Icom IC-R9500 Service Manual page 12

VCO2 BOARD
VCO2 BOARD provides the 2nd LO signals for receiving
the both of VHF and UHF bands, and contains 3 VCOs
oscillating 220 MHz, 720 MHz and 837.4 MHz LO signals.
The 220MHz band VCO is a totem pole typed one with
bipolar TRs (Q4100 and Q4101). 20MHz, and 837.4MHz
band VCOs are employed tank typed resonator with FETs
(Q4201 and Q4301) to obtain good C/N capability.
DOUBLER BOARD
1st LO signals for receiving 1GHz and below frequency are
doubled by doublers on the BOUBLER BOARD.
IC-R9500 employed doubler which produces 1st LO signals
for the receiving 1.8 GHz and above, and improved the
IP3 characteristic and sensitivity, and more, destroyed the
necessary of the converter circuits.
• VCO2 LOOP
220MHz
Q4101
720MHz
Q4201
837.4MHz
Q4301
LOOP
FIL
Ref 200kHz
IC4000
PLL
Ref 500kHz
IC
DATA/CK/PST2P
Q4100
BUFF
Q4400
BUFF
Q4200
BUFF
Q4300
BUFF
L21V
L22V
L23V
IC4501
ATT
AM P
The doubler circuit is balanced type and composed by
bipolar transistors (Q2200, Q2201). The employment of
transistors improved lower conversion loss than by diodes,
and the same capability of attenuating odd numbered
harmonics as by diodes.
FIL1 BOARD
Fil1 board doubles and fi lters the 1st LO signals for recieving
VHF and UHF bands. To suppress the directly oscillated
frequency (Fosc×1) MHz and harmonics (Fosc×N) MHz,
three staged fi lters are used.
FIL2 BOARD
Fil2 board doubles and fi lters 2nd LO signals. By expanding
the pass band width of the BPF, the BPF commonly used
for the 1st LO signals genarated by 220MHz, 720MHz and
837.4MHz VCOs. MMIC (IC4450) is inserted in front of the
fi lter to make up the 1st LO signal level.
ATT
VCO2
BOARD
ATT
3 - 4
LPF
6dB
HYB
LPF
2nd LO signals
to FIL2 BOARD