Baseband Processor For Mixed Mode Land Mobile Radio
CMX880
The shaping filter transfer characteristic has a flat group delay over the pass band for |f|<2880Hz, with a
magnitude response of approximately:
|P(f)| = (pf/4800) /sin(pf/4800)
for |f|<2880Hz.
For CQPSK transmitted signals the symbols are decoded into separate I and Q levels in accordance with Table
14. The I and Q signals are Raised Cosine, H(f) filtered, D-to-A converted and output to their respective
modulator output ports, I to MOD_1 and Q to MOD_2, as shown in Figure 16. The symbol decoder includes a
state memory that is used in conjunction with the symbol code to select the I and Q levels. The maximum
output range, corresponding to the levels of +1 and -1 of Table 14, need to be defined prior to the CMX880
transmitting a CQPSK signal. The default range is defined by writing the ‘+1’ and ‘-1’ limits by “C-BUS”
command.
Table 14 I and Q Level Encoding
Current Phase
Symbol Code
Bits
00
Next Phase
I Level
Q Level
State
0
0
0
0
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
5
5
5
5
6
6
6
6
7
7
7
7
State
1
3
5
7
2
4
6
0
3
5
7
1
4
6
0
2
5
7
1
3
6
0
2
4
7
1
3
5
0
2
4
6
+0.7071
-0.7071
-0.7071
+0.7071
0.0
-1.0
0.0
+1.0
-0.7071
-0.7071
+0.7071
+0.7071
-1.0
0.0
+1.0
0.0
-0.7071
+0.7071
+0.7071
-0.7071
0.0
+1.0
0.0
-1.0
+0.7071
+0.7071
-0.7071
-0.7071
+1.0
0.0
-1.0
0.0
+0.7071
+0.7071
-0.7071
-0.7071
+1.0
0.0
-1.0
0.0
+0.7071
-0.7071
-0.7071
+0.7071
0.0
-1.0
0.0
+1.0
-0.7071
-0.7071
+0.7071
+0.7071
-1.0
0.0
+1.0
0.0
-0.7071
+0.7071
+0.7071
-0.7071
0.0
+1.0
0.0
-1.0
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10
ã 2001 Consumer Microcircuits Limited
34
D/880/1
CMLMICRO [ CML MICROCIRCUITS ]
