Kenwood NXR-700H Service Manual page 23

+9V is applied to the Q1 collector power supply. –3V pro-
duced by IC701, IC702 and IC703 mounted on a negative
power unit (X45-385 D/5) is applied to the emitter power
supply. The collector current is monitored by the IC4 cur-
rent detection circuit. Detected DC voltage is input to pin
15 of IC30 (ADC).
4-2. 1st-Mixer circuit
The unwanted out-of-band RF components produced by
Q1 are attenuated by the BPF. Only the desired signal is
transmitted to the A1 Double Balanced Mixer (DBM). Here,
the desired signal is mixed with the first hetero signal.
49.95MHz is produced as the 1st Intermediate Frequency
(IF1).
4-3. 1st-IF circuits
The IF1 signal produced by the 1st-Mixer circuit is trans-
mitted through either one of two 1st-IF circuits with differ-
ent bandwidth. The signal passes through the WIDE band
consisting of D9, XF1, Q19, XF3, Q28 and D13 only in Ana-
log_Wide mode. Meanwhile, the signal passes through the
NARROW band consisting of D10, XF2, Q20, XF4, Q29, and
D14 only in Analog_Narrow, NXDN_Narrow or NXDN_Very-
Narrow mode.
XF1 and XF2 is 2 pole and XF3 and XF4 are 4 pole Mono-
lithic Crystal Filters (MCF). They are BPF for removing spu-
rious noise occurring close to the desired signal. The DC
switch consists of Q31, Q32, Q26 and Q25, switches the
WIDE and NARROW bands of the 1st-IF circuits.
CIRCUIT DESCRIPTION /
RX unit
RX ANT
X55-309
BPF
CN5
L132~135
TC1~4
+9V
IC701
Power supply unit
X45-385 D/5
Fig. 16 Front-end circuit / 图 16 前端电路
BPF
L136~139
TC5~8
Fig. 17 1st-Mixer circuit / 图 17 第 1 混频器电路
电路说明
+9V 施 加 于 Q1 集 电 极 电 源。 装 在 负 功 率 单 元 ( X45-385
D/5) 上的 IC701、IC702 和 IC703 产生的 -3V 施加于发射极电
源。集电极电流由 I C4 电流检测电路监测。检测的 D C 电压被
输入 IC30(ADC) 的针脚 15。
+9V
IC30
15
IC4
Q1
BPF
LNA
L136~139
TC5~8
CN701
+5V –5V –3V
IC702 IC703
4-2. 第 1 混频器电路
Q1 产生的不需要的带外 R F 分量由 B P F 衰减。仅所需的信
号被发送到 A1 双平衡混频器 ( D B M )。所需的信号在此处与第
一外差信号混合。产生 49.95MHz，作为第 1 中频 (IF1)。
A1
Mixer IF1
49.95MHz
1st local
195.95~223.95MHz
4-3. 第 1 IF 电路
第 1 混频器电路产生的 I F1 信号通过带宽不同的两个第
1 I F 电路中的任一个发送。信号仅以模拟宽模式通过由 D9、
X F1、Q19、X F3、Q28 和 D13 组成的 W I D E 带。同时，信号仅
以模拟窄、N X D N 窄或 N X D N 超窄模式通过由 D10、X F2、Q20、
XF4、Q29 和 D14 组成的 NARROW 带。
XF1 和 XF2 为 2 极、 XF3 和 XF4 为 4 极单片晶体滤波器 (MCF)。
它们是用于消除所需信号附近发生的寄生噪声的 B P F。D C 开
关 由 Q31、Q32、Q26 和 Q25 组 成， 用 于 切 换 第 1 I F 电 路 的
WIDE 带和 NARROW 带。
NXR-700H
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