Icom IC-7100 Service Manual Addendum page 227

3-3 LOCAL OSCILLATOR CIRCUITS (MAIN UNIT)
REFERENCE FREQUENCY OSCILLATOR CIRCUIT
The crystal oscillator (X2001) generates the 41.344 MHz ref-
erence frequency signal. This reference signal is applied to
the Local Oscillator (LO) circuits, through the buffer (Q2001
and Q2002), and used as the reference clock signal of DDS
or the 2nd LO signal.
3RD TX/RX LO CIRCUIT
The 41.344 MHz reference signal from the crystal oscillator
(X2001) is amplifi ed by the buffer (Q2001 and Q2002) and LO
AMP (IC2001), and then divided into 1/4 (10.336 MHz) by the
divider (IC2003), resulting in the 10.336 MHz reference clock
signal. The clock signal is applied to the DDS (IC2002).
Using the applied signal as the reference clock, the DDS
(IC2002) directly generates the 491 kHz 3rd TX LO signal.
The 491 kHz 3rd TX LO signal is amplifi ed by the LO AMP
(Q2003), and passed through the LPF (L2004 and C2018),
and then applied to the 3rd IF mixer (IC4502).
• LOCAL OSCILLATOR CIRCUITS
3rd mixer 2nd mixer
D4301,D4302
I C4502
2LO
3LO
124.032 MHz
419 kHz
6dB
ATT
IC2203
fc=110MHz
AM P LPF
31.125-81.125MHz
fc=83MHz
LPF
2LO
124.032MHz
3LO
419kHz
MAIN UNIT
124.5-184.5MHz
BPF
D2202 184.5-240.0MHz
6dB
X2 BPF
ATT
6dB
ATT
I C2202
fc=110MHz
BPF LPF DDS
Q2102
fc=131MHz
LO
LPF
AM P
2ND TX/RX LO CIRCUIT
The 41.344 MHz reference signal from the crystal oscillator
(X2001) is amplifi ed by the buffer (Q2001 and Q2002), and
then applied to the frequency multiplying circuit (Q2101),
which extracts the 3rd harmonic component, resulting in the
124.032 MHz 2nd LO signal.
The 124.032 MHz 2nd LO signal is passed through two HPFs
(L2103, C2105, C2108 and L2106, C2112, C2114) and split-
ter (L2104, L2105, C2110 and C2111), and then applied to
the LO AMP (Q2102).
The amplifi ed signal is applied to the 2nd IF mixer (D4301 and
D4302), through the LPF (L2109, L2110, C2119 to C2123)
and 6 dB attenuator (R4302 to R4304).
1st mixer
(VHF/UHF TX/RX and HF TX)
D3252,D3253
6dB
ATT
120-240.0MHz
BPF
IC2351
fc=180MHz
8dB
AMP
LPF
ATT
FI2151 Q2151
Q2152
2dB
SAW AM P X3
ATT
fc=120MHz
SPLITER
HPF
IC2002
fc=500kHz Q2003
LPF AM P DDS
3-8
Q3231,Q3232
3dB fc=795MHz
HF/VHF: 124.517-324.487 MHz
LPF
ATT
UHF:
1LO
124.5-154.5 MHz
BPF
"LOF1"
IC2401
154.5-184.5 MHz
AMP HPF
BPF
"LOF2"
184.5-240.0 MHz
BPF
"LOF3"
D2403 fc=160MHz
X2 HPF
240.0-272.5 MHz
BPF
fc=383MHz
"LOF4"
LPF
272.5-324.5 MHz
BPF
"LOF5"
D2752
IC2771
fc=350MHz
11dB
LPF X2 AM P
ATT
f c=130MHz
4dB
LPF
ATT
Q2101 Q2001 Q2002
f c=120MHz
HPF X3
I C2003
I C2001
1/4 AM P
524.487-594.487 MHz
fc=115 MHz IC2801
LO
HPF
AM P
6dB
ATT
6dB
ATT
5dB
ATT
5dB
ATT
6dB
ATT
3dB BPF
ATT
"LOF6"
BUFF
X2001
41.344 MHz