Frequency Synthesizer; Voltage Diagram - Icom IC-2300H Service Manual Addendum

4-3 FREQUENCY SYNTHESIZER

The 2300H has two VCOs; TX VCO and RX VCO.
While transmitting, the TX VCO (Q13, D7–D9, L5) is activat-
ed. The oscillating frequency is set by the value of C89, L5,
D7 and D8. Applying the voltage to both D7 and D8, the wide
oscillating frequency range is obtained. The modulation sig-
nal is applied to D9 to obtain Frequency Modulation.
While receiving, the RX VCO (Q14, D10–D11, L6) is activat-
ed. The oscillating frequency is set by the value of C88, L6,
D10 and D11. Applying the voltage to both D10 and D11, the
wide oscillating frequency range is obtained.
Q6, Q7 and Q8 compose a power supply line SW which tog-
gles the TX and RX VCOs.
• FREQUENCY SYNTHESIZER
X1
(15.3MHz)
REF
OSC
Q1
X3 BPF
IC3
IF IC

4-4 VOLTAGE DIAGRAM

Voltage from the power supply is routed throughout the transceiver, via the regulators and switches.
R5V SW5V
R5
+5
REG REG
Q12,Q39
Q15-Q16
RXC(EXP) T8C(EXP)
RX VCO
IC1
Q14,D10-D11
PLL LOOP
IC FIL
FIN
TX VCO
Q13,D7-D9
MOD
T8V VCO8 +8V
T8 VCO +8
REG REG REG
Q5,D4
Q2-Q3
IC6
The output signal from each VCO is passed through the buf-
fer (Q17) and applied to the PLL IC (IC1).
IC1 phase-compares the output of TCXO (X1) and VCO, and
the phase-difference is output as the charge pump current.
The current is passed though the loop fi lter to be converted
into the lock voltage, which controls the oscillating frequency
of each VCO.
The output of Q17 is passed through the buffer (IC10), and
used as the TX/RX LO signal.
D12-D13
Q17 IC10
TX/RX
LO
BUFF
AMP SW
LPF
1st mixer
Q28
SWHV C5V HV
C5V
REG
IC8
HVSW
Q23-Q25
W6
PWRON(CPU)
REVERSE
& OVER
VOLTAGE
PROTECT
D19
4 - 3
TX AMPs