Lesson 1/Learning Event 7
(c) A distortion test set may provide a test signal called a "fox"
message, it may send repeated letter combinations, or it may send reversals
(alternate marks and spaces); the choice belongs to the technical
controller. The advantage of generating signals within the test set is that
known values of distortion can be inserted in the signal as it is
transmitted over the send loop.
Whenever test signals are sent, traffic
must be removed from the circuit. If teletypewriter printers are not needed
in the test, they are either turned off or held closed by marking current.
(d) The digital distortion test sets used by DCS technical control
facilities are capable of providing test messages for sending, and of
measuring distortion on send loops as well as receive loops. Moreover, they
are capable of measuring distortion on high-speed data pulses.
d. Cable fault locator.
The test set determines the condition of
telephone lines.
Circuit and equipment installers, together with circuit
activators, are interested in the line conditions prior to making
interconnections. Technical controllers are also interested in the effect
that outside interference have on normal operations.
The cable fault
locator is capable of taking several measurements, the most important being
the determination if foreign battery, shorts between lines, grounded lines,
and open circuits.
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