opposite direction. This, in turn, causes the east receive relay to be magnetized in the opposite direction, which causes the
mark (M) contact to open. Thus, the east loop circuit will have no current.
g. In a polar half-duplex circuit when the west teletypewriter is sending, it prints home copy and, at the same
time, the east teletypewriter prints receive copy.
90.
The Polar Full-Duplex Teletypewriter Circuit.
a. In a polar full-duplex teletypewriter circuit (fig. 86), messages can be transmitted in both directions at the
same time. Hence, the volume of traffic that can be handled is twice that of a half-duplex circuit. When a third wire or
cable is added for the return path of current flow (full-metallic), the stations can be up to 20 miles apart.
b. The signal and circuit paths are similar to those of the polar half-duplex circuit except that the transmitting
contacts and selector magnet of each teletypewriter are not in series. The signal from the sending teletypewriter goes
directly to the line windings of its associated send relay; therefore, no home copy is printed.
c. The disadvantage of this circuit is that home copy cannot be printed. However, you can overcome this
disadvantage by using four teletypewriters as we have already shown in the neutral full-duplex circuit (fig. 83).
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