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• FREQUENCY SYNTHESIZER
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.
LPF
TX/RX
SW
BUFF
LO
AMP
FIL
LOOP
PLL
IC
X3
BPF
D12-D13
TX AMPs
1st mixer
IC10
Q17
Q14,D10-D11
Q13,D7-D9
REF
OSC
X1
IC1
IF IC
MOD
TX VCO
RX VCO
Q28
(15.3MHz)
IC3
FIN
Q1
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.
4-4 VOLTAGE DIAGRAM
Voltage from the power supply is routed throughout the transceiver, via the regulators and switches.
+5
REG
+8
REG
W6
T8
REG
HVSW
C5V
REG
C5V
+8V
SW5V
SWHV
Q23-Q25
IC8
IC6
Q15-Q16
T8V
R5V
R5
REG
HV
Q2-Q3
Q12,Q39
PROTECT
REVERSE
& OVER
VOLTAGE
D19
PWRON(CPU)
VCO
REG
VCO8
T8C(EXP)
Q5,D4
RXC(EXP)
