Belar AMM-3 User manual
AMM-3
AM
MODULATION
MONITOR
INSTRUCTIONS
Belar
Electronics
Laboratory,
Inc.
119
East
Lancaster
Avenue
P.O.
Box
826
Devon
PA
19333
WARRANTY
AND
ASSISTANCE
All
Belar
products
are
warranted
against
defects
in
materials
and
workmanship.
This
warranty
applies
for
one
year
from
the
date
of
delivery,
FOB
factory
or,
in
the
case
of
certain
major
components
listed
in
the
instruction
manual,
for
the
specified
period.
Belar
will
repair
or
replace
products
which
prove
to
be
defective
during
the
warranty
period
provided
that
they
are
returned
to
Belar
pre-
paid.
No
other
warranty
is
expressed
or
implied.
Belar
is
not
liable
for
consequential
damages.
For
any
assistance,
contact
either
your
Belar
Sales
Representative
or
Customer
Engineering
Service
at
the
Belar
Factory.
SECTION 1
GENERAL
INFORMATION
1-1
GENERAL
DESCRIPTION
The
Belar
AMM-3
AM
Modulation
Monitor,
(FCC
Type
Approval
#3-231)
is
an
all
solid
state
precision
AM
demodulator
designed
to
meet
the
Federal
Communications
Commission
requirements
for
measuring
the
total
modulation
characteristics
of
AM
broadcast
transmitters.
Since
the
input
circuitry
is
non-frequency
discriminating,
the
AMM-3
is
also
suitable
for
measuring
the
modulation
characteristics
of
shortwave
transmitters
as
well
as
VHF
transmitters.
Two
meters
and
two
peak
lights
are
provided
to
measure
positive
and
negative
modulations
simul-
taneously.
The
negative
modulation
meter
may
be
switched
to
read
carrier
level.
Separate
peak
indicators
are
provided
to
indicate
negative
peaks
in
excess
of
99%
and
positive
peaks
in
excess
of
125%.
The
AMM-3
incorporates
a
carrier-limits
alarm
and
a
modulation
calibrator
to
insure
the
accuracy
of
the
readings
at
any
time.
1-2
PHYSICAL DESCRIPTION
The
AMM-3
is
constructed
on
a
standard
EIA
5~
x
19-inch
rack
mount.
Calibration
adjustments
are
located
within
the
unit
and
are
accessible
through
the
back
cover.
The
AC
power
input,
RF
input,
and
monitor
outputs
are
located
at
the
rear
of
the
AMM-3
chassis
on
individual
connectors
and
rear
terminal
block.
The
AMM-3
is
completely
solid
state,
utilizing
all
silicon
transistors
and
integrated
circuits
for
long,
trouble-free
life.
LEDs
(light-emitting
diodes)
are
used
for
the
indicators
to
eliminate
lamp
burn-out.
The
individual
circuits
are
constructed
on
a
military-grade,
glass-epoxy,
plated,
printed
circuit
board.
High-reliability
military
and
industrial
grade
components
are
used
throughout.
1-3
ELECTRICAL DESCRIPTION
The
AMM-3
is
a
solid
state,
low-sensitivity,
precision
AM
demodulator
incorporating
a
highly
linear,
biased
diode
detector.
The
detector
circuit
will
accurately
demodulate
AM
envelopes
of
carriers
from
200
KHz
to
160
MHz.
Various
metering
and
testing
provisions
are
contained
within
the
monitor
to
measure
transmitter
output
characteristics.
These
provisions
include
a
peak-reading
positive
modulation
meter;
a
peak-reading
negative
modulation
meter
that
may
be
switched
to
read
carrier
level;
a
positive
peak
modula-
tion
light,
adjustable
from
1
to
199
%
peak
modulation;
a
negative
peak
modulation
light,
adjustable
from
1
to
99 %
peak
modulation;
a
peak
modulation
light
that
responds
when
the
negative
modulation
exceeds
99%; a
peak
modulation
light
that
responds
when
the
positive
modulation
exceeds
125%;
a
DC-type
modulation
calibrator
to
check
the
ratio
between
the
carrier
level
and
peak
modulation
reading;
a
carrier
alarm
light
that
responds
when
the
carrier
is
less
then
90 %
of
nominal
value
and
greater
than
105%
of
nominal
value
(this
may
be
set
to
other
values
by
the
change
of
potentiometer
settings).
Outputs
obtained
from
the
monitor
include
an
output
for
aural
monitoring,
a
distortion
meter
test
output,
a
transistor
driver
for
carrier
alarm,
and
a
transistor
driver
for
remoting
each
of
the
four
peak
lights.
FCC
type-approved
remote
metering
of
the
AMM-3
may
be
externally
provided
for
the
modulation
meters.
The
AMM-3
incorporates
an
analog
divider
to
provide
a
true
ratio
measurement
of
the
modulation
envelope
and
the
carrier
level.
The
analog
divider
continuously
references
the
demodulated
output
to
the
carrier
so
that
the
modulation
readings
are
independent
of
carrier
level.
The
carrier
level
is
derived
from
the
modulation
ca
ncellation
scheme
which
mak
es
the
carrier
level
referenced
independent
of
modulation
symmetry.
1-4
ELECTRICAL SPECIFICATIONS
RF
Frequency
Range
. . . . . . . . . .
200
KHz
to
160
MHz
RF
Sensitivity
.....
RF
Input
Impedance
. . . . · 5
to
10
Volts
RMS
·
1000
ohms
std.
(50
ohms
opt.
above
3
MHz)
positive
Modulation
M
eter
Range
........
0
to
133
%
positive
Negative
Modulation
Meter
Range.
. . . . . . . 0
to
100
%
negative
Carrier
Level
Meter
Range.
.
..
.....
0
to
133
%
Modulation
Meter
Accuracies*
. . . . . . . . .
2%
at
100
%
modulation
positive
Peak
M
odulation
Indicator
......
1
to
199
%
in
1%
Negative
Peak
M
odulation
Indicator
.
increments
(BCD
encoded)
1
to
99%
in
1%
increments
(BCD
encoded)
Peak
Modulation
Indicator
Accuracies*
....•
2%
100
%
Negative
Indicator*
. . .
..
.....
Adjustable
85
to
100
%
125%
Positive
Indicator*
. .
..
.
Adjustable
100
to
130
%
Carrier
Alarm.
. . .
..
....
.
Fi
x
ed
to
alarm
with
a
Frequency
Response
.
Pulse
Response
...
.
Distortion
.
...
.
Signal
to
Noise
Ratio.
Remote
Metering
•...•
Aural
Monitoring
Output
..........
.
Aural
Proof-of-Performance
Output.
Power
Requirem
e
nts
. . . . . . . . . . .
Operating
Temperature
Range
...
*
Over
a
±30%
input
carrier
level
change.
-10
%
and
+5
%
change
in
carrier
l e
vel.
0.5
dB
from
20-25,000
Hz
Overshoot
less
than
1%
·
0.25%
max.
at
99%
modulation
•
75
dB
·
Meters
may
be
remotely
metered
-
5000
ohms
external
loop
resistance
·
+lOdBm,
600
ohms
2.5
Volts
RMS
·
115/230
V,
50
to
400
Hz,
at
15
Watts
·
0°
C
to
+50
0C
1-5
MECHANICAL
SPECIFICATIONS
Dimensions
Net
Weight
. . . .
Shipping
Weight.
1-6
INSTRUMENT
IDENTIFICATION
. .
5~
x
19
x 8
inches
overall
(133
x
483
x 203mm)
10
pounds
(4.5
kg)
.
14
pounds
(6.4
kg)
The
instrument
is
identified
by
the
model
number
and
a
six-digit
serial
number.
The
model
number
and
serial
number
appear
on
a
plate
located
on
the
rear
panel.
All
correspondence
to
your
Belar
repre-
sentative
or
to
the
Belar
factory
in
regard
to
the
instrument
should
reference
the
model
number
and
complete
serial
number.
1-7
ACCESSORIES
The
Belar
AMM-3
Modulation
Monitor
may
be
used
for
remote
monitoring
of
an
AM
transmitter
with
either
the
Belar
MP-7
Remote
Meter
and
Flasher
Panel
or
one
of
the
Belar
AM
RF
Amplifiers--the
RFA-2
or
RFA-4.
The
MP-7
Remote
Meter
and
Flasher
Panel
contains
two
modulation
meters,
four
peak
lights,
and
a
carrier-alarm
light.
The
AM
RF
amplifiers
provide
preamplification
and
selectivity
to
permit
direct
off-air
monitoring
with
the
AMM-3.
2-1
INITIAL
INSPECTION
SECTION 2
INSTALLATION
Check
the
shipping
carton
for
external
damage.
If
the
carton
exhibits
evidence
of
abuse
in
handling
(holes,
broken
corners,
etc.),
ask
the
carrier's
agent
to
be
present
when
the
unit
is
unpacked.
Carefully
unpack
the
unit
to
avoid
damaging
the
equipment
through
use
of
careless
procedures.
Inspect
all
equipment
for
physical
damage
immediately
after
unpacking.
Bent
or
broken
parts,
dents
and
scratches
should
be
noted.
If
damage
is
found,
refer
to
Paragraph
2-2
for
the
recommended
claim
procedure.
Keep
all
packing
material
for
proof
of
damage
claim
or
,
for
possible
future
use.
2-2
CLAIMS
If
the
unit
has
been
damaged,
notify
the
carrier
immediately.
File
a
claim
with
the
carrier
or
transportation
company
and
advise
Belar
of
such
action
to
arrange
the
repair
or
replacement
of
the
unit
without
waiting
for
a
claim
to
be
settled
with
the
carrier.
2-3
REPACKING
FOR
SHIPMENT
If
the
unit
is
to
be
returned
to
Belar,
attach
a
tag
to
it
showing
owner
and
owner's
address.
A
description
of
the
service
required
should
be
included
on
the
tag.
The
original
shipping
carton
and
packaging
materials
should
be
used
for
reshipment.
If
they
are
not
available
or
reusable,
the
unit
should
be
repackaged
ln
the
following
manner:
a.
Use
a
double-walled
carton
with
a
minimum
test
strength
of
275
pounds.
b.
Use
heavy
paper
or
sheets
of
cardboard
to
protect
all
surfaces.
c.
Use
at
least
4
inches
of
tightly
packed,
industry
approved,
shock
absorbing
material
such
as
extra
firm
polyurethane
foam
or
rubberized
hair.
NEWSPAPER
IS
NOT
SUFFICIENT
FOR
CUSHIONING MATERIAL.
d.
Use
heavy
duty
shipping
tape
to
secure
the
outside
of
the
carton.
e.
Use
large
FRAGILE
labels
on
each
surface.
f.
Return
the
unit,
freight
prepaid,
via
air
freight.
Be
sure
to
insure
the
unit
for
full
value.
2-4
PREPARATION
FOR
USE
The
AMM-3
AM
Modulation
Monitor
is
designed
to
be
mounted
in
a
standard
19-inch
rack
mount.
When
mounted
in
a
rack,
a
slight
air
space
should
be
provided
above
and
below
the
unit.
When
the
monitor
is
mounted
above
high-heat
generating
equipment
such
as
vacuum-tube
or
power
supplies,
consideration
should
be
given
to
cool-
ing
requirements
which
allow
a
free
movement
of
cooler
air
around
the
AMM-3.
In
no
instance
should
the
ambient
chassis
temperature
be
allowed
to
rise
above
50
degrees
C
(122
degrees
F).
Mount
the
AMM-3
to
the
rack
mount
using
four
No.
10
screws
and
four
No.
10
non-marring
washers.
The
Model
AMM-3
requires
a
115/230
VAC,
single-phase,
50-400
Hz
power
source.
The
monitor
can
be
easily
converted
from
115
to
230
volt
operation
by
changing
the
position
of
the
slide
switch
located
on
the
rear
panel
so
that
the
designation
appearing
on
the
switch
matches
the
nominal
voltage
of
the
power
source.
Note
that
this
should
be
done
with
the
unit
disconnected
from
the
power
source.
The
Model
AMM-3
is
supplied
with
a
three-conductor
power
cable
which,
when
plugged
into
an
appropriate
receptacle,
grounds
the
unit.
The
offset
pin
of
the
power
cable
three-prong
connector
is
the
ground
wire.
To
preserve
the
grounding
feature
when
operating
the
unit
from
a
two-contact
outlet,
use
a
three-prong
to
two-prong
adaptor
and
connect
the
green
pigtail
on
the
adaptor
to
ground.
Attach
the
power
cable
between
the
unit
and
the
power
source
receptacle.
CAUTION:
BEFORE
APPLYING
ANY
RF
INPUT,
TURN
CARRIER LEVEL
CONTROL
MAXIMUM
COUNTERCLOCKWISE.
Connect
a
coaxial
cable
between
the
monitoring
probe
on
the
transmitter
(or
RF
Amplifier)
and
the
RF
INPUT
connector
J2,
at
the
rear
of
the
main
chassis.
CAUTION:
DO
NOT
APPLY
MORE
THAN
15
VOLTS
RF
TO
THE
MONITOR
OR
THE
RF
INPUT CIRCUIT
MAY
BE
DAMAGED.
If
desired,
connect
the
external
aural
monitoring
amplifier
to
terminals
11
and
12
on
TB-l.
Note
that
this
is
an
unbalanced
600
ohm
output
with
terminal
12
grounded.
A
remote
carrier
level
meter
may
be
connected
to
terminals
8
and
12
with
10
K
ohms
loop
resistance.
Remote
modulation
meters
may
be
connected
to
terminals
9
and
12
for
positive
and
10
and
12
for
negative
modulation.
Observe
the
proper
polarities
(terminals
8,
9
and
10
are
positive
terminals),
and
note
that
the
external
loop
resistance
requirements
must
be
met.
If
only
one
remote
meter
is
used,
the
other
modulation
metering
circuit
must
be
terminated
on
TB-l
in
order
for
the
internal
meters
to
read
correctly
when
the
remote
meter
switch
is
depressed.
For
example,
if
only
the
positive
remote
modulation
meter
is
used
and
the
remote
meter
switch
is
depressed,
the
positive
modulation
meter
will
read
correctly
but
the
negative
modulation
meter
will
read
approximately
6%
low
unless
a
7.5
K
resistor
is
placed
between
terminals
10
and
12
on
TB-l.
Remote
modulation
meters
should
be
obtained
-
from
Belar
in
order
to
conform
with
the
correct
ballistic
requirements.
A
remote
positive
peak
modulation
light
may
be
con-
nected
to
terminals
1
and
3
on
TB-l.
A
remote
negative
peak
modula-
tion
light
may
be
connected
to
terminals
1
and
4
on
TB-l.
Remote
100
%
negative,
125
%
positive,
and
carrier
alarm
lights
may
be
connected
to
the
appropriate
terminals
on
TB-l.
Note
that
terminal
1
is
a
5-volt
DC
source,
and
if
light-emitting
diodes
(LEDs)
are
used
for
the
lights,
series
resistors
must
be
used
to
limit
the
current
to
safe
values
for
the
LEDs
used.
The
remote
meters
and
lights
are
contained
in
the
MP-7
Remote
Meter
and
Flasher
Panel.
-100%
NEG
CARRIER
ALARM
POS
+125%
0 0 0 0 0
8jJ [E8J
NEGATIVE/CARRIER
PWR
CAR
NEGOPERCALZERONOISEREM
POSITIVE/NOISE
o
DDDCJCJDCJD
o
AMM-3
FRONT PANEL CONTROLS a INDICATORS
+125°,4
POS
PEAK
POS
AMP
NOISE
AMP
0 0 0 0
RI30
RI04
R50
-100%
NEe PEAK
0 0
RI32 RI2a
CARRIER
ALARM
LIMITS
UPPER
LOWER
R650
ORla
TBI-
J3
AUDIO
TEST
I 2 3 4 5 8 7 a 9
10
II
12
0
000000000000
Til-
l.
+ 5
VDC
2. CARRIER LIMIT ALARM
3.
+125%
MODULATION INDICATOR
4.
ADJ. NEGATIVE MODULATION PEAK INDICATOR
5.
ADJ. POSITIVE MODULATION PEAK INDICATOR
8.
-100%
MODULATION INDICATOR
7. IN'ORMER
AC
e.
CARRIER LEVEL
9. POSITIVE MODULATION /
NOI
.
SE
LEVEL METER
R75
10. NE8ATIVE MODULATION
/CARRIER
LEVEL METER
II.
AURAL MONITOR SIGNAL (600.n...)
12.
GROUND
CALIBRATE
0
RI20
J2
RI
JI
FI
RF
CARRIERSET 0
(0)50
Q
AC
o ® 0
(.1
I
o
POWER
.25A
30VAC
AMM-3
REAR CHASSIS CONNECTIONS a ADJUSTMENTS
3-1
INITIAL
OPERATION
SECTION 3
OPERATION
The
following
procedure
should
be
followed
for
placing
the
unit
into
initial
op~ration.
1.
Before
turning
the
unit
on,
be
sure
the
position
of
the
115/230
VAC
switch
on
the
back
apron
coincides
with
the
voltage
source
used.
2.
Depress
the
ZERO
switch,
NEG
mod
switch
and
release
the
REMOTE
switch.
Turn
CARRIER SET
control
on
the
back
apron
maximum
counterclockwise.
3.
Depress
the
POWER
switch.
Note
that
the
MODULATION
meters
are
approximately
zero.
Allow
a
few
minutes'
warm-up.
4.
After
warm-up,
the
MODULATION
meters
should
read
zero.
If
they
do
not
read
zero
but
are
only
off
a
few
percentage
points,
they
may
be
set
to
read
zero
with
the
mechanical
zero
controls
on
the
meters.
If
the
zero
is
off
more
than
a
few
percentage
points,
the
zero
should
be
set
according
to
step
8
of
the
modulation
processor
alignment
procedure
in
the
maintenance
section.
The
electrical
zeros
are
stabilized
by
feed-back
operational
amplifiers
and
normally
do
not
need
readjustments.
5.
Depress
CARRIER
switch.
Rotate
the
CARRIER SET
control
clockwise.
The
CARRIER
ALARM
light
will
go
out
at
approximately
90%
carrier
level.
Continue
to
rotate
the
control
so
that
the
CARRIER
level
meter
reads
100%.
Note
that
this
is
the
carrier
level
set
point
for
measuring
carrier
shift
and
carrier
level.
Note
that
the
modulation
readings
are
independent
of
carrier
level.
6.
Depress
the
CAL
switch.
The
MODULATION
meters
will
read
100%
to
verify
the
accuracy
of
the
calibration.
The
+125%
light
will
be
on.
The
-100%
light
will
be
on.
7.
Adjust
the
POSITIVE
digital
switch
to
the
point
where
the
POSITIVE
peak
modulation
light
just
turns
on.
This
setting
will
be
100
%.
Note
that
the
NEGATIVE
peak
modulation
light
is
on.
The
100
%
point
is
not
on
the
NEGATIVE
digital
switch
but
is
switched
in
with
the
CAL
switch.
8.
Depress
OPER
switch
and
the
moni~or
is
ready
for
operation
with
the
right
meter
reading
positive
modulation.
Note
that
the
left
meter
reads
negative
modulation
when
the
NEG
switch
is
depressed
and
carrier
level
when
the
CARRIER
switch
is
depressed.
3-2
NORMAL
OPERATION
For
normal
operation,
leave
the
AMM-3
in
OPER
and
NEG
switch
positions
when
broadcasting
super-modulation.
The
MODULATION
meters
will
read
positive
and
negative
modulations
simultaneously.
Nominal
changes
(±30%)
in
RF
level
will
not
affect
the
accuracy
of
either
the
MODULATION
meters
or
the
peak
lightsi
however,
the
CARRIER
ALARM
will
turn
on
at
deviations
greater
than
-10%
or
+5%.
The
POSITIVE
digital
switch
is
usually
set
to
a
level
slightly
lower
than
+125%,
say
+120%.
The
NEGATIVE
digital
switch
is
usually
set
to
a
level
slightly
lower
than
99%,
say
95%.
Then
the
modulation
may
be
set
for
frequent
recurrent
peaks
of
-95%.
Note
that
the
correct
type
of
audio
processing
limiter
must
be
used
for
this
type
of
operation.
The
separate
-100%
and
+125%
lights
are
used
for
the
limits
to
insure
the
maximum
level
of
modulation
without
exceeding
the
limits
set
by
the
FCC.
When
the
CARRIER
switch
is
depressed,
percent
carrier
shift
is
read
on
the
left
MODULATION
meter
as
a
change
~n
carrier
intensity
during
modulation.
Note
that
due
to
the
unique
modulation
cancellation
scheme
in
the
AMM-3
to
regenerate
unmodulated
carrier,
this
change
in
carrier
intensity
is
independent
of
modulation
symmetry.
In
this
manner,
accurate
carrier
shifts
are
measured.
3-3
TRANSMITTER
MEASUREMENTS
Normal
transmitter
proof-of-performance
measurements
may
be
made
with
the
AMM-3.
Frequency
response,
distortion,
and
noise
measurements
may
be
made
through
the
rear
panel
AUDIO TEST
jack
J3.
2.5
volts
RMS
is
available
at
100
%
modulation
so
that
most
distortion
and
noise
analyzers
may
be
used.
The
bandwidth
at
this
test
jack
is
limited
to
25
KHz
by
an
additional
low-pass
filter.
If
the
full
50
KHz
bandwidth
is
needed,
the
aural
output
from
terminals
11
and
12
on
TB-l
may
be
used.
The
output
level
from
these
terminals
is
5
volts
RMS
unterminated.
Percent
modulation
is
read
on
the
MODULATION
meters
and
percent
carrier
shift
is
read
on
the
left
MODULATION
meter
when
the
CARRIER
level
switch
is
depressed.
Note
that
positive
peaks
of
up
to
199% may
be
measured
with
the
POSITIVE
peak
modulation
light
since
the
overload
point
of
the
associated
circuitry
is
greater
than
200%.
Also
note
that
it
is
impossible
to
modulate
more
than
100
%
negatively
since
by
definition
100
%
negative
modulation
is
carrier
shut-off.
Conventional
monitors
may
read
more
than
100
%
negative
modulation
because
overshoots
may
be
generated
in
their
filters
at
carrier
shut-off
and
these
monitors
read
the
overshoot.
The
Belar
AMM-3
employs
a
phase
linear
filter
that
produces
no
overshoot
so
that
carrier
shut-off
produces
100%
negative
modulation.
AM
noise
on
an
unmodulated
carrier
may
be
measured
by
depressing
the
NOISE
switch.
This
switches
in
a
40
dB
amplifier
on
the
righthand
meter.
A 0
dB
meter
reading
corresponds
to
a 40
dB
signal-to-noise
ratio;
a
-20
dB
meter
reading
corresponds
to
a 60
dB
signal-to-noise
ratio,
etc.
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MAINTENANCE
TEST
EQUIPMENT
REQUIRED
VTVM
High
frequency
oscilloscope
with
5"
display.
Linear
modulator,
output
level
of
5-10
volts
RMS,
unrnodulated
(SEE
NOTE)
Low
distortion
oscillator
NOTE:
The
modulation
meter
and
peak
lights
respond
to
peak
values
of
modulation
so
that
if
there
is
distortion
in
the
modulator,
the
peak
indications
will
be
the
true
peak
values,
i.e.,
the
sum
of
fundamental
and
the
harmonics
or
distortion
products.
The
most
common
mistake
made
in
calibrating
AM
monitors
is
to
adjust
the
modulation
level
until
carrier
shut-off
is
reached.
This
is
defined
as
100%
negative
and,
indeed,
it
is
100%
negative,
but
the
positive
value
is
not
necessarily
100%.
If
the
distortion
is
3%
at
this
level
(typical
of
many
trans-
mitters),
the
positive
value
of
modulation
may
be
anywhere
from
97%
to
103%,
depending
on
the
phase
of
the
harmonics,
and
the
monitor
will
read
this.
For
this
reason,
the
monitor
should
be
calibrated
at
just
100%
negative
on
the
negative
indications
and
then
the
modulation
backed
off
to
90%
for
the
positive
indications
so
they
can
be
set
in
the
region
where
the
transmitter
is
more
linear.
POWER
SUPPLY
ALIGNMENT
1.
Set
mechanical
zero
on
both
meters.
2.
Turn
power
on
and
allow
to
warm
up
for
15
minutes.
3.
With
VTVM,
measure
voltage
at
Ul
Pin
7.
Voltage
should
be
+15.5
volts
±0.5
volts.
Adjust
R88
for
correct
reading.
4.
With
VTVM,
measure
voltage
at
Ul
Pin
4.
Voltage
should
be
-15.5
volts
±0.5
volts.
Adjust
R82
for
correct
reading.
MODULATION
PROCESSOR
ALIGNMENT
1.
Apply
an
unrnodulated
RF
level
of
5-10
volts
RMS
to
input,
J2,
of
monitor.
2.
Place
function
switch
'
in
CAR
position
and
adjust
Carrier
Set
potentiometer
(Rl)
on
rear
chassis
for
100%
on
the
left-hand
meter.
3.
Place
function
switch
in
ZERO
position.
4.
Disconnect
Carrier
Reference
(yellow/white)
wire
from
Pin
13.
Connect
a
jumper
wire
from
the
positive
terminal
of
filter
capacitor
C5
on
chassis
to
Pin
13
on
the
board.
Connect
oscilloscope
at
the
junction
of
R44
and
Q4.
Adjust
vertical
amplifier
for
maximum
sensitivity.
If
R38
is
in
need
of
adjustment,
a
120
Hz
ripple
will
appear
on
the
oscilloscope.
Adjust
R38
to
balance
the
120
Hz
ripple
to
zero.
Reconnect
Carrier
Reference
wire
to
Pin
13.
5.
Place
function
switch
in
ZERO
mode
and
the
probe
of
the
VTVM
at
the
junction
of
R44
and
Q4.
The
VTVM
should
measure
zero
volts.
Adjust
R32
for
correct
reading.
6.
Place
function
switch
in
the
OPERe
mode,
and
apply
a 1
KHz
tone
to
the
modulator
and
adjust
the
level
for
a
modulation
reading
of
80-90%,
as
observed
on
the
oscilloscope.
7.
Slowly
adjust
Carrier
Set
Potentiometer
(Rl)
on
rear
chassis
so
that
the
carrier
level
is
varied
from
50%
to
133%.
Place
left-hand
meter
in
NEG
position.
The
modulation
meters
should
remain
within
2%
as
the
carrier
input
level
is
adjusted.
If
they
do
not,
then
R30
should
be
adjusted
for
minimum
meter
variation
as
the
carrier
level
is
adjusted.
(If
the
positive
meter
shows
a
10
%
positive
variation
when
the
carrier
level
is
changed
from
133%,
to
50%,
then
the
meter
reading
should
be
reduced
by
15
%
when
the
carrier
level
is
set
to
50%
by
adjust-
ing
R30) .
8.
Re-check
step
5,
then
place
the
function
switches
in
ZERO
and
NEG
position.
The
negative
meter
should
read
zero.
Adjust
R55
for
correct
reading.
The
positive
meter
should
also
read
zero.
Adjust
R56
for
correct
reading.
Set
Carrier
Level
to
100
%.
9.
Apply
a 1
KHz
tone
to
the
modulator
and
adjust
level
for
100
%
negative
modulation
as
observed
on
the
oscilloscope.
Depress
OPER
on
function
switch.
"
Negative
meter
should
indicate
100
%.
If
not,
adjust
R25
for
correct
reading
(SEE
NOTE)
Repeat
steps
5)
,8)
,9)
to
achieve
optimum
op
eration.
10.
Depress
CAL
switch.
Ne
ga
tive
meter
should
indicate
100
%.
Adjust
R120
for
correct
indication.
The
positive
meter
should
indicate
100
%.
Adjust
R50
for
correct
reading.
PEAK
INDICATOR
ALIGNMENT
+125
%
Peak
Indicator
With
CAL
switch
depressed,
the
125
%
peak
indicator
should
be
on.
If
not,
adjust
R130
for
correct
indication.
positive
Peak
Indicator
With
CAL
switch
depressed
and
thumbwheel
switch
adjusted
for
100
the
Positive
Indicator
should
be
on.
Advance
the
thumbwheel
switch
for
a
reading
of
101.
The
Positive
Peak
Indicator
should
be
off.
If
not,
adj
ust
Rl04
so
that
the
peak
indicator
turns
on
at
100
and
off
at
101.
-100
%
Peak
Indicator
Depress
CAL
Switch.
-100
%
peak
indicator
should
be
on.
If
not,
adjust
R132
for
correct
indication.
Negative
Peak
Indicator
Depress
CAL
Switch.
Negative
peak
indicator
should
be
on.
If
not,
adjust
R128
for
correct
indication.
Carrier
Limit
Alarm
Indicator
Depress
CAR
switch.
Adjust
carrier
input
level
for
100
%
on
meter.
Carrier
alarm
indicator
should
be
off.
a.
Lower
Limit
Adjustment:
Set
carrier
level
for
90%
on
meter.
Carrier
alarm
indicator
should
be
on.
If
not,
adjust
R18
for
correct
operation.
b.
Upper
Limit
Adjustment:
Set
carrier
level
for
105%
on
meter.
Carrier
alarm
indicator
should
be
on.
If
not,
adjust
R6~
for
correct
operation.
NOISE
MEASUREMENT
CALIBRATION
Depress
OPER
switch.
Adjust
the
modulation
level
for
a r e
ading
of
100%
on
positive
meter,
and
a
modulating
frequency
of
400
Hz.
Reduce
the
modulation
level
40
DB.
Depress
Noise
Switch,
positive
meter
should
indicate
100%.
If
not,
adjust
R75
for
correct
reading.
REPLACEABLE
PARTS
INTRODUCTION
This
section
contains
information
for
ordering
replaceable
parts
for
the
monitor.
The
table
lists
the
parts
in
alphanumerical
order
of
their
reference
designations
and
provides
a
description
of
the
part
with
the
manufacturer's
part
number.
ORDERING
INFORMATION
To
order
a
replacement
part
from
Belar,
address
the
order
or
inquiry
to
Belar
and
supply
the
following
information
:
a.
Model
number
and
serial
number
of
the
unit.
b.
Description
of
part
including
the
reference
designation
and
location.
To
order
a
part
from
a
manufacturer
other
than
Belar,
provide
the
complete
part
description
and
the
manufacturer's
part
number
fr
om
the
table.
REFERENCE
DESIGNATORS
A =
assembly
J =
jack
S =
switch
C =
capacitor
L =
induct
or T =
transformer
DS
=
device
signaling
M =
meter
TB =
terminal
board
(lamp)
F =
fuse
P =
plug
W =
cable
FL
=
filter
Q =
transistor
X =
socket
R =
resistor
Y =
crystal
ABBREVIATIONS
CER =
COMP
=
CONN
=
ELECT=
F =
ceramic
composition
connector
electrolytic
farads
FLM
FXD
=
film
=
fixed
GE
=
germanium
K =
kilo
=
1000
M =
meg
=
1,000,000
METFLM
=
metal
film
MY
=
mylar
PC
=
printed
circuit
PF
=
picofarads
PIV
=
peak
inverse
voltage
POLY
=
polystyrene
PORC
=
porcelain
POT
=
potentiometer
SEMICON =
semiconductor
SI
= s
ilicon
U =
mi
c
ro
VDCW
=
DC
working
volt
s
W =
watts
WW
=
wire
wound
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