these currents are blocked by the coils in series with the telegraph sets in channels I and II, however, they are prevented
from reaching the sets. For example, if the condensers are assumed to have individual capacitances of ZuF, and the coils
to have inductances of .5 henry each, the capacitive reactance of each capacitor at a frequency of 200 hertz is
approximately 400 ohms, and the inductive reactance of each coil at this frequency is approximately 628 ohms. At 1,000
hertz, the capacitive reactance is only 80 ohms, and the inductance reactance is 3,140 ohms. At 50 hertz, however, the
capacitive reactance is 1,600 ohms, and the inductive reactance is only 157 ohms. Because of the basic operation of these
filters, therefore, the three telephone channels and four telegraph channels may be operated simultaneously without
mutual interference. Low-frequency ringing cannot be used on the telephone channels because of the attenuation that
occurs below 200 hertz. Instead, interrupted 1,000 hertz ringing is used.
(3) Figure 73 shows a line terminating and composite panel which contains a composite circuit and its associated
components.
FIGURE 73. Line Terminating and
Composite Panel
155
Previous Page
