Transmitter Circuits; Mic Amplifier (Front Unit); Tx Af Circuits; Tx Amplifiers - Icom ic-f5021 Service Manual

5-2 TRANSMITTER CIRCUITS

MIC AMPLIFIER (FRONT UNIT)

Audio signals from the connected microphone are applied to
the MIC AMP (IC5) via the microphone connector (J1). The
amplifi ed MIC signals are applied to the MAIN UNIT.

TX AF CIRCUITS

The MIC signals from the FRONT UNIT are 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
IC18
MCGO
A K2330
HPF
BAL
Limiter
Pre-empha.
CD4066
VRAF
MODI
MIC MUTE SWITCH
The pre-emphasized MIC signals are passed through the
MIC mute SW (IC14).
While receiving, the MIC mute SW (IC14) cuts the MIC line
off, and is controlled by "MMUT" signal from the expander
(IC17).
SPLATTER FILTER
The MIC signals from the MIC mute SW (IC14) are applied
to the splatter fi lter (IC16).
The splatter filter (IC16) is also used as the AF Summing
AMP for tone signals modulation (CTCSS, 2/5 TONE).
MODULATION CIRCUIT
MIC signals from the splatter filter (IC16) is level-adjusted
(=deviation adjustment) by the D/A converter (IC18), and
applied to the TX VCO (Q13, D16, 31) via modulation mute
SW (IC14) as the modulation signals.
The MIC signals are also applied to the reference frequency
oscillator (X2) as the modulation signals via D/A converter
(IC18) and REF AMP (IC19).
• MODULATION CIRCUITS
X2 IC4
IC19 CR-794
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 signals from the CPU (IC1)
"CENC0–CENC2" are passed through the LPF (IC5) for
waveform conversion, and applied to the MAIN UNIT as tone
modulation signals.
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 signals.

TX AMPLIFIERS

The frequency-modulated signal from the TX VCO is buffer-
amplifi ed by two buffers (Q11 and Q10), and applied to the
drive AMP (Q9) as the TX signal via the LO SW (D14). The
amplifi ed TX signal is applied to the FET HPA module (IC3)
via 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, then fed to
the antenna.
APC CIRCUIT
A portion of TX signal rectifi ed 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 HPA module (IC3) automatically by comparing
the rectifi ed voltage and the power setting voltage "T1."
• TX AMPLIFIERS APC CIRCUIT
Q8
From TX VCO
DRIVE
AMP
5 - 3
D3
IC 3
PWR ANT
LP F LPF LP F
AMP SW
IC2
APC
AMP
RX circuits
136-174 MHz
D11,D12
DET
LPF
PWR
D28
MUTE
SW
TMUT
T1