Icom IC-E92D Service Manual page 11

2ND IF AND DEMODULATOR CIRCUITS
(MAIN UNIT)
<A BAND>
The 1st IF signal from the 1st IF AMP (Q100) is applied to
the IF IC (IC100). The applied 1st IF signal is mixed with
the 61.2 MHz 2nd LO signal (generated by X450, buffered
by Q450) at the internal 2nd mixer, to be converted into the
2nd IF signal. The converted 2nd IF signal is output from pin
3, then passed through the 2nd IF filter (FI100) via IF SWs
(D102, 103).
• FM MODE
The filtered 2nd IF signal is backed to the IF IC from
pin 5, and saturation-amplified by the internal limit AMP.
The amplified 2nd IF signal is FM-demodulated by the
discriminator (X100), and the recovered AF signals (RX
AF signals) are output from pin 9, then applied to the AF
circuits via the AF mute SW (IC500, pins 8, 9).
• AM MODE
The filtered 2nd IF signal is amplified by 2nd IF AMP (Q103),
then applied to the AM demodulator circuit (Q104, 105,
D105) to be recovered to the AF signals. The demodulated
AF signals are applied to the AF circuits.
• 2ND IF AND FM DEMODULATOR CIRCUITS (A BAND)
R115
R116
D102
R117
FI100
O I
C137 C136
R114
C125
D103
R113
C126
C122
R118
R119
R111
3RD IF CIRCUIT (MAIN UNIT)
(FOR A BAND, WFM MODE ONLY)
The 2nd IF signal from the 2nd IF AMP (Q100) is applied to
the IF IC.
The applied 2nd IF signal is mixed with the 15.3 MHz 3rd
LO signal (generated by X450, buffered by Q450), to be
converted into the 1.95 MHz 3rd IF signal by the internal 3rd
mixer. The converted 3rd IF signal is output from pin 3, and
passed through the IF SWs (D102, 103), then backed to the
• 2ND IF AND FM DEMODULATOR CIRCUIT (B BAND)
FI200
C236
O I
C241
0.1
D202
C216
C238
FI201
C237
O I
R227
D203
R216
C222
C225
R231
R214
C220
C116
C115
C114
R108
C113
C123
IC100
1
OSCIN MIXIN
2
OSCOUT GND
3
MIXOUT N-REC
4
VCC N-DET
5
C124
IFIN RSSI
6
DEC I FOUT
7
FILOUT QUAD
8
FILI N AFOUT
C121
C117
R112
C138
EP200
C215
C214
R210
IC200
C223 1 16
OSCIN MIXIN
2 15
OSCOUT GND
3 14
M IXOUT N -RE C
4 13
VCC N-DET
C224
5 12
IFIN R SSI
6 11
DEC IFOUT
7 10
FILOUT QUAD
8 9
FILI N AFOUT
C221
C212
R215
<B BAND>
The 1st IF signal from the 1st IF AMP (Q200) is applied to
the IF IC (IC200). The applied 1st IF signal is mixed with
45.9 MHz 2nd LO signal (generated by X450, tripled by
Q451) at the internal 2nd mixer, to be converted into the
450 kHz 2nd IF signal. The converted 2nd IF signal is output
from pin 3, then passed through one of the 2nd IF filters.
The 2nd IF signal is passed through FI200 in FM/AM mode,
and passed through FI1201 in FM-N mode.
• FM/FM-N/DV MODE
The filtered 2nd IF signal is backed to the IF IC from pin
5, then saturation-amplified by the internal limit AMP.
The amplified 2nd IF signal is FM-demodulated by the
discriminator (X200), and the recovered AF signals (RX
AF signals) are output from pin 9, then applied to the AF
circuits via the AF mute SW (IC500, pins 4, 3).
• AM MODE
The filtered 2nd IF signal is amplified by another 2nd
IF AMP (Q202), then applied to the AM demodulator
circuit (Q203, 204, D205) to be AM-demodulated. The
demodulated AF signals are applied to the AF circuits.
• AM DEMODULATOR CIRCUIT (A BAND)
C
0
131
.1
R107
16
15
14
13
144
X100 1
12
C111
11
10
9
R106
4
L101
5
C109
C112
C108
R105
IF IC (bypassing FI100). The 3rd IF signal is FM-demodulated
by the discriminator (X100), and the recovered AF signals
(RX AF signals) are output from pin 9, then applied to the AF
circuits via the AF mute SW (IC500, pins 8, 9).
• AM DEMODULATOR CIRCUIT (B BAND)
234
0.1
C213
R209
62
1
X200
R205
C206
C207
C211
5
K
C208
R206
4 - 3
100
R124
R121
47K
2nd IF AMP
R122
for AM mode
Q103
Q104
R131
C143
C130
D105
R126
C134
C133
R127
R133 R132 R125
AM demodulator
C135
100
R217
2nd IF AMP
R219
for AM mode
R221
Q202
Q203
R305
C230
C261
1
R223
D205
C232
R224
C231
R225
R234 R306
AM demodulator
C233
C127
R120
C128
R123
D104
C129
R130
C142
C227
R218
C228
R220
D204
R233
C229
C226