Icom IC-F1000 series, Service Manual

Page: 9 / 38

4-1
SECTION 4. CIRCUIT DESCRIPTION
• RF CIRCUITS
• 1ST IF CIRCUITS
• 2ND IF CIRCUITS
LPF
ANT
SW
D19,D27
RF
AMP
Q39
BPF
D18
D25
BPF
D31
BPF
D29
BPF
From the TX circuits
1st IF circuits
ANT
T1 T2
TX/RX
SW
D16,D17
Q37
BPF
XTAL
FI1
IF
AMP
Q33
BUFF
Q31
BUFF
Q30
HPF ** LPF*
RX VCO
To the TX circuits
From the RF circuits To the 2nd IF&demodulator circuits
46.35MHz
1st IF mixer
PLL
IC
IC15
BPF
X3
TCXO
D/A
converter
IF IC
From the 1st IF
circuits
To the RX AF circuits
IC16
15.3MHz
45.9MHz
DISC
SQIN
IC10
NOIS
• RX AF CIRCUITS
Internal speaker
External speaker
From the demodulato
circuits
AF
AMP
IC1
J2
SP1
AF
AMP
J3
1
2
LPF
IC11
VOL1 R133
AMP LPF AMP
IC10
AFON
AFO
EMPH
EXP
HPF
IC4
4-1 RECEIVE CIRCUITS
RF CIRCUIT
The RX signal from the antenna is passed through the LPF
(L29 to L31, C333, C347 to C350, C352 and C403) and
antenna SW (D19 and D27) then filtered by the 2-staged
tuned BPF (D25 and D31) to eliminate unwanted out-of-
Band signal. The filtered RX signal is amplified by the RF
AMP (Q39), and filtered by another 2-staged tuned BPF
(D18, D29, D36 to D38) to obtain a good image response,
and then applied to the 1st IF circuit.
The tuned BPFs are tuned to the RX frequency by apply-
ing adequate tuning voltages (“T1” and “T2”) to the variable
capacitors.
1ST IF CIRCUIT
The RX signal from the RF circuits is applied to the 1st IF
mixer (Q37) 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 (FI1), amplified by the
1st IF AMP (Q33), and then applied to the 2nd IF circuit.
2ND IF CIRCUIT AND DEMODULATOR
The signal from the 1st IF circuits is applied to the IF
demodulator IC (IC16) which contains the 2nd IF mixer, 2nd
IF AMP, FM detector, and so on.
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 sig-
nal.
The 2nd LO signal is generated by tripling the 15.3 MHz
reference frequency signal oscillated by the reference fre-
quency oscillator (X3).
The converted 2nd IF signal is amplified by the 2nd IF AMP,
and then demodulated by the detector circuit.
The demodulated AF signal is applied to the RX AF circuit.
RX AF CIRCUITS
The demodulated AF signal from the IF demodulator IC
(IC16, pin 14) is applied to the baseband IC (IC4).
The processed AF signal is passed through the LPF (IC11),
which attenuates frequencies 3 kHz and above, and adjust-
ed in level by the D/A converter (IC10). The level-adjusted
AF signal is then applied to the AF power AMP (IC1).
The amplified AF signal is applied to the internal or external
speaker.
*:For [EUR] and [UK] versions.
**:For except [EUR] and [UK] versions.