Codan Radio Communications VT-3-150-SN User Manual
Audio Processor Board Instruction Manual
3-3
If no compression circuitry is required, the balanced input signals can be routed around the
compression circuitry by jumper JU11. Op-amp U2C then would provide the
buffering/amplification. It’s output would normally have pre-emphasis installed but could be
changed to flat if required through jumper JU9. The audio signal is then normally routed to U3A,
the summing amplifier/limiter and processed as mentioned in the previous paragraphs. Note
however, if compression is bypassed, the THD may be higher due to the reduced dynamic input
range causing more clipping.
compression circuitry by jumper JU11. Op-amp U2C then would provide the
buffering/amplification. It’s output would normally have pre-emphasis installed but could be
changed to flat if required through jumper JU9. The audio signal is then normally routed to U3A,
the summing amplifier/limiter and processed as mentioned in the previous paragraphs. Note
however, if compression is bypassed, the THD may be higher due to the reduced dynamic input
range causing more clipping.
If compression is bypassed and disabled by the removal of FM Audio Processor jumper JU36
which removes power from the compression IC, there will be 9mA of key down current saved. The
disadvantage is that the microphone circuit will be disabled due to the removal of the common
power to the compression IC.
which removes power from the compression IC, there will be 9mA of key down current saved. The
disadvantage is that the microphone circuit will be disabled due to the removal of the common
power to the compression IC.
BALANCED
INP U T L E VEL
INP U T L E VEL
CONTRO L
BA LANCED INPUT
X
Y
AUXILIARY INPUT
LEV E L CONTRO L
LEV E L CONTRO L
BALANCE D A GC PRE AMP
BA LANC E D
COMPRE S S I O N
CONTROL
COMPRE S S I O N
CONTROL
FLAT AUDI O
PRE-EM PHASIS
X
Y
X
Y
FLAT AUDIO
PRE-EM PHASI S
X
Y
TWO PORT POLARI TY
2
P1
1
P1
C10
10nF
10nF
1
2
3
JU5
3
2
1
100K0
R48
680nF
C7
4.7uF
C8
TP3
SEL
R57
N/I (22nF)
C32
Vcc
Rect In
Var G
Rect Cap
Output
Inv In
R3
THD
Trim
Trim
GND
2
3
1
7
5
6
8
13
4
SA571D
U1b
9
10
8
U2
MC33174
MC33174
c
R73
N/I
N/I
13
12
14
U2
MC33174
MC33174
d
4.0V
TP6
C9
1.0uF
1.0uF
C30
1.0uF
1.0uF
R82
10K0
10K0
R49
16k2
16k2
C14
10nF
10nF
4.0V
R76
16k2
16k2
C16
1.0uF
1.0uF
JU33
R62
15K4
15K4
R5
1M00
1M00
R4
18K2
18K2
R6
18K2
18K2
C15
3.3nF
3.3nF
R7
2K21
2K21
R10
49K9
49K9
330nF
C19
C2
1.0uF
1.0uF
R51
10K0
10K0
2
1
3
JU2
JU11
TP4
JU10
R52
100K
100K
R65
100K
100K
C38
3.3nF
3.3nF
R11
2K21
2K21
R40
49K9
49K9
2
1
3
JU14
1
2
3
R31
5K0
5K0
R30
604R
604R
R64
100K
100K
JU17
1
2
3
JU9
3
2
1
5K0
R38
+9.5V CONTIN UOUS
X
Y
M
+8.0V SWD
R56
0R0
0R0
2
3
1
JU36
Figure 5
Bypassing Compression
A second way to route around audio compression if data is not being used is to use the direct
modulation port P4-3 and go through JU28 to R48 and Op-amp U2C.
modulation port P4-3 and go through JU28 to R48 and Op-amp U2C.
Subaudible tones enter at P2-2 where their level is controlled by R42. A single jumper JU16
enables the audio path to U3A, the summing amplifier/limiter.
enables the audio path to U3A, the summing amplifier/limiter.