Icom IC-R7100 Service Manual page 13
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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3·1·15 BFO AND SSB DEMODULATOR
CIRCUITS (MAIN UNIT)
3·1·17
AM DEMODULATOR CIRCUIT
(MAIN UNIT)
The
BFO (Beat
Frequency
Oscillator) c
ircuit
consists
of
Q41
and
Q42.
The
oscillator
provides
a
beat
frequ ency
signaI
to the
SSB
demodulator c
ircui t (039-0 42)
lor
demodulati ng the
3
rd IF
sig
nal into
an
AF signal.
The
BFO freq
uency
is adj
usted at L4 in SSB
mode.
In
LSB mod e,
the CPU (IC5, pin
74)
on
the LOGIC
UNIT
outputs
a "
HIGH" signa I.
The "
HIGH"
signal furns 0
40
ON.
Therefore,
the capaci
tance of
CI80
and C181
is
added
to
L14,
C182
and C183
to
increase
the BFO
osci
llatlon
by
3
kHz.
The
3rd IF signal output
from 023 is
buff
er-amplified
at
0
30
and
is
th
en
applied to
an
AM demodulator
circuit
(C168, 0
57) to be
cemodutated into an AF
signal.
Th
e
AF signal
is applied to a
buffe r
amplifier (039)
tor
AF
signal switching and AF signal
level
adjustment
in
ather
modes.
3·1·18 AM/SSB/FMN AGC CIRCUIT
(MAIN UNIT)
The
AF
sig
naI output from Ihe SSB
demoduiator ci
rcuit
(039- 0 4 1)
Is
applied to
a buffer
amplifier (024)
for
AF
signa
1
switching
and
AF
signal
level
adjustment
in
ether
modes.
3·1·16 FM DEMODULATOR CIRCUIT
(MAIN UNIT)
A
po
rtion
of the 3
rd IF signal output from
0
30 is applied
to
an
AGC
detecto r circ uit.
The AGC
voltage
is
detected
at 056
and
is
then applied
to a OC
amplifier
(038).
In AM
or
SSB
mod e, the
"AM9"
or "
SSB9" line
bec omes
"
HIGH."
The "HIGH "
signaI turns
0
34
and
035
ON.
Th
erefore, R246
shortene
the time
constant.
C161
end
R247
are
connected in paralle l
with
the
AGC
time
consta nt
line
10 obtai n an appropriate time constant.
The
3rd IF signa l output trom
023 Is
buffer-amplifie d
at
030
and
is
th en
applied
10
a
limiter
amplifier
(ICIS)
to
elimlnate
the AM
signal
components.
The sig
na
I
output from
IC15 is applled to a ce ram ie
discriminator
(X3)
to be
demodulated into an AF signal.
The
AF signal
is
applied to
an
active filter
c
ircuit
(03
1,
0
32) to
suppress
the signaIs below 300
Hz.
In FM
mode,
Ihe "FM9"
line becomes
"LOW."
The
"LOW "
signa
I
turns
035
OFF.
Therefore,
C162 and
R246
are
connected in
parallel wi
th
the AGC
time
con-
stan t
line
1
0
obtaln
a reold
AGC
release time
.
R248 and R249
offset
the AGC
voltage
to
approximateiy
4
V
when
receiving
no signa!.
When the scan is
in
eperation.
the CPU (IC5,
pin 9
1) on
the LOGIC
UNIT
ou
tputs
a
"HiGH"
signal
tor 35
msec
.
on
the "IFBK" sig
nal
line.
The "
HIGH"
sig
nal turns 0
36
and 037 ON
to reset the AGC ci
rcuit.
o
DEMODULATOR AND AGC CIRCUITS
>IX
DET
015,016
10
~-l---ê~;}---[:;~~
RF
UNI T
r - - - - - r - - - - - - 1
AF.mp
0
28
c.nt
.Ignal
o
Xl
10.7MH:
0.1
BuHer
MIX
IC 13
Fi'
r---------l
I
lF
omp
I
o
AF."",
~
::--K~Jf-1FM
DETECTOR
0
18
?
:---j~~LJ-1
LIM
ITER
f-~-1
;
>-- l+-_
. WFM
IC12
l
Ignai
IF
amp
IF
I
mp
A,.
reu
IF .mp
055
0
29
I
~
i
"
r-,
~.
sso
I
V " /
NB
SW
455kH:
SS8
DET
Ilgl'Ill
I
030.....0
32
I
'X
"V
03a
.....
0.2
-
~2
/ '
0
"
.SSO
I
I
OFO
I
I
.
56.5
Of
453.5kH:
A
OC
Noll e
amp
WIDTH 2.8MH:
ACe
I
si
gnai
~
,.
I
csc
slN.""
IIM
"V 0
29
11 0
I
'-
V
I
è
1\ FI.
I
I
•
IFI~
&.lil.,
I
WIOTH
e.OMH:
022,
~O
I
1
No lS8
blanker circuIt
I
FI
S
/
L_________.
.2
V
V
10. 2.~Hz
WIOTH
15.0MHz
FIO
/
AF.mp
030
N<
l-
N< DE
T
r-"
Il
gMI
ACe
AOC
DET
OOT
V
0
..
.~.,.,
IIM
0
5&,038
limit"
M-
I
mp
•
N
C15
FM
DEr
1'!1.31,O32
050
FM
/ '
X3,,048.04a
V
.Igroll
10.7MHz
WFM
'lg~'-+lH
from
0
25
RF
UNIT
~
FM,AM
I
ignal
FIg. 7
3-7
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