3·1
·19 AF AMPLIFIER CIRCUIT
(MAIN AND
LOG
IC UNITS)
The AF signaI output trom Ihe demodulator c
ircu
its is
amplified al Q49. The amplified signal passes through
a squetcn
sw
i
lch
(al)
and is then applied
la
I
CS
(pin 2).
Pin 8
of
Ica is connected with tne
"AFUD
" signal line
from
Ihe
LOGIC
UNIT
. The audio
outpul
level Is
var
ied
by
the
[AF GAIN] control
(Rl)
on
Ihe
VR
UNIT and is
Ihen
applied
la
IC21 (pin 7)
on
tne LOGIC UNIT through
Ihe
"AFG"
signaI une. The signaI is applied to IC8 (pin
8) on Ihe MAIN UNIT. The AF signal is
output trom
ICS
(pin 3) and is theil power-amplified at an AF power
ampl
ifier (IC9)
10
dri
ve
a spea
ker
.
The amplified signal passes Ihrough a voltage limiter
circui
t (Oa,
09,
R49) and is Ihen applied
10
a comparator
(IC3b, pin 5). The noise sque
lch
relerenee voltage is
applied
la
pin 6 ot
IC3b
and is varied
by
tne (SOUELCH]
control on
Ihe
VR
UNIT. R5t adjusts tne input level of
IC3b (pin 6).
The noise
souelch is
oulpul
from IC3b (pin 7) and is then
applied
la
Ihe base
ol
047
Ihrough
010
.
051
sno
rt-
c
ircuits
tne output
Irom
IC3b
(pin 7) in SSB mode.
3·1·21 S·METER SaUELCH AND S·METER
CIRCUITS (MAIN UNIT)
The
AF
amp
lif
ier
(011)
amplil
ies
Ihe " VOIC" signal
Irom
I
he
optional
UT
·36 VO
ICE
SYNTHESIZ
ER
UNIT on the
SPEECH UNIT.
The s-meter squelch runenons in any mode. The
AGC
voltage is inverted and amplified at
1C4
a. The siçnal
outp
ut Irom lC4a (pin 1) passes Ihrough 0 11 and is Ihen
applied la a
comparator
(lC4b, pin 6). The
"ADSM"
v
oltage
line
Irom
011
is applied
la
IC15 (
pi
n 5).
3·1·20 NOISE SaUELCH CIRCUIT
(MAIN UNIT)
The noise soue
ren
fu
nctia
ns
in
AM
or
FMN mode. Some
naise
components
in the AF signa! trom the
ceram
ic
discrim
inator (X3)
are
applied
to
an
active
filter (IC17
).
The active filter (lC17) amplifies naise camponents of
frequencie
s
20
kHz and above, and outputs the resulting
signals from pin 1. Output signals are rectified at tne
doubler
circu
il
(059.
060
) and are then
converted
la
OC
voltage
. The
rect
ified notse voltage passes through a
differenlial
ci
rc
uit
(C179, R266) and is then applied to a
OC amplifier (IC3a, pin 3).
When
the scan is in
operalion
, the CPU (IC5. pin 91) on
Ihe LOGIC UNIT
outputs
a
"HIGH
" signal
lor
35
msec
. on
Ihe
"IFBK
" signal line. The
"HIGH
" signal
lurns
036
and
037
ON
to
deactivate the squetch
circuit.
The
pu
lse-type signaI Is applied
to
C179
thro
ugh
055
to
r rapid
charging
.
•
5-METER
SQUELCH CIRCUIT
The s-rneter squelch retere
nce
voltage passes thraugh a
OC ampli
lie
r
(07)
and Is Ihen applled la Ihe comparator
(IC4b. pin 5) Ihrough
016
and is varied
by
Ihe [SOUELCH]
con
tr
ol on the
VR
UNIT. R66 adjusts
Ihe
input level ot
lC4b
(p
in
5). Th
is
re
ference
vollage
is added
to
the S-
meier
vollage and is
Ihen
applled
la
the (S.METER] on
Ihe
FRONT PANEL Ihrough 0 15 to indi
cate
Ihe s
-me
rer
sque
lch
threshold level.
The s-rneter squelch is
outpui
Irom
lC4b
(pin 7) and is
Ihen
app
lied
to
the base
of
047
Ihrough
017
.
3
-1
·22 SaUELCH SWITCH CIRCUIT
(MAIN UNIT)
047
switches
02
ON
or
OFF depending on Ihe output
le
vell
rom Ihe cornoarators (IC3b. lC4b
).
03
controts
Ih
e
ga
te
vo
l
lage
of 0 1 by using Ihe
collec
lo
r voltage of 0 2.
Q1 cuts out the AF signaI when the sq
uelc
h is closed.
02
outputs
a " BUSY" signal la Ihe LOGIC
UN
IT and lighlS
up
the (BUSYI in
di
calor
on
Ihe FRONT PANEL when the
squelch is open.
]
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8
3 - 8
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