Transmitter Circuits - Icom IC-80AD Service Manual

4-2 TRANSMITTER CIRCUITS

TX AF CIRCUITS (LOGIC UNIT)
• FM MODE
MIC signals from the internal/external microphone (MIC
signals) are passed through the MIC gain SW (Q303),
and applied to the MIC AMP (Q302, 304). The amplified
MIC signals are passed through the mode SW (IC301)
which toggles the MIC line according to the operating
mode; FM or DV. The MIC signals are applied to the IDC
(Instance Deviation Controller; IC302B) circuit which limits
the amplitude of MIC signals (=deviation) to prevent over
deviation.
The amplitude-limited MIC signals are passed through
the splatter filter (IC302C) which cuts off the 3 kHz and
higher audio signals. The frequency-limited MIC signals are
entered to the MAIN UNIT via the mode SW (IC303), then
applied to the DAC (MAIN UNIT: IC600) for level (=deviation)
adjustment. The level-adjusted MIC signals are applied to
the modulation circuits.
• TX AF CIRCUITS
IC301
Q303 Q302,304
MC300
1
GAIN MIC MODE
AM P
SW SW
From ext. microphone
MODULATION CIRCUITS (VCO UNIT)
The modulation signals from the DAC (MAIN UNIT: IC600,
pin 2) are entered to the VCO UNIT, and applied to the
variable capacitors of VCOs.
• OPERATING ON VHF BAND
The modulation signals are applied to the D55 of the VHF
VCO (Q51, 52, D51–55) to obtain FM modulation. The
FM-modulated VCO output is buffer-amplified by Q200,
amplified by Q201 then entered to the RF UNIT as TX
signal.
• OPERATING ON UHF BAND
The modulation signals are applied to the D100 of the UHF
VCO (Q101, 102, D100–104) to obtain FM modulation. The
FM-modulated VCO output is buffer-amplified by Q200,
amplified by Q201 then entered to the RF UNIT as TX
signal.
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IC302B
Q306,307
IC302C
6
9
LPF
7
ID C
5
SPLATTER
7
Q309
IC300
ALC
LPF
AM P
CTCSS
?
CPU
?
IC3
4 - 4
• DV MODE
The MIC signals from the microphone (MC300) are passed
through the MIC gain SW (Q303) and applied to the MIC
AMP (Q302, 304). The amplified MIC signals are applied
to the ALC AMP (IC300) which automatically adjusts the
level of MIC signals to stable for digital processing, via
the mode SW (IC301). The level-adjusted MIC signals are
applied to the IDC circuit (IC302B) for amplitude-limiting.
The amplitude-limited MIC signals are passed through the
splatter filter (IC302C) which cuts off the 3 kHz and higher
audio signals.
The frequency-limited MIC signals are applied to the liner
CODEC IC (IC503) via the buffer (IC504A), and encoded
into the digital audio signal. The digital audio signal is then
applied to the DSP CODEC IC (IC506) and converted into
the AMBE signal. The AMBE signal is applied to the modem
IC (IC501) via the CPU (IC1). The modem IC converts the
AMBE signal into the analog signal, and output to the DAC
(IC600, pin 1) via the buffer (IC302D) and the mode SW
(IC303). The tone signal is level-adjusted by DAC (MAIN
UNIT: IC600), then applied to the modulation circuits as the
modulation signals.
LOGIC UNIT
IC504A
IC503
8
BUFF
LINEAR
2 1
5
CODEC
DSP
CODEC
IC506
IC501,502
IC302D
12
BUFF
MODEM
TX AMPLIFIERS (RF UNIT)
TX signal from VCO UNIT is applied to the LO AMP
(IC100) via the LO SW (D100). The amplified TX signal is
passed through the ATT (D101, 102) which is a port of the
APC circuit. The level-adjusted TX signal is amplified by
YGR (Q102), drive (Q101) and power (Q100) amplifiers in
sequence, to obtain TX output power. The power-amplified
TX signal is passed through the TX filters, power detector
and ANT SWs.
• OPERATION ON VHF BAND
The power-amplified TX signal from the power AMP (Q100)
is passed through the LPF, ANT SW (D9, 61, 62), power
detector (D59, 60) and two LPFs (as a harmonic filter), then
applied to the antenna via ANT connector (CHASSIS; J1).
• OPERATION ON UHF BAND
The power-amplified TX signal from the power AMP (Q100)
is passed through the BPF, power detector (D50, 53), ANT
SW, HPF and LPF (as a harmonic filter), then applied to the
antenna via ANT connector (CHASSIS; J1).
MAIN UNIT
IC600
1
D/A
Modulation signals
2
to the VCO UNIT
IC303
6
MODE
1
14
SW
7