Icom IC-E92D Service Manual page 12

RX AF CIRCUITS (LOGIC UNIT)
<A BAND>
The AF signals from the FM/AM demodulator circuits are
passed through the mode SW (M: IC500D) and one of the
AF filters (IC502 and Q501, or, Q502 only) whose audio
frequency response is set as stable for each RX mode (FM/
AM or WFM).
FM/AM-demodulated AF signals are filtered by IC502, and
FM (WFM)-demodulated AF signals are filtered by Q502.
The filtered AF signals are passed through the D/A
converter (DAC; IC600, pins 21, 22; 24, 23) for level
adjustment. The level-adjusted AF signals are entered to the
LOGIC UNIT via the RX AF mute SW (M: IC700, pins 8, 9),
and applied to the AF power AMP (IC400) to obtain audio
output power. The power-amplified AF signals are applied to
the internal speaker or output from [DATA/SP/MIC] jack.
<B BAND>
• FM MODE
The FM-demodulated AF signals from the mute SW (M:
IC500B) are passed through the mode SW (IC500A) and
AF filter (M: IC501).
• AM MODE
The AM-demodulated AF signals from the AM detector (M:
Q203, 204, D205) are directly passed through the AF filter
(M: IC501, pin 2).
• DV MODE
The FM-demodulated signals from the IF IC (M: IC200) are
passed through the tone filter (M: IC250). The filtered signals
are applied to the modem (IC501) via the tone selector (M:
IC703) and buffer (IC504B), to be converted into the DV data.
The DV data is applied to the CPU (IC1), and converted into
the AMBE signals. The AMBE signal is then applied to the
DSP CODEC IC (IC506) and decoded. The decoded AMBE
signals are converted into the analog audio signal by liner
CODEC IC (IC503). The converted AF signals are passed
through the mode SW (M: IC500A) and AF filter (M: IC501).
The filtered AF signals are passed through the D/A
converter (DAC; M: IC600, pins 13, 14; 16, 15) for level
adjustment. The level-adjusted AF signals are entered to
the LOGIC UNIT via RX AF mute SW (M: IC700C/D), and
applied to the AF power AMP (IC400) to obtain audio output
power. The power-amplified AF signals are applied to the
internal speaker or output from [DATA/SP/MIC] jack.
• RX AF CIRCUITS
LOGIC UNIT MAIN UNIT
[DATA/MIC/SP]
IC400
SP
CHASSIS
2
6
AF
AMP
AFON
POWER AMP
SP
SPSW
CONTROLLER
SW
Q402-405 Q400,401
IC503
LINEAR
CODEC
42
DSP
CODEC
IC506
97 32
CPU
IC1
20,21
72,73
11
9,10
RX AF MUTE
8
SW
IC700C/D:CD4066
LPF
IC703
IC150
TONE
TONE FILTER
SEL
11
IC250
10
7 3
TONE
FILTER
LPF
IC504B
MODEM
BUFF
11 7 6
IC501
SQUELCH CIRCUIT
The squelch circuit cuts off the AF output signals when
no RF signals are received. Detecting noise components
(approx. 30 kHz signals) in the demodulated AF signals, the
squelch circuit stops audio signals being emitted.
A portion of FM-demodulated AF signal from the IF IC
(M: IC100/IC200) is passed through the DAC (M: IC600)
for level (=threshould) adjustment. The level-adjusted AF
signals are passed through the noise filter (IC100, pins 7, 8
and R111–113, C121, 122/IC200, pins 7, 8 and R214–216,
C221, 222) to filter the noise components (approx. 30 kHz
signals) only. The noise components are rectified to produce
DC voltage corresponding to the noise level.
If the noise level is higher than the preset one, the internal
comparator set the "ANOISE"/"BNOISE" signal to the
CPU to "High", then the CPU turns the "AFON" signal
which controlls the AF power AMP (L: IC400) to "Low," to
inactivate the AF power AMP (L: IC400). At the same time,
the CPU turns the "ARMUTE"/"BRMUTE" signal which
controlls the RX AF mute SW (L: IC700) to "Low," to cut-off
the RX AF line.
NOISE SQUELCH DIAGRAM (A BAND)
To RX AF circuits
9 10
DAC
IC600
From IF IC
Noise filter
(IC100, Pin16)
NOISE SQUELCH DIAGRAM (B BAND)
To RX AF circuits
9 10
DAC
IC600
From IF IC
Noise filter
(IC200, Pin16)
IC600
IC501
2
3
AF
7
FIL 2
14 13
16
IC502
2
7
15
AF
11
FIL
D/A
22
21 Q502
AF
24
FIL
23
11
12
9
10
4 -4
7
Noise
8
AMP
Com-
Noise
parator
detector
IC100
7
Noise
8
AMP
Com-
Noise
parator
detector
IC200
<B-BAND>
FM-demodulated
IC500A
1
AF signals from IF IC (IC200)
M ODE
<B-BAND>
2
SW
FM-demodulated
AF signals from MUTE SW (IC500)
<B-BAND>
AM-demodulated
AF signals from AM demodulator (D205)
IC500D
9
8
<A-BAND>
M ODE
SW AM/FM-demodulated AF signals from
AM demodulator (D105)/mute SW (IC500)
FM-demodulated AF signals from IF IC (IC200)
Level-adjusted AF signals to IF IC (IC200)
FM-demodulated AF signals from IF IC (IC100)
Level-adjusted AF signals to IF IC (IC100)
"ANOIS"
13
"BNOIS"
13