Chapter 1 - Principles of Transmission Flashcards
What are the advantages of solid conductors vs stranded?
- less costly
- less complex termination system
- better transmission performance at higher frequencies
- less resistance
What are the advantages of stranded conductors vs solid?
- more flexible
- longer flex life
- less susceptible to damage during crimp termination process
What are the advantages of composite conductors?
Composite conductors are conductors made of nontraditional materials. Advantages include: - flexible - lightweight - inexpensive and easy to produce - easily embedded into other materials - low coefficient of expansion
What are the disadvantages of composite conductors?
- poor analog transmission characteristics, including high attenuation especially above 4000Hz
- poor digital transmission characteristics
- easily damaged unless encased in a rigid material
- inconsistent quality
What is dielectric constant?
The ratio of capacitance of an insulated conductor compared to the same uninsulated conductor in air. Air is a reference with a constant of 1.
Usually the lower the dielectric constant the better.
What is dielectric strength?
Measures maximum voltage that an insulation can handle without breakdown.
Higher the better.
What is dissipation factor?
The relative power loss in the insulation.
Lower the better
What is insulation resistance (IR)?
The insulation’s ability to resist the flow of current through it.
Typically expressed as megaohm-km or megaohm-1000 ft
longer the cable the smaller the IR
What is the main reason for twisting pairs of conductors?
To minimize crosstalk and noise by decreasing capacitance unbalance and mutual inductance coupling between pairs.
Twisting also improves balance and reduces noise coupling from external sources
What is pair to pair capacitance unbalance?
Measure of the electric field coupling.
What is mutual inductance?
Measure of magnetic field coupling.
What do cable shields do?
- reduce radiated signal from cable
- reduce effects of electrical hazards
- minimize the effect of external EMI on the conductors within the shielded cable
What impacts the effectiveness of a shield?
- type and thickness of shield material
- number and size of openings in shield
- effectiveness of bonding connection to ground
True or False
A conduit is the best possible shield.
True
What is a poor shield effectiveness rating?
Poor is less than 20dB
What is a fair shield effectiveness rating?
Fair means 20 to 40 dB
What is a good shield effectiveness rating?
Good is 40 to 60 dB
What is an excellent shield effectiveness rating?
Excellent means more than 60 dB
True or False
Drain wires can be used in place of a shield
False
Drain wires are used in addition to a shield to provide an easier means for grounding the shield.
What is the signal strength decibel defined as?
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.
What the three basic components of a transmission system in telephony?
- 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)
True or False
Loading coils can improve speech transmission quality by:
- compensate for the capacitance of a cable pair
- increase the capacitive current loading in the range of audio frequencies
False
Loading coals reduce the capacitive current loading in the range of audio frequencies
Everything else is true
Note: loading coals will block off frequencies above the voice range and adversely affect data transmission due to severe delay problems
What are the steps to convert analog signals to digital?
- Filtering
- Sampling
- Quantizing/companding
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.
True
What is a simplex transmission system?
Simplex transmission systems only send signals in one direction/
What is a half-duplex transmission?
A half-duplex is a transmission of signals in either direction, but only one at a time.
What is a full duplex transmission?
A full duplex describes a transmission of signals in both directions at the same time.
Why is asynchronous transmission less efficient than synchronous transmission?
It requires the addition of some combination of start and stop bits to the data stream. Synchronous transmission does not require start and stop bits.
What is basic rate Integrated Services Digital Network (ISDN)?
- digital transmission at a basic or primary rate
- intended for residential and small business users
- uses a digital signal consisting of two 64 kb/s B channels (assigned for voice and data) and one 16kb/s D channel (assigned for signaling and packet data)
- has a total information capacity of 144 kb/s (line rate = 160 kb/s)
What is primary rate Integrated Services Digital Network (ISDN) North America?
- intended for large business users
- total information capacity of 1.536 Mb/s (line rate = 1.544 Mb/s)
- Uses a digital signal consisting of 23 B channels and one D channel, each operating at 64 kb/s
What is the total information capacity for Integrated Services Digital Network (ISDN) Europe?
- Total information capacity of 1.92 Mb/s (line rate = 2.048 Mb/s)
What is Digital Subscriber Line (DSL)?
A way to provide high-speed, high-quality transmission of data, voice and video over existing balanced twisted-pair telephone lines.
What are the two different terms commonly used to describe different types of baseband signaling?
- Composite
- Component
What is the difference between composite and component analog?
Composite contains everything needed to construct a monochrome or color picture but contains no audio component.
Component uses three separate RGB components to generate an image. This helps minimize crosstalk and permits higher resolutions.
What is attenuation?
Attenuation is the ratio of output to input power (or voltage)
Weakening of the signal strength
What is delay skew?
Delay skew is the difference in propagation delay between any pairs within the same cable sheath.
What type of network cabling is the minimum accpeted?
Cat 3/Class C
What type of network cabling is the minimum recommended?
Cat 5e/ Class D
What is the best practice network cabling?
Cat 6/Class E
What Frequency is Cat 3/Class C/
16 MHz
What frequency is Cat 5 Class D? (CAT 5e per TIA)
100MHz
What frequency is Cat 6/Class E?
250MHz
What frequency is Cat 6A?
500 MHz
What are the advantages of media conversion?
- it can be cost effective
- moves can be simpler to implement
- less space in risers or conduits required
What is a balun?
A balun is an impedance matching device. Used to adapt balanced impedance of twisted pairs to unbalanced impedance of coax cables.
It additionally used to convert UTP cabling to coax.
What are the advantages of signal converters?
- decrease risk of transmission and EMI problems
- extend the unbalanced signal reach of a Data Terminal Equipment (DTE)
What are the four types of Power of Ethernet (PoE)?
- 802.3af (Type 1) : max power output of 15.4W with up to 12.95W to the Powered Device (PD)
- 802.3at (Type 2): max power output of 30W with up to 25.5W to the PD
- 802.3bt (Type 3): max power output of 60W with up to 51W to the PD
- 802.3bt (Type 4, reference same as Type 3): max power output of 90W with up to 73W to the PD
Fill in the blanks
Multimode optical fiber is best suited for premises applications where links are less than:
_______ for data rates of 155 Mb/s or less
_______ for data rates of 1 Gb/s or less
_______ for data rates of 10 Gb/S or less
_______ for data rates of 100 Gb/s or 40Gb/s or less
~ 2000m (6562 ft) for data rates of 155 Mb/s or less
~ 550m (1804 ft) for data rates of 1 Gb/s or less
~ 300m (984 ft) for data rates of 10 Gb/s or less
~ 100m (328 ft) for data rates of 100Gb/s or 40Gb/s or less
What is the maximum permissible end-to-end system attenuation for a given optical fiber link determined by?
It’s determined by the average transmitter power and the receiver sensitivity.
The optical fiber carrier transmission standard in North America is?
SONET
For an optical fiber system, the essential determinants of end-to-end bandwidth are the?
Transmitter and the optical fiber
True or false
The bandwidth for 50/125um multimode optical fiber is lower than that of 62.5/125um multimode fiber
False. It is higher
True or False
The attenuation of 62.5/125um multimode fiber is slightly higher than 50/125um optical fiber
True
What are the maximum attenuation values for singlemode optical fiber?
Outside cable = 0.4dB/km
Inside cable = 1.0dB/km
In a multimode optical fiber system, the maximum splice loss when using a mechanical splice should be ____ dB.
0.3dB
the same if using a fusion splice
In a single mode optical fiber system, the maximum splice loss when using a mechanical splice should be ____ dB.
0.3dB
the same if using a fusion splice
In a multimode optical fiber system, the avg splice loss when using a mechanical splice should be ____ dB.
0.1dB
Singlemode is the same
In a multimode optical fiber system, the avg splice loss when using a fusion splice should be ____ dB.
0.05dB
singlemode is the same
The option of tight twisting (for balanced twisted-pair cables) is used particularly within and between computers and other data processing equipment. Tight pair twist lengths are less than:
0.5 in
Series inductance is related to the:
A) Dimensions and separation of conductors
B) Dielectric loss of the insulation and jacket materials
C) Dimensions and separation of conductors and to the dielectric constant of the insulation and jacket materials
A) Dimensions and separation of conductors
