The J-4024/U os the interface between the TSEC/KG-84A and
teletypewriter sets in GRC-106 communications shelters.
According to the U.S. Army manual, "the TSEC/KG-84A is
a dedicated loop encryption device (DLED). It is used to encrypt/decrypt
teletypewriter and digital data traffic on dedicated links. It can be used
for local or remote operations and will operate in the DUPLEX and the HALF
DUPLEX modes. Unlike the TSEC/KW-7, which it replaces, the KG-84A will
operate in the DUPLEX mode without an additional device. It can operate
in the TRANSMIT and RECEIVE modes at the same time. When used with radio
teletypewriter sets AN/GRC-122, AN/GRC-142, AN/VSC-2, and AN/VSC-3, the
Installation Kit MK-2488/G must first be installed.
Interconnecting Box J-4024/U interfaces the KG-84A with Teletypewriter
Sets TT-98/FG, TT76/GGC, TT-122/TG, and TT-4/TG. For complete wiring details
of the KG-84A in radio teletypewriter sets, see appropriate technical manual.
Do not attempt to use the KG-84A without Installation Kit MK-2488/GR."
