Icom IC-R7100 Service Manual page 8
Wideband receiver
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Also See for IC-R7100:
- Insrtuction manual (44 pages) ,
- Service manual (93 pages) ,
- Service manual (71 pages)
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3-1
-3
RF CIRCUIT (RF UNIT)
The RF
circuit
ampUlies slgnals
within
the range ol
I
requency coverage and filters out-ot-band
signaIs.
The
RF
amplil iers
(al
-a4) employ gallium arsenic FITs
(35K12
1).
The
combinatIon
ol
the
RF
amplifiers
and
tuned
bandpass
filters expand the dynamic
range
and
enhance the sensitivity
tor
the high
frequency.
Each
tuned
amplifie r
has
approximately 10 dB gain.
06......0
10
employ varactor
diodes which
are
controlled
by
the
PLL
loek
voltage.
The voltage
is
current-ampüüed
at the OC amplilier
ci
rcuit (IC3a
,
ICl
a)
and
is
then
applied
to the
varactor
diodes.
These
varactor
diodes
tune
the
center trequency of
an RF
passband
tor
wide
bandwidth
receiving
and
9000
image response
rejection.
D50 protects
the
va
ractor diodes
trom being
charged
over
their maximum
voltage.
1
C4 lunetions
as
a compa rator
and
is controlled by the
BPF4 signal
line.
Pin
1
of 1
C4
outputs
positive
voltage
in a frequency range of
512-1024.9999 MHz, whiJe pin
7
of
1
C4
outputs
positive
voltage
In a frequ
ency
range
of
25.oooo-51 109999
MHz.
IC5 switches the power source of
BPF1
-
BPF4 ON
or OFF
by using "
Bl
- B4"
and "
BH"
signals
from
the
LOGIC
UNIT.
0
21
and
052 provide
the
conve
rted and
stabie
voltage
to
IC5.
The
25- 1024.9999 MHz
slgnals
are applied to
four
separate filters through switching
diodes
(05, 0
12,
0
19,
011, 0
18,
0
25) depending
on the
range
of
frequ
ency
coverage.
The
relay ci
rc uit
(RL1, RL2)
Is
used
instead
of
switc hing
diodes
tor
the frequencies above 512
MHz.
This devic e prevents a
diode
trom
causing
disto rtien
when receivlng
very
st
rong
signais.
(1) BPF1
(25.0000-89.9999
MHz)
The
25.oooo-89.9999
MHz
signals
pass
through a
parallel
resonant
circuit
(06,
L11
,
C15) to
suppress
half
of the
reeeive
frequency interference
sig nals
and
a
re
then
applied
to an RF
amplifier
(01) via a tuned
bandpass
filter
(07,
0
8,
L12-L14).
The
amplified
signa!s
are
applied
to a
2nd RF amplifier (07) through
a
tuned
band-
pass filter (Dg, 010,
L16-L1S).
(2) BPF2
(90.0000-249.9999
MHz)
The
90.0000-249.9999
MHz signals
pass
Ihrough
a
pa
rallel resonan, c
ircuit
(013,
L22, C25)
to
suppress
half
of
the receive frequ
ency
interference signaIs
and are
then
applied
to
a series
reso
nant
ci
rc uit (0 14, L70,
C61)
to
suppress st reng
signals
in a
frequency
range
of BO-
110
MHz,
sueh
as
FM
and
TV
broadca sting
stations.
The
signals are applied
to
an
RF
amplifier (02)
via
a
tuned bandpass
l
ilt er
(0
15,
L23-L25, C11
9).
The ampli-
lied
signaIs
are applied to a 2nd
RF amplifier (0 7)
through another
tuned
bandpass fil
ler
(0 17,
L27- L29,
C1
20).
01
3-015
and
0
17
employ
varactor
diodes
whlch are
controlled
by the
PLL
lock
voltage.
The
voltage
is
current·amplified
at
lhe OC
amplifier
circuit
(IC3a,
ICl
b)
a
nd
is then
applied to
the
varactor d
iodes.
These varac
tor
diodes tune the center Irequency
of an
RF
passband
lor
w
ide bandwidth reeeiving and goOO image
respon se
rejection.
0
51
protects
varaetor
diodes
Irom
being negatively
charged.
o
RF CIRCUIT
10
FIL1
fFl
l 2
UNI
_,
25.0000 89
9999MHz
-
•
..
,.
1\
Ql
AF "'""
I
~!
I
ICB
I
omp
OB-""!'
r-,
i%
I
r-,
I
~
•
34
I
I
l-;;.
«
,
I
I
I
L
__.
__ .J
I
178.1....,
I
1291.1MHz
BPF
Z
I
I
9O.0000- 2I9.9999MHz
•
•
Q'
I
I
,DI1
LPF CONT
I
'"~
LD
I
IC3b
I
I
\~OB
I
I
I
BPF3
cv
lIne
L_
___ ....J
trom
2SO.0000-511.9999MHz
VCO UNIT
•
•
Q3
••
l
LD
p:(I
~
U
oe
024
'rom
P'
OOUBL
UN
IT
N:1C CONT
AGC IIn.
0
20
'rom
BPF4
MAIN
UNIT
512..~.9999M
HZ
\"'&0/
AF UN
IT
.
PFCONT
CVllne
IC1, 1 C2
"om
VCO UN
IT
' , om
ATT
clrcull
FIg. 2
3-2
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