Kenwood TK-3230 Service Manual page 11

Transmitter System
■ Microphone Amplifi er Circuit
The audio signal from the microphone passes through
the MIC amplifi er (IC302). Then, the signal goes through the
base band IC (IC300) that has the 6dB/oct pre-emphasis cir-
cuit, band-pass fi lter (300 to 3kHz), amplifi er, and limiter. The
distortion components outside the audio band are removed
by the splatter fi lter.
■ Modulation Circuit
The MIC amplifi er (IC302) output passes through VR300
for modulation adjustment and goes to the modulation input
of the VCO circuit for variable reactance phase modulation.
■ Transmission Output Circuit
The VCO output is amplifi ed by a high-frequency amplifi er
(Q101, Q103 and Q104), passes through a high-frequency
antenna switch, passes through a low-pass fi lter and goes
to the antenna.
The transmission output is about 1.5W with 3.8V DC sup-
ply at battery terminal.
■ Low-Pass Filter Circuit
A three-stage Chebyshev type low-pass fi lter is located
between the antenna and transmit/receive switching circuit.
It removes harmonic components contained in the transmis-
sion output.
Fig. 5 Transmitter section confi guration / 图 5 发射部分构成
Fig. 6 Microphone amplifi er circuit / 图 6 麦克风放大器电路
CIRCUIT DESCRIPTION /
MIC AMP
MIC IC302 VR300
DRIVE FINAL
AMP AMP
Q103
Q104
Q303 D303 D301
MIC
SW DET
MUTE
MIC IC302
MIC amp
电路说明
发射系统
■麦克风放大器电路
麦克风的音频信号通过麦克风放大器 ( I C302)。随后信号
通过具有 6d B / o c t 预加重电路、带通滤波器 (300 ～ 3k H z )、
放大器和限幅器的基带 I C ( I C300)。音频频带外的失真成分
由边带滤波器进行消除。
■调制电路
麦克风放大器 (IC302) 输出信号通过 VR300 进行调制调整，
然后进入 VCO 电路的调制输入进行可变电抗相位调制。
■发射输出电路
VCO 输出信号由高频放大器 (Q101、 Q103 和 Q104) 进行放大，
然后依次通过高频天线开关和低通滤波器并进入天线。
电池端子采用 3.8V 直流供电时，发射输出功率约为 1.5W。
■低通滤波电路
三阶切比雪夫低通滤波器位于天线和发射 / 接收切换电路
之间，能够消除发射输出信号中所带的谐波成分。
PRE-DRIVE
VCO RF AMP
AMP
Q2,Q5 Q6 Q101
ANT
ANT SW
D101,D200,
D201 LPF
IC300
Amp IDC LPF
TK-3230
11