Daniels Electronics MT-3 Series, Инструкция по эксплуатации

Страница: 23 / 56

Theory of Operation
19
MT-3 FM Transmitter Mainboard Instruction Manual
IM20-MT3TXMN
X Y
X
Y
X
Y
10 POLE LOWPASS FI LTER
LIMITER TEMPERATURE
COMPENSATION
2
1 3
JU22
R16
100K
C17
10nF C49
10nF
+8.0V SWD
JU6
C50
4.7uF
JU7
SEL
R23
N/I
R24
SEL
R25
N/I
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
Limiter and Splatter Filter
B0
314
The microphone and balanced audio signals are summed and limited by U3A. Op-Amp U3B provides
audio level temperature compensation (for synthesizer sensitivity variations). Due to the many
different characteristics of various synthesizers, many components are selected for best performance
over the temperature range.
The audio is then filtered by a 10th order linear phase low pass splatter filter U3a and U3B (see
Figure 4). This is to provide the linearity and cut-off attenuation response required for narrow band
operation and digital applications.
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. Installing JU23 lowers the audio level by one half facilitating a quick conversion
of a wide band transmitter for narrow band operation. The output of U3D has many capacitors with
values selected depending on the installed synthesizer module type.
FIGURE 4