Chp 1 Flashcards
Solid conductor Advantage
Price
Conductivity at high frequency
Resistance
Less complex termination systems
Stranded conductor advantage
Flexibility
Less prone to damage (during termination, and over lifetime of flexing)
Most common conductors in ICT
Copper
Copper clad steel
Copper Alloy
Aluminum
Conductor used for electrical utility distribution, why
Aluminum Lightest conductor with 60% conductivity. Other characteristics; Good: ductility, corrosive resistance Poor: oxidative resistance Weight: approx 1/3 of copper Tensile strength: < 1/3 of copper Solderability: requires special techniques
Conductor for self supporting cable
Type & Application:
Copper clad steel, for aerial drops
Strongest conductor type
Type & application:
High strength alloys
used in aerospace and computer to meet specific characteristic requirements
Composite conductors
Type & Application:
Pourable mixture to cure in cast/casing for embedded conductor applications.
ICT use: DONT. Trash it, and use other conductors if provided with equipment
Insulators used for plenum
PVC
Insulatior properties
Dielectric strength
IR (insulator resistance)
Dielectric constant
Dissipation factor
Desired dissipation factor
Low.
This factor increases with signal frequency, and esp. concerning in MHz range (loss due to thermal exchange from “microwaves”)
Desired Dielectric strength
high
Desired dielectric constant
low, generally
Desired IR
High
IR is determined by cable length (inverse relationship)
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.
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.
Cross-talk measured by
Mutual inductance and capacitance unbalance
Tight twisting length
<12.7mm (.5”)
Tight twist transmission effect
Preserves twists better, and therefore transmits signal more effectively
Cable types using tight twists
CAT5e, 6, 6A & higher
Tight twist physical effect
Cable structure maintains better
Environmental design considerations
Max temperature
EMI sources
Cable characteristics affected by temperature
What, trait
Conductor, resistance
Insulator, Dissipation factor
Insulator, Dielectric constant
High temperatures likely to be found in
ceilings/plemuns
exterior walls
mechanical rooms
& cables using high levels of PoE
Why temperature matters
Directly proportional to attenuation
Attenuation is determined by mdeium’s
Dielectric constant
Dissipation factor
Conductor resistance
Design systems using the ____ temperature
potential highest
Cabling standard reference for design
All twisted-pair cables are referenced in the cabling standards at 20 °C +/- 3 °C (68 °F +/- 5.4 °F). For adjustment purposes, the attenuation increase is 0.2 percent per degree Celsius for temperatures above 20 °C (68 °F) for screened cables, 0.4 percent per degree Celsius for all frequencies and for all temperatures up to 40 °C (104 °F), and 0.6 percent per degree Celsius for all frequencies and for all temperatures from 40 °C to 60 °C (104 °F to 140 °F) for all unscreened cables.
Shielding cable
helps to maintain signal quality
Often used with shields for the purpose of____
What, fill in blank
Drain wires, providing a conveinent means to ground shield & maintain continuity across perforations/braids/etc
Phase is
What, units
Reference of time in respect to the signals period
Period is 360 degrees, i.e. 1/4 period = 90 degrees
Sinusoidal signal described mathematically
formula v(t)=A*sin(2 pi f t + ø) A=amplitude f=freq t=time ø=phase
Signal theory developed by
who
joseph fourier
Fourier’s Analog Signal Description
Any analog signal can be described by multiple sinusoidal signals. Each signal would be considered a component of the signal it represents.
Collectively, these signals are referred to as the signals SPECTRUM.
The difference across the frequencies which these signals have is the bandwidth of the signal.
Used to express strength of signals
dB, dBm (dB referencing 1mW),dBW (dB referencing 1W)
dB is
a ratio of power output to power input.
Often a standard unit is used to compare signals rather than using input
Echo
When a signal encounters a discontinuity in the impedance of the medium carrying the signal, some of the signal power is relected back to the transmitter.
Complex signals with many components use ___ instead of _____
Time, phase.
because phase can be described as delay in time
The application of inductors, called _________, placed at intervals along a cable improves speech transmission quality.
loading coils
Loading coils
- Compensate for the capacitance of a cable pair.
* Reduce the capacitive current loading in the range of audio frequencies.
In telephony, Data speed transmission depends on
signal frequency (& medium characteristics: capacitive balance & mutual impedance)
Higher frequencies travel _____ than low frequencies
faster
Loading coils solve the speech quality issue but create a _______ issue
transmission delay
Distance between loading coils determines the _____ frequency and have a _____ relationship
cut off
inverse
Most common distances between loading coils
1.37km (for D loading) & 1.83km (for H loading)
Issues in analog telephony
Issue, cause, solution, side effect
Distortion, change of mediums/impedance & distance, loading coils, signal delay
Echo, impedance change weakens signal cuz some bounces back, loading coils strengthen signal, signal delays
IP Telephony
Uses data cabling
Recommended dedicated jack so computer & phone dont compete
Life safety telecom applications should use POE & UPS
***Add cards with standards applicable to CAT3, CAT5, CAT6 from Table 1.17
*** ADD Table 1.18 cable lengths/transmission rates & applications
Although the cabling transmission parameters are complex, the inal result is that a transmission circuit should be cost-efective, meet applicable standards, and have:
• A uniform characteristic impedance that is matched to the equipment
.• Low insertion loss/attenuation.
• High SNR and available bandwidth.
• Velocity of propagation that is relatively constant with frequency
.• High NEXT and FEXT loss between pairs
.• High NEXT and FEXT loss between pairs in adjacent cables and connectors
.• High noise immunity.
