Daniels VT-3/140-SWA2, Instruction Manual

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3-2 Audio Processor Board Instruction Manual
The microphone and balanced audio signals are summed and limited by U3A. Op-amp U3B
provides audio level temperature compensation (for synthesizer and crystal oscillator sensitivity
variations). Due to the many different characteristics of the models of synthesizer and crystal
oscillators, the components are marked “SELect” and are identified later in this document (section
6.)
X Y
X
Y
X
Y
10 P OLE LO W PAS S FI LTER
L IMIT ER T EMPE RATUR E
COMPE N S ATI O N
2
1 3
JU22
R16
100K
C17
10nF
C49
10nF
+8.0V SWD
JU6
C50
4.7uF
JU7
SEL
R23
SEL
R24
SEL
R25
SEL
R26
SEL
R28
SEL
R17
SEL
R18
SEL
R20
In+
In-
Gnd
V-
Vout
V+
Rx
Div/Clk
1
2
3
4
8
7
6
5
U4
LTC1569-6
R66
22K1 R67
30K9
R68
3K48
R69
2K00
+8.0V SWD
P11
P12
P9
P10
2
3
4
1
11
U3
MC33174 a
6
5
7
U3
MC33174 b
1 2
R19
SEL
1 2
SEL
R27
1
2
C21
1.0uF
1
2
C6
1.0uF
4.0V 4.0V
+8.0V SWD
TP5
R84
10K0 R85
10K0
TP10
1 2
150pF
C43
TP14
1
2
3
JU24
1
2
3
JU3
Figure 4 Limiter and Splatter Filter
The audio then is filtered by a 10
th
Order Linear Phase Lowpass splatter filter. This filter improves
on the previous Butterworth filter design for data linearity and increased cutoff attenuation
responses mandated in today’s narrow band environment.
The filter output level is set by R29, the deviation control. From this point, the signal goes to U5 a
bilateral audio switch. U5 is normally configured to be always on. The output of U5 goes to the
final buffer amplifier U3D. By installing JU23 which lowers the audio level one half, a wideband
transmitter can be quickly re-configured into a narrowband transmitter in the field. The output of
U3D has many selectable capacitors which are chosen depending on the synthesizer or crystal
oscillator module that is connected to this main modulation port.