The comparator section of the convertor compares
the signals received in the diversity mode and allows
only the stronger signal to be passed on to the
communication patch panel.
Communication Patch Panel
The communication patch panel performs the
same function on the receive side as it does on the
transmit side.
Crypto Equipment
The crypto equipment decodes the received signal
so it can be printed out in its original form.
Teletype
The tty equipment converts the dc pulses from the
patch panel to a printed copy of the original message.
The tty shown is a page printer only and does not have
transmit capability.
AFTS SYSTEM
Figure 2-20 is a block diagram of a half-duplex uhf
system. Half-duplex communication can be in
either direction, but cannot happen at the same time.
The term half-duplex is qualified by adding send only,
receive only, or send or receive.
AFTS Transmit
Dc signals from the tty are sent to the com-
munications patch panel where they are fed to the tone
terminal set. The tone terminal set converts the dc
signals into audio tone-shift signals. The audio tone-
shift signals are patched to the transmit side of the
transceiver through the transmitter transfer
switchboard. The audio tone-shift signals are then used
to modulate the rf carrier for transmission.
AFTS Receive
The rf tone-modulated signals are received at the
antenna and then patched, via the multicoupler, to the
receive side of the transceiver, where demodulation to
audio tone-shift signals takes place. The signals are
then patched to the tone terminal set through the re-
ceiver transfer switchboard, where they are converted
back to dc signals. The dc signals are then patched
through the communication patch panel to the tty.
FACSIMILE
Facsimile (FAX) is a method of transmitting still
images over a communications system. The images
may be weather maps, photographs, sketches,
typewritten or printed text, or handwriting. Military
use of FAS is primarily limited to transmission and
reception of weather maps. Because of long
transmission times, its tactical uses are limited.
TEMPEST
Compromising emanations, generally called
TEMPEST, are unintentional data-related or
intelligence-bearing signals which, if intercepted or
analyzed, can disclose the classified information
transmitted, received, handled, or otherwise
processed by electrical information processing
equipment or systems.
The Navy uses MIL-STD-1680 (SHIPS),
Installation Criteria for Shipboard Secure Electrical
Processing Systems, as the guide for TEMPEST.
Within communications centers, ETs must understand
and be familiar with both RED and B L A CK
designated systems and equipment. The RED and
BLACK designations are explained in the following
paragraphs.
RED CRITERIA
The RED designation applies to all crypto
equipment, subscriber terminal equipment, and
interconnecting conductors involved in processing
classified plain language information. It also applies
Figure 2-20.—Half-dup1ex AFTS teletype system.
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