4-1-6 AF CIRCUITS (LOGIC UNIT)
The demodulated AF signals from the demodulator circuits are
amplifi ed and fi ltered in the AF circuits.
In FM mode, the demodulated AF signals from the
demodulator circuits are passed through the AF select
switch (IC4, pins 1, 7) and BPF (IC27, pins 1, 3 and 5, 7),
then applied to the AF amplifi er (Q18).
In other than FM mode, the demodulated AF signals from
the demodulator circuits are passed through the AF select
switch (MAIN-A/B; UNIT ;IC27, pins 8, 9; WFM, pins 3, 4;
AM, pins 1, 2; SSB), then applied to the AF amplifi er (Q18).
The amplified AF signal are applied to the electric volume
(IC17, pins 6, 7) for level adjustment. The level adjusted
AF signals are passed through the speaker mute switch
(Q12) and applied to the AF power amplifier (IC12, pin 1).
The power-amplified AF signals are applied to the internal
speaker via J1 (J6) or an external speaker/ear phone via the
phone switch (S1), attenuator (R19, R20) and J1 (J6).
In the USB (Universal Serial Bus) audio output mode, the AF
signals from the AF amplifi er (Q18) are applied to another AF
amplifi er (Q15). The amplifi ed AF signals are passed through
the USB audio selector (IC2038, pins 1, 3), then applied
to the USB audio IC (IC16, pin 12) then converted into the
USB audio data. The converted audio data is applied to the
connected PC via the USB HUB (IC32, pins 5, 6 and 2, 3).
4-1-7 SQUELCH CIRCUIT
• NOISE SQUELCH (MAIN-A/B UNITS)
The noise squelch mutes the AF output signals when no RF
signals are received. By detecting noise components in the
demodulated AF signals, the squelch circuit toggles the AF
power amplifi er ON and OFF.
A portion of the demodulated signals from the IF IC (IC24,
pin 9) are applied to the D/A converter (IC8, pin 1) for level
adjustment. The level-adjusted AF signals are output from
pin 2, and passed through the noise filter (R421, R417,
C520, C523). The fi ltered noise signals are then applied to
the noise amplifier (IC24, pins 7, 8) to be amplified noise
components only.
The amplified noise components are converted into the
4 - 3
16
+5V
X2
Q73
11
10
IF IC (IC24)
9
2
1
13
12
“NOISE” signal to the CPU (IC18, pin 16)
2nd IF signal from the 2nd IF circuits
“RSSI” signal to theAGC amplifier (Q67)
2
8
7
3
5
BPF
RSSI
Noise
Detector
Noise
Amp.
Limit’r
Amp.
Quodrature
Detector
3rd IF signal to the AM demodulator circuits
D/A converter
IC8
FM-demodulated signals
to the AF circuits
X2
TCXO
D68
D72
FI7
BPF
D93
D95
FI8
BPF
D69
D73
FI9
BPF
D94
D96
10.25 MHz
3rd LO signal
Q80
Q71
REF
amp.
REF
amp.
3rd IF amp.
Q62
<3rd IF AND DEMODULATOR CIRCUITS (FM)>
2
X3
11
12
IF IC (IC16)
9
17
2nd IF signal from the 2nd IF circuits
“RSSI” signal to the NB circuits
RSSI
Limit’r
Amp.
Limit’r
Amp.
Limit’r
Amp.
Quodrature
Detector
FM-demodulated signals
to the AF circuits
<2nd IF AND DEMODULATOR CIRCUITS (WFM)>
• AF CIRCUITS
IC27
IC17
Ele. VR
6
7
1
4
AF
selector
USB
audio
Q18
8
3
4
9
AF
Amp.
Q15
IC16
IC32
D+
1
2
6
5
2
3
12
D–
D+
USB connector
(J2)
To the PC
D–
AF
Amp.
Power
Amp.
IC12
Speaker (CHASSIS; SP1)
(CHASSIS; J6)
IC27
IC4
9
FM
IF IC
(IC24)
USB
HUB
1
2
Q12, D8
SP
mute sw.
AF
selector
7
1
5
1
7
3
8
WFM
IF IC
(IC16)
AM
AF mixer (IC23)*
MAIN-A/B UNIT LOGIC UNIT
AM demodulator
(D75)
SSB
From the BFO
BPF
Phone switch (S1)
ATT
*MAIN-A UNIT only
