Icom IC-R10 Service Manual

(4)
SSB/CW
The
signal from the
3rd mixer
passes
through the
ceramic
filter
(FI101) and
is amplified at
the 3rd IF
amplifiers
(Q151,
Q161)
and buffer
amplifier
(Q201).
The amplified
signals
are
applied
to
the
SSB/CW
detector (D201
,
D202)
and
mixed
with BFO signals
from the
BFO circuit
(LOGIC unit;
X231)
via the BFO
amplifier
(0951)
to
demodulate
AF
signals. The
demodulated
AF signals are
applied to
the AF
switch
(IC301b,
pin
11)
after
being
pre-amplified at
the AF
pre-amplifier
(0202).
•
Bandpass
filter
selection
Mode(s)
Bandpass
filter(s)
Passband width
NFM / AM
FI111
15 kHz
SSB
/
CW
FI101
4 kHz
WFM
—
—
4-1-6
SUB-BAND
RECEIVER
CIRCUIT (MAIN UNIT)
The
sub-band
receiver circuit
is employed by
the
band
scope
and SIGNAVI
functions.
A
portion of the
1st
IF signals from
the RF
unit
is
mixed with
the sub
2nd LO
signals
at
the
2nd mixer
circuit
(0411)
to be
converted
into 455
kHz sub
2nd IF
signal. The 2nd IF
signal
Is
applied
to the
IF
1C
(IC471
,
pin
5)
via the
IF filter
(FI411)
and
2nd
IF amplifier
(0421).
The IF
1C
(IC471)
outputs
signals to
lead the
CPU (LOGIC
unit; IC1)
under
conditions
of RSSI
or noise
squelch.
4-1-8
SQUELCH
CIRCUIT
(MAIN UNIT)
A noise
squelch
circuit cuts out
AF
signals
when no RF
signal is
received. By
detecting
noise
components
in the
AF
signals, the CPU
switches the
AF mute switch.
Some
of the noise
components
in the AF
signals
from IC71
(pin
9)
are passed
through the
active filter
(IC71
,
pins
8, 7),
and
then
applied
to
the
noise detector
section.
The
squelch
control pot (RF
unit;
R11) adjusts the
input
level of
the
active filter, and
the
level
is
used
for
the
squelch threshold
reference.
The
detected noise
signals
are
applied
to
the
CPU
(LOGIC unit;
IC1,
pin
65)
via the
“SQL” line.
The
CPU
then
analyzes the
noise condition and
controls
the
“MUTE”
port to
cut
off
the
AF
signal using the
AF mute
switch
(LOGIC
unit;
IC950).
4-1-9
VSC
CIRCUIT
(LOGIC
UNIT)
The VSC
(Voice Scan
Control) detects
AF
signals and
mutes
undesired
signals
such
as
unmodulated, beat
and
noise
component
signals.
When
the
VSC
function is ON
and
an
unmodulated
signal is received,
squelch
functions
the same
as closed
(no signal
condition)
even
when it’s
open, or
the scan
function
resumes for a
short period on
any scan
setting
during scanning.
A portion
of the AF
signals
from the low-pass
filter
(Q950)
is
applied
to the
VSC
control circuit
(IC201)
to
detect
demodulated
signals
while the VSC
function is
ON.
When
audio component
signals
are
included in the
AF signals, the
VSC 1C
(IC201
)
outputs a
low level
signal from
pin 13 to the
CPU (IC1
,
pin
1
)
to
release the
mute switch
(IC950).
4-1-7
AF
AMPLIFIER
CIRCUIT (MAIN
UNIT)
The
AF
amplifier circuit
amplifies
the demodulated
AF
signals to
drive
a
speaker.
The AF signals
from the
AF
switch (IC301) are
applied to
the
LOGIC unit
through
a
“DETOM” line.
The AF signals
are
amplified at
the
AF amplifier
(LOGIC
unit;
0950),
and are
then
applied to
the
AF mute
switch
(LOGIC unit; IC950).
The
output signals
from the
AF mute
switch (LOGIC
unit;
IC950)
are
applied to the
[VOL]
control
(RF unit; R11),
and
are
then
power-amplified at
the AF
amplifier (MAIN
unit;
IC361
,
pin
4)
to
drive a
speaker.
4-1-10
BFO
CIRCUIT
(LOGIC
UNIT)
The BFO (Beat
Frequency
Oscillator) circuit
consists of
X231,
IC231
and D231.
The oscillator
provides
a
beat
frequency
signal
(USB;
456.5 kHz, LSB;
453.5 kHz) to
the
SSB/CW
detector circuit
(MAIN unit; D201,
D202)
for
demodulating
the 3rd
IF signal
into AF signals.
The
oscillating
frequency for
each
mode
(LSB/USB/CW)
is
switched by
changing the
capacitance
of
a
varactor
diode
(D231).
When USB mode is
selected, the
CPU
(IC1, pin
3)
outputs
“LOW” level
voltage to D231 to
change the BFO
frequency to
456.5 kHz.
•
Squelch and
AF amplifier
circuits
4-3

Icom IC-R10 Specifications

General

Brand	Icom
Model	IC-R10
Category	Receiver
Language	English