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AFOUT
AF OUT
L:Wide
Q507
H:Narrow
From MPU
P60 (U206)
Fig.3
Squelch and Mute Circuit
3-1-5.
A noise component is obtained by passing FM
detection output (FM IC pin 9) through an operational
amplifier in the FM IC and band-pass filter consisting of
R549, R560, R591, C654, C655. The noise component is
U206
MPU
1st IF input
(38.85MHz)
U502
FM IC
2nd local OSC
(38.40MHz)
3-2.
AF signal system
3-2-1. Audio amplifier circuit
The demodulated signal from U501 goes to Audio
processor through U200 (AF filtered, low-pass filtered,
high-pass
filtered,
De-Scrambler,
de-emphasized).
The signal then goes through an AF amplifier U203B
(2/2), an AF volume control (W200), and is routed to an
CIRCUIT DESCRIPTION
Q509
U502
FM SYSTEM
IFOUT
QUAD
C580
R528
R551
T500
5R
SP MUTE
P61
RSSI
P04
SQ
P00
T500
16
15
14
13
12
11
MIX
RSSI
Noise
comp
Rectifier
Buffer
IF AMP
Local
OSC
1
2
3
4
5
6
CF500
450kHz
Fig.4
Expander,
and
rectified in the FM IC to produce a DC voltage, which is
output from the N-REC terminal (pin 14) of the FM IC as
squelch voltage.
The squelch voltage enters the SQ terminal (pin 50) of
the MPU (U206) and is compared with the reference
voltage preset in the MPU to control audio signal
ON/OFF.
To output sounds from the speaker, U206 sends a high
signal to the P61 line and turns U205 on through Q202
and Q206. (See Fig.4)
3-1-6. S Meter Circuit
The S meter voltage is output from the RSSI terminal
(pin 12) of the FM IC (U503) and input to the SM terminal
(pin 54) of the MPU. Then the voltage is converted from
analog to digital in the MPU to control the S meter display
on the LCD. (See Fig.4)
5R
U200
AF OUT
AQUA
10
9
U203B
AMP
LPF
Quadrature
detector
Noise
AMP
VOL
Inverter
AMP
7
8
R560
C654
C655
R591
R549
audio power amplifier (U205), where it is amplified and
output to the internal speaker. (See Fig.5)
3-2-2. Receive Signalling
3-2-2-1 Low-speed
data（CTCSS/DCS）
300 Hz and higher audio frequencies of the output signal
from IF IC are cut by IC (U502) within a low-pass filter.
U200 determines whether the CTCSS or DCS matches the
4
DJ-100
Q202,Q206
LS200
SW
SW
SP
U205
AF PA
J200
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