TK-2217
23
CIRCUIT DESCRIPTION /
电路说明
3) 中频放大电路
第一中频信号通过晶体滤波器 (XF201) 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（Q203）放大并进
入中频系统芯片（IC201）。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 38.4MHz 的第二
本振信号输出（TCXO 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（CF201）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（CD201）的正交检测器解调。经解调的信号进
入音频电路。
4) 宽 / 窄开关电路
可以通过开启宽窄开关对各信道进行宽窄设定。
WIDE (低电平) 和 NARROW (高电平) 数据被 IC405、45 管脚
输出。
当接收到 WIDE (低电平) 数据时，Q202 接通。
当接收到 NARROW (高电平) 数据时，Q202 断开。
Q202 伴随着宽 / 窄数据而接通 / 断开，IC201 检测器输出电平
经常变化用来维持宽或窄信号过程中的恒定输出电平。
5) 音频放大器电路
来自于 IC201 的解调信号通过 IC301 送到音频放大器。
信号通过 AF 音量控制，在音频功率放大器（IC302）进行放
大后输出到扬声器。
3) IF Amplifier Circuit
The first IF signal is passed through a four-pole monolithic
crystal filter (XF201) to remove the adjacent channel signal.
The filtered first IF signal is amplified by the first IF amplifier
(Q203) and then applied to the lF system IC (IC201). 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 first
IF signal with the 38.4MHz of the second local oscillator
output (TCXO X1) and produces the second IF signal of
450kHz.
The second IF signal is passed through the ceramic filter
(CF201) to remove the adjacent channel signal. The filtered
second IF signal is amplified by the limiting amplifier and
demodulated by the quadrature detector with the ceramic
discriminator (CD201). The demodulated signal is routed to
the audio circuit.
4) Wide/Narrow Switching Circuit
Narrow and Wide settings can be made for each channel
by switching the demodulation level.
The WIDE (low level) and NARROW (high level) data is
output from IC405, pin 45.
When a WIDE (low level) data is received, Q202 turn on.
When a NARROW (high level) data is received, Q202 turn
off.
Q202 turns on/off with the Wide/Narrow data and the IC201
detector output level is switched to maintain a constant
output level during wide or narrow signals.
5) Audio Amplifier Circuit
The demodulated signal from IC201 goes to AF amplifier
through IC301.
The signal then goes through an AF volume control , and is
routed to an audio power amplifier (IC302) where it is
amplified and output to the speaker.
Fig. 3 Wide/Narrow switching circuit /
图 3 宽 / 窄开关电路
Q202
L : Wide
H : Narrow
C214
RX-W/N
(IC405)
R211
R213
CD201
IFOUT
QUAD
IC201
FM IF SYSTEM
5R
AFOUT
Q203
