Introduction• Telecom cables form the backbone of the telecommunication infrastructure around the globe.• These communication cables transmit voice messages, computer data, and visual images via electrical signals to telephones, wired radios, computers and televisions. Contd…
• Copper has been used in electric wiring since the invention of the electromagnet and the telegraph in the 1820s.• Majority of the communication cables used copper as a conductor.• Optical Cables are replacing the traditional copper based cables.
Copper Based Cables• Traditional cables consist of copper conductors.• The invention of the telephone in 1876 created further demand for copper wire as an electrical conductor.• Despite competition from other materials, copper remains the preferred electrical conductor in nearly all categories of electrical wiring.
Properties of Copper Conductors• Electrical conductivity – Copper has the highest electrical conductivity rating of all non-precious metals.• Tensile strength – Copper can be bent, twisted, and pulled without stretching or breaking. Contd..
• Corrosion resistance – Copper resists corrosion from moisture, humidity, industrial pollution, and other atmospheric influences.• Ease of installation – It can be bent or twisted easily without breaking. – It can be stripped and terminated during installation or service with far less danger of nicks or breaks.
Processes for Copper Cable Manufacturing• Drawing of single copper conductor rolls from raw copper wire and single steel conductor rolls from raw steel wire .• Annealing treatment of copper conductor rolls.• Tinning treatment on steel conductors and annealed copper conductors.• QA testing of conductor rolls. Contd…
• Stranding of copper and steel conductors depending on the configuration of the cable.• Insulation of the stranded conductors depending on the configuration and use of the cable.• QA testing of the final cable roll before dispatching.
Cables Manufactured at OCF• Carrier Quad Cable.• Field Telephone Cable.• Twenty Conductor Cable.
Carrier Quad Cable Temp. Range -55°C to 90°C CR 24.5 Ohms/Km Pair Capacitance 50p F/m Impedence 144 Ohms at 10 Khz & above. 125 Ohms at 60 Khz & above. 120 Ohms at 100 Khz & above. Attenuation 0.9 dB/Km at 1.6 KHz 1.8 dB/Km at 16 KHz 3.2 dB/Km at 100 KHz CQC Cables are used to provide carrier trunk connections.
Field Telephone Cable Temp. Range -40°C to 80°C CR: 76 Ohms/Km Pair Capacitance 37p F/m Impedence 600 Ohms Attenuation 1.4 dB/Km at 1.6 KHz Breaking Load 76 Kgs
Twenty Conductor Cable Temp. Range -40°C to 80°C CR. 85 Ohms/Km Pair Capacitance 40p F/m Impedence 600 Ohms At 1.6 KHz Attenuation 2.0 dB/Km at 1.6 KHz Breaking Load 300 Kgs
Optical Fibers: Manufacturing and Cabling• Optical Fibers are thins long strands of ultra pure glass (silica) or plastic(polymers) that can to transmit light from one end to another without much attenuation or loss.• Optical fibers are widely used in fiber-optic communications.• The light source at the transmitting end is modulated by the electrical signal and this modulated light energy is fed into the Optical Fiber. Contd...
• The optical fiber elements are typically individually coated with plastic layers and contained in a protective tube suitable for the environment where the cable will be deployed.• It has following layers – Core- Made of highly pure glass with refractive index for the light to travel. – Cladding- A middle layer of glass with a lower refractive index. – An outer polymer jacket to protect the fiber for damage.
Why Optical Fibers?• Cost effectiveness & stable over long distances.• Available in different sizes, refractive index, index profiles, material and operating wavelength for different systems applications.• It can be handled in a more efficient manner than conventional electrical transmission cables.
Optical Fibers Copper CablesExtremely low loss (0.3db/km) Very high losses (30db/km)High bandwidth (7000 Limited bandwidthchannels)1/8th weight of copper Heavy for usageElectromagnetic Interference Affected by Electromagneticand Noise Proof Interference
Fiber Optic System Devices• Transmitter (laser diode or LED)• Fiber Optic Cables.• Receiver
Optical fiber as transmission medium• Optical fibers transmit data as light pulses.• Light propagates by means of total internal reflection.
Total Internal Reflection The angle of the light is always greater than the critical angle. Cladding does not absorb any light from the core. The extent that the signal degrades depends upon the purity of the glass and the wavelength of the transmitted light.
Classification of Optical Fibers• Optical fibers are classified on the basis of – Core and cladding materials. – Refractive index profile. – Modes of propagation.
Core and cladding materials: three varieties• Glass core and cladding( SCS: Silica Clad Silica) – Low attenuation and best propagation characteristics. – Least rugged: delicate to handle.• Glass core with plastic cladding(PCS: Plastic Clad Silica) – More rugged than glass; attractive to military applications. – Medium attenuation and propagation characteristics.
• Plastic core and cladding – More flexible and more rugged. – Easy to install, better withstands stress, less expensive, weighs 60% less than glass. – High attenuation: limited to short runs.
Refractive index profile: two types• Step index – Refractive index makes abrupt changes.• Graded index – Refractive index is made to vary as a function of radial distance from the center of the fiber.
Mode of Propagation: two types• Single Mode Fiber – Only one signal travels at a time.• Multimode Fiber – More than one signal is present.
Single Mode(mono-mode) fibers• Most important for long haul use.• Small core ( 7-10 µ) forces the light to follow a linear single path down its length.• Lasers are the usual sources of light.• Most expensive and delicate to handle.• Highest bandwidth and distance rating (more than 100 kms)
Multimode Fibers• Relatively large diameter core (50-100 µ).• Step index multimode cable has an abrupt change between core and cladding. It is limited to about 50 Mbps.• Graded index multimode fiber has a gradual change between core and cladding. It is limited to 1 Gbps.
Two major communication issues• Attenuation – Attenuation is signal loss over distance. – Light pulses lose their energy , flatten out as they travel down the cable.• Dispersion – Dispersion is broadening of light pulses with time. – It arises due to physical properties of the transmission medium.
Dispersion in MM/SM fibers• Single mode fiber sustains only one mode of propagation whereas multimode contains many modes.• Large radii of multimode fiber makes it easier to launch tight into fiber.• Even LED’s can excite multimode whereas for single mode lasers are required Contd…
Manufacturers Considerations• Refractive index profile.• Material composition and density fluctuation.• Core cladding interfaces.• Eccentricity.• Diameter.