Kenwood TK-2180 Service Manual page 10

TK-2180
5. Frequency Synthesizer Unit
5-1. Frequency synthesizer
The frequency synthesizer consists of the TCXO (X1),
VCO, PLL IC (IC1) and buffer amplifiers.
The TCXO 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 TCXO are done to
apply a voltage to pin 1 of the TCXO. The output of the TCXO
is applied to pin 8 of the PLL IC.
The VCO consists of 2VCO and covers a dual range of the
195.85~233.85MHz and the 136~174MHz. The VCO gener-
ates 195.85~233.85MHz for providing to the first local signal
in receive. The operating frequency is generated by Q7 in
transmit mode and Q6 in receive mode. The oscillator fre-
quency is controlled by applying the VCO control voltage, ob-
tained from the phase comparator (IC1) to the variable capaci-
tor diodes (D5, D7, D10 and D11 in transmit mode and D9
and D13 in receive mode).
The T/R pin of IC502 goes "high" in receive mode causing
Q8 and Q7 to turn off, and Q6 turn on. The T/R pin goes
"low" in transmit mode.
The outputs from Q6 and Q7 are amplified by buffer ampli-
fier (Q10) and doubled by 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 10 or 12.5kHz). The input signal from the pins 8
and 5 of the PLL IC is divided down to the 10 or 12.5kHz 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 CV of the VCO and locked to keep the
VCO frequency constant.
PLL data is output from DT (pin 112), PCK (pin 82) and PLE
(pin 81) of the microprocessor (IC502). 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 80 (UL) of the micropro-
cessor. When the PLL is unlocked, the UL goes low.
T/R
T/R
VCO
(TX : Low)
CV
LPF
20
PLL
15
UL
CPU
DT,PCK,PLE
IC502
Fig. 9 PLL block diagram
10
CIRCUIT DESCRIPTION
Q13 D100
BUFF SW
Q2
SW D205
Doubler
x2
To mixer
IC1
5
VC
TCXO
8
X1
IC602
6. Control Circuit
The control circuit consists of microprocessor (IC502) and
its peripheral circuits. It controls the TX-RX unit and transfers
data to the Display unit. IC502 mainly performs the follow-
ing;
1) Switching between transmission and reception by PTT
signal input.
2) Reading system, zone, 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 (IC502) and a flash
memory (IC500). A flash memory has a capacity of 4M bits
and contains the transceiver control program for the CPU. It
also stores the data for transceiver channels and operating
parameter that are written by the FPU. This program can be
easily written from an external devices.
The EEPROM (IC504) stores the last channel data, the
scan on status, and other parameters.
■ Flash memory
Note : The flash memory stores the data that is written by
the FPU (KPG-92D), and 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.
■ Real-time clock
The clock function is based on real-time clock IC (IC503).
When the power supply is off, it is backed up by an internal
secondary lithium battery
To
drive
amp
FC
BAL
Fig. 10 Memory circuit
IC502 IC504
EEPROM
CPU
FALSH
IC500