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4 - 3
4-2-5 APC CIRCUIT (MAIN UNIT)
The APC circuit stabilizes transmit output power.
The RF output signal from the power amplifier (IC4) is
detected at the power detector circuit (D21, D22, L31) and
is then applied to one of the differential amplifier inputs
(Q21, pin 3) via the High/Low control circuit (Q22, R135).
The applied voltage controls the differential amplifier output
(Q21, pin 1) and the bias voltage control (Q23). Thus the
APC circuit maintains a constant output power.
4-3 PLL CIRCUITS
4-3-1 GENERAL (MAIN UNIT)
The PLL circuit provides stable oscillation of the transmit fre-
quency and receive 1st LO frequency. The PLL circuit com-
pares the phase of the divided VCO frequency to the refer-
ence frequency. The PLL output frequency is controlled by a
crystal oscillator and the divided ratio of the programmable
divider.
IC8 on the MAIN unit is a dual PLL IC which controls both
VCO circuits for Tx and Rx, and contains a prescaler, pro-
grammable counter, programmable divider, phase detector,
charge pump, etc.
The PLL circuit , using a one chip PLL IC (MAIN unit; IC8),
directly generates the transmit frequency and receive 1st IF
frequency with VCOs. The PLL sets the divided ratio based
on serial data from the CPU on the LOGIC BOARD and
compares the phases of VCO signals with the reference
oscillator frequency. The PLL IC detects the out-of-step
phase and output from pins 8 for Tx and Rx. The reference
frequency (21.25 MHz) is oscillated at X2 (MAIN unit).
4-3-2 TX AND RX LOOP (MAIN UNIT)
The generated signal at the VCO (Q13, Q14, D11–D14)
enters the PLL IC (IC8, pin 2) and is divided at the pro-
grammable divider section and is then applied to the phase
detector section.
The phase detector compares the input signal with a refer-
ence frequency, and then outputs the out-of-phase signal
(pulse-type signal) from pin 8.
The pulse-type signal is converted into DC voltage (lock
voltage) at the loop filter (R211–R213, C252, C254), and is
then applied to varactor diodes (D13, D14) of the VCO to
stabilize the oscillated frequency.
T5
D21
D22
L31
"TMUTE" signal from the CPU
(LOGIC board; IC1, pin 51)
HV
5V
1
2
3
4
H/L
"TXDET" signal to the CPU
(LOGIC board; IC1, pin 2)
Q23
Q21
Q20
Q22
C177
R139
R138
Q18
YGR
amp.
RF signal
from PLL
to the antenna
RF detector
circuit
APC control circuit
Power module
IC4
R133
R136
R135
Shift register
Prescaler
Phase
detector
Loop
filter
Programmable
counter
Programmable
divider
X2
21.25 MHz
21.25 MHz signal to the
FM IF IC (IC1, pin 2)
VCO
Buffer
Buffer
Buffer
Q16
Q26
Q15
3
4
5
PSTB
IC8 (PLL IC)
PCK
PDATA
to transmitter circuit
to 1st mixer circuit
D17
D16
17
16
8
2
Q13, Q14, D11 D14
• APC CIRCUIT
• PLL CIRCUIT
Summary of Contents for IC-M302
Page 1: ...SERVICE MANUAL VHF MARINE TRANSCEIVER M302 ...
Page 29: ... BOTTOM VIEW DS4 DS5 DS7 DS6 DS2 DS3 9 4 ...
Page 30: ...J 1 R 1 1 5 HVS VOL1 VOL2 GND HV J1 to the MAIN unit W1 9 3 VR BOARD TOP VIEW BOTTOM VIEW 9 5 ...
Page 31: ...J 1 R 1 1 3 SQLI SQLV GND J1 to the MAIN unit W1 9 4 SQL BOARD TOP VIEW BOTTOM VIEW 9 6 ...
Page 32: ...9 7 R1 R3 R2 S2 S3 S4 R4 9 5 HM 141 TOP VIEW ...
Page 33: ...9 8 BOTTOM VIEW C1 S1 ...
Page 40: ......
Page 41: ...1 1 32 Kamiminami Hirano ku Osaka 547 0003 Japan S 14011IZ C1 2003 Icom Inc ...