Kenwood NXR-800H, Service Manual

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NXR-800H
23
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 /
电路说明
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)。
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。
Fig. 16 Front-end circuit /
图 16 前端电路
Fig. 17 1st-Mixer circuit /
图 17 第 1 混频器电路
BPF
L132,133
BPF
L134,135
Q1
LNA
IC4
IC30
+9V
15
RX ANT
CN5
RX unit
X55-310
IC701
+9V
IC702
+5V
IC703
–5V –3V
Power supply unit
X45-386 D/5
CN701
BPF
L134,135
A1
Mixer IF1
49.95MHz
1st local
390.05~420.05MHz (C)
350.05~380.05MHz (C2)