4 - 3
4-2 TRANSMITTER CIRCUITS
TX AF CIRCUITS
The TX AF circuits consist of microphone amplifier (MIC
AMP) and AF fi lters. The AF fi lter cuts off the signals except
voice signals (300 Hz or lower and 3 kHz or higher).
The audio signals from the internal microphone (MIC
signals) are passed through MIC mute SW and amplifi ed by
two MIC AMPs (#1 and #2).
The MIC signals from the external microphone "EXMIC” are
applied to the FRONT UNIT via [SP MIC] jack, and amplifi ed
by MIC AMP (#2).
The amplified MIC signals "MIC” are applied to the MAIN
UNIT via J401(FRONT UNIT) and J1 (MAIN UNIT).
The MIC signals from the FRONT UNIT are applied to the
baseband IC (IC10, pin 3) and processed.
SQUELCH CIRCUITS
• NOISE SQUELCH
The noise squelch cuts off the AF output signals when
no RF signals are received. Extracting noise components
(approx. 30 kHz signals) in the demodulated AF signals,
the squelch circuit turns the AF power amplifier and AF
switches ON and OFF.
A portion of FM-demodulated AF signal from the IF IC is
adjusted its level (=squelch threshold level) by DAC (D/A
converter; IC6, pins 1, 2), then passed through the noise
filter (M: IC1, pins 7, 8 and R42, 44–46, C68–70) to extract
the noise components (approx. 30 kHz signals) only. The
noise components are rectified to be converted into the
pulse-type signal by noise detector to produce DC voltage
corresponding to the noise level "NOIS". Then the DC
voltage is applied to the CPU (IC401, pin 41) and compared
with the reference level preset in the CPU.
If the CPU interpretes that the noise level is higher than
preset one, the CPU sets the "AFON" signal to "High" to
turn the AF power AMP controller OFF, and the AF mute
SW is turned OFF simultaneously. Thus closing the squelch
is accomplished.
• TONE SQUELCH
The tone squelch connects the RX AF line and activates
the AF power amplifier to emit the AF signals only when
receiving a signal which contains the tone frequency
matched with preset in the CPU. Detecting signal in the
demodulated AF signals, the tone squelch circuit turns the
AF power amplifier and AF switches ON and OFF.
<CTCSS/DTCS>
A portion of FM-demodulated AF signals from the FM IF
IC are passed through the tone filter (M: Q6, pins 5, 6) to
remove unwanted voice siganls. The filtered tone signals
are applied to the CPU (IC401, pin 44).
<2/5 TONE, DTMF>
A portion of FM-demodulated AF signals are output from
the baseband IC (M: IC10, pin 21), and passed through
the tone filter (M: R136, C220) to remove unwanted voice
siganls. The filtered tone signals are applied to the CPU
(IC401, pin 43).
The CPU compars the tone frequency/code preset in the
CPU, and if the applied tone frequency/code is matched to
preset one, the CPU controls the AF power AMP and AF
mute SW as same as "NOISE SQUELCH."
C512
R524
C405
R522
C437
C497
Q406
Q401, Q402
C510
R525
C513
R446
C404
W401
C421
R518
R407
R408
SP401
Q415
R511
R426
R519
R405
R513
W402
C496
C502
C481
C407
R401
R428
IC403
13
12
14
R539
C426
R520
C498
IC406
1
2
3
4
5 6 7 8
MC401
C503
C482
C435
R537
R433
R541
J402
1
2
3
4
5
6
C425
R523
C401
Q413
IC407
2
3
1
C406
R402
R445
R521
R538
R517
C423
R406
R430
R434
IC407
6
5
7
R432
R535
R512
R429
IC405
1
GND1 2
NC 3
OUT1 + 4
MODE 5
SVRR 6
SELECT 7
NC 8
OUT2 + 9
NC 10
GND2
11 VCC2
12 NC
13 OUT2-
14 IN2-
15 IN2+
16 IN1+
17 IN1-
18 OUT1-
19 NC
20 VCC1
SIGNAL
AFON
VCC
BEEP
DUSE
MIC
EXMIC
SPON
AFON
BPMAX
PWON
AFO
VR UNIT
W601
1
2
3
4
MIC/AF
MUTE SW
MIC AMP
#1
MIC AMP
#2
LPF
AF POWER AMP
CONTROLLER
AF POWER AMP
AUDIO
LEVEL
ADJUST
DAC
1
2
Noise
AMP
Fc=30 kHz
Active filter
From IF IC (Pin16)
To RX AF circuits
Noise detector
Rectify
“NOIS”
NOISE SQUELCH DIAGRAM
• TX AF CIRCUITS
