c. Although circuits for polar transmission are more expensive and difficult to install and maintain than those for
neutral transmission, polar transmission is superior when only wire facilities are used. You can transmit over a greater
distance with polar pulses because polar transmission is not readily affected by the distributed capacitance and inductance
in the line connecting the transmitting and receiving stations. Also, since current values are lower in polar transmission,
the power losses on the line are less.
82.
Introduction to DC Teletypewriter Circuits.
Direct current (dc) teletypewriter circuits get their name from the fact that direct current flows in the wires or
cables that connect the sending and receiving stations. You can use dc teletypewriter circuits for communication over
distances up to several miles.
83.
The Principal Parts of a Teletypewriter.
The teletypewriter we will use in this text to describe dc teletypewriter circuit consists of four principal parts
(fig. 79), as follows.
a. Voltage source. In teletypewriter schematic diagrams, the voltage source is usually shown as a battery. In
practice, rectifiers are normally used. Moreover, it is common to speak of the rectifier output voltage as the battery
voltage.
b. Transmit mechanism. This is also called a keyboard transmitter. Its purpose is to change the letters and
figures you type on the keyboard into the marks and spaces of the Baudot code. We'll represent the transmit mechanism
by the transmitting contacts schematic symbol. In this switch symbol, the left arrowhead represents the closed circuit
contact for marks and the right arrowhead represents the open circuit contact for spaces.
c. Receive mechanism. This is also called a page printing mechanism. Its purpose is to change the marks and
spaces into letters and figures which are printed on paper. We'll represent the receive mechanism by the selector magnet
schematic symbol. A selector magnet is an electromagnet. Its armature operates in one direction for marks and in the
other direction for spaces.
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