Kenwood NXR-700H Service Manual page 14

NXR-700H
2-2. Transmitter reference 19.2MHz PLL circuit
The transmitter reference 19.2MHz PLL circuit produces
a reference frequency signal for the transmitter modulation
19.2MHz PLL circuit, the Receiver unit (X55-309) Receiver
DDS circuit and the Control Unit (X53-414) DSP IC.
This circuit consists of Q401, Q402, Q412, Q415, Q416,
Q417, X401, IC404, and IC407.
The 5.99MHz or 10MHz signal produced by the internal/
external reference circuit is amplifi ed by IC407 and supplied
to the PLL IC (IC404) reference signal pin.
The VCXO (X401) signal enters buffer amp Q417 and is
amplifi ed by Q415. The higher harmonic wave is attenuated
by LPF and returns to IC404. Its phase is compared with
that of the reference frequency 10kHz.
The phase difference signal produced by the comparing
phase is converted to a DC voltage by a lag-lead type loop
fi lter. This DC voltage is input to the X401 control voltage
terminal for controlling the VCXO oscillating frequency.
The DC voltage passes through the IC401 operational am-
plifi er, and is output as a voltage signal (CVT-REF) for moni-
toring the reference 19.2MHz PLL circuit lock voltage.
The stabilized 19.2MHz reference oscillating signal en-
ters the Q417 buffer amplifi er and is amplifi ed by Q412 and
Q416. The higher harmonic wave is attenuated by LPF, fed
to IC302 and used as the reference frequency signal for the
transmitter modulation 19.2MHz PLL circuit.
The 19.2MHz reference oscillating signal is also used as
the reference signal for the receiver unit (X55-309) and con-
trol unit (X53-414).
It enters the Q417 buffer amplifi er for the receiver unit
(X55-309) and is amplifi ed by Q401. The higher harmonic
wave is attenuated by LPF and is output from CN406.
It enters the Q417 buffer amplifier for the control unit
(X53-414) and is amplifi ed by Q402. The higher harmonic
wave is attenuated by LPF and is output from CN405.
5V #3
Internal
/External
5.99MHz
Ref circuit
IC407
or
10MHz
Fig. 2 Transmitter reference 19.2MHz PLL circuit / 图 2 发射机基准 19.2MHz PLL 电路
14
CIRCUIT DESCRIPTION /
5V #3
IC401
OP-AMP
5V #3
IC404
PLL IC
8 2
1/R PD
Fref.=19.2MHz
R=1920
6
1/N
Fpd=10kHz
电路说明
2-2. 发射机基准 19.2MHz PLL 电路
发射机基准 19.2M H z P L L 电路产生发射机调制 19.2M H z
PLL 电路、接收机单元 (X55-309) 接收机 DDS 电路和控制单元
(X53-414)DSP IC 的基准频率信号。
该 电 路 由 Q401、Q402、Q412、Q415、Q416、Q417、X401、
IC404 和 IC407 组成。
内部 / 外部基准电路产生的 5.99MHz 或 10MHz 信号由 IC407
放大并提供给 PLL IC(IC404) 基准信号针脚。
V C X O ( X401) 信号进入缓冲放大器 Q417，由 Q415 放大。较
高的谐波由 LPF 衰减并返回 IC404。其相位与基准频率 10kHz
的相位进行对比。
通过相位对比产生的相位差信号由一个滞后超前式环路滤
波器转换为 DC 电压。该 DC 电压被输入用于控制 VCXO 振荡频
率的 X401 控制电压端子。
DC 电压通过 IC401 运算放大器， 输出为电压信号 (CVT-REF)，
用于监测基准 19.2MHz PLL 电路锁定电压。
经过稳定的 19.2M H z 基准振荡信号进入 Q417 缓冲放大器，
由 Q412 和 Q416 放大。较高的谐波由 L P F 衰减，送入 I C302，
并用作发射机调制 19.2MHz PLL 电路的基准频率信号。
19.2M H z 基准振荡信号还用作接收机单元 ( X55-309) 和控
制单元 (X53-414) 的基准信号。
它进入接收机单元 (X55-309) 的 Q417 缓冲放大器，由 Q401
放大。较高的谐波由 LPF 衰减，从 CN406 输出。
它进入控制单元 ( X53-414) 的 Q417 缓冲放大器，由 Q402
放大。较高的谐波由 LPF 衰减，从 CN405 输出。
CVT-REF
8V #2 8V #2
19.2MHz
X401 Q417 Q416
8V #2
Q415 Q401
Q402
5V #1 5V #1
19.2MHz
Q412
5V #2
CN406
19.2MHz
5V #2
CN405
19.2MHz
TX Mod
19.2MHz
PLL circuit
RX unit
Control
unit