FIGURE 69. Balancing Simplexed Line
(2) Interference from a poor splice may be reduced to a tolerance level by introducing an additional loss in the
circuit; this is accomplished by using a rheostat in the low-resistance side of the line (fig. 69). The low-resistance side is
ascertained by trial; that is, the rheostat is inserted first in one side of the line, and then in the other. When placed in the
low-resistance side, adjustment of the rheostat markedly equalizes the loss on each side of the line. When these losses are
equal, interference drops to a minimum.
70.
Advantages and Limitations of Simplex Circuit.
a. Advantages. One of the obvious advantages of the simplex circuit which make it useful in military
applications where time is an important factor is that it adds telephone or telegraph channel to a two-wire line without
interference, thus effecting a considerable saving of material and maintenance. Another advantage is the comparative ease
of installation.
b. Limitations. In spite of the considerable saving in time, material, and personnel obtained with simplex
circuits, they usually are not used to provide an additional telephone channel. The ground-return makes the line
susceptible to interference from noise and crosstalk. Also, the ground-return circuit signal is more susceptible to
interception by an enemy. Telegraph circuits, however, operate effectively on a ground-return system, and simplex
circuits frequently are used to provide an additional telegraph channel on a two-wire metallic line.
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