21
TK-885
CIRCUIT DESCRIPTION /
Fig. 2 Receiver system /
Wide/Narrow Changeover Circuit
The W/N port (pin 11) of the shift register (IC7) is used to
switch between ceramic filters. When the W/N port is high,
Q24 turns on and the ceramic filter SW diode (D22, D23) CF1
turns on to receive a Wide signal. At the same time, Q16
turns on and one of the filters is selected so that the wide
and narrow audio output levels are equal.
When the W/N port is low, Q23 turns on and the ceramic
filter SW diode (D22, D23) CF2 turns on to receive a Narrow
signal.
AF Signal System
The detection signal (DEO) from the TX-RX unit goes to
the audio processor (IC504) of the control unit. The signal
passes through a filter in the audio processor to adjust the
gain, and is output to IC502. IC502 sums the AF signal and
the DTMF signal and returns the resulting signal to the TX-RX
unit. The signal (AFO) sent to the TX-RX unit is input to the D/
A converter (IC5). The AFO output level is adjusted by the D/
A converter. The signal output from the D/A converter is added
with the BEEP signal (BPO) and the resulting signal is input
to the audio power amplifier (IC10). The AF signal from IC10
switches between the internal speaker and speaker jack (J1)
output.
Fig. 4 AF signal system /
LPF
ANT
BPF
BEF
Q201
AMP
Q15
AMP
IC2
AMP
IC200
MIX
XF1
BPF
D211
D209,210
ANT
SW
+
Q203
AMP
BPF
CF1/
CF2
IC11
MIX,IF,DET
X2
2nd
local OSC
1st local
OSC (HT)
DEO
CF1
(Wide)
CF2
(Narrow)
IFI
MXO
IC11
IF system
AFO
DET
OUT
C107
C100
C108
R114
R123
R133
R126
R125
R130
R131
+
+
Q16
DM
Q32 R121
W/N
IC7 11pin
Wide : H
Narrow : L
C118
D22
D23
Q23
5C
Q24
Wide : L
Narrow : H
Fig. 3 Wide/Narrow changeover circuit
AUDIO
PROCE.
SUM
AMP
D/A
CONV.
IC504
IC502
IC5
AF PA
IC10
SP
DTMF
BPO
AFO
DEO
CONTORL UNIT
Содержание TK-885
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