Kenwood TH-D74E Service Manual page 12

+B
(From TXRX PCB)
47C
(From TXRX PCB)
40C
(From TXRX PCB)
2.1.7 AF signal system
2.1.7.1 Reception AF circuit
Demodulation signal circuit
Reception AF signals demodulated by the respective IF ICs (IC281 and IC284) for the A-band and B-band are independently applied
to the main MPU/DSP (IC702) through the CODEC IC (IC707). Each signal is deemphasized under loudness control. Then the signals
pass through the CODEC IC (IC707), enter to the AF amplifier (IC880) for the last amplification of the signals, pass through the SP
MUTE switches (Q881 and Q883), and drive the SP.
Furthermore, the transceiver can save its power consumption in save mode by turning OFF the AVR (IC882) for the AF amplifier
(IC880) according to an AFM control signal from the main MPU (IC702).
Tone decode circuit
Reception AF signals for the A-band and B-band will be independently applied to the MPU/DSP (IC702) if the CTCSS, DCS, and
Weather Alert function are ON, and selected signal components will be amplified to a necessary level for decoding processing.
BEEP, DTMF circuit
The BEEP and DTMF signals generated from the main MPU/DSP (IC702) are applied to the AF Amplifier (IC880), and the signals
pass through the SP MUTE switches (Q881 and Q883) and drive the SP.
When the BEEP and DTMF signals are sent, the AF MUTE switch in the main MPU/DSP (IC702) will cause a MUTE-ON state, and
the signals will be sent separately from the reception AF signal.
Squelch circuit
The amount of noise (SQA and SQB) and the signal strength (SMA and SMB) obtained from the respective IF ICs (IC281 and IC284)
are retrieved by the main MPU/DSP (IC702) to control the AF MUTE switch.
1-12 (No.RA044<Rev.001>)
3.3V_AVR
IC714
1.8V_AVR
IC708
/33ADS
3.3V_AVR
IC712
1.8V_DCDC
IC718
IC724
IC722 1.2V_DCDC
3.0V_AVR
IC713
IC700 3.3V_AVR
33SDS
IC933 3.0V_AVR
GPS_ANT
_SW
IC932 3.3V_AVR
1.8V_AVR
IC931
Fig.9 Power supply circuit (CONT PCB)
40C
IC717
33AD
RAD
Q704
33M
MODBS
18M Q884
LOAD SW
18F
MICBS
Q886
12M
DACS
30M
33SD
30GPS
33BT
18BT
IC882 6.8V_AVR
AFBS
IC731 6.8V_AVR
For LEDs
LAMPS
31BU
3.1V_AVR
IC723 1.2V_AVR
CN703 BUTTON BATT
SW
MODAMP
SW
SW
AFB
6.8V
12BU
MICB
DAC