1St Vco Unit; 2Nd Vco Unit - Icom IC-RX7 Service Manual Addendum

to the RF AMP and IF AMP for AGC operation. The
demodulated AF signals are entered to the LOGIC UNIT via
AF SW (IC9).
REFERENCE FREQUENCY CIRCUIT
The reference frequency for both of 1st and 2nd VCO UNITs
is generated by the reference frequency oscillator TCXO
(X1).
The reference frequency signal is used as the 3rd LO signal
too.
• INTERMEDIATE FREQUENCIES (IF)
WFM
1st IF Frequency
2nd IF Frequency 20.75 MHz
3rd IF Frequency 1.55 MHz

4-2 1st VCO UNIT

The 1st VCO UNIT has 4 VCOs and each VCO oscillates 1st
LO signals for each band (SW, BC, VHF, UHF, 800 MHz and
1 GHz).
• Loop Filter
IC3 is a PLL IC, and the resulting signal of phase-comparison
is DC converted by the loop fi lter; active-fi lter (Q6, Q7, R24,
C38, C39) and passive fi lter (R35, C48), then the voltage (Lock
voltage) controls the oscillation frequency of VCOs.
• OSC AMP
Q12 is a OSC AMP, and amplifi es the OSC signals from the
MAIN UNIT, then the OSC signals are applied to IC3.
• 1VCO
1 VCO is the oscillator composed by Q1, D1, D2, L3, C3,
C4, and oscillates the 1st LO signals for receiving 510–741.5
MHz .
• 2VCO
2 VCO is the oscillator composed by Q2, D3, L6, C11, C16,
and oscillates the 1st LO signals for receiving 283–510 MHz
and 1130–1300MHz.
• 3VCO
3 VCO is the oscillator composed by Q3, D4, L9, C20, and
oscillates the 1st LO signals for receiving 83.5–283 MHz and
950–1130MHz.
• 4VCO
4VCO is the oscillator composed by Q4, D5, L12, C27, C28,
and oscillates the 1st LO signals for receiving 0.15–83.5
MHz and 741.5–950MHz.
• BUFFER AMP
The each VCO output signals are passed through the LO SW
(D7–10) and amplifi ed by the buffer AMP (IC2), then applied
to the both of PLL IC (IC3, via Q8) and MAIN UNIT as the 1st
LO signals.
• VCO OSCILLATION FREQUENCY
OSCILLATION FREQUENCY
VCO1 939.1000–1170.1495 MHz
712.1000–939.0999 MHz
VCO2
700.9000–875.8999 MHz
512.6000–712.0995 MHz
VCO3
525.9000–700.8999 MHz
429.25–512.5999 MHZ
VCO4
311.9500–520.8999 MHz
FM AM
429.1 MHz
19.65 MHz
450 kHz
RX FREQUENCY
510–741.0499 MHz
283–509.9999 MHz
1130–1304.9999 MHz
83.5–282.9999 MHz
950–1129.9999 MHz
0.15–83.4999 MHz
741.05–949.9999 MHz

4-3 2nd VCO UNIT

The 2nd VCO UNIT oscillates the 2nd LO signals. The VCO
oscillates 409.4500/448.7500 MHz signal in FM/AM mode,
and oscillates 408.3500/449.8500 MHz signal in WFM mode .
• VCO
The oscillator is composed by Q1, D1, C2–5, L1.
The VCO output signals are passed through the LPF that
composed by L3, C8, C9 and C10, and then applied to IC1
and MAIN UNIT as the 2nd LO signals.
• OSC AMP
Q3 is the OSC AMP and amplifi es the reference frequency
signal from the MAIN UNIT, then the reference signal is
applied to PLL IC (IC1).
• Loop Filter
The pulse-type signal from the PLL IC is DC-converted by
the loop fi lter (the lug lead fi lter) which is composed by C21,
R15 and R22, C1, to control the oscillating frequency of the
VCO.
• Ripple Filter
The ripple filter is composed by Q4, C32 and R21, and
removes ripples contained in the voltage line for regulated
voltage for the VCO.
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