Transmitter Circuits - Icom IC-F6012 Service Manual

5-2 TRANSMITTER CIRCUITS

MIC AMPLIFIER (FRONT UNIT)
Audio signal from the connected microphone is applied to
the MIC AMP (IC5), through the microphone connector (J1).
The amplifi ed MIC signal is applied to the MAIN-A/-B UNIT.
TX AF CIRCUITS (MAIN-A/-B UNIT)
The MIC signal from the FRONT UNIT is passed through
the D/A converter (as a MIC gain controller; IC18) for level
adjustment, and applied to the limiter AMP which is also
rolled to the pre-emphasis circuit (IC16).
• TX AF CIRCUITS
To the Reference
frequency oscillator
MCOT
D/A
IC16
MCGO
AMP
IC18
BAL
CD4066
VRAF
MODI
MIC MUTE SWITCH (MAIN-A/-B UNIT)
The pre-emphasized MIC signal is passed through the MIC
mute SW (IC14).
While receiving or transmitting DTMF, 2/5 tone and BIIS
signals, the MIC mute SW (IC14) cuts the MIC line off, and
is controlled by "MMUT" signal from the expander (IC17).
SPLATTER FILTER (MAIN-A/-B UNIT)
The MIC signal from the MIC mute SW (IC14) is applied to
the splatter fi lter (IC16).
The splatter filter (IC16) is also used as the AF Summing
AMP for tone signal modulation (CTCSS, 2/5 TONE).
MODULATION CIRCUIT (MAIN-A/-B UNIT)
MIC signal from the splatter filter (IC16) is level-adjusted
(=deviation adjustment) by the D/A converter (IC18), and
applied to the TX VCO (Q13, D16, D18), through the
modulation mute SW (IC14) as the modulation signal.
The MIC signal is also applied to the reference frequency
oscillator (X2) as the modulation signal, through D/A
converter (IC18) and REF AMP (IC19).
• MODULATION CIRCUITS
X2 IC4
CR-794
IC19 MB15A02
BAL
REF
REF PLL LOOP LV
AMP
OSC IC FIL
15.3 MHz
D18
From the D/A converter
From the MIC line SW
MIC
IC16
TONE
SPIN
MIC
Splat.
CDTS
line
SW
IC14
MOD
TX VCO
IC5
MIC
MICROPHONE
AMP
CONNECTOR
FRONT UNIT
Q11 Q10 D14,D15
To TX AMPs
TX/RX
BUFF BUFF
SW
Q13,D16,31
TX VCO
FM
MOD
CTCSS/DTCS SIGNALS ENCODING (FRONT UNIT)
The CTCSS/DTCS encoding signal from the CPU (IC1)
"CENC0–CENC2" is passed through the LPF (IC5) for
waveform conversion, and applied to the MAIN UNIT as tone
modulation signal.
2/5 TONE, DTMF ENCODING (FRONT UNIT)
Encoding signal from the CPU (IC1) named "SENC," is
passed through the LPF (IC5), and applied to the MAIN
UNIT as tone modulation signal.
TX AMPLIFIERS (MAIN-A/-B UNIT)
The frequency-modulated signal from the TX VCO is buffer-
amplifi ed by two buffers (Q11 and Q10), and applied to the
YGR AMP (Q9) as the TX signal through the LO SW (D14).
The TX signal is sequentially amplified by the YGR AMP
(Q9) and drive AMP (Q8). The amplified signal is applied
to the FET HPA module (IC3) through the LPF, and power-
amplifi ed to obtain TX output power level.
J1
The power-amplified TX signal is passed through the
antenna SW (D3) and LPF as a harmonic filter, and then fed
to the antenna.
APC CIRCUIT (MAIN-A/-B UNIT)
A portion of TX signal rectified by D1, D11 and D12 on
the TX line to detect TX power level. The rectified voltage
is applied to the APC AMP (IC2), and the APC AMP
controls the gain of drive AMP (Q8) and HPA module (IC3)
automatically by comparing the rectified voltage and the
power setting voltage "T1."
• TX AMPLIFIERS APC CIRCUIT
Q9
Q8
YGR DRIVE
AMP AM P
From TX VCO
5 - 3
D3
IC 3
PWR ANT
LP F LPF LP F
AMP SW
IC2
APC
AMP
RX circuits
D1,D11,D12
DET
LPF
PWR
D28
MUTE
SW
TMUT
T1