Receiver Circuits - Icom IC-F29DR Service Manual

SECTION 4.

4-1 RECEIVER CIRCUITS

RF CIRCUITS
The RX signal from the antenna is passed through the LPF
(L29, L32, L34, C191, C194, C199, C202 and C205), an-
other LPF (L30, C187 and C195) and antenna SW (D18
and D23), and then filtered by the 2-staged tuned BPF
(D17, D19, D21, D22, L26, L28, C182, C185, C186, C189
and C192) to eliminate unwanted out-of-band signals. The
fi ltered RX signal is amplifi ed by the low noise AMP (Q22),
and fi ltered by another 2-staged tuned BPF (D14, D15, L19,
L21, C140, C144, C148, C153 and C156) to obtain a good
image response, and then applied to the 1st IF circuits.
The BPFs are tuned to the RX frequency by applying ad-
equate tuning voltages ("T1" and "T2") to the variable capaci-
tance diodes.
• RF CIRCUITS
D18,23
From the TX circuit
D17,19,21,22
D14,15,42,43 Q22
BPF LNA
1ST IF CIRCUITS
The RX signal from the RF circuits is applied to the 1st IF
mixer (Q45) and mixed with the 1st LO signal from the RX
VCO, resulting in the 46.35 MHz 1st IF signal. The 1st IF sig-
nal is passed through the IF SWs (D1 to D4) and the crystal
fi lter (FI1: analog mode, FI2: digital mode) to be fi ltered, and
then applied to the 2nd IF circuits.
• 1ST IF CIRCUITS
353.65-423.65MHz
FI1
Q1,
XTAL
IC2 D1,2
DISC
IF IC A/D_SW
FI2
XTAL
CIRCUIT DESCRIPTION
ANT
ANT
LPF
SW
BPF
LPF
D3,4
BPF
Q45
46.35MHz
A/D_SW
1st_MIX
BPF
2ND IF AND DEMODULATOR CIRCUITS
The signal from the 1st IF circuits is applied to the IF IC (IC2)
which contains the 2nd IF mixer, 2nd IF AMP, FM detector,
squelch circuit and AF AMP 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, which is generated by the refer-
ence frequency oscillator (TCXO: X1).
• WHILE OPERATING IN THE ANALOG MODE
The demodulated AF signal is applied to the AF custom IC
(IC5), and amplifi ed by the AF AMP, and then applied to the lin-
ear codec. The AF signal is converted into a digital audio sig-
nal, then processed by the DSP (IC15), and then decoded
into an analog audio signal.
The AF signal is applied to the RX AF circuits.
• 2ND IF CIRCUITS
IC5 AF CUSTOM IC
AFVOL
AFO
REF
VCON
BUFF
BAL
MOD
MICI
MIC
AMP HPF
RX AF CIRCUITS
The demodulated AF signal from the linear codec is passed
through the LPF, and then adjusted in level by the D/A con-
verter.
The level-adjusted AF signal is output from the AF custom
IC (IC5), and amplifi ed by AF AMP (IC8). The amplifi ed AF
signal is amplifi ed by the AF power AMP (IC6), and then ap-
plied to the internal or external speaker.
• RX AF CIRCUITS
J4
EXT_SP
J3
INT_SP
4-1
BEEP
BUFF
BUFF
MOD
DMO
LINEAR
LPF
CODEC
ALC
MOD
TX/RX
AMP
LINE
SW
CTRL
LIMIT
AMP
Q31,32
Q35,36 D35
AF
PWR
CL
AFON
CTRL MUTE
IC6 IC8
AF
AMP AFVO
AMP
DISC
IC15
DSP
AFO