Icom ID-51E User Manual page 13

DIGITAL DEMODULATION CIRCUIT (LOGIC UNIT)
While operating in the DV mode, the demodulated signal
(digital audio signal) is passed through the LPF (R305, R336,
R339, C334 and C337) and amplifi ed by the AF AMP (IC300,
pins 2 and 1). The amplifi ed signal is passed through the LPF
(Q300 and Q302) and amplifi ed by another AF AMP (IC300,
pins 13 and 14), and then applied to the A/D converter (IC19,
pin 3) to be converted into the digital audio signal.
The digital audio signal is demodulated by the DSP (IC18,
pins M10 and L11), and then applied to the linear codec
(IC25) to be decoded into an analog audio signal.
The decoded AF signal is applied to the RX AF circuit.
RX AF CIRCUIT (LOGIC AND MAIN UNITS)
• Band A
The demodulated AF signal is passed through the mode SW
(IC390, pins 4 and 3) and AF fi lter (IC300, pins 9 and 8, 5
and 7), and then applied to the D/A converter (MAIN UNIT:
IC11, pin 18) to be adjusted in volume level.
• Band B
The demodulated AF signal is passed through the AF fi lter
(IC350, pins 2 and 1, 5 and 7) and mute SW (IC351, pins 2
and 1), and then applied to the D/A converter (MAIN UNIT:
IC11, pin 1) to be adjusted in volume level.
The level-adjusted AF signal is amplifi ed by the buffer (MAIN
UNIT: IC20, pins 3 and 4), and then applied to the AF power
AMP (MAIN UNIT: IC2, pin 1), through the ATT (MAIN UNIT:
Q20).
The amplifi ed AF signal is output to the internal speaker
(CHASSIS: SP1) or external speaker, through the [SP] jack
(MAIN UNIT: J4).
• DIGITAL DEMODULATION AND RX AF CIRCUITS
IC2 Q20
J4
VO+
AF
ATT
AMP
VO-
[SP] jack
Int. speaker
MAIN UNIT
SP1
CHASSIS UNIT
IC390
IC300,Q301
IC11
AAF
AF
MODE
FIL
SW
IC20
D/A
BUFF
BAF
Radio AF
RADIO RECEIVE CIRCUITS
• FM BAND (76–108 MHz)
The RF signal from the antenna or earphone is passed through
two LPFs (L513, L515, L516, C547, C549, C553, C555 and
C556), ANT SW (D506 and D903), RF SW (D781), ANT SW
(D782 and D783) and LPF (L781, L782, C783 to C786), and
then applied to the RF AMP (Q780).
The amplifi ed signal is applied to the radio IC (IC441, pin 2),
through the ATT (D908) and limiter (D904).
• AM BAND (0.52–1.71 MHz)
The RF signal from the antenna is passed through two LPFs
(L513, L515, L516, C547, C549, C553, C555 and C556),
ANT SW (D506 and D903), and LPF (L402, L403, C407–
C411), and then applied to the RF AMP (Q908).
The amplifi ed signal is applied to the radio IC (IC441, pin 4),
through the ATT (Q906 and Q907) and limiter (D905).
The radio IC (IC441) demodulates input signals and output to
the RX AF circuit.
• RADIO RECEIVE CIRCUITS
IC441
IC955
<- RX AF
circuit
RADIO
BUFF
IC
-Band A:FM/FM-N mode-
-Band A:DV mode-
IC19
IC18
IC25
DAFO
LINEAR
DSP A/D
CODEC
-Band A:FM/AM mode-
IC351
MUTE
SW
LOGIC UNIT
4 - 4
ANT
SW
From the TX circuit
RF
LIMIT ATT LPF
AMP
D905 Q908
Q906
Q907
RF
LIMIT ATT LPF
AMP
D904 D908 Q780
IC300 Q302,Q300 IC300
ADET
AMP LPF AMP LPF
IC350,Q350
BDET
AF
FIL
LPF LPF
- 0.52M-1.71MHz -
- 76M-108MHz -
ANT RF
SW SW
D782, D781
D783
From the
2nd IF circuit
(Band A).
From the
2nd IF circuit
(Band B).