NGT—Technical description (2011/2012)
128 NGT Transceiver System Technical Service Manual
Internal voice encryptor
Voice encryption is possible with the NGT when a plug-in Encryptor PCB is fitted via P8
to the Application Processor Handset I/F 3 V PCB (2011)/Application Processor
Handset & Data I/F PCB (2012). The microprocessor on this PCB detects that the
Encryptor PCB is present at power up and enables the control firmware.
The encryptor is controlled by the TxD, RxD and SILENCE lines. The WAKE line is
used to reduce the current drain when the encryptor is not in use.
When encryption is enabled, encrypted receive audio is fed via DEC_IN to the
Encryptor PCB. The de-crypted audio comes out of DEC_OUT. This signal is fed into
the system audio.
In Transmit mode, the microphone audio is fed into ENC_IN on the Encryptor PCB
where it is encrypted then fed through ENC_OUT to the DSP audio compressor, and
then to the transmitter.
When the encryptor is not enabled, all audio bypasses the Encryptor PCB.
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