Codan Radio Communications VT-3-150-SN User Manual
Audio Processor Board Instruction Manual
3-1
3
THEORY OF OPERATION
Voice band audio normally enters the Balanced Input at P1-1 and P1-2 while microphone audio
enters at P1-3. Potentiometer R31 sets the Balanced compression level of U1B while R2 sets the
microphone compression level of U1A. Each amplifier has a dynamic range of 25 dB. Jumper
JU17 is only installed when using very low input levels (-20 to –25 dBm) and allows better tuning
range for R31. The output of the compression amplifiers are normally set for Pre-emphasis
(6dB/Octave) but can be set for flat audio if required by jumpers JU1 and JU2.
enters at P1-3. Potentiometer R31 sets the Balanced compression level of U1B while R2 sets the
microphone compression level of U1A. Each amplifier has a dynamic range of 25 dB. Jumper
JU17 is only installed when using very low input levels (-20 to –25 dBm) and allows better tuning
range for R31. The output of the compression amplifiers are normally set for Pre-emphasis
(6dB/Octave) but can be set for flat audio if required by jumpers JU1 and JU2.
BALANC ED
INP U T L EVE L
INP U T L EVE L
CONTROL
FLAT AUDIO
PRE-EMPHASIS
MICROP HO NE INP U T
L EVE L CONTROL
L EVE L CONTROL
BALANCED INPUT
X
Y
+9.5V CONTINUOUS
NOT INSTALLED FOR DIGITAL MOD.
A UXILIARY INPU T
LEV E L CON TROL
LEV E L CON TROL
X
Y
MICR O P HONE AG C PREAMP
B ALA NCED A GC P REAMP
X
Y
B AL A NCE D
C O MP RES S IO N
C O NTR O L
FLAT AUDIO
PRE-EMPHASIS
MICRO P HO N
COMP R ESSI
CON TROL
CON TROL
X
Y
X
Y
X
Y
FLAT AUDIO
PRE-EMPHASIS
X
Y
TWO PORT POLARITY
SUB TONE 1 INP U T
CONTROL LEV E L
CONTROL LEV E L
3
P1
2
P1
1
P1
4
P1
3
P3
3
P2
1
P2
4
P2
+9.5V CONTINUOUS
C10
10nF
10nF
4K53
R46
C5
10nF
10nF
1
2
3
R2
5K0
5K0
FB1
+8.0V SWD
+8.0V SWD
1
2
3
JU5
47uF
C13
3
2
1
100K0
R48
680nF
C7
4.7uF
C8
TP3
SEL
R57
N/I (22nF)
C32
Rect In
Var G
Rect Cap
Output
Inv In
R3
THD
Trim
Trim
15
14
16
10
12
11
9
U1
SA571D
a
680nF
C42
TP12
4.7uF
C26
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
2
P2
JU16
9
10
8
U2
MC33174
MC33174
c
R74
N/I
N/I
R73
N/I
N/I
13
12
14
U2
MC33174
MC33174
d
4.0V
TP6
R43
11K8
11K8
C39
2.2uF
2.2uF
3
2
1
5K0
R42
C35
1.0uF
1.0uF
C1
1.0uF
1.0uF
C9
1.0uF
1.0uF
C30
1.0uF
1.0uF
R82
10K0
10K0
C37
3.3nF
3.3nF
R49
16k2
16k2
C14
10nF
10nF
4.0V
R76
16k2
16k2
C16
1.0uF
1.0uF
JU33
C51
1.0uF
1.0uF
1
2
3
JU12
R39
15K4
15K4
R41
137K
137K
R59
20K0
20K0
R62
15K4
15K4
R5
1M00
1M00
C25
1.0uF
1.0uF
R60
18K2
18K2
R61
18K2
18K2
R8
2K21
2K21
R9
49K9
49K9
R4
18K2
18K2
R6
18K2
18K2
330nF
C36
C15
3.3nF
3.3nF
R7
2K21
2K21
R10
49K9
49K9
330nF
C19
C2
1.0uF
1.0uF
R51
10K0
10K0
2
1
3
JU1
2
1
3
JU2
JU11
TP11
TP4
JU10
R52
100K
100K
R65
100K
100K
C38
3.3nF
R11
2K21
2K21
R40
49K9
49K9
2
1
3
JU14
1
2
3
R31
5K0
5K0
R30
604R
604R
TP2
215R
R1
R64
100K
100K
R56
0R0
0R0
C4
1.0uF
1.0uF
2
3
1
JU36
JU17
1
2
3
JU9
1
2
3
5K0
R63
3
2
1
5K0
R38
MICROPHONE INPUT
SUBTONE INPUT 1
TONE/DIGITAL I/P
Figure 3
Microphone and Balanced Input Circuitry