Icom IC-FR3000 manual Transmitter Circuits, Receiver Mute Circuits Logic Unit, MIC Mute

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).

nal is applied to the CPU (IC 33) via the serial signal line.

The DTCS signal passes through a low-pass filter circuit (IC12, pins 1, 3, 8, 10), and is then applied to the signal amplifier (IC12, pins 12, 14). the amplified signal is 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(IC31). The decoded signal is applied to the CPU (IC33, pins 82, 85, 86). The CPU analyzes the DTMF signal.

The DTMF switch (IC30) selects the signal from telephone line or RX unit.

• 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 signal amplifier (IC8, pins 13, 14). The amplified signal is applied to the CTCSS decoder IC (IC29, pin 16) and the detected sig-

3-2 TRANSMITTER CIRCUITS

3-2-1 AF AMPLIFIER CIRCUIT (LOGIC UNIT)

•IN CASE 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_MOD1”, “E_MOD2” and “TELAFO” sig- nals at IC2. The mixed signals pass though the high-pass fil- ter (IC2, pins 1, 2, 6, 7) via the pre-emphasis circuit (IC2, pins 8, 9).

•TONE SIGNALS CIRCUITS (LOGIC UNIT)

DISC signal from RX unit

AMP

IC9

CTCSS

LPF AMP

CTCSS

DETECTOR

BUS

To the AF amplifier

IC29

DTCS

IC8 IC8

LPF AMP

DATA

DTCSI

CPU; IC33

IC12 IC12

2/5TONE	LPF
	25TI
	IC12

DTMF DTMF

SW

IC30

DTMF

DECODER

IC31

DATA BUS

•AF AMPLIFIER CIRCUITS (LOGIC UNIT)

From the FRONT

MIC

AMP

SW-D

unit

MIX

PRE

HPF

LIMIT

SIG

SPLAT To TX unit

EMP

MIX

FIL

From the REMOTE

E_MOD

SW-C

AMP

IC2

IC3

IC3

IC4

connector

From the telephone

TELAFO

RPT AF signal AFATTO RPT AF

circuit

AMP

SW-B

from IC25

MUTE IC14

From the ACC

E_MODE2 AMP

From the REMOTE

E_MOD3

AMP

connector

SW-A

connector

IC26

25TONE

BEEP

LPF

IC13

CW

MIC MUTE

DTMF

From CPU (IC33)

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