Marine VHF Audio and Signalling Processor
CMX885
b7-0 set the order of the Audio Filter processing. This feature can be used to optimise the signal to noise
performance of particular radio hardware designs. Each filter/process block can be specified in any order.
Each two-bit field specifies the order in which the process will be executed in Tx mode, therefore it is
imperative that each set of bit fields be different. The reverse sequence is used in Rx mode. The Voice
Filter and Soft Limiter will always be implemented as the final block in the Tx sequence.
The default settings are:
o
o
o
Pre-emp:
Scramble:
300Hz HPF:
00
10
11
which will implement the line-up as shown in Figure 16 and Figure 17:
Pre-emph
(optional)
Scrambler
(optional)
Voice LPF &
Soft Limiter
Audio in
300Hz Filter
+
CTCSS
Figure 16 Default Tx Audio Filter Line-up
De-scrambler
300Hz Filter
De-emph
(optional)
Discrim
Voice LPF
Audio
(optional)
Figure 17 Default Rx Audio Filter Line-up
An alternative, preferred, line-up is shown in Figure 18 and Figure 19, for the following settings:
(P4.9 = $004B):
o
o
o
Pre-emp:
Scramble:
300Hz HPF:
01
10
11
Pre-emph
(optional)
Scrambler
(optional)
Voice LPF &
Soft Limiter
Audio in
300Hz Filter
Figure 18 Preferred Tx Audio Filter Line-up
De-scrambler
(optional)
De-emph
(optional)
Discrim
Voice LPF
300Hz Filter
Audio
Figure 19 Preferred Rx Audio Filter Line-up
© 2010 CML Microsystems Plc
57
D/885/3
CMLMICRO [ CML MICROCIRCUITS ]
