFFERENT CABLE CONTRUCTIONS

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5.1.1 What is "Fibre Optics"?

• A fiber optic cable consists of a bundle of glass threads, each of which is capable of transmitting messages modulated onto light waves

• Not a "new" technology • Concept over a century old • Used commercially for 35 years

• A technology that uses glass (or plastic) threads (fibres) to

transmit data

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Fibre Advantages • Greater bandwidth than metal cables (10GHz vs 16kHz) • Data can be transmitted digitally rather than analogically • Less susceptible than metal cables to interference • Immunity to static interferences

• Lightnenings • Electric motors • Fluoreshent light

• Higher enviroment immunity: weather, temperature, etc. • Thinner and lighter than metal wires • Longer Lasting • Security: tapping is difficult • Economics:

• Low transmission loss (dB/km) • Fewer repeters • Less cable

Remember: Fiber is non-conductive Hence, change of magnetic field has No impact!

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• All light from fibre will harm eyes

• Fibre is extremely hard to work with

• Fibre is fragile

• Fibre is expensive

• You need expensive and complicated installation and test equipment

Myths of Fiber Optics

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5.1.2 Fibre Optic Construction

Core

Glass with a higher index of refraction than cladding

IT carries signal

Cladding

Glass with a lower index of refraction than the core

Buffer

Protects the fiber from damage and moisture

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Fibre Construction

There are 3 main components:

COATING

CLADDING

CORE

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Fibre Optic Types Re-cap on fundamentals

• Light is "guided" down the centre of the fiber called the "core”

• The core is surrounded by a optical material called the "cladding"

• The fiber is coated with a protective plastic covering called the "primary buffer coating"

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Fibre Optics fundamentals

• Total Internal Reflection • Rays of light referred to as modes

Transmitter Receiver

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• Total Internal Reflection was demonstrated in the 1850 • Uses for this at the time were limited to water features etc

Fibre Optics fundamentals

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Fiber Optic Data Links

• Fiber optic transmission consists of a transmitter on one end of a fiber and a receiver on the other end

• The transmitter takes an electrical input and converts it to an

optical output from a laser diode or LED • The receiver converts the light back into an electrical signal at the

other end

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Fiber Optic Data Links

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Fibre GBIC Modules

Switch and module slots combinations GBIC Modules Typically LC (small form factor)

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Fiber Wavelength

• Wavelength is colour of light

• The range of light is called the spectrum • Humans see from 400-700nm • Fiber uses 850, 1300 and 1550 nm

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Fiber Attenuation

• Attenuation is loss of light signal • Absorption is light lost through

cladding and heat • Scattering is light colliding with

atoms • Scattering is largest cause of loss

Absorption & Scattering

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Why 850, 1300 and 1550 nm

• Fiber optics uses infrared light • Typically at 850, 1300, 1310 and

1550 , because attenuation of the fiber is much less at those wavelengths

• Between these points losses are

higher (called water bands) • The attenuation of glass optical

fiber is caused by two factors: • Absorption • Scattering

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Fiber Optic Types

Multi Mode

Single Mode

5.1.3

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MULTIMODE • Multi mode has light travelling in many rays... called modes • It comes in 50micron and 62.5micron • Uses both LED’s for transmission and Lasers.. • Wavelengths for multimode are between 850 to 1300nm • Will run up to 10gb speeds. Mainly as building backbones • Distance limitations are up at about 600m

SINGLEMODE • Singlemode fiber has a much smaller core, only about 9 micron • Light travels in only one ray • Single mode fibres do not exibit dispersion and have longer ranges • This gives them much greater bandwidth than multimode. • Mainly used for used for long fiber runs. • Wavelengths for singlemode are between 1310 to 1550 nm

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OPTICAL FIBER THEORY

Fiber Optic Types

OM2/OM3/OM4 OM1 OS1/OS2

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Fibre Optic Types

OM1

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Fiber Optic Types

OM2

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Fibre Optic Types

OM3

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Fiber Optic Types

OM4

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Size Does Matter !

CAUTION: You cannot mix and match fibers!

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Dispersion & Fiber Optic Bandwidth

Step index multimode was the first fiber design

Graded index multimode fiber uses variations in the composition of the glass in the core to compensate for the different path lengths of the modes.

Singlemode fiber shrinks the core down so small that the light can only travel in one ray.

Multimode & Singlemode fiber are the two most common types

Modal Dispersion

5.1.4

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Fibre Optic Bandwidth

Chromatic Dispersion

• Is the spread of light as it travel down the fibre

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Fibre Bandwidth

Fibre type

Bandwidth at 850 nm (MHz-km)

OFL (led)


OFL (led)


EMB (Laser)

62.5/125

(OM1) 160 500 ---

50/125

(OM2) 500 500 ---

50/125

(OM3) 1500 500 2000

50/125

(OM4) 3500 500 4700

PS: 62.5/125 and 50/125 micron fibres both use the same connectors

OFL = overfilled launch EMB = effective modal bandwidth

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Indicative Link Lengths

Application Multimode Fiber Type

62.5/125 μm 50/125 μm 850 nm laser-optimized

50/125 μm 850 nm laser-

optimized50/125 μm

TIA 492AAAA (OM1)

TIA 492AAAB (OM2)

TIA 492AAAC (OM3)

TIA 492AAAC(OM4)

Wavelength nm 850 1300 850 1300 850 1300 850 1300

10/100 BASE-SX m 300 300 300 300

100BASE-FX m 2000 2000 2000 2000

1000BASE-SX m 275 550 800 880

10GBASE-S m 33 82 300 550

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Fiber optic system ability to transmit data depends on the optical power at the receiver BER or Bit Error Rate is a function of power at the receiver BER is the inverse of signal-to-noise ratio, e.g. high BER means bad signal to noise ratio Too much power, and the receiver amplifier saturates Too little power, and noise becomes a problem as it interferes with the signal The received power depends on 2 basic factors: 1. how much power is launched into the fiber by the transmitter. 2. how much power is left by attenuation in the fiber run

Bit Error Rate

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Fiber Optic Link Power Budget

Cable plant Loss Calculation

Total Loss = (0.5 dB X # connectors) + (0.2 dB x # splices) + loss length of cable (dB / Km)

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Fiber Optic Link Power Budget

Cable plant Loss Calculation

Total Loss = (0.5 dB X # connectors) + (0.2 dB x # splices) + loss length of cable (dB / Km)

Cable Length 2.0 2.0

Fiber Type Multimode Singlemode

Wavelength (nm) 850 1300 1300 1550

Fiber Atten. dB/km 3 [3.5] 1 [1.5] 0.4 [1/0.5] 0.3 [1/0.5]

Total Fiber Loss 6.0 [7.0] 2.0 [3.0]

0.5km

Connectors 0.5dB x 5 = 2.5dB Splices 0.2dB x 1 = 0.2dB Cable 3.0dB x .5km = 1.5dB Total Loss = 4.2dB

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OS1 and OS2 • OS1 and OS2 are cabled Single Mode optical fibre specifications

• Cables with either OS1 or OS2 performance are constructed from B1.3 optical fibres (also known as ITU specification G.652D) or B6_a fibres (a less bend sensitive singlemode optical fibre which is similar to, and compatible with, B1.3. Also known as ITU specification G.657)

• OS1 or OS2 performance is not related to Single Mode optical fibres according to ITU specification G.655 (Non Zero Dispersion Shifted fibre)

• The European Standard EN 50173-1:2007 states that both OS1 and OS2 cabled optical fibres can only be constructed from B1.3 (or ITU G.652D) and B6.a (or ITU G.657) optical fibre according to EN 60793-2-50

• Unfortunately, ISO/IEC have not made this logical leap - even in the latest proposed amendment of ISO/IEC 11801 (which now features both OS1 and OS2).

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G.652D vs G.655

• ITU-T G.652D: fibres with improved attenuation performance

• ITUT-T G.655: fibres with low chromatic dispersion

• ITUT-T G.656: fibres with medium chromatic dispersion

Example = link of 460 km

Standard attenuation for traditional fibre optic (G.652.D)= 0.4 dB/km

Average splice loss = 0.1 dB every 10Km

Cable excess length = 5% 483 km

Typical equipment dynamic range = 22 dB

Power Margin = 1 dB

Cable loss: 483 x 0,4 = 193,2 dB

Splice loss: 48,3 x 0,1 = 4,83 dB

Total loss = 198 dB

198/21 ≅ 9 huts

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Singlemode Fiber Standard

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Singlemode Fiber Performance

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Outside Plant or Premises ?

Fiber Optic Construction Types

5.1.5

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Fiber Optic Installations Outside Plant

Require more hardware (and more investment in the tools and test equipment)

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Outside Plant (OSP) • Used mainly by Telephone companies,

CATV and Internet ISPs • Typically it goes relatively long distances up to

hundreds of kilometres.

• Outside plant installations like this are always single mode fibre

• Optimised cable designs for resisting moisture

and rodent damage.

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Fiber Optic Installations Premises

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Fiber Optic Installations Premises

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Fiber Optic Types

Premises Cabling Premises cabling is cabling installed in a building or campus It involves shorter lengths, rarely longer than a few hundred metres Cables are usually multimode.

No fiber cable should be installed indoors unless it is listed for flame retardancy, Low Smoke and Halogen Free Most connectors are now SC (“Stab and Click” or “Subscriber Connector)) with a few STs (“Stab and Turn” or “Straight Tip”) here and there. Termination is by installing connectors directly on the ends of the fibers, primarily using adhesive technology or occasionally some other variety of termination method.

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Fiber Optic Cable Construction

• Simplex and zip cord • Tight Buffered • Breakout cables • Loose tube cables • Ribbon Cable • Armored Cable • Aerial cable

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They have a Kevlar (aramid fiber) strength member and are jacketed for indoor use. The jacket is usually 3mm (1/8 in.) diameter. Zipcord is simply two of these joined with a thin web. It's used mostly for patch cord and backplane applications

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• Simplex and zip cord • Tight Buffered

Or Distribution Cable

• Breakout cables • Loose tube cables • Ribbon Cable • Armored Cable • Aerial cable

• Usually Small in size • For short dry conduit runs • Riser cable

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• made of several simplex cables bundled together

• is a strong, rugged design • suitable for conduit runs • quick termination to

connectors.

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• composed of several fibers inside small plastic tube,

• ideal for outside plant trunking applications • It can be used in conduits, strung overhead

or buried directly into the ground. • must be carefully handled and protected to

prevent damage

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• highest packing density • laid out in rows, typically of 12 fibers • can have up to 864 fibers in one cable • gel-filled for water blocking.


Fibre Optic Cable Construction

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• Simplex and zip cord

• Tight Buffered

• Breakout cables

• Loose tube cables

• Ribbon Cable

• Armored Cable

• Aerial cable

• Cable installed by direct burial

• in areas where rodents are a problem.

• usually have metal armouring

• cable is conductive, must be grounded.



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• for outside installation on poles.

• can be lashed to a messenger or another cable

• have metal or aramid strength members



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Choosing A Cable Type

What hazards will it face? • Cable's job is to protect the fibers from the hazards. • What chemicals will the cables be exposed to? • What Temperatures will the cables be exposed to? • What sort of physical stresses will the cable be

exposed to?

5.1.6

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Choosing A Cable Type


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FIBER OPTICS INSTALLATION PROCEEDURES

5.2

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Where is Fiber different to standard copper cable when it comes to installing ?

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FIBER INSTALLATION

INSTALLATION GENERAL GUIDELINES

• Conduct a thorough site survey prior to cable placement.

• Develop a cable pulling plan. • Follow proper procedures. • Do not exceed cable minimum bend radius • Do not exceed cable maximum recommended load. • Leave extra cable • Document the installation

5.2.1

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• Conduct a thorough site survey prior to cable placement. • Develop a cable pulling plan. • Follow proper procedures. • Do not exceed cable minimum bend radius. • Do not exceed cable maximum recommended load. • Leave extra cable • Document the installation

FIBER INSTALLATION


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FIBER INSTALLATION


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FIBER INSTALLATION


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FIBER INSTALLATION


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FIBER INSTALLATION


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• Conduct a thorough site survey prior to cable placement.

• Develop a cable pulling plan. • Follow proper procedures. • Do not exceed cable minimum bend radius. • Do not exceed cable maximum recommended load. • Leave extra cable • Document the installation

FIBER INSTALLATION


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• Properly assess cable for pulling first

• Do not to attach connector prior to pulling

• Prevent moisture getting in

• Keep spacing in duct to below 53%

PULLING CABLES

5.2.2

FIBER INSTALLATION


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PULLING CABLES

FIBER INSTALLATION


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PULLING CABLES

FIBER INSTALLATION


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EG: Cable (10mm) / Duct (20mm) = 0.5 or 50% 1 cable.. 10mm / 0.5 (50%) = 20mm duct required

PULLING CABLES

FIBER INSTALLATION


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Planning the Run

• If newly installed, conduits should be a minimum size of between 40mm to 50mm.

• Design the conduit run with as

few bends as possible. • Do not attempt to pull the cable

around a corner

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Installing the cable

• Rope Size: It is important to use a rope size that give minimal stretching during the pull.

• Communication between the person feeding and the person pulling the cable is absolutely essential.

• Do not attempt to pull the cable around a corner • A generous amount of cable pulling lubricant on

the entire run

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PULLING PROCEEDURES

Direct Attachment

Direct Attachment: Strength member is tied directly to the pulling fixture.

The cable end must be sealed to prevent intrusion of moisture while pulling.

PULLING CABLES

FIBER INSTALLATION


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Indirect Attachment

Pulling forces are distributed over the outer cable structure

"Kellems Grip“

Kellems Grip -Cable Sock

PULLING PROCEEDURES PULLING CABLES

FIBER INSTALLATION


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TENSILE LOADING & BEND RADIUS

5.2.3

FIBER INSTALLATION

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TENSILE LOADING

There are two different types of tension in fiber optic cables • Most important is maximum load installation • Also known as “pulling tension”, “installation load”, “short

term tension”, and “dynamic load”

• Measured in Newton's

• Maximum allowable – Check manufacturers specs can vary from as low as 220 N force to as much as 3500 N, depending on the cable construction.

FIBER INSTALLATION

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BEND RADIUS

There are two different types of bend radius • Dynamic bend radius

or “Short Term Bend Radius” - tightest recommended bend while installing - larger of the two specified bend radii.

• Static bend radius

or “LongTerm Bend Radius” - tightest recommended bend while the cable is under a minimum tension

FIBER INSTALLATION

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Short Term (Installation) Long Term (Installed)

Outside Plant Cable 20x Cable Diameter 15x Cable Diameter

Premise Cable 15x Cable Diameter 10x Cable Diameter

BEND RADIUS

There are two different types of bend radius • Dynamic bend radius • Static bend radius

FIBER INSTALLATION

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INSTALLATION SPECIFICATIONS

General Guidelines

5.2.4

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General Guidelines

Twisting cable Do not twist the cable. Twisting the cable can stress the fibers.

Vertical cable runs Drop vertical cables down rather than pulling them up whenever possible. When laying cable out for a long pull, use a “figure 8“ This prevents TWISTING

Use Of Cable Ties Fiber optic cables, like all communications cables, are sensitive to compressive or crushing loads.

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DESIGNING A FIBER NETWORK

General Guidelines

5.2.5

What is “fibre optic network design?”

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1. Consider customer’s requirements

2. Select correct active media

3. Select correct fibre type

4. Select correct cable type

5. Plan ahead on splicing requirements.

6. Choose correct connectors

7. Carry out loss calculations

8. Install the cable plant…..

The Process To Follow

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1.Consider Customer’s Requirements

What data rates will be required on the Network ?

• Gigabits to the desktop

• 10gigabit backbone

• Types of switches etc…


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2. Select Correct Active Media What sort of active media is preferred

• Media Converters

• Connector types on modules


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3. Select correct fibre type

• Consider the range of the link

• Short links use multimode, long links use singlemode


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4. Select correct cable type • Determine the working environment

• Simplex and zip cord

• Tight Buffered

• Breakout cables

• Loose tube cables

• Ribbon Cable

• Armored Cable

• Aerial cable


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5. Plan ahead on splicing requirements.

• Calculate no. of splices • Calculate splice points • Select method of splicing


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6. Choose correct connectors

• Connectors need to fit with active media products

• Connectors need to fit with the

termination method decided upon


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7. Carry out loss calculations

Total Loss = (0.5 dB X # connectors) +

(0.2 dB x # splices) + loss length of cable (dB / Km)


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ANTIGONE consulting

Roberto Fornasiero via Cesare Battisti, 13 35040 Villa Estense (PD) – Italia tel. +39 340 9932458 [email protected]

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