Transmitter Circuits - Icom IC-FR3000 Service Manual

3-1-6 RECEIVER MUTE CIRCUITS (LOGIC UNIT)
• NOISE SQUELCH
The noise squelch circuit cuts out AF signals when no RF
signals are received. By detecting noise components in the
AF signals, the squelch circuit switches the AF mute switch.
Some noise components in the AF signals from the FM IF IC
(RX unit; IC2, pin 9) are passed through the SQL level con-
troller (VR unit; R2). The level controlled signals are applied
to the active filter section in the FM IF IC (RX unit; IC2, pin
8). Noise components about 10 kHz are amplified and out-
put from pin 7 (RX unit; IC2).
The filtered signals are converted to the pulse-type signals
at the noise detector section and output from pin 13 (RX
unit; IC2).
The NDET signal from the FM IF IC (RX unit; IC2) is applied
to the CPU (IC33, pin 40). The CPU analyses the noise con-
dition and controls the AF mute signal via "AFMUTE1" line
(IC40, pin 4) to the AF mute switch (IC16, pin 5).
• TONE SIGNALS
The tone squelch circuit detects AF signals and opens the
squelch only when receiving a signal containing a matching
subaudible tone (CTCSS or DTCS).
The CTCSS signal passes through a low-pass filter circuit
(IC8, pins 1, 3, 5, 7, 8, 10), and is then applied to the CTCSS
decoder IC (IC29, pin 16). The detected signal is applied to
the CPU (IC 33) via the serial signal line.
• TONE SIGNALS CIRCUITS (LOGIC UNIT)
DISC signal
from RX unit
AMP
IC9
• AF AMPLIFIER CIRCUITS (LOGIC UNIT)
MIC
From the FRONT
unit
From the REMOTE E_MOD
connector
From the telephone
TELAFO
circuit
From the ACC
E_MODE2
connector
CTCSS
AMP
LPF
IC8
IC8
DTCS
LPF
AMP
IC12
IC12
2/5TONE
LPF
IC12
DTMF DTMF
DTMF
DECODER
SW
IC30
IC31
SW-D
AMP
SW-C
AMP
SW-B
AMP
SW-A
AMP
IC13
MIC MUTE
The DTCS signal passes through a low-pass filter circuit
(IC12, pins 1, 3, 8, 10), and is then applied to the DTCS
decoder which is inside the CPU (IC33, pin 52) via the
"DTCSI" line.
The 2/5TONE signals are passes through a low-pass filter
circuit (IC12, pins 5, 7) and are then applied to the 2/5 TONE
decoder which is inside the CPU (IC33, pin 51) via "25TI"
line.
The DTMF signal is pass through the DTMF switch IC (IC30
pin 7) and is then applied to the DTMF decoder which is
inside the CPU (IC33, pins 82, 85, 86).
The DTMF switch (IC30) selects the signal from telephone
line or RX unit.

3-2 TRANSMITTER CIRCUITS

3-2-1 AF AMPLIFIER CIRCUIT (LOGIC UNIT)
• INCASE OF THE AF SIGNALS FROM THE MIC JACK
The AF signals from the MIC jack (FRONT unit; J7) are
amplified at the AF amplifier (IC1). The amplified signals are
mixed with the "E_MOD", "E_MOD2" and "TELAFO" signals
from IC1. The mixed signals pass though the high-pass filter
(IC2, pins 1, 2, 6, 7) via the pre-emphasis circuit (IC2, pins
8, 9).
The filtered signals are applied to the limiter amplifier (IC3),
and are then mixed with the DTMF signal from the CPU
(IC33, pin 43) via the TX-signal filter (IC3, pins 8, 10, 12, 14).
To the AF amplifier
CTCSS
DETECTOR
IC29
CPU; IC33
DATA BUS
PRE
HPF
MIX
EMP
IC2
RPT AF signal
AFATTO
RPT AF
from IC25
MUTE
From the REMOTE
E_MOD3
connector
25TONE
BEEP
CW
DTMF
From CPU (IC33)
3 - 2
SIG
SPLAT
LIMIT
MIX
FIL
IC4
IC3
IC3
IC14
AMP
IC26
LPF
To TX unit