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Time Domain Reflectometry (TDR) Technology
Factory Defaults
You can set all programmable features to their original,
factory settings. This function does not delete stored
telephone numbers. The defaults are:
•
Backlight timer: 30 seconds
•
Power-down timeout: 2 minutes
•
Hook flash duration: 500 ms
•
Pause time: 4 seconds
•
Speaker timeout: 2 minutes
•
Speakerphone microphone: on
•
Handset volume: level 4
•
Speaker volume: level 4
•
Tone/Pulse: tone
•
Receive-Only Loud Speaker mode: disabled
•
DTMF Digit Grabbing: off
•
Velocity of propagation: 66
To restore factory defaults:
1
Press Q.
2
Press M, press C to put the flashing cursor next
to Settings, then press M again.
3
Press C to put the flashing cursor next to
FactDfaults, then press M.
4
Press R or L to select Yes.
5
To save your selection before you exit or go back
to the main menu, press
M. The display briefly
shows In Progress.
To go back to the previous menu, press Q. Or,
press
C or D until Back shows, then press
M.
Time Domain Reflectometry
(TDR) Technology
A time domain reflectometer senses reflections of
electrical signals on a cable and shows where the
reflections occur on the cable. Because faults such as
shorts and opens cause reflections, a TDR can show you
the location of faults on a cable.
The TDR sends a pulse down the two conductors in a
cable. When the pulse goes across a change in the
impedance of the conductors, some of the energy of
the pulse is reflected back to the test set. Changes in
impedance are caused by changes in the physical
relationship between the two conductors. For example,
an open, a short, or a change in the distance between
the conductors causes a change in impedance.
The test set measures the time from when it sent the
pulse to when it received the reflection. Then, it uses
this time and the speed of the signal in the cable to
calculate the distance to the change in impedance:
VOP (velocity of propagation) is the ratio of the speed
of a signal in the cable to the speed of light. Typically,
the speed of a signal in a cable is between 60 % and
80 % the speed of light.
The test set also looks at the polarity of the reflected
pulse (Figure 5). If the impedance of the cable
increased, the polarity of the reflection is the same as
the pulse from the test set. This occurs if there is an
open on the cable. If the impedance decreased, the
polarity of the reflection is opposite. This occurs if there
is a short on the cable.
If there is more than one fault on the cable, the test set
shows the distance to the nearest fault.
Time
2
VOP X 983571088
X
Distance in feet =
)
(
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