c. Whether you are sending or receiving at the west teletypewriter, current flow is from the battery through your
transmitting contacts, selector magnet, current adjust potentiometer and through the line. It then flows through the
corresponding parts in the east teletypewriter, to ground, to ground at the west teletypewriter, and back to the battery.
d. When you are receiving a message at the west teletypewriter, you can interrupt the operator at the east
teletypewriter to ask him a question by pressing the BREAK key. This operation automatically opens the circuit and
nothing is printed at either station. The east teletypewriter operator knows this is a signal for him to stop sending and wait
for your message.
FIGURE 81. Half-Duplex Teletypewriter
Circuit (One Way Reversible)
for Neutral Signals.
The Full-Duplex Teletypewriter Circuit.
a. Using a full-duplex teletypewriter circuit like the one shown in figure 82, you can transmit and receive
messages at the same time. Thus, this circuit can handle twice the traffic of a half-duplex circuit.
b. A full-duplex circuit consists of two separate series circuits, each of which has a voltage source, transmitting
contacts, current adjust potentiometer, a line wire or cable, and a selector magnet. Because the transmitting contacts of
one teletypewriter are not in a series with the selector magnet of that teletypewriter, neither teletypewriter will print home
copy. However, each teletypewriter prints receive copy.
c. The current path for transmission from west to east is from the negative side of the battery at the west
teletypewriter in sequence through: