Kenwood TK-3118 Service Manual

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13TK-3118TK-260 :K, K25) SquelchPart of the AF signal from the IC enters the FM IC again, andthe noise component is amplified and rectified by a filter outsideamplifier Q1 and produce DC level by D1 corresponding to thenoise level.The DC signal from the FM IC goes to the analog port of themicroprocessor (IC300). IC300 determines whether to outputsounds from the speaker by checking whether the inputvoltage is higher or lower than the preset value.To output sounds from the speaker, IC300 sends a high signalto the MUTE and AFCO Iines and turns IC309 on throughQ313, 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 synthesizerThe PLL circuit generates the first local oscillator signal forreception and the RF signal for transmission.1) PLLThe frequency step of the PLL circuit is 5 or 6.25kHz.A 12.8MHz reference oscillator signal is divided at IC1 by a fixedcounter to produce the 5 or 6.25kHz reference frequency. Thevoltage controlled oscillator (VCO) output signal is bufferamplified by Q7, then divided in IC1 by a dual-moduleprogrammable counter . The divided signal is compared in phasewith the 5 or 6.25kHz reference signal in the phase comparator inIC1. The output signal from the phase comparator is filtreredthrough a low-pass filter and passed to the VCO to control theoscillator frequency. (See Fig.4)FM IF IC IC2IF AMP DETQ1D1HPFAMPLPFIC307QT/DQTQ316W/N SWIC300MPUBUSYMUTEAFCOTI655655AF AMPIC306LPF HPF Q313SWIC309AF PA AMP Q324SWSWSPQ321, 323, 3206) Receive signalingQT/DQT300 Hz and higher audio frequencies of the output signalfrom IF IC are cut by a low-pass filter (IC307). The resultingsignal enters the microprocessor (IC300). IC300 determineswhether the QT or DQT matches the preset value, andcontrols the MUTE and AFCO and the speaker output soundsaccording to the squelch results.CIRCUIT DESCRIPTION / 电路说明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)