|  | 9.7 | Range of Equipment for Testing Structured Cabling Projects
| 9.7.6 | TDRs (time domain reflectometers)
In LAN installations that use UTP cables, distance measurements can determine whether the connections at the patch panels, and at the telecommunications outlets, are good. To understand how this works, you must understand how a TDR works. A TDR measures distance on a cable by sending an electrical signal through the cable. The signal is reflected when it encounters the most distant open connection. In order for it to determine which connections in a cable run are faulty, you must attach the TDR to the patch cord at the patch panel. If it reports the distance to the patch panel, instead of a more distance point, then you know there is a connection problem. You can use the same procedure, at the opposite end of the cable, to measure through the RJ-45 jack located at the telecommunications outlet.
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