Kenwood NXR-800H Service Manual page 17

2-6. Driver circuit
The driver circuit amplifi es the transmitter frequency sig-
nal to the level required for input to the Final Unit (X45-386
A/5).
This circuit consists of RF amplifiers Q201, Q202 and
Q203, switches Q204, Q205 and Q206, and operating am-
plifi er IC201.
DC switches Q204, Q205, and Q206 turns the power
supply voltage of RF amplifi ers Q201, Q202, and Q203 on
and off.
The transmitter main PLL circuit output is attenuated by
attenuators R201, R202 and R203, by approximately 7dB.
So, the input level to Q201 is approximately –12dBm (63µW).
Q201 amplifi es it by approximately 12dB. So, the output
level is approximately 0dBm (1mW).
The Q201 output is amplifi ed by Q202 by approximately
10dB. Furthermore, it is amplified by Q203 by approxi-
mately 10dB. The Q203 output is approximately +20dBm
(100mW). This output level is output from driver output con-
nector CN802 and is connected to the Final Unit (X45-386
A/5).
Q203 has an AGC (Auto Gain Control) circuit. D201 recti-
fi es a part of the Q203 output and converts it into DC volt-
age. It is compared with the control voltage (D_PC) by the
operation amplifi er IC201. The Q203 Gate terminal voltage
is controlled for the stabilizing Q203 output (+20dBm).
8V #1
TX main
PLL circuit
440~
470MHz (C)
400~
430MHz (C2)
2-7. Modulation level adjustment circuit
The level adjustment circuit adjusts the modulation signal
level to provide the required level of modulation. This circuit
consists 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 from
this.
IC304 is an electronic volume control IC.
The modulation waveform balance adjustment, maximum
AF Dev. change, and adjustment are performed according to
data 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 transmitter
main PLL.
IC305 is an inverting amplifi er (B/2) for inverting the am-
plification (A/2) of the modulating signal and synthesizing
CIRCUIT DESCRIPTION /
Q204~206
SW
ATT
Q201 Q202
Fig. 6 Driver circuit / 图 6 驱动电路
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 ( X45-386
A/5) 所需的电平。
该电路由 R F 放大器 Q201、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 Q201、
Q202 和 Q203 的电源电压。
发射机主 P L L 电路输出由衰减器 R201、R202 和 R203 衰减
约 7dB。因此，Q201 的输入电平约为 -12dBm(63µW)。
Q201 将其放大约 12dB。因此，输出电平约为 0dBm(1mW)。
Q201 输出由 Q202 放大约 10d B。此外，它由 Q203 放大约
10d B。Q203 输出约为 +20d B m (100m W )。该输出电平从驱动器
输出连接器 CN802 输出并连接到最终单元 (X45-386 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_PC) 相比较。Q203 栅极电压受到控制以稳定
Q203 输出 (+20dBm)。
8V #1'
Q203
D201
8V #1'
IC201
IC201
(A/2)
(B/2)
D_PC
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。
NXR-800H
CN802
Final
unit
440~470MHz (C)
400~430MHz (C2)
+20dBm
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