TM 11-5820-922-40-1
(AFSK) tones, consisting of 1575 Hz for
signal). The Rcv TTY signal is used to
a Mark and 2425 Hz for a Space. The
control the dc loop circuitry. The out-
put of the dc loop is either 20, 60, or
AFSK audio tones are then applied to the
receiver/exciter assembly to generate
0 milliamperes and is used to drive the
the Xmt RF output in teletype operation.
teletypewriter.
transmit operation, coded TTY pulses
FILTER. The radio frequency interfer-
from the teletypewriter are used in the
ence (rfi) filter is used to protect the
dc loop to produce Mark/Space current
TTY-FSK converter from voltage spikes
pulses. The Mark/Space pulses control a
and rfi which may be picked up on the
frequency divider circuit driven by a
local teletypewriter transmit and
crystal oscillator. The combination gen-
receive lines.
erates the audio frequency shift keying
