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4.84
The
carrier level
(in
c.w. mode)
is
manually
adjusted
by
the front
panel Vernier
potentiometer,
which
is
fed
with
ad.c.
reference
level
provided by
IC4,
zener
diode
D40, and
associated
components.
4.85
The
reference d.c.
level
from
IC4/6
Is
set
by
AOT
resistor
R161.
The
reference
d.c.
level
is
fed via
R151
to
Q20.
In
the
absence
of
any audio
input
at
pin 23,
this
reference
will set
the carrier level via
Q20
and
Q19,
manually
adjusted
by
the
Vernier
potentiometer
between
terminals
25 and
21
.
Potentiometers
R153 and R143
set
the
a.m.
depth
to
be
the
same
at
the
extremes
of
the
Vernier
control.
4.86
From
the
Vernier potentiometer
the carrier
reference (and audio
signal
If
on
AM)
are fed through the
shaper
buffer IC8,
R
1 1
8
and
D37
to
one
Input of the
a.I.c.
comparator
IC9,
thus
providing
the
reference described
In
para.
4.83.
The purpose
of
D37
is
to
provide temperature
compensation
in
the
peak
detector
circuit
and
for
this
reason
D36,
D37
and
D38
are
mounted
In
physical contact.
X2
Output
4.87
A
d.c.
carrier
reference voltage
is
set
by
AOT
resistor
R159 and
fed
to
tag 'C
1
of the
Output
switch
S12/IF
(Fig. 20) via line
RN3a.
In
switch position 'X2
1
this
voltage
is
fed
to
the
modulation
input
at
pcb
pin 23,
setting the carrier level as
previously described.
Simultaneously,
wafer
S
1
2/1
F inserts
attenuating
resistance
R26
into
the
meter
path, causing the
meter
to
read
half the true
output
level.
The
,
X2'
facility
is
inoperative
In
the
a.m. mode.
AM
Audio
Input
4.88
The audio
signal
from
the Internal oscillator (or external
modulation
source)
Is
fed
via
switches
S8 and
S
1
2/1
F
(Fig. 20)
to
pin
23 on
the
Output
System
p.c.b.
It
Is
then fed
via the carrier
reference path
to
the
a.I.c. comparator
IC9.
4.89
ALC
information
is
provided
via the
peak
detector diode
D36
which
tends
to
be
non-linear near
the
trough
of the
modulation envelope
when
modulating
to
a
high
percentage
at relatively
low
carrier levels.
The
function
of the
AF
Shaper
IC6,
and
the
transistors
in
the
package
ICS,
is
to
Introduce
sufficient a.f.
shaping over
a
wide
temperature range
to
compensate
for
any
non-linearity
in
D36
and
thus
ensure
an
undistorted
modulating
waveform
at the
output
of the
comparator
IC9.
The shaper
is
calibrated
by
adjustment
of
R109.
OUTPUT
AMPLIFIER
11-1404
(9081
H and
9Q82H
ONLY)
4.89a
The
increased
maximum
output
level of
models 9081
FI
and
9082H
is
achieved by
means
of
an
additional amplifier
between
the
output system assembly
and
the
attenuator,
(see Fig. 22).
The
amplifier
module
is
mounted
adjacent
to
the attenuator.
No
parte
list
or repair
information
for
the
amplifier
is
given
in this
manual.
In
the
event
of failure the
complete module
should
be replaced.
9082C
Vol
.2
4-14
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