TK-3501
8
CIRCUIT DESCRIPTION
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
2.5 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 446.00~446.20MHz and the 407.15~407.35MHz. The
VCO generates 407.15~407.35MHz 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 PLLEN (pin 20) of the MCU (IC400). 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 22 (PLLLD) of the
MCU. When the PLL is unlocked, the PLUL goes low.
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.
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.
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).
INV
VCO
PLL
MCU
IC400
CLOCK,PLLEN
IC1
PLLLD
8
1
5
14
RF
SW
LPF
To RX mixer
LSDO
Q6
BUFF
Q5
TCXO
X1
SW
To
TX AMP
T/R_SHIFT
(TX: Low)
D100
D200
Q1
CV
AMP
DATA,
HSDO
LSDO
IC400
MCU
IC300
DAC
AF
AMP
TCXO
50
49
19
20
FADJ
VCO
24
MOD
21
BEEP
18
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