TK-3140
9
5. Frequency Synthesizer Unit
5-1. Frequency synthesizer
The frequency synthesizer consists of the VCXO (X1), VCO,
PLL IC(IC1) and buffer amplifiers.
The VCXO generates 16.8MHz. The frequency stability is
2.5ppm within the temperature range of -30 to +60˚C. The
frequency tuning and modulation of the VCXO are done to
apply a voltage to pin 1 of the VCXO. The output of the VCXO
is applied to pin 8 of the PLL IC.
The TK-3140’s VCO consists of 2VCO and covers a dual
range of the 405.15~445.15MHz (K), and the 450~490MHz (K).
The VCO generates 405.15~445.15MHz (K), for providing to
the first local signal in receive. The operating frequency is
generated by Q3 in transmit mode and Q2 in receive mode.
The oscillator frequency is controlled by applying the VCO
control voltage, obtained from the phase comparator (IC1) to
the variable capacitor diodes (D1, D3, D7, and D8 in transmit
mode and D2, D4, D9 and D10 in receive mode).
The T/R pin of IC312 goes “high” in receive mode causing
Q4, Q6 and Q3 to turn off, and Q2 turn on. The T/R pin goes
“low” in transmit mode.
The outputs from Q2 and Q3 are amplified by buffer amplifier
(Q5) come to the amplifiers.
The PLL IC consists of a prescaler, fractional divider,
reference divider, phase comparator, charge pump. This PLL
IC is fractional-N type synthesizer and performs in the 40.50
or 60kHz reference signal which is eighth of the channel step
(5, 6.25 or 7.5kHz). The input signal from the pins 5 and 8 of
the PLL IC is divided down to the 40, 50 or 60kHz and compared
at phase comparator. The pulsed output signal of the phase
comparator is applied to the charge pump and transformed
into DC signal in the loop filter (LPF). The DC signal is applied
to the pin 1 of the VCO and locked to keep the VCO frequency
constant.
PLL data is output from DP (pin 73). CP (pin 74) and EP
(pin 72) of the microprocessor (IC309). The data are input to
the PLL IC when the channel is changed or when transmission
is changed to reception and vice versa. A PLL lock condition is
always monitored by the pin 30 (UL) of the microprocessor.
When the PLL is unlocked, the UL goes low.
CIRCUIT DESCRIPTION
Fig. 9 PLL block diagram
T/R
(TX : Low)
T/R
VCO
CV
5
IC1
PLL
8
BUFF
BUFF
LPF
DP,CP,EP
CPU
UL
IC309
VCXO
IC302
FC
BAL
Q8
SW
D101
To
drive
amp
Q1
X1
To mixer
SW
MB
D100
18
6. Control Circuit
The control circuit consists of microprocessor (IC309) and
its peripheral circuits. It controls the TX-RX unit and transfers
data to and from the display unit. IC309 mainly performs the
following;
1) Switching between transmission and reception by PTT
signal input.
2) Reading system, group, frequency, and program data
from the memory circuit.
3) Sending frequency program data to the PLL.
4) Controlling squelch on/off by the DC voltage from the
squelch circuit.
5) Controlling the audio mute circuit by decode data input.
6) Transmitting tone and encode data.
6-1. Memory circuit
Memory circuit consists of the CPU (IC309) and a flash
memory (IC308), a flash memory has a capacity of 2M bits
that contains the transceiver control program for the CPU and
data such as transceiver channels and operating features.
This program can be easily written from an external devices.
Data. such as operating status, are programmed into the
EEPROM (IC310).
●
Flash Memory
Note : The flash memory holds data such as written with the
FPU (KPG-74D), firmware program (User mode, Test mode,
Tuning mode, etc.) This data must be rewritten when replacing
the flash memory.
●
EEPROM
Note : The EEPROM stores tuning data (Deviation, Squelch,
etc.).
Realign the transceiver after replacing the EEPROM.
Fig. 10 Memory circuit
IC309
IC308
CPU
IC310
EEPROM
FLASH
6-2. Low battery warning
The battery voltage is monitored by the microprocessor (IC309).
When the battery voltage falls below the voltage set by the Low
Battery Warning adjustment, the red LED flashes to notify the
operator that it is time to replace the battery. If the battery voltage
falls even more (NiCd, NiMH: approx. 5.8V, Li-ion: approx 6.1V),
a beep sounds and transmission is stopped.
Low battery warning
The red LED flashes during
transmission
The red LED flashes and
continuous beep sounds
while PTT pressed
Battery condition
The battery voltage is low but
the transceiver is still usable.
The battery voltage is low and
the transceiver is not usable
to make calls.
