Handbook for Sound Engineers

Transmission Techniques: Wire and Cable 415

PS-NEXT. PS-NEXT, or power-sum near-end crosstalk,
is the crosstalk between all of the sending pairs to a
receiving pair. With four-pair cable, this is more impor-

tant than NEXT.

FEXT. FEXT, or far-end crosstalk, is the measure of the
unwanted signal from the transmitter at the near end
coupling into a pair at the far end.

EL-FEXT. EL-FEXT, or equal level far-end crosstalk, is

the measure of the unwanted signal from the transmitter

end to a neighboring pair at the far end relative to the

received signal at the far end. The equation is

(14-3)

Power sum equal-level far-end crosstalk is the computa-

tion of the unwanted signal coupling from multiple

transmitters at the near end into a pair measured at the

far end relative to the received signal level measured on

the same pair.

Return Loss (RL). RL is a measure of the reflected

energy from a transmitted signal and is expressed in

dB, the higher the value, the better. The reflections are

caused by impedance mismatch caused by connectors,

improper installation such as stretching the cable or too

sharp a bend radius, improper manufacturing, or

improper load.

Broadcasters are very familiar with return loss,

calling it by a different name, SWR (standing wave

ratio) or VSWR (voltage standing wave ratio). In fact,

return loss measurements can easily be converted into

VSWR values, or vice versa. Return loss can be found

with the equation

(14-4)

where,

Difference is the difference (absolute value) between the

desired impedance and the actual measured

impedance,

Sum is the desired impedance and the actual measured

impedance added together.

• The desired impedance for all UTP data cables
  (Cat 5, 5e, 6, 6a) is 100:


• The desired impedance for all passive video, HD,
  HD-SDI or 1080p/60 components is 75:


• The desired impedance for all digital audio twisted
  pairs is 110:

Figure 14-8. Maximum distances between areas for UTP cable.

Equipment

room (ER)

main cross

connect

ER

intermediate

cross-

connect

Tele-

communicatons

closet

Information

outlet

Work

500 m/1650 ft 300 m/1000 ft area

Jumper/patch cords:

6 m/20 ft

90 m/300 ft 3 m/10 ft

Backbone cabling Horizontal cabling

Jumper/

patch cords:

20 m/65 ft

800 m

Table 14-19. Color Code for UTP Cable

Pair No. 1st Conductor Base/Band 2nd Conductor

1 White/Blue Blue

2 White/Orange Orange

3 White/Green Green

4 White/Brown Brown

Table 14-20. Diameter and Bend Radius for 10GbE

Cabling

Cable Diameter Bend Radius

Category 6 0.22 inch (5.72 mm) 1.00 inch (4 × OD)

Category 6a 0.35 inch (9 mm) 1.42 inch (4 × OD)

Category 6 FTP 0.28 inch (7.24 mm) 2.28 inch (8 × OD)

Category 7 STP 0.33 inch (8.38 mm) 2.64 inch (8 × OD)

Cable diameters are nominal values.

Figure 14-9. UTP and S/UTP cable design.

Conductor

Conductor

Insulation

Insulation

Pair

Pair

Sheath

Sheath

Shield

Pair shield

Pair shield

UTP STP

S/UTP S/STP

EL FEXT– FEXT Attenuation–=

RL 20 Difference

Sum

= log----------------------------