20
Issue 1, December 2003
61223404L2-5A
7. Resistance Values. See
Each of the three segments associated with span
powering two H4Rs and a H4TU-R must satisfy
the DC resistance budgets in addition to the
recommended loop attenuation requirements. In
general, 22 and 19 AWG segments will be
restricted by their loop attenuation while the DC
resistance will restrict the segment reach for 26 and
24 AWG. When designing a dual H4R loop, the
first segment should have lower DC resistance than
the second segment.
Single H4R spans do not require any restriction
due to DC resistance.
NOTE
A circuit that otherwise meets attenuation and
other requirements for cable reach will
encounter span powering problems if resis-
tance values are excessive.
The segment resistance (
Ω
segment
) is determined using
this equation:
Ω
segment
= L
26
*
Ω
26
+ L
24
*
Ω
24
+ L
22
*
Ω
22
+ L
19
*
Ω
19
where L
#
is the length of # AWG cable (kft., excluding
bridged taps) and
Ω
26
is the DC resistance of #AWG cable.
Note: Interpolated between 70
°
F and 120
°
F data. Extrapolated from 70
°
F and 120
°
F data.
Table 9. Single Pair DC Resistance Value
Resistance (ohms/kft)
AWG
70°F
90°F
120°F
140°F
19
16.465
17.183
18.261
18.979
22
33.006
34.446
36.606
38.046
24
52.498
54.789
58.225
60.516
26
83.475
87.117
92.581
96.223
