Kenwood TK-3360 Service Manual page 14

TK-3360
The oscillator frequency is controlled by applying the VCO
control voltage, obtained from the phase comparator (IC1) to
the variable capacitor diodes (D7 and D9 in transmit mode
and D3 and D5 in receive mode).
The TX pin of IC809 goes "low" in receive mode caus-
ing Q4 and Q7 turn on. The TX pin goes "high" in transmit
mode causing Q5 turn on.
The outputs from Q4 and Q5 are amplifi ed by buffer am-
plifi er (Q8, Q2) and then sent to PLL IC.
The PLL IC consists of a prescaler, reference divider,
phase comparator, charge pump (The frequency step of the
PLL circuit is 5 or 6.25kHz). The input signal from the pins
10 and 17 of the PLL IC is divided down to the 5 or 6.25kHz
and compared at phase comparator. The pulsed output sig-
nal of the phase comparator is applied to the charge pump
and transformed into DC signal in the loop fi lter (LPF). The
DC signal is applied to the CV of the VCO and locked to
keep the VCO frequency constant.
PLL data is output from PLLDAT (pin 45), PLLCLK (pin 47)
and PLLLE (pin 46) of the MCU (IC809). The data are input
to the PLL IC when the channel is changed or when trans-
mission is changed to reception and vice versa. A PLL lock
condition is always monitored by the pin 48 (PLLLD) of the
MCU. When the PLL is unlocked, the PLLLD goes low.
5. Control Circuit
The control consists of the MCU (IC809) and its peripher-
al circuits. It controls the TX-RX unit. IC809 mainly performs
the following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading channel information, frequency, and program
data from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off via the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit via the decode data in-
put.
6) Transmitting tone and encode data.
14
CIRCUIT DESCRIPTION /
Q8
TX VCO BUFF
(TX: High)
CV
LPF
IC1
21 17
PLL
7 10
PLLLD
MCU
PLLLE,PLLCLK,PLLDAT
IC809
Fig. 6 PLL block diagram / 图 6 PLL 方块图
电路说明
振荡频率由加在 V C O 上的控制电压控制，控制电压从可变
电容二极管 ( 在发射模式是 D7 和 D9，在接收模式是 D3 和
D5) 的相位比较器 (IC1) 处获得。
IC809 的 TX 针脚在接收模式时为 "低" 电位， 使 Q4 和 Q7 打开。
TX 针脚在发射模式时为"高"电位，使 Q5 导通。
Q4 和 Q5 的输出由缓冲放大器 ( Q8, Q2) 放大，然后发送到
PLL IC。
PLL IC 由预计数器、基准除法器、相位比较器、电荷泵组
成 (PLL 电路的频率步长为 5kHz 或 6.25kHz)。PLL IC 的针
脚 10 和 17 的输入信号下分成 5k H z 或 6.25k H z，并在相位比
较器处进行比较。相位比较器的脉冲输出信号加在电荷泵上，
并转换成环路滤波器 ( L P F ) 的 D C 信号。D C 信号加在 V C O 的
CV 上并锁定，使 VCO 的频率恒定。
PLL 数据从 MCU(IC809) 的 PLLDAT( 针脚 45)，PLLCLK( 针
脚 47) 和 PLLLE( 针脚 46) 输出。当信道改变时，或当由发射
变为接收或由接收变为发射时，数据输入 P L L I C。P L L 的锁
定条件总是由 M C U 的针脚 48( P L L L D ) 监控。当 P L L 失锁时，
PLLLD 为低电位。
Q9 D18
RF
SW To
AMP
RF AMP
Q2 D17
BUFF SW
To mixer
VC
Baseband
TCXO
IC
X1 IC812
5. 控制电路
控制电路是由微处理器 ( I C809) 和外部电路构成。它控制
收发单元。IC809 的主要功能如下 :
1) 根据 PTT 的输入信号来转换发射和接收状态。
2) 从存储电路读出信道信息、频率以及编程数据。
3) 发送频率数据给 PLL。
4) 根据静噪电路输出的 DC 电压来控制静噪的开启和关闭。
5) 根据解码数据控制音频静音。
6) 发射 Tone 及编码数据。