Circuit Description; Rf Circuits - Icom IC-2300H Service Manual Addendum

SECTION 4.

4-1 RF CIRCUITS

The RX signal from the antenna is passed through the LPF
(L36, L39, L41, L42, C291, C295, C296, C298, C300, C303,
C304, C306, C307), antenna SW (D29–D32) and tuned BPF
(D23, L34, C279), and then applied to the RF AMP (Q32).
The amplifi ed RX signal is passed through a two-staged
tuned BPF (D22, D34, L27, L28, C213, C224, C227, C236,
C238, C242, C249), and then applied to the 1st IF circuits.
• RF CIRCUITS
MAIN UNIT
D22,D34
Q32
<- 1st IF circuits
RF
BPF
AMP
1ST IF CIRCUITS
The RX signal from the RF circuits is applied to the 1st mixer
(Q28), to be mixed with the 1st LO signal from the RX VCO
(Q14, D10–D11, L6), resulting in the 46.35 MHz 1st IF sig-
nal. The 1st IF signal is passed through the 1st IF fi lter (FI3)
to remove unwanted signals, and then applied to the 1st IF
AMP (Q27). The amplifi ed 1st IF signal is applied to the 2nd
IF circuits.
• 1ST IF CIRCUITS
MAIN UNIT
Q27
<- 2nd IF circuits
IF
AMP

CIRCUIT DESCRIPTION

D24-D25
D29-D32
ANT
TX circuits LPF
SW
D23 D26 D28
BPF ATT
LIMIT
Rx;136.000-174.000MHz
LPF
D17
46.35MHz
RF circuits <-
XTAL
LIMIT
BPF
Q28
FI3
2ND IF CIRCUITS
The 1st IF signal from the 1st IF circuits is applied to the IF
IC (IC3).
The IF IC contains the 2nd mixer, 2nd IF AMP, detector, and
so on, in its package.
The 1st IF signal is mixed with the 2nd LO signal at the in-
ternal 2nd mixer, resulting in the 455 kHz 2nd IF signal. The
2nd IF signal is passed through the 2nd IF fi lter (FI1: for wide
mode, FI2: for narrow mode) to remove sideband noise, and
then applied to the internal 2nd IF AMP. The amplifi ed 2nd IF
ANTENNA
signal is applied to the quadrature detector circuit for frequen-
cy-demodulation.
The demodulated AF signal is output from the IF IC (pin 9),
and then applied to the RX AF circuits on the LOGIC UNIT.
• 2ND IF CIRCUITS
<- RX AF circuits
DETO
4 - 1
X1 Q1
REF
X3 BPF
OSC
IC3 2nd IF circuits <-
IF IC
Q4,D1-D2,D5-D6
X2
W/N
SW
MAIN UNIT
CERAMIC CERAMIC
BPF BPF
FI2
FI1