4.
To verify an open, turn the handcrank on the test telephone and notice
the amount of force you must use to turn it.
5.
An open line will allow the handcrank of the test telephone to turn
freely without resistance and signaling will not be transmitted or received
(Chapter 11, FM 24-20).
6.
Short circuit occurs when the conductors of a pair come in contact
with each other (Chapter 11, FM 24-20). Most shorts occur at the ties and
at the terminal.
a. If a field wire pair is jerked or pulled too hard, the insulation
may be cut or crushed in its own tie to a tree or pole; that is, the
conductors may cut their own insulation in the tie because of too much
tension.
This usually causes a short circuit on the line.
If an aerial
span has too much tension, the conductors will usually short circuit
themselves by cutting their own insulation at the tie.
b. Short also occurs on line at terminal connections.
Bare ends or
some of the strands of stripped conductors sometimes are not properly placed
on binding posts. When this happens, the bare strands of conductors of the
same pair usually touch.
7.
To verify a short circuit, turn the handcrank on the test telephone
and notice the action of the handcrank (paragraph 3-2c, TM 11-5805-201-12).
8.
A short is present when the handcrank turns hard with jerky motion
(Chapter 11, FM 24-20).
Opens and shorts are the two faults that cause
complete line failure most frequently.
9.
The two faults that cause cross talk between lines, as well as noisy
lines, are cross and ground.
10. When a line is grounded, one or both line conductors are in contact
with a grounded object (Chapter 11, FM 24-20).
This produces weak
communications, noise, and weak reception over a wire line.
a. When one conductor of a local-battery line is grounded, the line is
balanced.
The line picks up noise inductively from other adjacent lines.
If the soil near the ground is moist or wet and rich and dark, the ground
contact on the conductor will probably be of low resistance.
If the soil
near the ground is dry and light clay, sandy, or rocky, the ground contact
on the conductor will probably be of high resistance.
b.
On local battery lines, low-resistance ground usually causes the
line to
pick up noise as well as weak reception. Noise and weak reception
usually
comes from induction caused by line grounded with the metallic
contact
with the earth.
3
Previous Page
