Circuit Description; Receiver Circuits - Icom IC-F3001 Service Manual

SECTION 4.

4-1 RECEIVER CIRCUITS

RF CIRCUITS
The RX signal from the antenna is passed through the LPF
and antenna SW, then filtered by the 2-staged tuned BPF
to eliminate unwanted out-of-band signal. The filtered RX
signal is amplified by the RF AMP, and filtered by another
2-staged tuned BPF to obtain a good image response, then
applied to the 1st IF circuits.
The tuned BPFs are tuned to the RX frequency by applying
adequate tuning voltages; "T1" and "T2" to the variable
capacitors.
• RF CIRCUITS
From the TX circuits
D28
Q22
To the 1st IF circuits
RF
BPF
AMP
T2
1ST IF CIRCUITS
The RX signal from the RF circuits is applied to the 1st IF
mixer and mixed with the 1st LO signal from the RX VCO,
resulting in the 46.35 MHz 1st IF signal. The 1st IF signal is
filtered by the crystal filter, amplified by the 1st IF AMP, then
applied to the 2nd IF circuits.
• 1ST IF CIRCUITS
Q10
RX VCO
BUFF
Q24
To the 2nd IF&demodulator circuits
IF
AMP

CIRCUIT DESCRIPTION

ANT
D1,D22
ANT
LPF
SW
D24,D26
BPF
T1
D5,D6
Q8
LO
To the TX circuits
BUFF
SW
ATT
FI1
Q23
46.35MHz
From the RF circuits
XTAL
BPF
1st IF mixer
2ND IF CIRCUITS AND DEMODULATOR
The signal from the 1st IF circuits is applied to the IF
demodulator IC which contains the 2nd IF mixer, 2nd IF
AMP, FM detector, etc. in its package.
The 1st IF signal is applied to the 2nd IF mixer and mixed
with the 2nd LO signal resulting in the 450 kHz 2nd IF
signal.
The 2nd LO signal is generated by tripling the 15.3 MHz
reference frequency signal oscillated by the reference
frequency oscillator (TCXO).
The converted 2nd IF signal is filtered by the crystal filter/
filters to eliminate unwanted signal, and amplified by the
2nd IF AMP, then demodulated by the detector circuit which
employs a discriminator as the phase shifter.
The demodulated AF signal is applied to the RX AF circuits.
• 2ND IF CIRCUITS
X2
15.3MHz
TCXO
Q26
PLL IC2
X3 MB15A02
IC
45.9MHz
BPF
D/A
D31,D32
converter
W/N
SQIN
450kHz
DISC
CERAMIC
BPF
IC57
R2A20178
To the RX AF circuits
4 - 1
IF IC
I C3:NJM2591
FI2
450kHz
CERAMIC
X1
BPF
SW
FI3 Discriminator
W/N
Q27,
SW
D33,D34
NOIS
NWC
From the 1st IF
circuits