Kenwood TK-2207 Service Manual page 16

TK-2207
2) Drive and Final Amplifier
The signal from the T/R switch (D101 is on) is amplified by
the pre-drive (Q102) and the drive amplifier (Q103) to 50mW.
The output of the drive amplifier is amplified by the RF power
amplifier (Q106) to 5.0W (1W when the power is low). The
RF power amplifier consists of two MOS FET stages. The
output of the RF power amplifier is then passed through
the harmonic filter (LPF) and antenna switch (D103 and
D104) and applied to the antenna terminal.
Fig. 7 Drive and final amplifier and APC circuit / 图 7 驱动、终端放大器以及 APC 电路
3) APC Circuit
The APC circuit always monitors the current flowing through
the RF power amplifier (Q106) and keeps a constant current.
The voltage drop at R127, R128 and R129 is caused by the
current flowing through the RF power amplifier 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 IC405. The output of IC101(2/2)
controls the VG of the RF power amplifier, drive amplifier
and pre-drive amplifier to make both voltages the same.
The change of power high/low is carried out by the change
of the reference voltage.
4) Encode Signalling
(1) QT/DQT
QT,DQT data of the QTTCXO Line is output from pin 28 of
the CPU. The signal passes through a low-pass CR filter
and goes to the TCXO(X1).
The QT,DQT data of the QTVCO Line is output from pin 24
of the CPU. The signal passes through a low pass CR filter,
mixes with the audio signal, and goes to the VCO modulation
input. TX deviation is adjusted by the CPU.
16
CIRCUIT DESCRIPTION /
AGC
MIC
LPF
DTMF
Fig. 6 Microphone amplifier / 图 6 话筒放大器
Q102 Q103
From
Pre-DRIVE
DRIVE
T/R SW
AMP
AMP
(D101)
VD
5T
+B
R127
R128
R129
PCTV
(IC405)
电路说明
IC301
AQUA VCO
IC405
QTVCO LPF
X1
QTTCXO LPF TCXO
CPU
2) 驱动器和终端放大器
来自于 T/R 开关 (D101 ON) 的信号被前置驱动放大器 (Q102)
和驱动放大器 (Q103) 放大到 50mW。
驱动放大器的输出被 RF 功率放大器 (Q106) 放大到 5.0W (当
低功率时为 1W)。RF 功率放大器由 2 个 MOS FET 构成。RF
功率放大器的输出通过谐波滤波器 (LPF) 和天线开关 (D103
和 D104) 并且送到天线终端。
D103
Q106 D104
RF
ANT
LPF
POWER AMP
SW
VG VG
VDD
IC101 IC101
(1/2) (2/2)
3) 自动功率控制 (APC) 电路
APC 电路一直监视通过射频功率放大器 (Q106) 的电流并保
持电流稳定。经过射频功率放大器的电流的变化会引起
R127， R128和R129的电压降低， 此电压送到差分放大器 IC101
(1/2) 。
IC101 (2/2) 将IC101 (1/2) 的输出电压与来自IC405的参考电压
进行比较。
IC101 (2/2) 的输出电压控制射频功率放大器， 驱动放大器， 预
驱动放大器的 VG，使电压保持一致。
功率高 / 低的变化是通过变更参考电压来实现的。
4) 编码信令
(1) QT/DQT
QTTCXO 线的 QT,DQT 数据从 CPU 的 28 管脚输出。信号通过
低通 CR 滤波器，并且送到 TCXO (X1)。
QTVCO 线的 QT, DQT 数据从 CPU 的 24 管脚输出。信号通过
低通 CR 滤波器，与音频信号混合，然后输入到 VCO。TX 频
偏被 CPU 调整。
ANT