TM
11-5820-922-40-1
THEORY OF OPERATION
SECTION I
OVERALL FUNCTIONAL DESCRIPTION
gate. A detector circuit produces an
envelope of the Rcv Audio In and applies
DESCRIPTION (Figure 2-1).
the signal to a filter which removes all
frequencies above 25 Hz (normal voice
2-2. The amplifier-converter, when used
envelope range). The voice envelope is
in conjunction with an rf amplifier, a
then applied to a comparator for compar-
receiver/exciter, a coupler, and an
ison with the audio envelope. If the
antenna, constitutes a single-sideband
voice envelope is present (voice signals
(SSB) transceiver. Refer to TM 11-5820-919-40-1 for
are being received), the comparator pro-
information on Receiver/Exciter RT-1209/URC; for
duces a Squelch Control signal to turn
the other components refer to TM 11-5820-924-12.
on the squelch gate. If the voice enve-
The amplifier-converter provides amplification of
lope is not present (no voice signals
received audio signals to drive the loudspeaker
being received), or if noise is too
mounted on the front panel. Teletypewriter (TTY)
high, the squelch gate is turned off.
signal conversion is also performed in TTY receive
This prevents the Rcv Audio In signal
and transmit. Functionally, the amplifier-converter
from being presented to the operator
contains the following:
when noise is high or when there is no
voice (or cw) input.
operation, the PTT signal from the
used as a protection filter for the
receiver/exciter gates off the squelch
It blocks high-
amplifier-converter.
gate circuit. This action mutes the
power rf radiation, and is necessary
loudspeaker, while transmitting, to pre-
because of the close proximity of
vent audio feedback from the loudspeaker
the radiating antenna to the
to the microphone.
amplifier-converter.
converter converts dc signals from a
a protection device for the amplifier-
local teletypewriter to audio signals
converter. It passes signals below 3000
(Xmt Audio) for the receiver/exciter.
Hz, and blocks rf energy which emanates
The TTY-FSK converter also converts
from the system antenna.
received TTY signals (Rcv Audio In)
to dc signals to drive the local
2-5. AMPLIFIER-SQUELCH.
The amplifier
teletypewriter.
squelch circuitry automatically quiets
the Rcv Audio by reducing its response
to incoming signals (Rev Audio) below a
teletype operation, the Rcv Audio In
preselected level. During transmit
from the receiver/exciter is applied to
operation, the amplifier-squelch mutes
a Mark filter and a Space filter. The
the loudspeaker.
two filters separate the Mark frequency
(1575 Hz) and the Space frequency (2425
In voice com-
Hz) within the Rcv Audio In. The out
munication, the Rcv Audio
In from the
puts from the filters are detected to
receiver/exciter assembly
is applied to
produce the Rcv TTY signal (a binary
a clipper/limiter circuit
and the squelch
