Kenwood NXR-700H Service Manual

NXR-700H172-6. Driver circuitThe driver circuit amplifies the transmitter frequency sig-nal to the level required for input to the Final Unit (X45-385A/5).This circuit consists of RF amplifiers Q202 and Q203,switches Q204, Q205 and Q206, and operating amplifierIC201.DC switches Q204, Q205, and Q206 turns the powersupply voltage of RF amplifiers Q202, and Q203 on and off.The output of the divide-by-2 IC (IC811) is attenuated byattenuators R209, R210 and R211, by approximately 10dB.So, the transmitter signal input level to Q202 is approxi-mately –4dBm (0.4mW).Q202 amplifies it by approximately 15dB. So, the outputlevel is approximately +11dBm (12.6mW).The output from Q202 is attenuated by attenuators R217,R218 and R219, by approximately 3dB, and amplified byQ203 approximately by 12dB. So, the output from Q203 isapproximately +20dBm (100mW). This output level is out-put from the driver output connector CN802 and connectedto the Final Unit (X45-385 A/5).Q203 has an AGC (Auto Gain Control) circuit. D201 recti-fies a part of the Q203 output and converts it into DC volt-age. It is compared with the control voltage (D_PC) by theoperation amplifier IC201. The Q203 Gate terminal voltageis controlled for the stabilizing Q203 output (+20dBm).Q202 Q203TX mainPLL circuit8V #1FinalunitD201ATTSWATT146~174MHzD_PCIC201(A/2)IC201(B/2)8V #1’CN802146~174MHz+20dBm8V #1’Q204~206Fig. 6 Driver circuit / 图 6 驱动电路2-7. Modulation level adjustment circuitThe level adjustment circuit adjusts the modulation signallevel to provide the required level of modulation. This circuitconsists of IC301, IC304, IC305, and IC308.The audio signal comes from the Control Unit (X53-413)through pin 4. The modulating signal is input to IC304 fromthis.IC304 is an electronic volume control IC.The modulation waveform balance adjustment, maximumAF Dev. change, and adjustment are performed according todata from the MPU using the FPU.The modulation signal is produced by the modulating low-pitched tone to the transmitter modulation 19.2MHz PLL cir-cuit and adds the high-pitched modulation to the transmittermain PLL.IC305 is an inverting amplifier (B/2) for inverting the am-plification (A/2) of the modulating signal and synthesizingCIRCUIT DESCRIPTION / 电路说明2-6. 驱动电路驱动电路将发射机频率信号放大到输入末级单元 ( X45-385A/5) 所需的电平。该电路由 R F 放大器 Q202 和 Q203、开关 Q204、Q205 和Q206 以及运算放大器 IC201 组成。D C 开关 Q204、Q205 和 Q206 打开和关闭 R F 放大器 Q202 和Q203 的电源电压。二分频 I C ( I C811) 的输出由衰减器 R209、R210 和 R211 衰减约 10dB。因此，到 Q202 的发射机信号输入电平约为 -4dBm(0.4mW)。Q202 将其放大约 15d B。因此，输出电平约为 +11d B m(12.6mW)。Q202 的输出由衰减器 R217、R218 和 R219 衰减约 3d B，由Q203 放大约 12d B。因此，Q203 的输出约为 +20d B m (100m W )。该输出电平从驱动器输出连接器 C N802 输出并连接到末级单元 (X45-385 A/5)。Q203 有一个 AGC( 自动增益控制 ) 电路。D201 对 Q203 的部分输出进行整流，将其转换到 D C 电压。运算放大器 I C201 将其与控制电压 ( D _ P C ) 进行比较。对 Q203 栅极电压加以控制以稳定 Q203 输出 (+20dBm)。2-7. 调制电平调整电路该电平调整电路调整调制信号电平，以提供所需的调制电平。该电路由 IC301、IC304、IC305 和 IC308 组成。音频信号经第 4 针来自控制单元 ( X53-413)。调制信号由此输入 IC304。IC304 是一个电子音量控制 IC。调制波形平衡调整、最大 A F D e v . 变化以及根据来自 M P U的数据 ( 基于 FPU) 进行调整。调制信号由到发射机调制 19.2M H z P L L 电路的调制低调音和把高调调制加到发射机主 PLL 电路产生。IC305 是一个反相放大器 (B/2)，用于变换调制信号的放大(A/2)，合成 VCXO(X301) 控制电压和调制信号。