Kenwood TK-2118 Service Manual Download

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TK-2118

TK-260

:K, K2

5) Squelch

Part of the AF signal from the IC enters the FM IC again, and

the noise component is amplified and rectified by a filter outside
amplifier Q1, and produce DC level by D1 corresponding to the
noise level.
The DC signal from the FM IC goes to the analog port of the
microprocessor (IC300). IC300 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, IC300 sends a high signal
to the MUTE and AFCO Iines and turns IC309 on through
Q313, Q320, Q321, Q323 and Q324.(See Fig. 3)

Fig. 3 AF Amplifier and squelch /

图3 音频放大器和噪音抑制电路

3. PLL frequency synthesizer

The PLL circuit generates the first local oscillator signal for
reception and the RF signal for transmission.

1) PLL

The frequency step of the PLL circuit is 5 or 6.25kHz.

A 12.8MHz reference oscillator signal is divided at IC1 by a fixed
counter to produce the 5 or 6.25kHz reference frequency. The
voltage controlled oscillator (VCO) output signal is buffer
amplified by Q7, then divided in IC1 by a dual-module
programmable counter . The divided signal is compared in phase
with the 5 or 6.25kHz reference signal in the phase comparator in
IC1. The output signal from the phase comparator is filtrered
through a low-pass filter and passed to the VCO to control the
oscillator frequency. (See Fig.4)

FM IF IC

IC2

IF AMP

DET

HPF
AMP

LPF

IC307

QT/DQT

Q316
W/N SW

IC300

MPU

USY

MUTE

AFCO

AF AMP

IC306

LPF

HPF

Q313

IC309

AF PA AMP

Q324

Q321, 323, 320

CIRCUIT DESCRIPTION /

电路说明

6) Receive signaling

QT/DQT

300 Hz and higher audio frequencies of the output signal

from IF IC are cut by a low-pass filter (IC307). The resulting
signal enters the microprocessor (IC300). IC300 determines
whether the QT or DQT matches the preset value, and
controls the MUTE and AFCO and the speaker output sounds
according to the squelch results.

5) 噪音抑制电路

来自FM IC的部分音频信号再次输入到FM IC，在放大器Q1

出来由滤波器对噪音部分进行放大和整流，并由相应于噪音电
平的D1产生直流电平。
直流信号进入微处理器的模拟端口 (IC300)。IC300通过检测输
入电压是否高于或低于预设值来决定是否通过扬声器输出声
音。
要通过扬声器输出声音，I C 3 0 0 向静音和自动频率控制振荡器
连线发送一个高电平信号并开启IC309通过Q313, Q320, Q321,
Q323和Q324。(参见图3)

6) 接受信令

QT/DQT

来自于中频芯片输出信号的3 0 0 H z 和更高的音频被低频滤波

器 (Q307) 截断。所得到的信号输入微处理器 (IC300)。IC300确
定QT或DQT是否匹配预设置，并且根据噪声抑制电路的结果控
制MUTE和AFCO以及扬声器输出声音。

3. 锁相环频率合成器

锁相环电路生成用于接收的第一本振信号和用于发送的射频
载波信号。

1) 锁相环电路

锁相环电路的步进频率为5或6.25kHz。12.8MHz的参考振荡

器信号通过一个混合计数器在IC1中被分频并生成5或6.25kHz的
参考频率。压控振荡器 (VCO) 输出的信号通过Q7缓冲放大器,
然后在I C 1 中被可编程脉冲吞除计数器分频。被分频的信号在
带有5或6.25kHz参考信号的相位比较器的IC1中被比较。从相位
比较器输出的信号进入一个低通滤波器后，并通过压控振荡器
来控制振荡频率。(参见图4)