Nortel Networks DCT1900 - Manual (Page 302)

Technical Product Manual - DCT1900
Installation Instructions, Use of TDR
25-2 Install-DCT1900/R8/mw
© 2000-2005
10. A waveform similar to the one shown in Figure 25-1 should be displayed, however the vertical
pulse will be located at the left edge of the screen. This is the transmitted pulse the TDR uses
to determine the length of the cable.
11. Rotate the horizontal POSITION control (10) until the vertical line it controls is all the way
against the left edge of the screen. At this point, the upper right corner of the display should
show either 0.00 ft. or some negative value.
12. Connect the pair to be measured to the test cable using the alligator clips. At this point the pair
should not be connected to either the base station or the radio exchange, and should be left
open-circuited at the far end. Adjust the DIST/DIV control (5) until the display shows not only
the transmitted pulse on the left (as in Figure 25-1) but also the reflected pulse farther to the
right. This pulse should have the same polarity (positive) as the transmitted pulse. It may be
necessary to adjust the Vertical Scale (4) control and/or the Pulse Width control (8) so that the
transmitted and reflected pulses are clearly defined and separated as in Figure 25-2.
Figure 24-2 Transmitted and Reflected Pulses
Now, adjust the horizontal Position control (10) until the vertical line it controls is exactly at the
leading edge of the reflected pulse. At this point, have someone short the pair at the far end while
observing the display. The reflected pulse should invert as the pair is shorted. If not, the pair may
be open at some point or you may be testing the wrong pair. Correct the condition and retest until
the proper result is obtained.
Have the person at the far end remove the short and observe that the reflected pulse returns to
positive polarity and that it is still aligned with the vertical line. If the pulse has shifted, this is an
indication that the pair may be open on one side. Correct the condition and retest until the proper
result is obtained.
Note the indication in the upper right corner of the display, indicated in feet. Multiply this indicated
length in feet by the constant .001025 microseconds/foot. This will yield the delay of the pair in
microseconds.
Example: Assume a reading of 167.7 ft.
167.7 ft. x .001025 = .17189 microseconds
Record the calculated delay in microseconds. This value will be used to determine the proper
value to enter when adding a Remote Base Station using the Cordless System Manager software
for windows.
As the system allows entries only in increments of 0.1, it will be necessary to round.