Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.
FM Detector, Stereo Decoder, Amplifier
Figure 9-26 IF demodulator circuit
The IF signal is demodulated in the 7710 (LA1836M), the IF
Radio IC. This IC has a coil FM detector that is aligned (for
alignment instructions see chapter "Electrical Alignments").
The stereo decoder is integrated and needs no adjustment.
The demodulated signal is filtered with 1730/1740. These filters
are pre-aligned and are reducing the pilot- and sub carrier
frequency. This is necessary to prevent wrong operation of the
expander circuit.
Figure 9-27 Sliding stereo circuit
There is a sliding stereo circuit for reducing the stereo noise at
low signal field strengths. Transistor 7705 is short-circuiting the
Audio Left and Audio Right signals at low field strengths. The
crossover level must be aligned (for alignment instructions see
chapter "Electrical Alignments"). There is also a "mute level"
alignment, which is set at 10 V RF input level. At this signal
level, the wireless audio link is muted.
I
GND
NC
O
TRIG
FF
FF
FF
PILOT
DET
PHASE
DET
VCO
ANTI BIRDIE
DECODER
SW
VCC
FM
AM
GND
FM
AM
DRIVE
TUNING
COMP
REG
BUFF
IF
FM
AM
DET
AM
ALC
BUFF
MUTE
SWITCH
STEREO
DRIVE
STEREO
FM
FM IF
DET
LEVEL
S-CURVE
DET
AM
IF
AM
S-METER
AGC
AM
RF-AMP
MIX
AM
OSC
I
GND
NC
O
F715
F714
2n7
2765
2n7
2764
2703
18n
3727
330R
2702
18n
2709
1n5
3712
10K
3713
2K2
2713
47n
470p
2710
FXM2
1
2
3
7
8
4
5
6
1740
3728
330R
1u
2725
3722
47K
2712
47n
3715
6K8
10u
16V
2720
3731
2740
220p
1K5
3729
5K6
3724
3K3
3730
1K5
2705
16V
10u
16V
2704
10u
10u
2715
47n
2714
220p
2711
17
ST-LED
8
TU-LED
7
VCC
10
MPXLO
20
MPXRO
21
MPXVCO
23
OSC
29
PCLPFIL
15
REG
4
RIGHT-IN
19
RIGHT-O
3
FM-IFIN
1
FMDET
9
FMSD
30
GND
6
LEFT-IN
18
LEFT-O
16
MPXIN
2
2
2
AMAGC
26
AMLC
25
AMRFIN
2
7
AMSD
12
AM_|FM
14
AM|FM-IF
11
24
AM|FMDO
FM-IFIB
7710
LA1836M
AFC
28
AM
13
AM-IFIN
5
AM-MO
4u7
2718
2723
1u
F715
F708
3
7
8
4
5
6
1730
FXM2
1
2
F708
3745
3746
6K8
3717
2730
220p
4k7
3741
F714
2707
10u 16V
47n
2708
2721
16V 10u
3742
100R
565K7
1720
2724
470n
+8V
+8V
+8V
RECEIVER/BACKEND
MUTE
LEVEL
I.F. RADIO
CL36532008_083.eps
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7706
BC857B
F747
7705
BF545A
100K
3704
3714
22K
F747
BAS316
6711
S
R
P20
P21
CL36532008_084.eps
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