CH 01 - Principles of Transmission Flashcards
What is the most common electrical conductors for ICT wire and cables?
- Copper.
- Copper-covered steel.
- high-strength copper alloys.
- Aluminum.
Copper:
- Sets the standard for comparing the conductivity of other metals. Annealed copper is used as the reference value (eg. 100% Conductivity).
- Good Ductility.
- Good Solderability.
- Good Corrosion Resistance.
- Good Oxidation Resistance.
- 1,001 ft of 10 AWG solid conductor weights 31.4 lbs.
- Tensile Strength - 36,259 psi.
Cover Covered Steel:
- Typically used as a conductor for aerial, self-supporting drop wire.
- Good Ductility.
- Good Solderability.
- Good Corrosion Resistance.
- Good Oxidation Resistance.
- 1,001 ft of 10 AWG solid conductor weights 28.8 lbs.
- Tensile Strength - 55,114 psi.
High Strength Copper Alloys:
- A mixture of copper and other metals to improve certain copper alloy properties and characteristics of copper.
- 85% conductivity rating.
- Best Ductility.
- Good Solderability.
- Poor Corrosion Resistance.
- Good Oxidation Resistance.
- Tensile Strength - 79,771 psi.
Aluminum:
- Bluish Silver-white malleable ductile.
- Poor oxidation.
- 60% conductivity rating.
- Good Ductility.
- Solderability requires special techniques.
- Good Corrosion Resistance.
- Poor Oxidation Resistance.
- 1,001 ft of 10 AWG solid conductor weights 9.5 lbs.
- Tensile Strength - 10,008 psi.
Advantages of solid conductors:
- Less costly.
- Less complex termination systems.
- Better transmission performance at high frequencies.
- Less resistance.
Advantages of stranded conductors:
- More flexible.
- Longer flex life.
- Less susceptible to damage during crimp termination processes.
Composite conductor:
A term used to describe conductors constructed from non-traditional materials (eg. metallic resins, graphite).
Advantages of composite conductors:
- Flexible.
- Lightweight.
- Inexpensive and easy to produce.
- Easily embedded into other material.
- Low coefficient of expansion.
Disadvantages of composite conductors:
- Poor high attenuation analog transmission characteristics above 4,000 Hz.
- Poor digital transmission characteristics.
- Easily damaged unless encased in rigid material.
- Inconsistent quality.
- not recommended for use with modern telecommunications networks.
AWG
- American Wire Gauge.
- AWG Sizing system has become generally accepted in North America.
Insulation
- Insulation is used to isolate the flow of current by preventing direct contact between:
- Conductors
- A conductor and its environment.
- Historically, telecommunications cable conductors were insulated with PVC and PE.
- PVC was commonly used for ISP.
- PE was commonly used for OSP.
Certain materials provide lower smoke and flame spread characteristics as well as improved transmission performance:
- FEP (Fluorinated ethylene propylene) eg. Teflon®, NEOFLON FEP™)
- ECTFE (Ethylene chlorotrifluoroethylene) eg. Halar®
FEP
- Fluorinated ethylene propylene
- Dielectric Constant: 2.1
- Dissipation Factor: 0.0005
PE
- Polyethylene
- Dielectric Constant: 2.3
- Dissipation Factor: ___
ECTFE
- Ethylene chlorotrifluoroethylene
- Dielectric Constant: 2.5
- Dissipation Factor: 0.01
PVC (non-plenum rated)
- Polyvinyl Chloride
- Dielectric Constant: 3.4
- Dissipation Factor: ___
PVC (plenum rated)
- Polyvinyl Chloride
- Dielectric Constant: 3.6
- Dissipation Factor: 0.04
XL Polyolefin
- Cross Linked
- Polyvinyl Chloride
- Dielectric Constant: 3.8
- Dissipation Factor: ___
Dielectric Constant
- The ratio of the capacitance of an insulated conductor to the capacitance of the same conductor uninsulated in the air. Air is the reference with a dialectric constant of 1.0.
- Low dielectric constant is desirable.
Dielectric Strength
- Measures the maximum voltage that an insulation can withstand without breakdown.
- A high value is preferred (withstand voltage stress)
Dissipation Factor
- The relative power loss in the insulation is due to molecular excitement and subsequent kinetic and thermal energy losses.
- A low dissipation factor is preferable.
IR
- The insulation’s ability to resist the flow of current through it.
- There is an inverse relationship between insulation resistance and cable length.
Balanced Twisted Pair Overview
- Metallic conductor cables commonly use balanced twisted-pair conduction.
- The main reason for twisting pairs of conductors is to minimize crosstalk and noise by decreasing capacitance unbalance and mutual inductance coupling between pairs.
Balanced Twisted Pair Overview
- Twisting conductors improves the balance (physical symmetry) between conductors of a pair and reduces noise coupling from external noise sources.
- Pair-to-pair capacitance unbalance is a measure of the electric field coupling between two pairs if a differential voltage is applied on one pair and a differential noise voltage is measured on another pair in close proximity. .
Balanced Twisted Pair Overview
- Mutual inductance is a measure of the magnetic field coupling between two pairs if a differential current is applied on one pair and a differential noise current is measured on another pair in close proximity.
- The conditions under which crosstalk is measured include both capacitance unbalance and mutual inductance coupling effects.
Pair Twists
Generally, a counterclockwise twist length between 50mm and 150 mm (1.97” and 6”) is used for voice and low-frequency data cables. Adjacent pairs are generally designed to have twist length differences of at least 12.7mm (.5”). These specifications vary according to the manufacturer.
Tight Twisting
- The option of tight twisting, where pair twist lengths are less than 12.7mm (.5”) is used particularly within and between computers and other data processing equipment.
- Category 5e, category 6, category 6A and higher category cables employ tight twisting for optimum transmission performance.
Environmental Consideration
Temperature Effects:
-One concern is the attenuation invrease at higher cable temperatures above 20C (68F).
