Icom IC-R7100 Service Manual page 15

3·1·23 VSC CIRCUIT (MAIN UNIT)
The VSC (Voice Scann ing Contral) delects the AF signal
dUling scanning and skips undesired signaIs suc h as
unmodulated signaIs. beal signaIs and norse component
signa/s.
The AF signal outpul Irom Ihe squelch switc h (0 1) passes
Ihrough an aclive l ilter c ircuil (ICl a, R6-R13, CG-Cl 0)
which altenuates the components of frequencies 1 kHz
and above. The filtered signa' is amplified sulticiently al
ICl b and is Ihen detecled at 02. Tbe detected voltage
is c harged at elS and is then applied to a comparator
(IC2b). Pin 7 of IC2b outputs
a
" HIGH" signaI only when
rece iving AF signaIs.
e15 and
R22 set the c harge time. The release time is
set
al R23 .
04, OS and OS2 control a relay circuit (RL1 ) lor the
[REC REMOTE] jack on Ihe REAR PANEL. RL1 Is turned
ON by the " MO" signal Irom Ihe LOGIC UNIT when
receiving AF siqnals. VSC operation is given priority even
when the squelc h is open. When the VSC function is
aclivated, RL1 is turned OFF by the "M O" signal trom
tne LOGIC UNIT.
3·1 ·24 CENTER DETECTOR AND CENTER
METER CIRCUITS (MAIN UNIT)
The c ente r detector circuit adjusts the cente r frequencies
ol Ihe IF signaIs in the WFM and FM demodu lator
ci rcuits.
R224 adju sts the mismatch of the center frequencies by
using tne offset voll age from R224, R22S and R229.
The center signaI passes through a
De
ampl ifier (Q1 7 or
04 3). The amplilied signal is inverted and ampli lied at
IC2a.
• CENTER DETECTOR CIRCUIT
The resu l1ing signaI is output trom IC2a (pin 1) and
IS
Ihen appli ed la IC1S (pin 4).
The center signaI is applied la a window cernparator
(ICSa, ICSb).
R76 adjusts tne olfsel vollage 10
0
V output from ICS
when Ihe receive trequency is matched with the center
frequency. When the receive frequency is not mat ebeo
with
the center
Irequency, Ihe cathodes ol 0 16 and 0 19
become " HIGH." The scanning control circuit prevents
malfunction caused by adjacent c hannels and spurious
emissions.
3·1·25 SCANNING CONTROL CIRCUIT
,
(MAIN UNIT)
Output signaIs from tne squelch and center delector
circuits are applied to the base of 0 9. 0 9 turn s OFF only
when bath of them are "LOW." In otner words,
0 9
turns
OFF whe n the squelch is open in the center frequency.
The coltector of 09 provides the " STOP" signal la Ihe
LOGIC UNIT. The "STOP" signaI becomes "HIGH" when
the scanning tunetion stops. When the scan is in
ope ratlon, Ihe CPU (ICS, pin 9 1) on tne LOGIC UNIT out-
puts a "H IGH" signal tor 35 msec . on the " IFBK" signal
lin e. The " HIGH" signaI is applied to D66 and tur ns
Q9 ON
1 0
deact ivate the sca nning ci rcuit. Q6 and D20
turn OFF the output from the c enter de tec tor circuit in
SSB mode.
3-1-26 IF FILTER SWITCHING CIRCUIT
(MAIN UNIT)
The mode signaIs Irom Ihe LOGIC UNIT selec t tne IF
filters in the separate modes by using the diode matrix
(OSl, OS2, 067, D66), tne mode voltage switching circuit
(033, 046, OS3, OS4) and a voltage buffer (ICG). The
voltage buffer (ICS) conve rts Ihe mode signals la the
needed levels to drive eac h mode.
WFM9
IC12
-
........
AF slgnal
'"
X;
M
10.7 MHz
RI38
a:
WFM
)
DET
R137
-
0
fl1
'"
R320
10
11 1
ö1
CENTE
r
C'RCU
455kHz R220
R2l9
WFM9
M
M
'"
AF slgnal
~l
'"
0 43
Cl"1
a:
R228
061
,çi
SOl.
h
"I~
'"
R276
slgnal
119
•
030 1" '"
'"
-;~
o '"
'"
FM DET
a:
0
!;> .....
X3
~
0>
'"
R218
0>
LimIte r
. .
'"
~
R222
R225
0
a:
r::
-
'" '"
0>
'"
°l
l~
a:
C137 "-'C15
,d,.
a:
:!l
0>
M
+
0>
'"
°l
:l!~
. .
15 1
'"
-
0
a:
9V
R
IT
FIg.
9
3-9