Kenwood TK-2000 Service Manual page 9

4. Frequency Synthesizer Circuit
4-1. Frequency Synthesizer
The frequency synthesizer consists of the TCXO (X1),
VCO, PLL IC (IC1) and buffer amplifiers.
The TCXO generates 19.2MHz. The frequency stability is
5.0 ppm within the temperature range of –30 to +60°C.
The frequency tuning and modulation of the TCXO are
done to apply a voltage to pin 1 of the TCXO. The output of
the TCXO is applied to pin 1 of the PLL IC.
The VCO consists of 1VCO and covers a dual range of
the 144.00~174.00MHz and the 182.85~212.85MHz. The
VCO generates 182.85~212.85MHz for providing to the first
local signal in receive.
The PLL IC consists of a prescaler, reference divider,
phase comparator, charge pump (The frequency step of the
PLL circuit is 5 or 6.25 kHz).
PLL data is output from DATA (pin 19), CLOCK (pin 18)
and PLDL (pin 20) of the MCU (IC400). The data are input to
the PLL IC when the channel is changed or when transmis-
sion is changed to reception and vice versa. A PLL lock con-
dition is always monitored by the pin 22 (PLUL) of the MCU.
When the PLL is unlocked, the PLUL goes low.
Q5
VCO
T/RSHF BUFF
(TX: Low)
CV
LPF
5
Q1
PLUL
INV
14
IC400
DATA,
CLOCK,PLDL
MCU
Fig. 5 PLL block diagram
5. Control Circuit
The control consists of the MCU (IC400) and its peripher-
al circuits. It controls the TX-RX unit. IC400 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
input.
6) Transmitting tone and encode data.
CIRCUIT DESCRIPTION
Q6 D100
RF
SW To
AMP
RF AMP
D200
SW To mixer
IC1
8
X1
1
PLL TCXO
LSDO
Note:
The EEPROM stores tuning data (Deviation, Squelch,
etc.).
Realign the transceiver after replacing the EEPROM.
6. Signaling Circuit
6-1. Encode
■ Low-speed data (QT, DQT)
Low-speed data is output from pin 49 (LSDO) of the MCU
(IC400). The signal passes through a low-pass CR filter. The
signal is mixed with the audio signal and goes to the VCO
and TCXO (X1) modulation input after signal processing in
the DAC IC (IC300).
■ High-speed data (DTMF)
High-speed data (HSD) is output from pin 50 (HSDO) of
the MCU.
The signal passes through a low-pass CR filter. TX devia-
tion making an adjustment by MCU is applied to the DAC IC
(IC300). The signal is mixed with the audio signal and goes
to the VCO and TCXO.
6-2. Decode
■ QT/DQT
The output signal from IF IC (IC200) enters the MCU
(IC400) through IC300. IC400 determines whether the QT
or DQT matches the preset value, and controls the SPMUT
and the speaker output sounds according to the squelch re-
sults.
IC400
MCU
49
LSDO
50
HSDO
Fig. 6 Encode
7. Power Supply
There are five 5V power supplies for the MCU:
5M is always output while the power is on.
5C is a common 5V and is output when SAVE is not set
to ON.
5R is 5V for reception and output during reception.
5T is 5V for transmission and output during transmission.
5MS is 5V for the SP/MIC connector and the DAC IC
(IC300)
TK-2000
IC300
DAC
21 24
TCXO
FADJ
20
18
19
VCO
MOD
12
AF
BEEP
AMP
9