Kenwood TH-D72A Service Manual page 10

TH-D72A/D72E
J701 (2/2)
EXT.
SP
INT.
SP
IC727
TNC
MCU
IC728
TNC
ASIC
7-2. Transmission AF circuit
■ Modulation signal circuit
The transmission AF signal from the microphone is am-
plified by the MIC amplifier (IC712) that accompanies the
AGC amplifi er (IC714), and passes the MIC MUTE switch
(Q714) controlled with the Main MCU (IC737), and is input
to E-volume (IC721) through the Pre-emphasis circuit (IC716)
composed of the IDC and splatter-filter. The transmission
AF signal that the level is adjusted here is input to VCO B as
high-speed modulation signal (MOD).
The Tone and DTMF signals made from the Main MCU
(IC737) are mixed with the transmission AF signal and input
to E-volume (IC721) through the the pre-emphasis circuit
(IC716). Similarly, the 1200bps Packet-T Data made from
J701 (1/2)
EXT.
MIC
INT.
MIC
IC727
TNC
MCU
IC728
IC735
TNC
ASIC
SW
10
CIRCUIT DESCRIPTION
Q703
IC734
AF
SW
Q702
DC
SW
IC732 IC733
Q728
1200 R-data
9600 R-data
Q729
Figure 6-1 Reception AF circuit
IC712
MIC
Q712,Q713 IC714
D725,D726 B/2
AGC
IC714
D716
A/2
DET
1200 T-D data
9600 T-D data
Figure 6-2 Transmission AF circuit
Q718
Q711 Q717,Q715
AF VOL
De-
AF
emphasis
SW
SPM
AFM
DC
Q709
SW
WXCTIN_A
BEEP
IC737
SAVE2
DTMF WXCTIN_B
Main
MCU
the TNC ASIC (IC728) is mixed with the transmission AF
signal and is input to E-volume (IC721) through the pre-
emphasis circuit (IC716). On the other hand, the 9600bps
Packet-T Data made from the TNC ASIC (IC728) does not
pass through the pre-emphasis circuit but is input directly to
E-volume (IC721). The transmission AF signal that the level
is adjusted here is input to the TCXO (X511) as a low-speed
modulation signal (TC).
■ VOX circuit
The transmission AF signal is amplifi ed by the VOX am-
plifi er (IC714), and detected with the DC-detector (D716). As
a result, the obtained DC voltage is input to the Main MCU
(IC737), and observes the level of the audio signal.
Q714
IC716
AF Pre-emphasis
SW
IDC/SPL
MICM
TONE
IC737
DTMF
Main
MCU
VOX_IN
AF
Q716
SW
IC721
DET_A
E-
Volume
DET_B
IC722
(B/4,C/4,D/4)
PKD_BND
SW IC
IC720
SQA
SQB
SMA
SMB
IC721
MOD
MOD
TCXO
E-
Volume
REF_A
REF_A
REF_B
TC & REF_B