* Chapter 1 - Principles of Transmission

Question 1

An electrical conductor is

Answer 1

any material that can carry an electrical charge from one point to another

Question 2

The most common electrical conductors in the ITS industry are

Answer 2

Copper, Copper Covered Steel, High Strength copper alloys and Aluminum

Question 3

Copper (Conductor Description)

Answer 3

Sets the standard for connectivity of other metals, Annealed copper is used as the reference value (100% conductivity.

Question 4

Copper-covered (Conductor Description)

Answer 4

Also known as copper clad steel, it combines the conductivity of steel copper with the strangth of steel. It is typically used as a conductor for aeiral, self supporting drop wire.

Question 5

High-Strength (Conductor Description)

Answer 5

A mixture of copper and other metals to improve certain copper alloy properties and characteristics of copper. Alloys such as cadmium-chronium copper and zirconium copper offer important weight reductions or greater strength. These factors are especially important in aerospace and other applications.

Question 6

Aluminum (Conductor Description)

Answer 6

Most commonly used in electrical utility distribution lines. It is a malleable ductile light metallic element that has good electrical and thermal conductivity, high reflectivity and resistance to oxidation. It has about 60% conductivity compared with copper and is lighter in weight.

Question 7

Advantages of Solid Conductors

Answer 7

Less Costly - Less complex Terminations - Better Transmission performance at high frequencies - Less Resistance

Question 8

Advantages of Stranded Conductors

Answer 8

More Flexible - Longer flex life - Less susceptible to damage during crimping process

Question 9

Composite Conductor

Answer 9

Term used to describe conductors constructed from nontraditional materials.

Question 10

Advantages of Composite Conductors

Answer 10

Flexible - Light - Inexpensive and easy to produce - Easily embedded into other materials - Low coefficient of expansion

Question 11

Fluorinated Ethylene Propylene (FEP)

Answer 11

Teflon, NEOFLON FEP.

Question 12

Teflon is a trademark of

Answer 12

E.I. du Pont de Nemours & Company.

Question 13

NEOFLON FEP is a trademark of

Answer 13

Daikin America Inc

Question 14

Halar is a trademark of

Answer 14

Solvay Solexis

Question 15

AWG

Answer 15

American Wire Gauge = Generally accepted cable sizing system in North America.

Question 16

Insulation (also called a dielectric)

Answer 16

Used to isolate the flow of current by preventing direct contact between: Conductors, A conductor and its environment.

Question 17

Insulation (dielectric) is typically made of

Answer 17

Plastic materials - applied by a variety of methods. Extruded polymers are generally used as insulation

Question 18

Cables with a lower dielectric constant and disposition factor have

Answer 18

better transmission performance including lower attenuation characteristics and lower capacitance

Question 19

Dielectrics ______ the electromagnetic coupling between conductors by increasing seperation

Answer 19

reduce

Question 20

Dielectric Constant

Answer 20

The ratio of the capacitance of an insulated conductor to the capacitance of the same conductor uninsulated in the air. Generally a low dielectric constant is desirable

Question 21

Dielectric Strength

Answer 21

Measures the maximum voltage that an insulation can withstand without breakdown. A high value for dielectric strength is preferred.

Question 22

Insulated conductors in telecom applications have a typical dielectric strength between _____ and ____V per millimeter.

Answer 22

7500 and 30,000 V per millimeter (300 and 1200 V per mil)

Question 23

Dissipation Factor

Answer 23

The relative power loss in the insulation due to molecular excitement and subsequent kinetic and thermal energy losses. A low dissipation factor is peferrable

Question 24

Insulation Resistance (IR)

Answer 24

The insulation ability to resist the flow of current through it. Typically expressed in megohmkilometer or megohm1,000 feet

Question 25

As cable length increases, the insulation resistance becomes________

Answer 25

smaller

Question 26

The main reason for tight twisting pairs of conductors is to

Answer 26

Minimize crosstalk and noise by decreasing capacitance unbalance and mutual inductance coupling between pairs.

Question 27

A _____ twist between ___ and ___ inches is used for voice and low frequency cables

Answer 27

Counterclockwise, 2in and 6in (.50mm and 150mm)

Question 28

Adjacent pairs are generally designed to have a twist length difference of at at least__________

Answer 28

12.7mm or .5 inches.

Question 29

EMI

Answer 29

Electromagnetic Interference

Question 30

What is EMI?

Answer 30

stray electrical energy radiated from electronic equipment and electronic systems (including cables). EMI can cause distortion or interference to signals in other nearby cables and systems

Question 31

High Temperatures can be routinely encountered in

Answer 31

Exterior Building Walls
Ceiling spaces, including plenums
Mechanical Rooms

Question 32

Attenuation increases with temperature because of increased:

Answer 32

Conductor Resistance
Insulation dielectric constant
Dissipation Factor

Question 33

A temperature coefficient of ______ per degree Celsius is not uncommon for some Category 3 cables

Answer 33

1.5%

Question 34

What is a shield?

Answer 34

A metallic covering or envelope enclosing the:

• Insulated conductor
• Individual group of conductors within a core
• Cable core

Question 35

Shields are made of..

Answer 35

Foil or Braided Metal Strands

Usually tinned copper, bare copper, aluminum, or another electrically conductive material

Question 36

When properly terminated, bonded and grounded (earthed) cable shields can

Answer 36

• Reduce the radiated signal from the cable
• Reduce the effects of electrical hazards
• Minimize the effect of external EMI on the conductors within the shielded cable

Question 37

The effectiveness of a shield depends on factors such as the..

Answer 37

• Type and thickness of the shield
• Number and size of the openings in the shield
• effectiveness of the bonding connection to the ground

Question 38

What are the steps to convert analog signals to digital?

Answer 38

• Filtering
• Sampling
• Quantizing/compounding

Question 39

True or False
The sampling rate must be at least twice the highest frequency component of the analog signal to faithfully reproduce the analog signal as a digital signal.

Answer 39

True

Question 40

What is a simplex transmission system?

Answer 40

Simplex transmission systems only send signals in one direction

Question 41

What is the signal strength decibel defined as?

Answer 41

Decibel is defined as:
dB = 10log(P1/P2)

It is the power of signal P1 relative to reference power P2.

3dB indicates a power ratio 2x. So +3dB would double the power.

Question 42

What the three basic components of a transmission system in telephony?

Answer 42

• source of energy (acoustic energy of speech is converted to electrical signal)
• medium to carry the energy (a balanced twisted pair is commonly used)
• receiving device (transducer in the receiver headset acts a small loudspeaker and converts the electrical signal back to sound energy)

Question 43

True or False
A conduit is the best possible shield.

Answer 43

True