Kenwood TK-3148 Service Manual

Also see for TK-3148: Service manual

Contents

TK-3148133-5. Squelch circuitThe output from IC200 enters FM IF IC again, thenpassed through a band-pass filter. And passed through aband-pass filter IC201 (2/2). The modulation input. The noisecomponent output from IC201 (2/2) is amplified by Q208and rectified by D201 to produce a DC voltage correspond-ing to the noise level.The DC voltage is sent to the analog port of the MCU(IC309). And IC200 outputs a DC voltage (RSSI) correspond-ing to the input of the IF amplifier. The MCU reads the RSSIsignal via pin 93.IC309 determines whether to output sounds from thespeaker by comparing the input voltage of pin 91 and pin 93with the preset value.4. Transmitter System4-1. Microphone amplifierThe signal from the internal microphone goes through themute switch (Q301).When the SP-MIC is not attached, the microphoneswitching terminal (MSW) on the universal connector be-comes High, and mute switch (Q301) is turned ON. Whenthe SPMIC is attached, MSW is connected to GND at insideof SPMIC. For this reason, Q301 is turned OFF, the internalmicrophone is muted, and only the input of the external mi-crophone is supplied to the microphone amplifier of the TX-RX unit.The signal from microphone passes through the micro-phone mute switch (Q502 is off in TX), the limited circuitin D501 and amplified by IC501 (1/2) and passes throughthe high-pass filter, the ALC circuit, the low-pass filter, thehigh-pass filter, and preemphasis/IDC circuit in IC500 on thesmall board. When encoding DTMF, mute switch (Q501) isturned OFF for muting the microphone input signal.The signal passes through the D/A converter (IC307) forthe maximum deviation adjustment, and enters the sum-ming amplifier consisting of IC305 (1/2), and is mixed withthe low speed data from the MCU (IC309).The output signal from the summing amplifier passesthrough the D/A converter (IC307) again and goes to theVCO modulation input.The other output signal from the summing amplifierpasses through the D/A converter (IC307) again for the BALadjustment, and the buffer amplifier (IC302 (2/2)), and goesto the TCXO modulation input.3-5. 静噪电路I C200 的输出再次进入调频中频芯片，然后通过片上的带通滤波器。并通过带通滤波器 I C201(2/2)。调制输入。I C201(2/2) 输出的噪音成分被 Q208 放大并且被 D201 整流生成一个相对应于噪音电平的直流电压。直流电压被发送到 MCU(IC309) 的模拟端口。IC200 生成一个相对应于中频放大器输入的直流电压 ( R S S I )。M C U 通过管脚 93 读取 RSSI。I C309 将管脚 91 和管脚 93 的输入电压与预设值进行比较后决定是否通过扬声器输出声音。4. 发射部系统4-1. 话筒放大器来自于内置话筒的信号进入静音开关 (Q301)。当扬声器 - 话筒不接上时，通用接口上的话筒开关端点(MSW) 变为高电平，静音开关 (Q301) 接通。当扬声器 - 话筒接上时，MSW 与扬声器 - 话筒内的地线连接。因此，Q301 断开，内置话筒静音，并且只有外置话筒的输入提供给 T X - R X 单元的话筒放大器。来自麦克风的信号通过麦克风静音开关 ( 发射时 Q502 关断 )，D501 中的限幅电路，经过 I C501(1/2) 放大，并通过高通滤波器，A L C 电路，低通滤波器，高通滤波器，以及小板IC500 上的预加重 /IDC 电路。当编码 DTMF 时，静音开关 (Q501)关闭，以阻断麦克风输入信号。信号通过数 / 模转换器 ( I C307) 进行最大频偏调整，然后进入由 I C305(1/2) 组成的总和放大器，并且与来自于MCU(IC309) 的低速率数据混合。来自于加法放大器的输出信号再次通过数 / 模转换器(IC307) 并进入 VCO 调制输入。来自于总和放大器的其他输出信号再次通过数 / 模转换器(IC307) 进行 BAL 调整，并通过缓冲放大器 (IC302 2/2)，然后进入 TCXO 调制输入。12DETBPFAMP BPFAMPDETRSSI NOISEAMPIC309MCUIF AMP79193IC200: FM IF ICQ208IC201(2/2) D201SQ closeSQ openPresetvalueANT input levelSQ voltageANT input levelRSSI voltagePreset valueFig. 5 Squelch and RSSI voltage vs ANT input level / 图 5 静噪和 RSSI 电压与 ANT 输入电平CIRCUIT DESCRIPTION / 电路说明