Kenwood TK-2107G Service Manual

TK-2107G123-2. VCOThe operating frequency is generated by Q4 in transmitmode and Q3 in receive mode. The oscillator frequency iscontrolled by applying the VCO control voltage, obtainedfrom the phase comparator, to the varactor diodes (D1 andD2 in transmit mode and D3 and D4 in receive mode). TheT/R pin is set high in receive mode causing Q5 and Q7 toturn Q4 off, and turn Q3 on . The T/R pin is set low in trans-mit mode. The outputs from Q3 and Q4 are amplified by Q6and sent to the buffer amplifiers.3-2. 压控振荡器在发射模式中通过 Q4 产生操作频率，在接收模式中通过Q3 产生操作频率。通过相位比较器到变容二极管 ( 在发射模式中为 D1 和 D2，在接收模式中为 D3 和 D4) 采用压控振荡器控制电压来控制振荡频率。在接收模式中，由于 Q5 和 Q7 切断 Q4 并且导通 Q3，所以发射 / 接收管脚设置为高电平。在发射模式中，发射 / 接收管脚设置为低电平。Q3 和 Q4 的输出通过 Q6 被放大并被发送到缓冲放大器。3-3. Unlock detectorIf a pulse signal appears at the LD pin of IC1, an unlockcondition occurs, and the DC voltage obtained from D7, R1,and C1 causes the voltage applied to the UL pin of the mi-croprocessor to go low. When the microprocessor detectsthis condition, the transmitter is disabled, ignoring the push-to-talk switch input signal. (See Fig. 5)4. Transmitter4-1. Transmit audioThe modulation signal from the microphone is amplifiedby IC500 (1/2), passes through a preemphasis circuit, andamplified by the other IC500 (1/2) to perform IDC operation.The signal then passes through a low-pass filter (splatterfiIter) (Q501 and Q502) and cuts 3kHz and higher frequen-cies. The resulting signal goes to the VCO through the VCOmodulation terminal for direct FM modulation. (See Fig. 6)4-2. QT/DQT encoderA necessary signal for QT/DQT encoding is generated byIC403 and FM-modulated to the PLL reference signal. Sincethe reference OSC does not modulate the loop characteris-tic frequency or higher, modulation is performed at the VCOside by adjusting the balance. (See Fig. 6)3-3. 失锁检测器如果 IC1 的 LD 管脚上出现高电平，则产生失锁状态，并从D7,R1 获得直流电压，且 C1 产生的提供给微处理器 UL 管脚的电压降低。当微处理器检测到此情况时，不能进行发射，无视通话转换开关输入信号。( 参见图 5)4. 发射部4-1. 发射音频来自于话筒的调制信号通过 I C500(1/2) 被放大，经过一个预加重电路，并通过另一个 IC500(1/2) 放大后进行 IDC 处理。然后信号通过一个低通滤波器 ( 分离滤波器 ) ( Q501 和 Q502)并滤除比 3k H z 频率更高的部分。得到的信号进入压控振荡器直接进行调频调制。( 参见图 6)4-2. QT/DQT 编码器QT/DQT 编码所需的信号通过 IC403 产生，被锁相环电路的基准频率调整。由于基准振荡器不能对频率环路特性外的频率进行调制，因此通过分配器在压控振荡器一侧进行调制。( 参见图 6)Fig. 4 PLL circuit / 图 4 锁相环电路Fig. 5 Unlock detector circuit / 图 4 失锁检测器电路CIRCUIT DESCRIPTION / 电路说明PLLdata12.8MHzREF OSC1/N1/MIC1: PLL ICPhasecomparatorChargepumpLPF5kHz/6.25kHz5kHz/6.25kHzD1,2 Q4TX VCOQ6BUFF AMPQ2RF AMPQ5,7T/R SWD3,4 Q3RX VCOIC1PLL ICLDD7C1R15CIC403MCUUL