电路说明 - Kenwood TK-3000 Service Manual

TK-3000
2-2. First Mixer
The signal from the front end is mixed with the fi rst local
oscillator signal generated in the PLL circuit by Q203 to pro-
duce a fi rst IF frequency of 38.85 MHz.
The resulting signal passes through the XF200 MCF to
cut the adjacent spurious and provide the optimum charac-
teristics, such as adjacent frequency selectivity.
2-3. IF Amplifi er Circuit
The fi rst IF signal is passed through a four-pole mono-
lithic crystal fi lter (XF200) to remove the adjacent channel
signal.
The fi ltered fi rst IF signal is amplifi ed by the fi rst IF ampli-
fi er (Q202) and then applied to the lF system IC (IC200).
The IF system IC provides a second mixer, second local
oscillator, limiting amplifier, quadrature detector and RSSI
(Received Signal Strength Indicator).The second mixer
mixes the fi rst IF signal with the 38.4MHz of the second lo-
cal oscillator output (TCXO X1) and produces the second IF
signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(CF200) to remove the adjacent channel signal. The fi ltered
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
discriminator (CD200).The demodulated signal is routed to
the audio circuit.
2-4. Audio Amplifi er Circuit
The demodulated signal from IC200 is amplified by
IC305, IC303 and goes to AF amplifi er through IC302.
The signal then goes through an volume control (VR500),
and is routed to an audio power amplifi er (IC302) where it is
amplifi ed and output to the speaker.
To output sounds from the speaker, IC400 sends a high
signal to the SPMUT line and turns IC400 on through Q300,
Q301, Q302 and Q306.
3. Transmitter System
3-1. Microphone Amplifi er Circuit
The signal from microphone amplifi ed by IC301 and goes
through mute switch (IC300).
IC304 is composed of high-pass fi lter, low-pass fi lter and
pre-emphasis/IDC circuit.
The output signal from the DAC IC (IC300) goes to the
VCO modulation input.
12
CIRCUIT DESCRIPTION / 电路说明
MIC
IC301
BUFF
MIC
AMP
IC304
Fig. 3 Microphone amplifi er circuit / 图 3 麦克风放大器电路
2-2. 第一混频器
前端的信号与 PLL 电路产生的第一本振信号在 Q203 混频，
生成 38.85MHz 频率的第一中频信号。
生成的信号通过 XF200 MCF。
2-3. 中频放大电路
第一中频信号通过晶体滤波器 (X F200) 消除相邻信道的信
号。经滤波的第一中频信号被第一中频放大器 (Q202) 放大并
进入中频系统芯片 (IC200)。
中频系统芯片提供第二混频器、第二本振信号、限幅放大
器、正交检测器和 RSSI( 接收信号强度指示器 )。第二混频器
将第一中频信号与 38.4MH z 的第二本振信号输出 (T CX O X1)
进行混频，并生成 450kHz 的第二中频信号。
第二中频信号通过陶瓷滤波器 (C F200) 继续消除相邻信道
的信号。经滤波的第二中频信号被限幅放大器放大并被带有
陶瓷鉴频器 ( C D200) 的正交检测器解调。经解调的信号进入
音频电路。
2-4. 音频放大器电路
来 自 于 IC200 的 解 调 信 号 被 I C305 放 大， 并 通 过
IC302,IC303 送到 AF 放大器。
信号通过 AF 音量控制 (VR500)， 在音频功率放大器 (IC302)
进行放大后输出到扬声器。
由扬声器输出声音时，IC400 发送高电平信号给 SP MU T，
通过 Q300、Q301、Q302 和 Q306 打开 IC400。
3. 发射机系统
3-1. 麦克风放大器电路
麦克风的信号被 IC301 放大，然后通过静音开关 (IC300)。
IC304 由高通滤波器、 低通滤波器和预加重 /IDC 电路组成。
DAC IC(IC300) 的输出信号送入 VCO 调制输入。
IC300
VCO
DAC
X1
TCXO
LSDO
LSDO