Circuit Description; Receive Circuits; Rf Circuit; 2Nd If Circuit And Demodulator - Icom IC-F1000 Service Manual

SECTION 4.

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.
• RF CIRCUITS
From the TX circuits
D18 D29
Q39
1st IF circuits
RF
BPF
BPF AMP
T2
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.
• 1ST IF CIRCUITS
Q30
RX VCO
BUFF
Q33
To the 2nd IF&demodulator circuits
IF
AMP
*:For [EUR] and [UK] versions.
**:For except [EUR] and [UK] versions.

CIRCUIT DESCRIPTION

ANT
D19,D27
ANT
LPF
SW
D25 D31
BPF BPF
T1
D16,D17
Q31
TX/RX
To the TX circuits
BUFF
SW
HPF**
LPF*
FI1
Q37
46.35MHz
From the RF circuits
XTAL
BPF
1st IF mixer

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.
• 2ND IF CIRCUITS
X3
15.3MHz
TCXO
IC15
PLL
IC
45.9MHz
BPF
IC10
SQIN
DISC
D/A
converter
To the RX AF circuits
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.
• RX AF CIRCUITS
EXP EMPH
AMP
LPF
IC10
IC11
4-1
IF IC
From the 1st IF
IC16
NOIS
IC4
HPF
LPF AMP
IC1
AFO AF
AMP
AF
AMP
AFON
circuits
From the demodulato
circuits
External speaker
J2
J3
1
2
SP1
Internal speaker