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."