Kenwood TK-3230 Service Manual page 10

TK-3230
The second IF signal passes through ceramic fi lter (CF200)
to remove unwanted signals.
The second IF signal passing through the ceramic fi lter
passes through the limiter amplifi er consisting six differen-
tial amplifi ers and is detected.
The amplified second IF signal is demodulated by the
quadrature detector with the ceramic discriminator (CD200).
The demodulated signal is routed to the audio circuit.
■ Squelch Circuit
A squelch circuit is provided to prevent no-signal noise or
weak signals from outputting to a speaker during transmis-
sion.
■ AF Circuit
The FM IC output passes through the base band IC
(IC300). The signal then goes through an AF volume con-
trol, and is routed to an audio power amplifi er (IC303) where
it is amplfi ed and output to speaker. This IC have BTL ampli-
fi er function. At internal speaker, BTL amplifi ed. At external
speaker, IC switch off the 1 channel amplifi er by connectors
information.
Narrow and wide setting can be made for each channel
by switching the demodulation level. The WIDE (low level)
and NARROW (high level) data is output from IC403, pin
69. When a Wide (low level) data is received, Q200 turn on.
When a NARROW (high level) data is received, Q200 turn
off.
Q200 turns off/on with the wide/narrow data and the
IC200 detector output level is switched to maintained a con-
stant output level during wide or narrow signals.
Fig. 4 IF amplifi er, Squelch and AF circuits / 图 4 中频放大器 , 静噪 , AF 电路
10
CIRCUIT DESCRIPTION /
SP AMP BUSY
52 76
IC403
BEEP
RSSI
MCU
12 75
Q201
38.85
MHz 16
1st IF
MIXIN
IF amp
38.4MHz
X1 Q202
12.8MHz
TCXO X3
PLL
IC303
Amp
INT. SP
Amp
J300
SW
EXT. SP
电路说明
第二中频信号通过陶瓷滤波器 (CF200) 消除不需要的信号。
通过陶瓷滤波器的第二中频信号随后通过由六个不同放大
器组成的限幅放大器并进行检测。
放 大 后 的 第 二 中 频 信 号 由 积 分 检 波 器 通 过 陶 瓷 鉴 频 器
(CD200) 进行解调。已解调的信号转发给音频电路。
■静噪电路
静噪电路用于防止无信号的噪声或微弱信号输出到扬声器。
■ AF 电路
FM IC 输出信号通过基带 IC (IC300)。随后信号通过 AF 音
量调整，并发送给音频功率放大器 (IC303)，在这里经过放大
并输出到扬声器。该 IC 具有 BTL 放大器功能。在内部扬声器，
B T L 被放大。在外部扬声器，I C 通过连接器信息关闭 1 信道
放大器。
通过切换解调电平，各个信道均可进行窄宽设置。宽信号
( 低电平 ) 及窄信号 ( 高电平 ) 数据从 IC403( 针脚 69) 输出。
接收到宽信号 ( 低电平 ) 数据时， Q200 打开。 接收到窄信号 ( 高
电平 ) 数据时，Q200 关闭。
在宽或窄信号期间，Q200 随宽 / 窄信号数据打开 / 关闭，
IC200 检波器输出电平切换为保持恒定输出电平。
IC200
MIX
DET
9
AFOUT
Amp
10
Q200
CD200
CF200
SW
450kHz
W/N
IC300
HPF LPF Amp
RXAF
Q301
VR301
AF VR
AF
23
RXIN