Kenwood NX-220 Service Manual page 20

NX-220
by the current fl owing through the RF power amplifi er and
this voltage is applied to the differential amplifier (IC101
1/2). IC101 (2/2) compares the output voltage of IC101 (1/2)
with the reference voltage from IC610, and the output of
IC101 (2/2) controls the VGG of Q103 and Q104 to make the
both current constant. The change of power high/low is car-
ried out by the change of the reference voltage. Q106, Q107
and Q108 are turned on and Q105 and Q109 are turned off
during transmission and the APC circuit is active.
Fig. 5 Drive and fi nal amplifi er and APC circuit / 图 5 驱动器和末级放大器和 APC 电路
5. PLL Frequency Synthesizer
5-1. TCXO (X401)
The TCXO (X401) generates a reference frequency of
16.8MHz for the PLL frequency synthesizer. This reference
frequency is applied to pin 9 of the PLL IC (IC403) and is
connected to the IF circuit as a 2nd local signal through the
Tripler (Q301).
The frequency adjustment is achieved by switching the
ratio of dividing frequency. The resolution of the adjusting
frequency is approximately 4Hz.
5-2. VCO
There is a RX VCO and a TX VCO.
The TX VCO (Q402) generates a transmit carrier and the
RX VCO (Q401) generates a 1st local signal. For the VCO
oscillation frequency, the transmit carrier is 136 to 174MHz
and the 1st local receive signal is 185.95 to 223.95MHz.
The VCO oscillation frequency is determined by one sys-
tem of operation switching terminal "T/R" and two systems
of voltage control terminals "CV" and "ASSIST".
The operation switching terminal, "T/R", is controlled by
the control line (/T_R) output from the ASIC (IC610). When
the /T_R logic is low, the VCO outputs the transmit carrier
and when it is high, it outputs a 1st local receive signal.
The voltage control terminals, "CV" and "ASSIST", are
controlled by the PLL IC (IC403) and ASIC (IC610) and the
output frequency changes continuously according to the
applied voltage. For the modulation input terminal, "VCO_
MOD", the output frequency changes according to the
applied voltage. This is used to modulate the VCO output.
"VCO_MOD" works only when "/T_R" is low.
20
CIRCUIT DESCRIPTION /
from
Pre-Drive
T/R SW (D413)
VCC for Pre-Drive AMP
from PD SW (Q110)
R153
+B
R154
R155
Reference voltage
from IC610
电路说明
1/2) 上。I C101(2/2) 将 I C101(1/2) 的输出电压与 I C610 的
基准电压进行比较，同时 I C101(2/2) 的输出信号对 Q103 和
Q104 的 V G G 进行控制，使两者的电流保持恒定。功率高 / 低
的变化通过基准电压的变化来执行。在发射时 Q106、Q107 及
Q108 开启，Q105 和 Q109 关闭，同时 APC 电路激活。
Q102 Q103 Q104
Drive Final
AMP AMP AMP
IC101
(1/2)
5. PLL 频率合成器
5-1. TCXO(X401)
TCXO(X401) 生成 16.8MHz PLL 频率合成器的基准频率。该
基准频率作为第 2 本振信号通过三倍频器 ( Q301)，被加载到
PLL IC(IC403) 的第 9 脚并送至 IF 电路。
通过切换分频比进行频率调整。调整频率的分辨率约为
4Hz。
5-2. VCO
设有一个 RX VCO 和一个 TX VCO。
TX VCO(Q402) 生成发射载波，RX VCO(Q401) 生成第 1 本振
信号。对于 V C O 震荡频率，发射载波为 136 至 174M H z，第 1
本振接收信号为 185.95 至 223.95MHz。
V C O 震荡频率由一个操作切换端子"T / R"系统和两个电压
控制端子"CV"和"ASSIST"系统确定。
操作切换端子"T/R"由 ASIC(IC610) 控制线路 (/T_R) 的
输出信号进行控制。/T_R 逻辑低时， VCO 输出发射载波； 高时，
输出第 1 本振接收信号。
电压控制端子"C V"和"A S S I S T"由 P L L I C ( I C403) 和
A S I C ( I C610) 控制，输出频率根据加载的电压持续改变。对
于调制输入端子"VCO_MOD" ，输出频率根据加载的电压改变。
籍此调制 VCO 输出。 "VCO_MOD"仅在"/T_R"低时工作。
ANT
D102,D103
ANT
LPF
SW
VGG
IC101
(2/2)