Table of Contents
Advertisement
4-3-4 VCO CIRCUIT (MAIN UNIT)
The VCO outputs from Q4–Q6 are buffer-amplified at the
buffer amplifiers (Q7 and Q9), and are then sent to the Tx/Rx
switch (D5 and D6). The receive LO signal is applied to the
1st mixer circuit (Q1) through a low-pass filter, and the trans-
mit signal is applied to the pre-drive amplifier (Q10). A por-
tion of the VCO output is reapplied to the PLL IC (IC2, pin 2)
via the buffer amplifier (Q8).
4-4 DSC CIRCUITS
4-4-1 DSC ENCODE CIRCUIT
(LOGIC BOARD AND MAIN UNIT)
The DSC signal created at CPU (IC1), is passed through the
buffer amplifier (Q8), and applied to the D/A convertor
(R55–R73) to convert into the analog signal. The analog sig-
nal passes through the low-pass filter (MAIN unit; IC7D),
and is then applied to the VCO circuit to modulate the DSC
signal.
4-4-2 DSC DECODE CIRCUIT
(MAIN UNIT AND LOGIC BOARD)
The AF signal from the FM IF IC (IC1, pin 9) are filtered at
the low-pass filter (Q28) to suppress unwanted higher noise
signals. The filtered signals are converted analog signals
into digital signals at the DSC decoder IC (IC6), and are then
applied to the CPU (LOGIC board; IC1, pin 18).
4-5 LOGIC CIRCUITS (LOGIC BOARD)
• CPU
IC1 is an 8 bit signal chip micro-computer and contains LCD
driver, serial I/O, timer, A/D converter, programmable I/O,
ROM and RAM.
• SYSTEM CLOCK CIRCUIT
X1 is a ceramic oscillator and ocillate 9.8304 MHz system
clock for the CPU (IC1).
• RESET CIRCUIT
IC6 is a reset IC. When turn power ON, IC6 outputs a reset
signal ("LOW" pulse) to the CPU (IC1, pin 15) via the "RES"
line.
• LOW BATTERY DETECTOR
HVS voltage is divided by R74, R75 and is applied to the low
battery detector section in the CPU (IC1, pin 91) via the
"LBAT" line.
• DIMMER CIRCUIT
CPU (IC1), Q2, Q3 and Q4 are dimmer circuit and control
the 4 steps the LCD backlight (DS3–DS8).
4-6 POWER SUPPLY CIRCUITS
LINE
The voltage from the connected DC power sup-
HV
ply.
Same voltage as the HV line which is passed
HVS
through the [PWR] switch (VR-A board; R1).
Same voltage as the HVS line. The voltage is
VCC
applied to the optional microphone (HM-127).
Common 5 V converted from the HVS line at the
5V
5V regulator circuit (MAIN unit; IC8).
Transmit 5 V controlled by the 5V control circuit
(MAIN unit; Q24, Q25) using the SEND signal
T5
from CPU (LOGIC board; IC1). The controlled
voltage is applied to the transmitter circuit.
Receive 5 V controlled by the R5 control circuit
(MAIN unit; Q22, Q23) using the RCV circuit
R5
from CPU (LOGIC board; IC1). The controlled
voltage is applied to the receiver circuit.
4 - 4
DESCRIPTION
Hide quick links:
Advertisement
Table of Contents
