Lesson 1/Learning Event 7
c. Other test equipment.
(1) Signal generator.
A signal generator provides a signal that is
usually patched into an in-type jack of a patch board. When so patched, the
plug causes jack contacts to insert the signal into the circuit and to
disconnect the circuit leading up to the in-type jack. Traffic ceases to
flow, and the test signal from the signal generator is transmitted to the
distant end facility.
(2) Decibel meter. A decibel meter measures signal level at the output
(receive) of a circuit or item of equipment. A decibel meter therefore is
always patched into an out-type jack of a patch board. When so patched, the
plug causes jack contacts to open the circuit following the out-type jack,
and the line leading to that jack terminates in the decibel meter. Traffic
ceases to flow.
(3) Digital distortion test set.
An instrument designed to measure
characteristics of DC telegraph signals without opening the circuit loop,
because normally there is current in a telegraph circuit.
The distortion
test set therefore measures distortion of the signal as it passes through
the test set.
Traffic flow is normally unimpeded.
In this respect a
distortion test set is similar to a milliammeter and must be patched into
the MON jack.
(a) Telegraph distortion is always measured first in the receive loop of
an operating telegraph circuit; there is no need to measure distortion in
the send loop if none exists in the receive loop. The overall performance
of the circuit is the difference between the distortion measured in the
receive loop and the send loop.
(b) Telegraph distortion is measured by a meter or by an oscilloscope
pattern or both.
When arranged for measuring distortion, the test set
receives the signal and indicates the distortion.
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