ter) quickly indicates line or equipment trouble. Using
neutral signaling, this may only indicate that a steady
space is being transmitted. This condition is known as
running open. The teletype appears to be running
because it is decoding the constant spaces that cause
the type hammer to continually strike the type box, but
there is no printing or movement across the page.
When teletypewriters are wire-connected
(looped), the exchange of information between them is
direct. When they are not physically joined, exchange
of information is more complex. Dc mark and space
intervals cannot be sent through the air. The gap
between the machines must be bridged using
transmitters and receivers. The transmitter carrier
wave is used to carry the mark and space information.
A keyer is used to change the dc pulses from the tty into
mark and space modulation for the transmitter carrier
wave. The receiver and a convertor are needed to
change the rf signal back to dc pulses.
RADIO ACTUATED TELETYPE
The Navys two basic RATT systems are the tone
modulated system known as audio frequency tone shift
(AFTS), and the carrier frequency shift system known
as radio frequency carrier shift (RFCS). The RFCS sys-
tem is commonly called frequency shift keying (fsk).
For fsk systems, the transmitter provides a source
of rf excitation. Figure 2-15 illustrates a basic fsk
Figure 2-15.Basic carrier frequency shift (RFCS) system.