TH-D72A/D72E
10
Figure 6-1 Reception AF circuit
DC
SW
DC
SW
De-
emphasis
AF
SW
Q711
Q709
IC720
SQA
SQB
SMA
SMB
AF
SW
Q703
J701 (2/2)
Q702
Q728
IC733
IC732
IC728
TNC
ASIC
TNC
MCU
IC727
EXT.
SP
INT.
SP
Q729
1200 R-data
SAVE2
BEEP
SPM
AFM
DTMF
IC737
Main
MCU
WXCTIN_A
IC722
(B/4,C/4,D/4)
WXCTIN_B
Q718
Q717,Q715
E-
Volume
PKD_BND
SW IC
IC721
DET_A
DET_B
IC734
AF VOL
9600 R-data
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
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.
Figure 6-2 Transmission AF circuit
Pre-emphasis
IDC/SPL
AF
SW
AF
SW
Q714
Q716
MIC
AGC
J701 (1/2)
IC728
TNC
ASIC
TNC
MCU
IC727
EXT.
MIC
INT.
MIC
1200 T-D data
DTMF
TONE
MICM
VOX_IN
IC716
IC737
Main
MCU
E-
Volume
IC721
MOD
TCXO
REF_A
REF_B
MOD
REF_A
TC & REF_B
IC712
IC714
B/2
IC714
A/2
Q712,Q713
D725,D726
DET
D716
SW
IC735
9600 T-D data
CIRCUIT DESCRIPTION