Receiver Circuits; Transmitter Circuits - Icom IC-3200A Service Manual

SECTION
3
CIRCUIT
DESCRIPTION
3
-
1
RECEIVER CIRCUITS
3-1-1
VHF
ANTENNA SWITCHING
CIRCUIT
(PA UNIT)
Incoming
VHF
signals
from
the
antenna connector
are
passed through a
Chebyshev Low-pass
filter
consisting
of
L3, L4, L6,
Cl
2,
Cl
3,
Cl
4,
and Cl
5,
and
are fed
to
the
antenna
switching
circuit.
While
receiving,
D2
is
turned
ON.
Receive signals from
a
low-pass
filter
are
passed through
another
filter
consisting of
Cl
0,
L2 and Cl
7,
and
are fed to J1
on
the
MAIN
UNIT.
3-1-2
VHF RF AMPLIFIER CIRCUIT (MAIN
UNIT)
Signals
from
J1 are
passed through the L1-L2
bandpass
filter,
and
are amplified by Q1. Amplified signals
from
Q1
are
passed through
the L3-L4-L5
bandpass
filter,
and
are
mixed
with the
local oscillator signal
from the
PLL
circuit
in
Q2
to
produce a
first
IF
signal of
30.875MHz.
3-1-3
UHF
ANTENNA
SWITCHING CIRCUIT
(PA UNIT)
Incoming
VHF
signals
from
the
antenna connector
are
passed through
both a
Chebyshev
low-pass
filter
consisting
of
LI
3,
LI
4,
C35,
C36 and C37 and
a
Chebyshev
low-pass
filter
consisting of L11, L13, C32,
C33 and C34
before being
fed
into
the
antenna
switching
circuit.
While
receiving,
D5
is
turned
OFF. Receive
signals from the low-pass
filter
are
passed through another
filter
consisting
of L10,
C30,
C39
and
C40,
and
are fed
to
J3
on
the
MAIN
UNIT.
3-1-4
UHF
RF AMPLIFIER CIRCUIT (MAIN
UNIT)
Signals from J3 are
passed through
a tuned
circuit
consisting
of L1
1
,
C21 and
C22,
and
the output
is
amplified
by Q5.
The
output from
Q5
is
passed through bandpass
filter
L13, amplifier Q6,
bandpass
filter
LI
5,
and
is
mixed
with the
local oscillator signal
from
the
PLL UNIT
to
produce
a
first
IF
signal of
30.875MHz.
3-1-5
IF
AMPLIFIER CIRCUIT (MAIN
UNIT)
The
first
IF
signal
from
the
mixer
is
passed through
the
L8-C1 2
tuned
circuit,
is
filtered
by
crystal
filter
Fit
,
is
passed
through
the
L9-C15 tuned
circuit,
and
is
amplified by Q4.
D3
and
D4
function as a
limiter for
strong
signals.
The
amplified
signal
from
Q4
is
fed to pin
16
of IC1. IC1
incorporates a
second
oscillator,
a
second
mixer, a limiter
and a
discriminator
on
a single chip.
The
signal
from
pin
16
of IC1
is
mixed
with the
second
oscillator signal to
produce
the
455kHz
signal
at
pin 3
on
IC1
.
The 455kHz
signal
is
filtered
by
ceramic
filter
FI2
and
is
fed
to pin 5 of IC1
where
it
then
enters the limiter amplifier.
The
amplified signal
is
fed to
the
discriminator
through ceramic
discriminator unit XI.
The
audio
signal
exits
from
pin 9
on
IC1.
3-1-6
AUDIO AMPLIFIER CIRCUIT (MAIN
UNIT)
The
audio signal
from
pin 9
on
IC1
is
amplified
by Q10,
is
filtered
by
active
filter
Q11,
and
is
fed
through J7 and
the
VOLUME CONTROL
to pin
1
on
105.
IC5
is
the audio
power
amplifier.
The
amplified
audio
signal
from IC5
is
fed
to
the
speaker through
J10.
3-1-7
SQUELCH
CIRCUIT (MAIN
UNIT)
The
audio
signal
from
pin
9
on
IC1
is
also fed to the noise
amplifier
through C69,
R50,
J8,
C70,
and
the
SQUELCH
CONTROL
and
then
is
input to pin
1
0
on
IC1
.
The
amplified
noise
signal exits
from
pin
1 1
on
IC1
,
is
rectified
by D1
1
and
D12,
and
is
controlled
by
09
through
R54.
3-1-8
S-METER CIRCUIT (MAIN
UNIT)
S-meter
signals
from
pin 5
on
IC1 are amplified by IC3
through
C66 and
R49, are passed through
L20,
are
rectified
by
D9
and DIO, and
are fed to the
LCD
driver circuit
on
the
LOGIC A
UNIT
through
J12. In
the
VHF
mode,
the
band
signal
turns
ON
Q12
to
adjust the gain
of
IC3 by
means
of
R82, equalizing the
S-meter
level
between
VHF
and UHF.
3
-
2
TRANSMITTER CIRCUITS
3-2-1
MIC AMPLIFIER CIRCUIT
(PLL UNIT)
The microphone
output
is
fed
into
IC5A
through
C60andthe
08
amplifier.
IC5A
includes a
differential
amplifier
and
a
limiter amplifier
with
R2
as the
UHF
deviation gain
adjustment
and R3
as
the
VHF
deviation gain adjustment.
Preemphasis
of
6dB/octave
is
introduced
between 300Hz
and
3kHz.
The
signal
is
then fed
to
the
FM
modulator
in
the
TX
VCO
UNIT
through a low-pass
filter
consisting of
IC5B,
R45, R46, R49, C51, C52,
and
C53.
3-2-2
MICROPHONES USED WITH THE
IC-3200A/E
The
IC-3200A/Ecomesfactoryequipped
with a high-quality
electret
condenser microphone. The
type
of
supplied
microphone
varies with
each
transceiver
model.
The
microphone
types are
listed
below.
IC-3200A
(#03)
;
IC-HM14
(DTMF
Encoder)
IC-3200E
(#04)
;
IC-HM15
(1750Hz
Tone
Burst)
IC-3200A
(#05)
:
IC-HM12
1.
IC-HM14
(DTMF
Encoder)
MIC
Plug the
IC-HM14
into
the
MIC
CONNECTOR
on
the
front
panel
for
immediate
transceiver operation.
If
you
wish
to
use
a
different
microphone
with the IC-3200A, be sure
it
has
the
proper output
level
before
making any connections.
Particular
care should be exercised
when
wiring a
different
microphone
since the internal electrical
switching system
in
the transceiver
depends on proper connections being made.
See
the
diagram on page 3-2
for
proper
MIC
wiring
instructions.
3—
1