Kenwood TK-2168 Service Manual page 10

TK-2168
4) Encode Signalling
(1) QT/DQT
QT,DQT data of the LSDTCXO Line is output from pin 22 of
the CPU. The signal passes through a low-pass CR filter
and goes to the TCXO(X1).
The QT,DQT data of the LSDVCO Line is output from pin
20 of the CPU. The signal passes through a low pass CR
filter, mixes with the audio signal, and goes to the VCO
modulation input. TX deviation is adjusted by the CPU.
5. Power Supply
There are 3.5V power supply for PLL circuit and five 5V
power supplies for the microprocessor: 5M,5MS,5C,5R, and
5T. 5M is always output while the power is on. 5M is always
output, but turns off when the power is turned off to prevent
malfunction of the microprocessor.
5C is a common 5V and is output when SAVE is not set to
OFF.
5R is 5V for reception and output during reception.
5T is 5V for transmission and output during transmission.
6. Control Circuit
The control circuit consists of a microprocessor (IC805) and
its peripheral circuits. It controls the TX-RX unit. IC805 mainly
performs the following:
(1) Switching between transmission and reception by the
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 the decode data input.
(6) Transmitting tone and encode data.
1) Frequency Shift Circuit
The microprocessor (IC805) operates at a clock of
7.3728MHz. This oscillator has a circuit that shifts the
frequency by BEAT SHIFT SW (Q810).
A beat sound may be able to be evaded from generation if
"Beat Shift" is set to ON when it is generated in the internal
spurious transmission modulated sound of a transceiver.
C834
Q810
Hi: OFF
LOW: ON
Fig. 10 Frequency shift circuit
10
CIRCUIT DESCRIPTION
X801
XOUT
IC805
BSHIFT
2) Memory Circuit
Memory circuit consists of the CPU (IC805) and an EEPROM
(IC804). An EEPROM has a capacity of 64k bits that contains
the transceiver control program for the CPU and data such
as transceiver channels and operating features.
IC805
CPU
Fig. 11 Memory circuit
3) Low Battery Warning
The battery voltage is checked using by the microprocessor.
The transceiver generates a warning tone when it falls below
the warning voltage shown in the table.
(1) The red LED blinks when the battery voltage falls below
the voltage (1) shown in the table during transmission.
(2) The red LED blinks when the battery voltage falls below
the voltage (2) shown in the table during transmission.
Note:
The transceiver checks the battery voltage during reception
even when, in the FPU, the Battery Warning status function
is set to "On TX" (default setting).
However, the LED does not blink during reception. During
transmission, the LED blinks to generate the warning tone
of a low battery voltage.
(3) The transceiver immediately stops transmission when
the battery voltage falls below the voltage (3) shown in
the table. A message tone beeps while the PTT switch
is released.
Battery Case Li-ion Battery Ni-Cd Battery Ni-MH Battery
(1) 6.2[V] 6.5[V]
(2) 7.6[V] 7.1[V]
(3) 5.9[V] 6.2[V]
R833
SB
Fig. 12 Low battery warning
IC804
EEPROM
6.2[V] 6.2[V]
6.8[V] 7.0[V]
5.9[V] 5.9[V]
IC805
88
CPU