2-20. CIPHER TEXT.
The RT can be used to receive and transmit cipher text (CT) information when the COMSEC module is installed in
the RT. Audio, data, and control signal are routed automatically to and from the COMSEC module.
When a cipher text signal is received, it is routed through the COMSEC module. See figure FO-11. The COMSEC
module will ground the IRNSTI-P line to indicate CT operation.
The received signal (RDCT) is routed to the
COMSEC module. The decrypted signal (AR/DDR) is returned. If it is an audio signal, it follows the normal audio
path. If it is a digital signal, it will follow the normal digital path. The COMSEC module provides the DDCO signal.
When an audio signal is received in the FH and CT modes, the ECCM module deinterleaves the data stream. The
COMSEC module recovers the audio signal from the data stream.
When transmitting, the signal sent to the COMSEC module can be either audio (AT) or 16 kb/s digital (DDT). See
figure FO-12. The RED DDMC-N line is set to logic 1 for audio. It is set to logic 0 for digital. The COMSEC PTT-N
line is grounded for transmit. The ICOM control module routes the signals to the COMSEC module. The encrypted
signal (TDCT) is returned and routed to the switching module.
Audio and data signals are interleaved in the FH mode after encryption.
2-21. SNAP INTERFACE.
The RT provides seven signals for operation with a SNAP. The SNAP is cabled to J10 on the mounting adapter.
See figure FO-14. They are as follows:
Logic 1 = FH, logic 0 = SC.
Digital data stream that provides operating frequency.
Logic 0 pulse used with SERIAL DATA.
Clock used with SERIAL DATA.
Directs SNAP to perform self-test.
Logic 0 indicates RT is changing frequency.
1 A1 2-75
Logic 1 = transmit, logic 0 = receive.
1 A1 2-76
The SNAP returns the results of its self-test on the FAULT6 line. If it fails self-test, the RT will display "FAIL6".