Kenwood TK-2217 Service Manual page 26

2) VCO
The operating frequency is generated by Q4 in transmit
mode and Q3 in receive mode. The oscillator frequency is
controlled by applying the VCO control voltage, obtained
from the phase comparator, to the varactor diodes (D4 and
D7 in transmit mode and D5 and D9 in receive mode). The
RX pin is set high in receive mode causing Q5 turn on.
The TX pin is set high in transmit mode. The outputs from
Q3 and Q4 are amplified by Q6 and sent to the RF amplifiers.
3) Unlock Detector
If a pulse signal appears at the LD pin of IC1, an unlock
condition occurs, and the DC voltage obtained from C4,R5
and D1 causes the voltage applied to the microprocessor
to go low. When the microprocessor detects this condition,
the transmitter is disabled, ignoring the push-to-talk switch
input signal.
4. Transmitter System
1) Microphone Amplifier
The signal from the microphone passes through the IC301.
When encoding DTMF, it is turned OFF for muting the
microphone input signal by IC301.
The signal passes through the Audio processor (IC301) for
the maximum deviation adjustment, and goes to the VCO
modulation input.
CIRCUIT DESCRIPTION /
LPF
LPF
PLL IC IC1
PLL DATA
REF OSC
X1
12.8MHz
Fig. 5 PLL circuit / 图 5 PLL 电路
电路说明
2) VCO
所使用的频率在发射模式时由 Q4 生成，在接收模式时由
Q3 生成。
通过将从相位比较器所获得的 VCO 控制电压输送给可变二
极管 (在发射模式时为 D4 和 D7，在接收模式时为 D5 和 D9)
来控制振荡频率。在接收时 RX 脚被设定为高，使 Q5 接通。
发射时 TX 脚被设定为高。Q3 和 Q4 的输出被 Q6 放大并且传
送给 RF 放大器。
Q4
D4, 7
TX VCO
Q6
BUFF AMP
Q3
D5, 9
RX VCO
Q5, 7
T/R SW
5kHz/6.25kHz
1/N
PHASE CHARGE
COMPARATOR
PUMP
1/M
5kHz/6.25kHz
3) 失锁检测器
如果脉冲信号出现在 IC1 的 LD 管脚上，则发生了失锁的情
况，从 C4，R5 和 D1 获得的 DC 电压使微处理器的输入电压
变低。微处理器检测到这个情况后发射被禁止，忽略 PTT 开
关的输入信号。
4. 发射部系统
1) 话筒放大器
来自于话筒的信号通过 IC301。当编码 DTMF 时，话筒输入
信号被 IC301 关闭。
信号通过音频处理器 (IC301) 进行最大频偏调整，然后送到
VCO 调制输入。
TK-2217
Q2
BUFFER
IC2
1/ 2
RX
TX
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