TK-3178
(
L
)
14
2-6. Squelch Circuit
Part of the AF signal from the IC enters the FM IC (IC701)
again, and the noise component is amplifi ed and rectifi ed by
a fi lter and an amplifi er to produce a DC voltage correspond-
ing to the noise level.
The DC signal from the FM IC goes to the analog port of
the microprocessor (IC7). IC7 determines whether to output
sounds from the speaker by checking whether the input
voltage is higher or lower than the preset value.
To output sounds from the speaker, IC7 sends a high sig-
nal to the AM2 line and IC5 sends a high signal to the AM1
line, and turns IC18 on through Q23, Q24, Q27, Q28 and
Q35. (See Figure 4)
2-6. 静噪电路
FM IC(IC701) 输出的 AF 信号的一部分再进入 IC，噪声成
份通过滤波器和放大器进行放大和修正，生成与噪声电平相
应的 DC 电压。
DC 信号通过 FM IC 被送到微处理器的模拟端口 (IC7)。IC7
通过检测输入的电压是高于还是低于预设值来决定是否从扬
声器输出声音。
由扬声器输出声音时，IC7 发送高电平信号给 AM2 线和 IC5
发送高电平信号给 A M1 线，通过 Q23、Q24、Q27、Q28 和 Q35
打开 IC18。( 见图 4)。
SP
Q22
SW
IC16
VOL
IC18
AF PA
Q23,24,27
SW
SW
Q28,35
IC5
Shift register
2-tone
IC15
BPF & Compalater
CLK, DATA,STD, LOADN
IC10
IF AMP
IC11
LPF
IC13
AQUA-L
IC701
FM IF
SIGNAL
DTMF
ANSQL
IC7
MCU
LSDI
QT/DQT
HSDI
AM2
AM1
Fig. 4 Audio amplifi er circuit and squelch circuit /
图 4 音频放大器电路和静噪电路
3. Transmitter System
3-1. Microphone Amplifi er Circuit
The signal from microphone amplifi ed by IC13 (1/2) and
limited by AGC circuit composed of D30, D31, Q25 and
Q26, and goes through mute switch (Q30). IC13 is com-
posed of high-pass fi lter, low-pass fi lter and pre-emphasis/
IDC circuit.
The signal enters the summing amplifier consisting of
IC12 (2/2), and passes through the D/A converter (IC16) for
the maximum deviation adjustment, and is mixed with the
low speed data from the MCU (IC7).
The output signal from the D/A converter goes to the
VCO modulation input. The other output signal from the D/
A converter passes through the D/A converter (IC16) again
for the BAL adjustment, and the buffer amplifi er (IC17), and
goes to the TCXO modulation input.
3. 发射机系统
3-1. 麦克风放大器电路
麦克风的信号被 I C13(1/2) 放大，并受由 D30、D31、Q25
和 Q26 组成的 A G C 电路的限幅，然后通过静音开关 ( Q30)。
IC13 由高通滤波器、低通滤波器和预加重 /IDC 电路组成。
信号送入由 I C12(2/2) 组成的加法放大器，通过最大频偏
调节的数模转换器 (IC16)，然后与 MCU(IC7) 的低速数据混合。
数模转换器的输出信号送入 V C O 调制输入。数模转换器的
其他输出信号再次通过 BAL 调节的数模转换器 (IC16) 和缓冲
放大器 (IC17)，然后送入 TCXO 调制输入。
MIC
Q30
IC13
(1/2)
AMP
IC12
(2/2)
SUM
AMP
IC17
X701
BUFF
AMP
TCXO
VCO
AGC
SW
AQUA-L
IC13
IC16
D30,31
Q25,26
D/A
O2
I2
IC16
D/A
O8
I8
LSD
OUT
MMUTE
Fig. 5 Microphone amplifi er circuit /
图 5 麦克风放大器电路
CIRCUIT DESCRIPTION /
电路说明
