Section 4 Circuit; Receiver - Icom IC-R10 Service Manual

4-1
RECEIVER CIRCUITS
4-1-1
ANTENNA SWITCHING
CIRCUIT
(RF UNIT)
Received
signals enter the
RF
unit
from the
antenna
connector
(J1)
and pass
through a
limiter
(D1)
and an
attenuator
circuit
(D2).
The
signals are then applied
to
the
RF
circuit
via the
antenna
switching
circuit
(D51,
D151,
D171, D211, D231) which suppress
out-of-band signals.
4-1-2
RF
CIRCUIT
(RF UNIT)
The
RF
circuit
amplifies
the received signals within the
range of
frequency coverage
and
filters
out-of-band signals.
(1)
0.5
MHz-74.9999
MHz
signals
RF
signals
(0.5
MHz-74.9999 MHz)
from
an antenna
switching
circuit
(D51)
pass through a low-pass
filter
(L51,
L52).
The
filtered
signals are amplified
at
an
RF
amplifier
(Q51) through each bandpass
filter
depending on
the
receiving frequency.
The
amplified signals are then applied
to
the
1st
mixer
circuit
(IC271) through the
band
switching
diode (D253).
The
signals
below
1.9
MHz
pass through a low-pass
filter
(L55,
L56)
via
the
band
switching diode (D52),
and are then
applied
to
the
RF
amplifier
circuit
(Q51) via
the
band
switching
diode
(D53).
The
1
.9
MHz-29.9999
MHz
signals
pass through the
band
switching
diode (D61) and low-pass
filter
(L61, L62).
The
1.9
MHz-14.9999
MHz
signals
pass through the
band
switching
diode (D81)
and bandpass
filter
(L82, L83, L91, L92),
and
are then applied
to
the
RF
amplifier
circuit
(Q51) via
the
band
switching
diode
(D82).
The
15.0
MHz-29.9999
MHz
signals
pass through the
band
switching diode (D101)
and high-pass
filter
(LI 02, LI 03)
and are then applied
to
the
RF
amplifier
circuit (Q51)
via the
band
switching
diode (D102).
•
RF
filters
Receive frequency
[MHz]
sw
diodes
BPF
select
signal
Components
0.5-
1.8999
D52,
053
80
L55,
L56
1.9-14.9999 D81
,
082
81 L82, L83, L91,
L92
15.0-29.9999
0101,
0102 82
L102, LI
03
30.0
-
74.9999 0121,
0122 83
L122,
L123
The
30,0
MHz-74.9999
MHz
signals
pass through the
band
switching diode (D121)
and high-pass
filter
(LI
22, LI 23),
and are then applied
to the
RF
amplifier
circuit
(Q51) via the
band
switching
diode (D122).
(2)
75.0
MHz-199.9999
MHz
The
75.0
MHz-199.9999
MHz
signals
pass through the
tunable
bandpass
filter
(D152, LI
52)
via
the
band
switching
diode (D151),
and
are then amplified
at
the
RF
amplifier
(Q151)
and pass through another tunable
bandpass
filter
(D153, LI 55).
The
filtered
signals
are applied
to
the
1st
mixer
circuit
(IC271) via the
band
switching
diode
(D154).
(3)
200.0
MHz-499.9999
MHz
The
200.0
MHz-499.9999
MHz
signals
pass through the
tunable
bandpass
filter
(D172,
LI
72)
via
the
band
switching
diode (D171),
and
are then amplified
at
the
RF
amplifier
(Q171)
and pass through another tunable bandpass
filter
(D173,
LI 75).
The
filtered
signals are applied to the 1st
mixer
circuit
(IC27
1
)
via
the
band
switching
diode (D1
74).
(4)
500.0
MHz-699.9999
MHz
The 500.0
MHz-699.9999
MHz
signals
pass through a
tunable
band
pass
filter
(D213, L213, L214)
via the
band
switching
diode
(D211),
and
are then amplified
at
an
RF
amplifier
(Q211) and pass through another tunable
bandpass
filter
(D214, L216, L217).
The
filtered
signals are
applied
to
the
1st
mixer
circuit
(IC271)
via
the
band
switching diode (D154).
(5)
700.0
MHz-1300.0000
MHz
The
700.0
MHz-1300 MHz
signals
pass through a high-
pass
filter
(L232, L233)
via
the
band
switching
diode
(D231),
and
are then amplified
at
the
RF
amplifier
(Q231)
and pass
through a
tunable
bandpass
filter
(D238, L240).
The
filtered
signals
are applied
to
the
1st
mixer
circuit
(IC271) via the
band
switching
diode (D236).
•
Tunable band pass
filters
and
RF
amplifiers
Receive frequency
[MHz]
.
BPF
select
signal
Varactor
diodes
RF
amplifier
84
0152,
0153
Q151
200.0-
499.9999
85
0172,
0173
Q171
500.0-
699.9999
86
0213,
0214 Q211
700.0-
1300.0000 87
0238
Q231
RF
filter
and
amplifier
circuits