Transmitter Circuits - Icom IC-M506 Service Manual

4-2 TRANSMIT CIRCUITS
TX AF CIRCUITS (MAIN UNIT)
The AF signal from the microphone (MIC signal) is passed
through the MIC mute SW (IC502, pins 1, 2), and then ap-
plied to the MIC AMP (IC513, pin ).
The MIC signal from the HM-195/HM-205RB is passed
through the ATT (R531 and R532), MIC mute SW (IC502B,
pins 4, 3), and then applied to the MIC AMP (IC513, pin ).
• MIC AMP CIRCUITS
IC502
MIC-IN
AF
MUTE
HM-195/HM-205RB
IC502B
HM-205B
MAIN UNIT
FRONT UNIT
TX AF CIRCUITS (MAIN UNIT)
The amplifi ed MIC signal is applied to the noise canceller IC
(IC901, pin 28).
The processed MIC signal is output from pin 36, passed
through the AF SW (IC505, pins 8, 9), and then applied to the
D/A converter (IC19, pin 22) to be adjusted in level.
The level-adjusted AF signal is output from pin 23, and
passed through the AF MUTE SW (IC882, pins 8, 9), and
then applied to the IDC AMP (IC513B, pin 6), which limits the
amplitude of MIC signal to prevent the over deviation. The
amplitude-limited signal is output from pin 7, and passed
through the LPF (IC513C, pins 10, 8), and then applied to the
modulation circuits.
• TX AF CIRCUITS
IC505D
IC901 IC19 IC882C
From the
MIC AMP circuits
AF
AF
NOISE
D/A
CANCELLER
MUTE
SW
MODULATION CIRCUITS (MAIN UNIT)
The MIC signal from the TX AF circuits is applied to the VCO
(Q3, Q4 and D2–D4). The modulation signal is applied to D2,
to obtain Frequency Modulation.
The modulated VCO output signal is passed through the buf-
fers (Q5 and Q7), and then applied to the TX AMP circuits as
a TX signal, through the LO SW (D7).
• MODULATION CIRCUITS
Q2
Q8
D1
D 3,D4 Q5
From the
TX AF circuits
VCO
SHIFT BUFF
All manuals and user guides at all-guides.com
IC513A
To the TX AF circuits
MIC
AMP
AF
ATT
MUTE
HM-195
OPTIONAL
COMMANDMIC
IC513C
IC513B
To the modulation
Pre-
circuits
IDC
LPF
emphasys
D7,D8:
Q7
To the
TX AMP circuits
TX/RX
BUFF
SW
TX AMP CIRCUITS (MAIN UNIT)
The TX signal is amplifi ed by the YGR (Q21) and power AMP
(IC1), and then passed through the TX output power detec-
tor (D12 and D13), ANT SW (D14), and LPF (L22, L23 and
C104–C106), before being sent to the antenna.
APC CIRCUITS (MAIN UNIT)
The voltage produced at the LPF (L21, C101 and C102) is
rectifi ed by D12 and D13, and is used as the TX power sens-
ing voltage.
The voltage is applied to the APC AMP (IC2, pin 3), and the
output voltage controls the gate bias voltage of power AMP
(IC1) to keep the TX output power constant.
• TX AMP CIRCUITS
Q21
From the modulation
circuits
YGR
AMP
4-3
RX circuits
ANT
D16
D14,D15
ANT
LPF
SW
IC1:
PWR
LPF
AMP