Tait TM8000 Series, Applications Manual, Page: 110 / 136

110 Connecting Third-Party Products TM8000 3DK Hardware Developer’s Kit Application Manual
September 2003 © Tait Electronics Ltd
Encryption Module
Hardware
Configuration
1. Configure the encryption module hardware as shown in Figure 5.6 .
2. Adjust encryption module for unity through-gain. At least 11dB
headroom above the 1kHz 60% rated system deviation level will be
required throughout the audio processing chain on the module to
avoid clipping with speech signals.
3. Input pre-emphasis is required. A typical pre-emphasis circuit is
shown in
Figure 5.7 . If this not available on the module it will need
to be added as a separate circuit at the module input. Alternatively the
input buffer on the module can be modified if its topology matches
that of
Figure 5.7 .
Use the following procedure to choose the component values in
Figure 5.7 :
a. Choose C1. 1nF is a typical value.
b. Determine R1: R1 =1 /(35300 *C1)
c. Determine R2: R2= 5.9* R1 for unity gain. Scale R2 propor-
tionally to change gain.
d. Ensure that C2 is zero.
e. Use the nearest preferred component values.
4. Ensure that de-emphasis is applied on both transmit and receive.
If this cannot be done via software then the de-emphasis control line
will need to be overridden by a hardware modification.
Encryption Module
Software
Configuration
To make configuration changes via over-the-air rekeying (OTAR), the
module needs to be installed in the radio and be operational.
Key Management For key management refer to the relevant sections of the encryption module
manufacturer’s documentation.
Figure 5.7 Encryption module - typical pre-emphasis circuit
C1
R1
R2
C2
half rail
to next encryption module
audio processing block
AUD_TAP_OUT
+
–