Transmit Circuits; Tx Af Circuit (Control And Main Units); Tx Af Circuit; Modulation Circuits - Icom IC-2730A Service Manual

4-2 TRANSMIT CIRCUITS

TX AF CIRCUIT (CONTROL AND MAIN UNITS)

When the microphone is connected to the controller:
The AF signal from the microphone is applied to the MIC
AMP (CONTROL UNIT: IC102, pin 2), through [MIC] (CON-
TROL UNIT: J101). The amplifi ed MIC signal is applied to the
MIC line SW (MAIN UNIT: IC100, pin 1) on the MAIN UNIT,
through the control cable.
When the microphone is directly connected to the MAIN UNIT:
The AF signal from the microphone is applied to the MIC
AMP (MAIN UNIT: IC101, pin 5), through [MIC] (MAIN UNIT:
J100).
The amplifi ed MIC signal is passed through the MIC line
SW (MAIN UNIT: IC100, pins 11, 10), MIC gain SW (MAIN
UNIT: Q151 and Q152), MIC mute SW (MAIN UNIT: IC100,
pins 9, 8) and the HPF (MAIN UNIT: R774, C861 and C862),
and then adjusted in amplitude by the IDC AMP (MAIN UNIT:
IC112, pins 3, 1), and passed through the splatter fi lter (MAIN
UNIT: IC112, pins 13, 14) and LPF (MAIN UNIT: IC103,
pins 6, 7), and then applied to the D/A converter (MAIN UNIT:
IC102, pin 13).
The level-adjusted MIC signal is passed through the modula-
tion mute SW (MAIN UNIT: VHF band IC205, pins 2, 1/UHF
band IC205, pins 3, 4), and then applied to the modulation
circuit as the modulation signal.

TX AF CIRCUIT

From the
optional
IC307
unit
BTMIC
BUFF
J100
1
IC100
Q151/Q152 IC100
2
MIC
3
MIC
MUTE
IC101
GAIN
4
SW SW
SW
5
MIC
MIC 6
AMP
7
8
J6
CONTROL UNIT
1
MIC
2
3
4
5
6
J101
8V
1
MICU/D
2
EXTMIC
IC102 3
PTT
4
MICE [MIC]
5
MIC
MIC
6
AMP
GND
7
MICIN
8
IC112 IC112
IC103 IC102
HPF IDC LPF
LPF D/A
Splatter
IC104 RPT
Left band RX signal
RPT
SW
Right band RX signal
MAIN UNIT
MODULATION CIRCUITS (MAIN UNIT)
The modulation signal from the TX AF circuit is applied to the
VCO as the frequency modulation signal.
VHF BAND
The modulation signal is applied to the VHF VCO (Q211,
D203, D204, D206, D228 and D342).
The modulated VCO output signal is amplifi ed by the buffer
(Q215), passed through the LO SW (D208), amplifi ed by the
LO AMP (Q240), and then applied to the TX AMP circuit as
the TX signal, through another LO SW (D50).
UHF BAND
The modulation signal is applied to the UHF VCO (Q232,
D223, D224, D227, D229 and D236).
The modulated VCO output signal is amplifi ed by the buffer
(Q235), and then applied to the TX AMP circuit as the TX
signal.

MODULATION CIRCUITS

Q232
D236
D223
D224
D227
D229
IC205
VCOMOD
MOD
MUTE
Q211
D342
D203
D204
D206
Q215
D228
BUFF
L_VHF
LVCO
4-5
Q235
BUFF UHF TX CIRCUIT
R_UHF
Q240 D50
LO
TX/RX
VHF TX CIRCUIT
AMP
SW