Information Technology Reference
In-Depth Information
nique. Either style of tester is acceptable, both to the TIA working committees and
to qualified independent evaluators.
The bottom line is: Choose the specific tester that will do the best job for you.
TDRs/OTDRs
Although cable scanners use a form of TDR to perform the important certification
measurements, a traditional TDR may provide additional insights into cable opera-
tion. Expensive laboratory TDRs may not be needed, as some of the field testers men-
tioned in the previous section now incorporate TDR graphics in their instruments.
The actual graph of a cable's reflections can reveal many things about the han-
dling and installation of the LAN wiring that simple Pass/Fail reports and raw meas-
urements obscure. A typical TDR screen is shown in Fig. 15.11.
Optical fiber has a more sophisticated testing requirement than does metallic
cabling. The same low-loss characteristics that make fiber optics important in trans-
mitting longer distances make loss measurements critical to ensuring fiber cable per-
formance. Optical cable is also subject to impairments from bending and stress that
cause additional signal loss.
FIGURE 15.11
A time-domain reflectometer displays discontinuities and anomalies. (Courtesy of Tektronix.)
