Icom IC-2100H

3-1-7
SQUELCH
CIRCUIT
(MAIN
and
LOGIC
units)
•
NOISE
SQUELCH
The
noise
squelch circuit
cuts
out AF signals
when
no RF
sig-
nals are
received.
By
detecting
noise
components
in the
AF
signals,
the
squelch circuit
switches
the AF
mute
switch.
A portion
of the
AF signals
from
the FM IF
1C
(IC6,
pin
9)
are
applied
to the
active filter
section
(IC6, pin
8).
The
active
fil-
ter
section
amplifies
and filters
noise
components.
The
fil-
tered
signals
are applied
to the
noise
detector
section
and
output
from
pin 14
as the
“SQL” signal.
The
“SQL” signal
from
IC6
(pin14)
is
applied
to the
CPU
(LOGIC
unit;
IC1,
pin
98).
The
CPU
analyzes
the
noise
con-
dition
and outputs
the
“RMUT’
and “AMUT’
signals
via
the
I/O
expander
1C
(LOGIC
unit; IC10)
to toggle
the
detector
(Q25)
and AF
(Q28)
mute
switches.
Even when
the
squelch is
closed,
the AF
mute
switch
(Q28)
opens
at the
moment
of
emitting
beep tones.
•TONE
SQUELCH
The
tone
squelch
circuit
detects
AF signals
and
opens
the
squelch
only
when
receiving
a
signal
containing
a matching
subaudible
tone
(CTCSS).
When
tone
squelch
is
in
use,
and
a signal
with
a
mismatched
or no
subaudible
tone
is
received,
the tone
squelch
circuit
mutes the
AF
signals
even
when
noise
squelch
is
open.
A
portion
of the
AF
signals
from
the FM IF
1C
(IC6,
pin
9)
passes
through
the
low-pass
filter
(LOGIC
unit;
IC6)
to
remove
AF (voice)
signals
and
is
applied
to the
CTCSS
decoder
inside
the
CPU
(LOGIC
unit;
IC1,
pin
1)
via
the
‘TONE
IN” line
to
control
the DET
and AF
mute
switches.
3-2
TRANSMITTER
CIRCUIT
3-2-1
MICROPHONE
AMPLIFIED
(LOGIC
unit)
The
microphone
amplifier
circuit
amplifies audio
signals
with
+6
dB/octave
pre-emphasis
characteristics
from
the
micro-
phone
to a level
needed
for the
modulation
circuit.
The
AF
signals
from
the
microphone
are
adjusted
for
imped-
ance-matching
at the MIC
sensitivity
control
circuit
(IC4, D4).
The
adjusted
signals
pass through
the MIC
mute switch
(Q4),
and are
then
amplified
at the microphone
amplifier
(Q5)
and
the
limiter
amplifier
(IC5a)
which
has a
negative
feedback
circuit
for
+6
dB/octave
pre-emphasis.
The
amplified
signals
are
applied to
the
low-pass
filter
(IC5b)
to filter
out RF
components
and
are then
applied
to the
MAIN
unit
as the
“MOD”
signal.
3-2-2
MODULATION
CIRCUIT
(MAIN
unit)
The
modulation
circuit
modulates
the
VCO oscillating
signal
(RF
signal)
using the
microphone
audio
signals.
The
audio
signals
(MOD)
change the
reactance
of
D1 to
modulate
the
oscillated
signal
at the
TX-VCO
circuit
(Q1,
Q2).
The
modulated signal
is
amplified
at the buffer
amplifier
(Q4)
and
LO
amplifier
(Q6),
then applied
to the
drive
ampli-
fiers.
3-2-3
DRIVE
AMPLIFIER
CIRCUIT
(MAIN
unit)
The
drive
amplifier
circuit
amplifies
the
VGO
oscillating
signal
to the
level
needed
at the
power
amplifier.
The
RF
signal
from
the
LO
amplifier
(Q5)
passes
through
the
T/R
switch
(D5)
and
is
amplified
at the
pre-drive
(Q13)
and
drive
(Q14)
amplifiers.
The
amplified
signal
is
applied
to the
power
amplifier
circuit.
3-2-4
POWER
AMPLIFIER
CIRCUIT
(MAIN
unit)
The
power
amplifier
circuit
amplifies
the
driver
signal
to an
output
power
level.
The
RF
signal
from
the
drive
amplifier
(Q14)
is
applied
to
the
power
module
(1C4) to
obtain
55 W
(25
W
for
Taiwan
version,
1
0 W
for the
IC-21
00-T
Thailand
version)
of RF
power.
The
amplified
signals
is
passed
through
the
antenna
switch-
ing
circuit
(D7),
ARC
detector
circuit
(LI
8,
D8,
D9),
and low-
pass filter
(LI
9,
L20,
C62-C64)
and
is
then
applied
to
the
antenna
connector.
Collector
voltages
for the
driver
(Q13)
and
control
voltage
for
the
power
amplifier
(IC4,
pin
2)
are
controlled
by the
ARC
cir-
cuit to
protect
the
power
module
from
a
mismatched
condi-
tion
as well
as to
stabilize
the
output
power.
3-2-5
APC
CIRCUIT
(MAIN
unit)
The
ARC
circuit
protects
the
power
amplifier
from
a mis-
matched
output
load
and
stabilizes
the
output
power.
The
ARC
detector
circuit
(L10,
D8,
D9)
detects
forward
sig-
nals
and reflection
signals
at D8
and
D9
respectively.
The
combined
voltage
is
at
minimum
level
when
the
antenna
impedance
is
matched
at
50 Q
and is
increased
when
it is
mismatched.
The
detected
voltage
is
applied
to the
differential
amplifier
(IC3,
pin
3),
and
the
power
setting
voltage
is
applied
to the
other
input
(pin
1)
for
the
reference.
When
antenna
impedance
is
mismatched,
the
detected
volt-
age
exceeds
the
power
setting
voltage.
The
output
voltage
of
the
differential
amplifier
(IC3,
pin
4)
controls
the
input
current
of
the
power
module
(IC4)
and
drive
amplifier
(Q14)
to
reduce
the
output
power
via
the
ARC
controller
(Q18,
Q19).
•
APC
circuit
3-2
for free by
RadioAmateur.eu