Belar FMM-1 User manual

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WARRANTY AND ASSISTANCE
All Belar
product
s are warranted again
st
defects in materials
and
workmanship. This warranty applies
for
one
year
from
the
d
ate
or
delivery,
or
, in
the
case
of
certain ma
jor
components
listed in
the
instruction manual, for
the
specified period. Belar will repair
or
replace
product
s which prove
to
be defective during
the
warranty
period provided
that
they
are
returned
to
Belar. No
other
warranty is expressed
or
implied. Belar is
not
liable
for
consequential damages.
For
any
assis
tan
ce,
contact
either
your
Belar Sales Representative
or
Customer Engineering Service
at
the
Belar factory.
I

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TABLE
OF CONTENTS
SECTION 1 PAGE
GENERAL INFORMATION
........
. .
..
.......
3
1- 1 GENERAL DESCRIPTION
........
.
...
3
1- 2 PHYSICAL DESCRIPTION . . .
..
.......
3
1- 3 ELECTRICAL DESCRIPTION
....
.....
.4
1- 4 ELECTRI
CA
L SPECIFICATIONS .
......
4
1- 5 MECHANICAL SPECIFICATIONS
..
.
....
5
1- 6 INSTRUMENT IDENT
IF
ICAT
ION
.......
5
1- 7
ACCESSOR
IE
S
.....
. . .
..
.
.........
5
SECTION 2 PAGE
INSTALLATION .
...
..
.
........
.
..
.
........
7
2- 1
IN
IT
IAL INSPECTION
......
.
..
.
.....
7
2- 2 CLAIMS
.......
.
......
. . .
........
7
2- 3 REPACKING FOR SHIPMENTS .
..
. . .
..
7
2- 4 PREPARATION FOR
USE
....
.
......
.7
SECTION 3 PAGE
OPERATIONS
.......
..
....
.
.............
..
9
3-1
INITIAL
OPERATION . .
..
...........
9
3-
2
NORMAL
OPERATION
.............
.9
3-
3 LOCAL
OSC
I
LLATOR
FREQUENCY CALIBRATION .
.......
9
3-
4 TRANSMITTER MEASUREMENTS
......
9
SECTION 4 PAGE
PRINCIPLES OF OPERA
TI
ONS
. . .
..
.
........
.
11
4-1
BLOCK DIAGRAM
DESCR
IPTI
ON
.....
11
4-2
DETA
IL
ED CIRCUIT DESCRIPTION
..
.
11
4-2
- 1 O
sc
ill
ator, T
ri
pier & Mixer
Ci
rcuit
.....
.
11
4-2
- 2 Oscillator, Counter
Di
sc
ri
m
in
a
to
r
&Amplifi
er Circui
ts
......
.
....
.
..
13
4-2
- 3 Amplifier, Metering &
Flasher Circuits
.........
. .
....
. . 14
SECTION 5
PAGE
MAINTENANCE
...
....
.
..................
15
5- 1 INTRODUCTION .
................
15
5- 2 PERFORMANCE CHECKS
.......
.
...
15
5- 2- 1
Po
wer
and
Oven
Che
ck
......
.
......
15
5- 2- 2 O
sc
illator
Leve
l
Che
ck
..............
15
5- 2- 3 Frequency Meter Amplifier
Che
ck
......
15
5-2
- 4 Freq Meter Discriminator
Check
.......
15
5- 2- 5 Mod Meter Amplifier Zero
Che
ck
....
. .15
5-2
- 6 Modula
tion
Cal
ibrator Check .
.........
15
5- 2- 7
Rem
ote Meter Switch Check . . . .
......
15
5- 2- 8
Per
cent Mod Po
te
nti
ometer
Che
ck
......
15
5- 2- 9 Modulat
io
n
Pol
arit
y
Che
ck
...........
15
5- 2- 10 Carrier Lev
el
Ch
eck .
..
.
....
...
.....
15
5- 2-
11
Oper
at
e
Ch
eck . .
.....
.....
.......
15
5- 2- 12 De-emph
as
is S
wit
ch
Ch
ec
k . .
..
.
......
16
5- 3 ADJUSTMENTS, CALIBRATION &
5-
3-1
5- 3- 2
5-3-3
5-
3-4
5-3
- 5
5- 3- 6
5- 3- 7
5- 3- 8
5- 3- 9
5- 3- 10
5- 3-
11
5- 3- 12
TROUBLESHOOTING
............
16
Power & Oven . .
..
. .
.....
.
.......
16
Oscillator
Level
. .
..
.
..
. . . .
........
16
Frequency Meter Amplifier
...........
16
Freq Meter Discriminator . .
........
. . 16
Mod Meter
Amp
lifier
Ze
ro
..........
.16
Modulation Calibrator
..........
.
..
.17
Remote Meter Sw
it
ch
......
..
......
17
Percent Mod Potentiometer
..
..
...
. . . .
17
Modulation Polari
ty
. .
..
.
...........
17
Carr
ie
r
Level
.....................
17
Operate
............
.
..
.
..
...
.
..
17
De
-e
mphasis Sw
it
ch
....
.
..
..
...
.
...
17
SECTION 6 PAGE
REPLACEABLE PARTS .
...
. . .
..
. .
..........
23
6- 1 INTRODUCTION
..
.....
...
.
......
23
6- 2 ORDERING INFORMATION
.........
23
SECTION 7
PAGE
SCHEMATICS
..........
.
.......
. . . .
..
. . . .29
LIST
OF
ILLUSTRATIONS
1- 1
1- 2
1- 3
1- 4
2- 1
3-
1
4-1
4-2
5- 1
5- 2
FMM- 1 FREQUENCY
AND
MODULATION MONITOR
..
..
......
3
FRONT PANEL VIEW . . . .
..
.........
4
REAR PANEL VIEW . . . .
..
..
. .
......
4
MECHANICAL DIMENSIONS
....
...
...
5
REAR PANEL CONNECTIONS
..
.
.....
6
OPERATING
CON
TR
OLS .
..
.
........
8
BLOCK
DIAGRAM
.
..
.
..
. . .
.......
10
WAVEFORMS
..
.
....
.
.....
.
......
12
Al
CARD . .
..
.
....
.
............
18
A2
CARD
..
. . . .
..
.
..
...........
19
5- 3
5- 4
5- 5
7- 1
7- 2
7- 3
7- 4
A3
CARD .
..
.
..
.
....
.
...
..
. .
..
. 20
TOP VIEW, COVER OFF
...
.
....
. . .
21
BOTTOM VIEW, COVER OFF . . . . . . . .22
OSCI
LLATOR, TRIPL
ER
& MIXER
CARD A1,
SC
HEMA
TI
C
..
.
........
30
OSCILLATOR, COUNTER & AMPLIFIER
CARD
A2,
SC
HEM
AT
IC
..
.
..
. . . . . .
31
AMPLIFIER, METERING & FLASHER
CA
RD
A3, SCHEMATIC
.......
...
.33
FREQUENCY & MOD
UL
A
TI
ON
MONITOR
CHASSIS. SCHEMA
TI
C
...........
35

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3
SECTION 1
GENERAL
INFORMATION
1- 1 GENERAL DESCRIPTION
The Belar
FMM-
1
FM
Frequency and Modulation
Monitor,
Figure
1-1,
[FCC
Type
Approval Number
3-
129] is a
wideband, all solid state
FM
monitor
designed
to
meet the
Federal Communications Commission requirements
for
measuring
the
center frequency and
total
modulation
characteristics
of
monaural
as
well
as
multiplexed FM
transmitters having a center frequency range
of
88
to
108
MHz.
In
addition,
the
FMM
- 1 may be
used
as
a
low
distortion and
low
noise
FM
demodulator
for
drivingaudio
monitor
amplifiers and
the
companion Belar FMS- 1 Stereo
Frequency and Modulation
Monitor
and one
or
more
SCM
- 1 SCA Frequency and Modulation Monitors.
Th
e
FMM
- 1
incorporates
a deviation
type
modulation
calibrator
to
insure the accuracy
of
the modulation readings
at
any time.
..
1- 2 PHYSICAL DESCRIPTION
The
FMM-1,
Figure 1-
2,
is constructed on a standard 5¼
x
19
inch rack
mount.
Seldom
used
controls
and
test points
are
located under the hinged
front
cover bar. Factory
adjustments
are
located
wit
hin the shielded compartments
of
the
monitor.
The
AC
power input, RF input, and
monitor
outputs
are
located
at
the rear
of
the
FMM-1
chassis
on individual connectors
or
on rear terminal blocks
as
shown in Figure 1- 3. The FMM- 1 is completely solid
state utilizing all silicon transistors
for
long, trouble-free
life. The individual circuits
are
constructed on
military
grade, glass-epoxy, plated printed
circuit
boards. High
reliabil
ity
industrial and
military
grade components
are
used
throughhout.
Fi
gure 1- 1

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4
1- 3 ELECTRICAL DESCRIPTION
The
FMM-
1 is a solid state. low sensitivity, crystal
controlled, superheterodyne
FM
receiver incorporating a
highly linear and stable pulse counting discriminator
that
measures
the
center frequency deviation and demodulates
t he FM transmission. Various metering
and
testing
provisions are contained within
the
monitor
to
measure
transmitter
output
characteristics. These provisions include
a center frequency deviation meter; a peak reading
total
modulati
on
meter, switchable
to
eith
er
positive or negative
modulation polarity; a peak modulation light, independent
of
modulation polarity,
that
responds
to
both
positive and
negative directions; metering circuits
to
set
the
incoming
RF level and
to
standardize
the
center frequency deviation
meter with
the
calibrating oscillator; a deviation
type
modulation calibrator
to
standardize
the
modulation level.
Outputs obtained from the monitor include a monaural
output
for aural monitoring, a distortion meter
test
output
[both monaural
output
and distortion meter
output
have
front panel switched de-emphasis) , a wideband test
output,
four wideband
outputs
for driving associated multiplex
demodulators,
an
AM
noise diode
output,
and an incidental
AM
noise diode
output
. FCC
Type
Approved r
emote
metering
of
the FMM-1 may be externally provided for
the
center frequency deviation meter, modulation meter. and
peak
lig
h
t.
1- 4 ELECTRICAL SPECIFICATIONS
RF
Input
Sensitivity
...
. . .
.......
.
....
0.2
to
10
volts RMS.
RF
Input
Impedance
...
..
..
.
...
.
.....
. . .
....
50
ohms
.
RF
Frequency Range .
......
.....
.
...
.. ..
.
88
-
108
MHz.
Deviation Meter Range
..
......................
±3 kHz.
Modulation Meter Range
............
133% (
100
%
at
75
kHz) .
Modulation Cali
brator
.....
...
.......
...
100%
at
75
kHz.
Modulation Meter Accuracy .
....
Better
than
5%over entire scale.
Peak Modulation Indicator
.. ..
. .
....•.....
. .
50
to
120%.
Frequency response
..............
-±
0.1
db,
50
-
75,000
Hz,
3
db
down
at
180
kHz.
Oi
stonion
...
..
.......
...
. .
...
0.1% max.
50
-
75,000
Hz.
Signal-
to
-Noise Ratio
....
...
..
75
db
with
75
usec de-i!mphasis.
Outputs
.........
...
.......
4 wideband isolated
outputs
to
drive
the
FMS- 1 stereo
unit
and
one
or
more
SCM
- 1
SCA
unit
s,
wideband test
output
, di
stonion
meter
output
, aural monitoring
output
,
AM
noise
output,
a
nd
Incidental
AM
noise
output.
Remote
Metering
.....
...
Both
ca
rrierdevi
ation
and modulation
meters
may
be
remotely
met
ered,
5000
ohms
ex
terna
l
loop
resistance.
.....
...
-.-,_ -
--
. ---
..
--
·--
...
...
..
....
. --
..
..
'
...
-
C
OIH'OIITl
OUTPUf
'°
••
· U
14
••••
•
•
Figure 1- 2
TII
- I I I 4 t t , I I
..
II
11
•
,-&
•
-,
,.
.....
.,
••••
Figure 1- 3
-·
tat-I
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..
.
,.
o.tA
0..166
•

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5
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Tc
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.,
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...
t;:
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SIDE
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19
17i\
(
CHASSIS)
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____________
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z
FRONT VIEW
Figure 1- 4
1- 5 MECHANICAL SPECIFICATIONS
Dimensions
..
....
. .
..
.
...
.
..
5¼ x
19
x 11 7
/8
inchesoverall
Detailed Dimensions •
...
.
..
.....
....
...
.....
Figure
1-4
Net
Weight
..
.
..
..
...
.
......
...
.
..
......
..
15
pounds
ShippingWeight . .
..
.
..........
......
....
. .19 pounds
1- 6 INSTRUMENT IDENTIFICATION
The instrument
is
identified
by
the model number and a six
digit serial number.
The
model number and ser
ial
number
appear
on
a pl
ate
located
on
the
rear panel, Figure
1-3.
All
correspondence
to
your
Belar representative or
to
the Belar
factory in regard
to
the instr
ument
should reference the
model number and complete serial number.
1- 7 ACCESSORIES
The
Belar
FMM
- 1
FM
Frequency and Modulation
Mo
ni
tor
may
be
used
for
the
remote
monitoring
of
an
FM
transmitter with
eit
h
er
the
Belar MP
-1
Remote Meter
Panel or
the
Belar RFA- 1 RF Amplifier.
The
MP-1
Meter
Panel contains a peak indicator lam
p,
a carrier frequency
deviation meter and a m
odulat
i
on
meter,
bot
h designed for
5000
ohms
loop resistance.
The
RFA- 1 RF
Amp
lifi
er
provides pre-amplification and selectivity
to
permit direct
off-air monitoring with the FMM-1.

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6
I
,.
(")
0 STEREO
~ ®~
,,
~
~
0 ®~
(/)
SCA
~
~
. I
-
0 SCA
@~
C
-i
~
C
cil
SCA
@~
'-
-4
tD
I'\)
-
s -
GROUND
s N
MONITOR
OUTPUT
INC. A.M.
®~
s
~
+25V
s •
+25V
A.M. NOISE
@;
s OI
}'
REMOTE
&~ s
a,
+
MOD.
METER
s
...,
r.
REMOTE
R.F. I
NPUT
@~
s
0D
FREQ.
METER
-4
s
co
}
tD
EXT.
MOD.
--
PEAK
LIGHT
--s 0
-
UI
{ -
< -s -
19VAC
~
.._ -
UI
0
.,
--
N
?
:E
...
, -s -
GROUND
m N
gi ::0
--
-
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(")
-
J!
----
0
~
..,,
►-
0 N
..,,
UIN
►
Figure
2-
1

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7
SECTION 2
INSTALLATION
2- 1
INITIAL
INSPECTION
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 reusabl
e,
the
unit
should be repackaged in
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
MA
TE
RIAL.
d.
Use
heavy
duty
shipping
tape
to
secure
the
outside
of
the
carton.
e.
Use
large FRAGI
LE
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
T
he
F
MM
- 1 Frequency and 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
as
the
heat generated
by
the
crystal oven should be dissipated. When
the
monitor
is
mounted above high
heat
generation equipment such as
vacuum-
tube
power supplies, consideration should be given
to
cooling requirements which allow a free movement of
cooler air through and around
the
FMM
- 1. In
no
instance
should
the
ambient chassis temperature be allowed
to
rise
above
50
degrees C
(122
degrees
Fl.
M
ount
the
FMM
- 1
to
the
rack
mount
using
four
No.
10
screws and four No.
10
countersunk finishing washers.
The Model
FMM
- 1 requires a
105
to
125 VAC single
phase,
50
to
60
Hz
power source. Consult Belar for
operation with
other
power sources.
Attac
h a three wire,
grounded line cord
to
TB1 with
the
ground wire
to
terminal
2 and the AC line wires
to
terminals 1 and 3.
Connect a
50
ohm
coaxial cable [RG-58) between
the
monitor probe
on
the
transmitter [or RF amplifier) and
the
RF
input
connector
J7,
at
the
rear of
the
main chassis.
CAUTION:
DO
NOT
APPLY
MORE
THAN
10
VOLTS
RF
TO
THE
MONITOR
OR
THE
RF
INPUT
LEVEL
CONTROL
MAY
BE
DAMAGED
.
If desired, connect external aural monitoring amplifier
to
terminals 1 and 2
on
TB
2. Note
that
this
is
an unbalanced
600
ohm
output
with terminal 1 grounded. A
remote
center
frequency deviation meter
and
remote modulation
meter may be connected
to
terminals
7,
8 and 5, 6
respectively,
if
desired. Observe
the
proper polarities
[terminals 6
and
7 are positive) and
note
that
the
external
loop resistance
not
including meters must
be
5000
ohms.
These meters must
be
obtained from Belar Electronics
laboratory,
Inc. in ord
er
to
comp
ly with FCC regulations
on
remote
metering. A remote peak modulation lamp may
be
connected
to
te
rminals 9 and 10. CAUTION:
DO
NOT
SHOAT TERMINAL 9 TO GROUND.
The
remote meters
and lamp are contained in
the
MP
- 1 Remote Meter Panel.

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8
DS3
•
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DS2
•PEAK MOO. LIGHT
M- 1-- -
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_ .
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•MOD.
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.19
•WIDEBANDTEST
S2
·FREQ.CAL•
RS
.
MOO
. METER ZERO
Figure
3-
1
1. POWER
SW
ITCH-When
dep
ressed
turns
the
unit
on
. Power is
app
lied
to
the
crystal oven
from
the
line
and
is
independent
of
the
power
switch.
2. PO
WER
INDICATOR-Lower
amber
light
between
the
meters
indicates
that
the
unit is
turned
on
.
3. OVEN INDICATOR-Upper
red
light
between
the
mete
rs
indicates
that
heat
is being
app
li
ed
in
the
crystaloven.
4.
RF
SWI
TCH-When depressed indicates
the
RF level
on
the
percentage modul
ation
meter.
5.
REMOTE SWITCH-When in
off
(released) position removes
both
metering circuits
fr
om
the
remote
mete
ring terminals
and
substitutes
the
equivalent resistances.
6. OSCILLATOR SWITCH-When depressed indicates
the
oscill
ato
r
level
on
the
percentage modulation meter.
7 .
FUNCTION
SW
ITCH-When
in
OP position disables a
ll
calibration circuits
and
places
the
unit
in
operation
for
measuring
frequency deviation
and
total
modulation.
8. FUNCTION SWITCH-When in
AM
P BAL position,
the
inputs
to
the
frequency differential
amp
lifier are
shorted
, a
ll
owing it
to
be
calibrated.
9. FUNCTION
SW
IT
CH- When
in
FREQ
CAL position,
the
650
kHz
ca
librating osci
ll
ato
r is
turned
on
and
applied
to
the
pulse
counter
frequency discr
im
i
nat
or allowing it
to
be
ca
librated.
10
. FUNCTION SWITCH-When in
MO
D CAL position applies a
standard deviation
to
the
monitor
to
check
modu
lation calibration.
11.
FREQ
ZERO
POTENTIOMETER-
Standa
rd
izes
the
width
of
the
output
pulse
of
the
pulse
counte
r discriminator
to
re
ad
zero in
function 9 above.
12. AMP BALANCE POTENTIOMETER-Adjusts
the
DC balance
of
the
frequency differ
en
ti
al
amp
lifier in function 8 above.
13
. MOD METER BALANCE-
Ad
justs
the
percentage modulation
meter
to
read
zero
with
no
modulation.
14
. DE-EMPHASIS
SW
ITCH-When released removes-
the
75
usec
de11mphasis fr
om
the
monitoring amplifier.
This
is also effective
on
the
audio
test
output
jack.
15.
POLARITY
SW
ITCH-Allows
the
percentage modulation meter
to
read either positive
or
negative modulation
po
larities. Depressed
it reads positive, released
it
r
eads
negative polarities.
16. PERCENT- MODULATION POTENTIOMETER-Pre-sets
the
peak modul
ation
l
amp
to
flash
at
the
indicated
modulatio
n setting.
This cir
cuit
is
independent
of
modu
l
at
i
on
polarity and can be
activated
by
e
ither
a positive
or
negative
modu
l
ation
peak
or
both
.
17
. WIDEBAND
TE
ST
J
ACK-Para
llels
the
wideband
outputs
to
the
Add-On FMS- 1
Stereo
and SCM- 1 SCA units. Permits
tests
to
be made
on
the
output
of
the
counte
r-discriminator
suc
h
as
linearity
and
ste
r
eo
composite wavefOl'm tests.
1
8.
AUDIO TE
ST
JACK-
Test
output
from
the
monitori
ng
amplifier. Permi
ts
linearity tests, frequency response
tests,
and
FM
noise
tests
to
be made
from
the f
ront
panel,
with
de11mphasis in
Of
out
according
to
function
14
.
19.
FREQ
ADJ
US
T- Adjusts
the
frequency
of
the
l
oca
l oscill
atOI'.
THIS MUST BE ADJUSTED WITH AN INSULATED ALIGNMENT
SCREWDRIVER. '

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9
SECTION 3
OPERATION
3- 1
INITIAL
OPERATION
The
following
procedure
should
be
followed
for
placing the
unit
into
initial
operation.
Refer
to
Figure
3-1
for
location
of
the
control
functions:
1. Before
turning
the
unit
on,
depress
the
AMP BAL switch
and release
the
REMOTE METER switch.
2.
Depress
the
POWER switch
and
a
ll
ow
a
15
minute
warm
-
up.
3.
Depress
the
OSC
switch;
the
reading
on
the
percentage
modulation
meter
should
be
approximately
100%
or
more.
4.
Turn
the
RF
level
control
on
the
back
of
unit
maximum
counterclockwise.
App
ly
RF
input
to
the
RF
input
jack.
Depress
the
RF switch
and
adjust
the
RF
level
contro
l
unt
il
the
percentage
modulation
meter
reads
100%.
The
monitor
wi
ll
operate
with
as
little
as
20%,
but
for
AM noise
calibration,
the
100%
level is used.
5. With
the
function
switch
in AMP BAL,
adjust
AMP BAL
POTENTI
OM
E
TE
R
to
r
ead
center
zero
on
the
carrier
deviation
meter
and
adjust
the
MOO
ZERO
POTENTIOMETER
to
read zero
on
the
modulation
meter.
6.
With
the
function
switch in
FREQ,
adjust
FREQ
CAL
POTENTIOMETER
to
read
center
zero on the carrier
devi
ation
meter.
7.
Dep
ress the MOO CAL
switch;
the
modulation
meter
will read 100%
to
verify
the
accuracy
of
the
calibration.
8.
Depress
OP
switch
and
the
monitor
is
now
ready
for
operation.
3- 2 NORMAL OPERATION
F
or
normal
operation,
leave
the
FMM-1
in OP [operate]
position. Changes in RF level wi
ll
not
affect
the
accuracy
of
the
unit.
It
may
be
necessary
to
occasionally
adjust
the
FR
EQ
CAL P
OTEN
TIO
METER
as
in
step
3-1-6
above.
T
he
PEAK MOD POTENTIOMETER is usually
set
to
100
%
so
that
t he PEAK
LI
GHT
will flash
at
a
modu
l
ation
peak
of
100
%
or
greater
. Since
this
indicator is
independent
of
modulation
polarity
[i.e.,
it
responds
to
both
positive and
negative peaks] ,
it
may flash
when
the
modulation
meter
does
not
indicate
the
peak.
The
modulation
meter
polarity
is
switched
by
S4.
Note
that
when
the
MOD CAL switch is depressed,
the
calibrating signal is applied
not
only
to
the
metering
circuit
but
also
to
the
peak light
and
monitoring
amplifier. Hence
the
60
H
ertz
square wave
tone
will
be
heard
in
an
aural
monitoring
amplifier.
3- 3 LOCAL OSCILLATOR
FREQUENCY CALIBRATION
The
FMM- 1 is furnished
adjusted
to
the
customer's
frequency.
The
monitor
may
be
ca
librated against an
external
frequency
standard
as
follows:
The
transmitter
is
first
set
exactly
to
the
assigned
frequency
using
an
outside
frequency
measurfng service. Measure
transmitter
frequency
as
per
steps
5,
6
and
8
under
OPERATION,
Paragraph
3-1
.
If
the
indicated
center
frequency
deviation is
not
zero,
the
local
oscillator
frequency
may
be
adjusted
with
the
crystal
tuning
capacitor
C5
[
through
the
front
panel]
to
bring
the
deviation
to
zero.
3- 4 TRANSMITTER MEASUREMENTS
Normal
transmitter
proof-of
-performance measurements
may
be
made
with
the
FMM- 1.
Frequency
response,
distortion
,
and
noise
measurements
may
be
made
through
the
front
panel
AUDIO
TEST
jack
JS
. Five
vo
l
ts
RMS is
available
at
100
%
modulation
so
that
most
distortion
and
noise analyzers
may
be
used. Measurements
may
be
made
with
or
without
de-emphasis
by
activation o.f S3.
Th
e
modulation
meter
has
a f l
at
frequency
respol")se
characteristic so
that
with
a pre-emphasized
transmitter,
the
audio
input
level will have
to
be
adjusted
according
to
the
standard
75
usec pre-emphasis curve.
AM noise
measurements
may
be
made
at
J6
on
the
back
panel. With
the
RF
level
at
1
00
%,
the
norma
l
output
of
J6
for
1
00
% AM is O
db
(0.78
volts]
into
a high impedance
[500K
or
greater] .
Hence
a
standard
AC vol
tmeter
such as
contained
in a
distortion
analyzer
may
be
used.

www.SteamPoweredRadio.Com
10
i
RF
I
INPUT
.
-
88-108
MHZ
I
I
I
I
I
I
L
Figure 4--1
OSCILLATOR-MIXER
ASSEMBLY
Al
MIXER
03
FREQUENCY
TRIPLER
87-108
MHZ
02
CRYSTAL
OSCILLATOR
29-36
MHZ
01
+25V
0
PRE-REGULATED
POWER
SUPPLY
01, 02,
03
7I
_J
,----0
,--
650
KHZ
_
INPUT
I
LIMITER
02,
03
+15V
CRYSTAL
OSCI
LLATOR
650
KHZ
01
I
L_
SCHMITT
TR
I
GGER
.
-
04,
05
VOLTAGE
REGULATOR
018,
019,
020
1,
-,...,_--C>----.
COUNTER
ASSEMBLY
A2
MONOSTABLE
LOWPASS
MUL
Tl
VIBRATOR
-
BUFFER
.
FIL
TEA
. ,
06,
07,
08
010
FL1
1~
DIFFERENTIAL
BUFFER
-
AMP
09
r
Q13,
014,
015
016,
017
AMPLIFIER
ASSEMBLY
A3
I
--,.--
--
..
--"--
,,-
- - - - - - - 7
1
I
I
I
I
I
,.
.
L
__
PHASE
SPL
I
TTER
01
PHASE
SPLITTER
Q13
MONITOR
AMPLIFIER
015,
016
017,
018
.
VOLTMETER
AMPLIFIER
02.
Q3,
Q4
SCHMITT
COMPARATOR
Q11,
012
...
.
-
PEAK
RECT
I
FIER
CR
1
MONOSTABLE
MUL
TIVIBRATOR
1---;.--1
07,
08
DC
AMPLIFIER
05,
06
LAMP
SWITCH
09
I
I
I
I
_
_______
_J
.
~
PERCENT
/~
MODULATION
-
.
---7
AMPLIFIER
011,
012
I
_
__
J
I
MODULATION
METER
PEAK
LIGHT
I
FREQ.
DEV.
C
1 C
2 C
3
:
.,
4
BASEBAND
OUTPUTS
t
t
f

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11
SECTION 4
PRINCIPLES
OF
OPERATION
4-1
BLOCK DIAGRAM DESCRIPTION
Figure
4-1
is a simplified block diagram
of
the
FMM
- 1
FM
Frequency
and
Modulation Monitor.
Th
e signal paths
are shown
but
the
detailed switching circuitry has been
omitted
for clarity.
The incoming RF sample is applied
to
the
mixer, A
103,
along with
the
tripled local oscillator frequency
to
form an
intermediate frequency
[I
Fl
of
650
kHz. This signal
is
a
fully modulated
FM
signal [Figure
4-2
-1] centered
around
650
kHz
and
is applied
to
the
pulse-
counter
discriminator assembly Card
A2.
The limiter amplifies and removes any
AM
component from
the
IF signal.
The
signal is squared
by
the
Schmitt
trigger,
whose
output
is differentiated
to
form
a sharp trigger
[
Figures
4- 2- 2
and
6)
to
drive
the
monostable
mu
l
tivibrator,
A2O6,
7
and
8 .
Th
e monostable
mu
ltivibrator generates a pulse
of
fixed length
and
amplitude [Figure 4-
2-3)
eac
h time it receives a trigger.
Th
us
the
output
of
the
multivibrator
is
a seri
es
of
pulses
with a fixed length and amplitude whose spacing depends
on
the
incoming frequency. Figure 4- 2- 7 illustrates this
output
with an
FM
modulated signal. Note how
the
spacing
increases
and
decreases as
the
frequency is deviated
about
650
kHz. This
output
is
integrated
by
the
low-pass filter
whose average AC
output
is
equivalent
to
the
original
FM
modulation.
The
output
of
the
monostable multivibrator
is
also applied
to
the
buffer amplifier A2O9 and integrated
by
an
RC
network
to
provide
an
average
DC
signal
proportional
to
the
carrier
center
frequency.
This
DC
signal
is
amplified
by
the differential amplifier
and
applied
to
the
carrier deviation meter.
The
output
of
the
integrating filter
is
amplified and applied
to
the
modulation
metering and peak flasher circuits
on
Card
A3.
The modulation metering circ
uit
consists
of
a phase splitter
to
allow either
the
positive
or
negative modulation
po
larity
to
be selected, a feedback amplifier, a peak diode
detector
circuit,
and
current amplifier
to
drive
the
modulation
meter. The peak diode
detector
circuit has a very short
charging time
constant
to
allow
the
modulation meter
to
accurately respond
to
complex waveforms
of
multiplex
signals as well as short duration bursts
of
program material.
T
he
flasher circuit consists
of
an amplifier, phase
sp
litter,
Schmitt voltage comparator, and monostable multivibrator.
The signal
is
split
by
the
phase inverter and
both
phases
are
applied
to
the
Schmitt comparator which has a dual input.
The comparator will
only
respond
to
positive levels
that
exceed a given value determined
by
the
setting
of
the
percent modulation control. But since
the
phase inverter
inverts
the negative modulation, each input
of
the
comparator
receives
a
positive
going
signal-one
co
r
responding
to
the
positive modulation and one
corresponding
to
the
negative modulation,
thus
making
it
independent
of
modulation polarity. Each time
the
level
exceeds
the
pre-
set
level,
the
Schmitt
comparator supplies a
pulse
to
the monostable multivibrator.
Th
e width
of
the
pulse formed
by
the multivi
brator
is
set
to
3 seconds
duration as required
by
the
FCC.
The
multivibrator turns
on
the
transistor switch
A309
to
allow
the
peak lamp
to
flash.
The
monitoring amplifier is a feedback amplifier with
push-pull
output
to
provide a low distortion signal for aural
monitoring and audio tests. De-emphasis
is
accomplished
by
controlling
the
frequency response
of
the internal gain and
feedback loop.
The supply voltage is regulated
to
25
volts
by
the
pre-regulator [
01,
02,
and
CR6).
The
supply
to
the
pulse
counter
and oscillator mixer circuits
is
further regulated
by
the
precision 15 volt regulator [A2O18, A2O19, A2O20,
and A2CR9) .
4
-2
DETAILED
CIRCUIT DESCRIPTION
4
-2-
1 OSCILLATOR, TRIPLER
AND MIXER CIRCUIT
The incoming RF is attenuated
by
R
18
[RF levelI and
applied
to
pin 5
of
the
Oscillator, Tripler and Mixer Card.
Diodes A1
CR
1 and A1
CR
2 prevent excessive RF levels
from overloading
the
FET mixer A1
03
. Diode A1CR3
is
used
to
measure the RF level and its
DC
output
is
applied
to
the
modulation meter when
S6
[CARRIER LEVEL)
is
depressed.
The
crystal oscillator is a modified Clapp-Gouriet oscillator.
This
type
of
oscillator circuit
is
known for its frequency
stability.
The
feedback ratio
is
determined
by
the
ratio
of
A1C3 and A1C4. Since these capacitors
are
large
in
comparison
to
the
transistor A1Q1 capacities,
the
transistor
has little
effect
on
the
frequency. The crystal isconnected
to
pins 7 and
8.
The series
tuned
circuit A1C1, A1L1 forces
the
crystal
to
operate
in
the
thirdMe
mode.
The
crystal is stabilized
at
a temperature o 5 d rees C
by
the
oven
Y1
. Variable
Capacitor C5 (FREOU NCY ADJUST) adjusts the crystal
frequency
to
that
required
by
the
channel frequency.
The
output
of
the
crystal oscillator
is
multiplied by 3
in
the
tripler stage A
102
. I
ts
final frequency
is
then
650
kHz
above
the
in
coming RF carrier frequency and
is
mixed in
A
103
to
produce a difference frequency of 650 kHz. The
output
of
the
mixer
is
filtered
by
the
low-pass filter A1C12,
A1RFC5, and
the
cable capacity interconnecting pin 2
to
the
input
of
Card A2.

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4-2-2
OSCILLATOR, COUNTER
DISCRIMINATOR AND AMPLIFIER
CIRCUITS
When
the
operate [OP) switch S2
is
depressed,
15
voe
from pin 7 is applied
to
pin 4
to
turn
on
diode A2CR1 so
that
the
650
kHz intermediate frequency, Figure 4
-2-1,
is
applied
to
the
limiter,
A202
and
3.
This stage
amp
lifies
and
removes any amplitude modulation component th
at
may
be
present
on
the signal.
The
Schmitt trigger
A204
and
5
squares
the
signal
by
developing a pulse each
time
the
signal
crosses
the
zero axis in
the
positive direction.
The
output
of
the Schmitt trigger
is
differentiated, Figure 4- 2-
2,
and
applied
to
the
monostable multivibrator, A2Q6,
7,
and 8
through diode A2CR4.
The monostable multivibrator differs from
the
conventional
multivibrator in
that
the
timing capacitor A2C16
is
charged
through a constant current source, A2Q7, instead
of
a
resistor. Zener Diode A2CR5 regulates
the
voltage
to
the
base
of
transistor A2Q7, and silicon diode A2CR6 provides
temperature compensation for
the
emitter-base junction
of
A2Q7. Potentiometer, R6 [FREQ
CAL],
in series with R5
[COARSE FREQUENCY CAL) connects
the
pins 9 and
10
to
set
the
current through A2Q7.
The
current through
A2Q7 sets
the
slope
of
the
charging current
of
the
timing
capacitor A2C16 which determines
the
pulse width
of
the
multivibrator. This modification
of
the
multivibrator
!1eatly increases
both
its stability and linearity when
wed
asa pulse counter discriminator.
The
output
of
the
monostable multivibrator, Figure
4--2-3,
is
buffered
by
an
emitter
follower
A2010
and
is
integrated
by
the
low-pass filter
Fl
1,
Figure
4--2-4.
This
filter
counts
[averages]
the
number
of
pulses over a
unit
time interval
by
filtering
out
the
650
kHz pulses
and
on
ly
passing
the
modulation, Figure 4- 2- 9.
The
output
of
the
low-pass filter is amplified
by
A201
1 and buffered
by
the
emitterfollower A2Q12.
The
modulation
output
[baseband
output)
is
taken
off
pin
12
to
drive subsequent portions
of
the
monitor.
Th
e
output
of
the monostable multivibrator
is
also buffered
by
transistor A2Q9.
The
emitter
of
A2Q8
is
direct
coup
l
ed
to
the
base
of
A2Q9. Diodes A2CR7
and
8 form
the
emitter load so
that
the
linearity
of
the
multivibrator is
preserved. This
type
of
coupling decreases
the
rise time
of
the
pulse
output
of
A209
and enables transistor A2Q9
to
be driven between cut-off and saturation
to
form a
precisely defined rectangular pulse
of
maximum stability
for frequency measurements.
The
output
of
transistor A2Q9
is
integrated
by
the
RC
network
A2R60
and A2C27
to
provide a DC
that
is
proportional
to
frequency.
Th
is
DC
is compared with
the
reference DC from
the
precision voltage divider,
A2R40
and A2R41,
by
the
differential amplifier
A2Q13-17.
Any
difference
in
voltage then corresponds
to
a frequency
deviation
and
is amplified
by
the
differential amplifier and
applied
to
the
carrier deviation meter through pins 16 and
20. A2C26 couples
the
unfiltered modulation
to
the
reference input
of
the
differential amplifier
to
prevent low
13
mo
d ulating frequencies from affecting the frequency
reading. The reference
DC
vo
lt
age isderived from
the
same
15 volt supply
that
powers
the
monostable multivibrator
to
form a bridge
ci
rcuit so
that
the
frequency measurement is
relatively independent
of
supply voltage.
T
he
15
volt regulator
Is
the
series
type
to
provide
bot
h
vo
lt
age regulation and a low impedance
to
power the A2
Card.
A2Q
18
is
the
pass transistor and
A2019
and
20
amplify
the
error difference between the
output
and
reference zener diode, A2CR9.
A2R52
sets the
output
to
15
volts.
The
calibrating oscillator A2Q1 is a conventional Colpitts
crystal oscillator. When
the
FREQ
CA
L switch S2 is
depressed,
15
voe from pin 7 is
app
li
ed
to
pin 3 which
supplies power
to
the
calibrating oscillator and also
turns
on
diode A2CR2 so
that
the
650
kHz calibrating signal is
applied
to
the
limiter,
A202
and A2Q3. Note
that
diode
A2CR1 is now
turned
off
in
this
mode
of
operation. The
calibrating signal allows
the
pulse width
of
the
monostable
multivibrator
to
be
standardized
to
correspond wi
th
the
DC
reference level
of
the
differential
amp
lifier.
Modulation calibration is accomplished
by
gating
the
650
kHz calibrating signal
on
and
off
through
the
limiter. When
the
MOO
CAL switch S2
is
depressed,
the
calibrating
oscillator is turned
on
as before.
19
vol
ts
,
60
H
ertz
is
also
applied
to
pin 2
to
gate
the
li
miter stage
A203
on
and
off
at
a
60
Hertz rate.
The
effective
FM
frequency deviation
is
from
Oto
650
kHz
or
650
kHz peak
to
peak;
the
650
kHz
deviation is reduced
to
150
kHz
by
the
precision resistance
divider A2R38 and A2R39.
The
square wave
output
from
pin 13, through switch
S2,
is
applied
to
the
Amplifier Card
Assembly
A3
and
the
Composite
Output
Jacks
Jl
-
4.
Capacitor A2C22 removes
the
overshoot from
the
leading
edge
of
the
square wave.
25
VDC
is supplied
to
pin 1 through R4,
on
the
main
chassis,
and
to
pin
11
to
power the buffer
A2010.
R4
drops
the
25
volts
to
pin 1
to
approximately 21 volts
to
reduce
the
power dissipated in
the
series regulator
A2018.
4-2-3
AMPLIFIER, METERING
AND FLASHER CIRCUITS
The
inputs
to
the
monitoring amplifier, metering circuit,
and peak flasher circuit are individually calibrated.
The
modulation metering circuit consists
of
a phase splitter
to
allow
eit
h
er
the
positive
or
negative modulation polarity
to
be selected, a feedback amplifier, a peak diode detector
circuit, and curr
ent
amplifier
to
drive
the
modulation
meter.
The
baseband signal
is
app
lied
to
the
phase splitter
A301
to
allow either
the
positive
or
negative modulation
to
be
selected
by
switch
S4
[MOD
POLARITY]
on
main
chassis. Potentiometer A3R5 adjusts
the
gain
on
the
negative polarity
to
exact
ly match
the
positive polarity.
The
wideband
feedback amplifier consists
of
three
transistors
A302,
3 and 4. Potentiometer A3R15 adjusts
the
gain
of
the
amplifier
to
that
value required for
calibration. Diode rectifier A3CR1 rectifiesthe positive half
of
the
signal
to
charge
the
capacitor A3C7
to
a DC level

www.SteamPoweredRadio.Com
14
corresponding
to
peak value
of
the
signal. The charging
time constant is extremely
short
and
is
determined by
the
low
output
impedance
of
the
feedback amplifier, diode
resistance
and
A3C7. This
short
time constant allows
the
modulation meter
to
accurately respond
to
complex
waveforms
of
multiplex signals
as
well as short duration
bursts
of
program material. Resistor A3R20 controls
the
discharge time
of
A3C7.
Field-effect transistor A3O5 provides a high impedance
to
the
rectifier circuit
and
transistor A3O6 provides
the
current gain
to
drive
the
modulation meter.
Not
e
that
pins
12,
13
and
14
are connected
to
the
MOD
METER ZERO
potentiometer, RS,
on
the
main chassis
to
form a bridge
circuit. RS balances
the
bridge
for
zero current with no
signal. With a signal,
the
voltage increases
on
the
emitter
of
transistor A3O6
to
inbalance
the
bridge and current flows
through resistors
A3R24
and
25.
A sample
of
the
current
through A3R24 is applied
to
the
internal modulation meter
M2
in series with A3R23; pins
10
and
11
connect
to
the
modulation meter via switches
S6
and
S7.
Resistor A3R
23
oontrols
both
the
damping and
the
rise time
of
the
modulation meter. When a remote meter is used
to
read
modulation, a sample
of
the
current through A3R25
is
applied
to
the
remote meter. Pins
11
and
13
connect
the
remote modulation meter
via
the
REMOTE METER switch
S5. An external 6.2K
ohm
resistor must
be
used in series
with
the
remote meter
for
correct damping and rise time.
Thisresistance may include
the
line resistance.
The peak flasher circuit consists
of
an amplifier, phase
splitter,
Schmitt voltage comparator
and
monostable
multivibrator. The baseband signal
is
applied
to
the
low
gain ampli(ier A3O14 which is direct coupled
to
the
phase
splitter
A3013.
Potentiometer A3R49sets
the
span
for
the
PERCENT-MODULATION potentiometer R9
on
the
front
panel. The Schmitt comparator has a dual input,
A3011
and
12
to
accept
both
negative
and
positive modulations
respectively
.
The
PERCENT
-
MODULATION
potentiometer R9
is
connected
to
pins 15,
16,
and
17
to
set
the
firing
level
of
the
comparator. Hence, each
time
the
modulation
exceeds
the
pre-
set
level,
the
Schmitt
oomparator fires
and
develops a pulse
to
trigger
the
monostable multivibrator. The monostable multivibrator
A3O7 and S produces a rectangular pulse
of
three seoonds
duration which drives
the
lamp switch A3O9. The
PEAK
MOD
light DS2
is
the
oollector load for transistor A3O9.
The power
for
the
light
is
supplied by rectifier
CR
1 and
capacitor
Ct.
A remote PEAK
MOD
light is driven by the
same power supply and switch and may
be
connected
to
terminalsTB2- 9 and
10
.
The monitoring amplifier is a three stage feedback amplifier
to
provide a low distortion signal
for
both
aural monitoring
and
audio tests. The baseband signal
is
applied
to
the
input
stage A3O1S which
both
amplifies
the
signal and sums
the
feedback voltage in
the
emitter. Transistor A3O17 provides
additional amplification
to
drive
the
output
transistors
A
3015
and
16
. Since
the
output
transistors are a
complementary pair,
they
operate in push-pull. Diodes
A3CR4
and
5 provide forward bias
to
allow
the
output
transistors
to
operate class
AB
.
Feedback is taken from
the
output
and applied
to
the
emitter
of
the
input stage through A3R57. When terminals
24
and
26
are connected
to
each
other
and terminals
23
and
27
are connected
to
each other,
the
feedback follows a
75
useoond pre-emphasis curve so
that
the
resultant
output
is
de-emphasized acoording
to
a
75
usecond curve. A3C22
controls
the
gain
and
phase
of
the
amplifier so
that
it
is
unconditionally stable.
The
DE
-EMPHASIS switch
S3
makes
the
necessary connections. A3R51 provides
the
600
ohm
output
impedance
to
drive
an
aural monitoring
amplifier
and
A3R52 provides
the
10K
ohm
output
impedance for audio tests.
The main power supply consists
of
a full wave bridge
rectifier followed by a voltage regulator. Transistor
01
is
the
pass transistor and
is
driven
by
the
current amplifier 0 2
which has its base referenced
to
zener diode CR6. Diode
CR7 provides short circuit protection along with R3. When
excessive current is drawn from
the
regulator,
the
voltage
drop
across
R3
along with
the
emitter-base voltages
of
01
and
02
exceeds
the
voltage
drop
across CR7 and
the
current
is
limited
to
a safe value
to
prevent damage
to
the
transistors. Diode
CR
1 and capacitor
Ct
provide power
to
operate
the
PEAK
MOD
light.

www.SteamPoweredRadio.Com
I
I
15
SECTION 5
MAINTENANCE
5-1
INTRODUCTION
This section contains maintenance and service information
for
the
FMM- 1 Frequency and Modulation
Monitor
.
Included
are Performance Checks, Adjustments and
Calibra
tion
Procedures and Troubleshooting Techniques.
5-2
PERFORMANCE CHECKS
The FMM- 1
is
self-checking
to
adegree. Before performing
the
check procedure,
release
all push buttons
[out
position) depressing
or
leaving depressed the AMP
BAL
switch
S2
and the MOD POL switch S4.
No
connections
should
be
made
to
the back terminals
or
connectors except
for
the line cord
to
TB
1.
5- 2- 1
POWER
AND
OVEN CHECK
With
AC
power connected
to
the
FMM- 1 and
the
power
switch
off
[released) , the oven light
DSl
should cycle on
and
off
approximately every 30 seconds
after
initial
warm-up.
When
on, heat
is
applied
to
the oven. Depressing
the
POWER
switch
Sl
turns the
unit
on,
and power light
DS3 indicates
that
the power
is
on.
5- 2- 2 OSCILLATOR
LEVEL
CHECK
Depressing
the
OSC
level switch
S7
indicates
the
oscillator
level
on the
MODULATION
meter M2. The reading
of
the
level
should
be
greater than 100% and should
be
noted
for
future reference.
5- 2- 3 FREQUENCY METER
AMPLIFIER
CHECK
Depress
the AMP
BAL
switch
S2
and adjust AMP
BAL
potentiometer
R7 maximum clockwise
to
maximum
counterclockwise; the FREQUENCY meter
Ml
pointer
should
go
off
scale
in the positive
and
negative direction
respectively. Return
the
pointer
to
zero
for
normal
operation.
5- 2- 4 FREQ METER DISCRIMINATOR CHECK
Depress
the
FREQ
CAL
switch
S2
and adjust
the
FREQ
CAL
potentiometer
R6
ma
x
imum
clockwise
to
maximum
counterclockwise;
the
FREQUENCY meter
Ml
pointer
should
go
off
scale
in
th
e positive and negative direction
respe
ctively. Return
the
pointer
to
zero
for
normal
operation.
5-2
- 5 MOD METER
AMPLIFIER
ZERO CHECK
Depress
the
AMP
BAL
switch S2 and adjust the MOD
ZERO potentiometer
RS
maximum clockwise
to
maximum
counterclockwise; the
MODULATION
meter
M2
pointer
should move in a positive and negative direction about zero.
Return the pointer
to
zero
for
normal operation.
5- 2- 6
MODULATION
CALIBRATOR CHECK
Depress
the MOD
CAL
switch S2. The MODULATION
meter M2 should
read
100%. The FREQUENCY meter
Ml
may move
off
from
zero
to
plus
or
minus a few hundred
cycles.
5- 2- 7 REMOTE METER SWITCH CHECK
Depress
the MOD
CAL
switch
S2.
The MODULATION
meter
M2
should
read
100
%. Adjust the FREQ
CAL
potentiometer
R6
to
a reading
of
plus 1 kHz.
Depress
the
REMOTE METER switch S5.
This
MODULATION
meter
M2 reading should
decrease
approximately
6%
and the
FREQUENCY meter
Ml
should return
to
zero.
Release
the
REMOTE METER switch S5 and the meters should return
to
the
previous
readings. Return the FREQ
CAL
potentiometer
R6
to
normal
as
in
step 5- 2- 4.
5- 2- 8 PERCENT MOD POTENTIOMETER CHECK
Depress
the MOD
CAL
switch S2. Adjust the PERCENT
MODULATION
potentiometer R9
to
just
turn
on
the
PEAK
MODULATION
light DS2. The light should
turn
on
at 100%. The light
will
continue
to
flash on and
off
at a
rate
of
3 seconds on
to
afraction
of
a
second
off
.
5- 2- 9
MODULATION
POLARITY
CHECK
Depress
the MOD
CAL
switch S2. The MODULATION
meter M2 should
read
100%.
Release
the MOD POL switch
S4 and the
MODULATION
meter should continue
to
read
100
%.
5- 2- 10 CARRIER
LEVEL
CHECK
Turn RF level control R18 maximum counterclockwise.
Apply
RF carrier
to
the RF INPUT connector J7
[40
milliwatts is more than sufficient
to
drive the monitor
to
100% carrier level indication).
Depress
RF switch S6
and
adjust RF level control R18
until
the MODULATION
meter M2 reads 100%.
If
considerable
range
remains on
R18, the RF
output
from
the transmitter should
be
reduced
by
adjusting the coupling probe in the transmitter.
5- 2-
11
OPERATE CHECK
With
the
RF carrier applied
as
in
step
11,
depress
the
OPERATE switch S2. The FREQUENCY meter
Ml
will
indicate
the
frequency deviation
from
the
assigned
channel
frequency. The
MODULATION
meter
M2
will
indicate the
presence
of
modulation.
The
PEAK MODULATION light
DS2
will
indicate positive
and
negative modulation
peaks
according
to
the setting
of
the PERCENT MODULATION
potentiometer.
It
may
be
noted
that
the
MODULATION
meter
M2
may
not
track at all times
with
the PEAK
MODULATION
light while monitoring program material.

www.SteamPoweredRadio.Com
16
Thi
s is
due
to
the
assymetrical n
atu
re
of
certain
types
of
program material, i. e.•
the
positive a
nd
negative
peaks
are
not
equal
in
amp
l
it
,
ude.
Since
t
he
PEAK MODULATION
l
ig
ht
circuitry autonnatically selects
the
higher
of
the
two
polarities, it
can
reglister a peak
opposi
te
to
the
polarity
to
which
the
MODULATION
meter
is set.
5
-2-
12
DE
-EMPHASIS SWITCH CHECK
With a
15
kHz
modu1lated signal applied
to
the
monitor,
the
monit
or
amplifier
output
may
be
monitored
at
the
AUDIO
TEST
jack
JS
. Depre·ssing the DE-EMPHASIS switch
S3
wi
ll
cause a
17
db
decrease in
output
level,
and
releasing
S3
will
return
the amplifier
to
a
flat
response. N
ote
that
the
600
o
hm
monitori
ng
amplifier
output
on
T
B2
is also
de·emphasized
by
this
sw
it
ch.
5- 3 ADJUSTMENTS, CALIBRATION
AND TROUBLESHOOTING
Th
e following
guide
for
adjustments,
calibration a
nd
troubleshooting
fo
ll
ows
th
e same
numbering
sequence
as
the
PERFORM
ANCIE
CHECKS
for
ease
of
service.
5-3-1
POWER
ANID
OVEN
a.
If
the
oven lig
ht
DSl
fails
to
light,
check
fuse
F2
[0
.
25A].
b.
If
the
oven light
DSl
l
ig
h
ts
but
fails
to
cycle
on
and
o
ff
,
remove
oven
from
unit.
If
the
oven
is
cold,
ch
eck
continuity
of
t he h
eate
r winding
between
pins 3
an
d 4 of
the
oven.
If
the
oven
is
hot
, the th
ermostat
circuit
is
stuck
closed
and
the
ove
n
should
be
r
ep
laced with a
new
unit.
No
te
t
ha
t
both
malfunctions
will
result
in
an
indicated
ca
rr
ier
frequency
e1rror.
The
monitor
oven
should
no
t
be
operated
with
a
st
1uck
thermostat
as
the crystal
may
be
damaged
from
overheating.
Th
e
monit
or
may
be
ope
r
ated
temporarily
wit
h
t~a
oven
fuse
remo
ved.
c.
If the
ove
n
lig
ht DS1 fails
to
light
but
the oven
heats
,
check t
he
oven light.
d.
If t
he
power
li!Jht
DS3
fails
to
light,
check
fuse F1
[0.5A].
e.
If
the
power
lig
ht
DS3
lights
but
the
mon
it
or
is
inoperative, check
the
voltage
on
terminal 3
of
T
B2
to
ground.
Normal
voltage
is
26
VDC. If
the
vo
lt
age is high
[3
7
VDC],
0 2 or C:R6 is defective. If
the
voltage is
0,
01
is
open
or
a
ma
lf
uncti
,
on
exists
in
the
pre
-
regulator
.
f.
If the
powe
r li~
1h
t
DS3
fa
il
s
to
light
and
the
monitor
functions
normally
, c
he
ck
the
power
l
ig
h
t.
5-3
-2
OSCILLATOR LEVEL
a.
If
the
oscillator
level re
ads
0,
transistor
A
101
is
malfunctioning.
b.
If
t
he
osc
illator level r
eads
above
80
%
but
not
the
normal peak, adjust:A1L1 for
an
indicated peak
on
M2.
c.
If
the
oscillator level will
not
peak
w
ith
the
adjustment
of
A1
L1
, t
he
crysta
l
Yl
[in oven]
may
be
defective.
5-3
-3
FREQUENCY
METER AMPLIFIER
a.
If
the
FREQUEN
CY
meter
Ml
pointer
fails to
go
off
scale in
both
t
he
positive
and
negative
direction,
transistors
A2O14
and
15
are
satu
r
ated
and
A2R47
should
be
r
ep
laced
wi
th
the
next
high
er
value (9.1
Kor
10Ko
hm
s].
b. If
the
FREQUENCY
meter
Ml
pointer
fails
to
move
and
th
e r
est
of
the
monitor
functions
normally.
release
REMOTE ME
TER
switc
h
S5.
Note
that
if
remote
mete
rs
are
used
and
t
he
malfunction
is clear
ed
wh
en
the
switch
S5
is released, a
ma
l
function
exists
on
the
remote
meter
lines.
c.
If releasing the REMOTE METER switch
S5
does
not
clear
the
malfunction,
A2Q13
and
17
are
malfunctioning.
5- 3- 4
FREQ
METER DISCRIMINA
TOR
a.
If
the
FREQUENCY
meter
Ml
pointer
fails
to
go
off
scale in
bot
h
the
positive a
nd
negative directions,
return
the
FREQ
CAL
potentiometer
R6
to
its
midpo
int
and
adjust
the
coa
rse
frequency
potentiometer
R5
to
z
ero
M1.
b.
If the
FREQUEN
CY
meter
M1
is
off
sca
le
and
ca
nnot
be
brought
on
scale
with
R
6,
as
in
step
(a)
above,
but
the
modulation
ca
libr
ato
r
functions
normally
as
in
step
5-2-6,
check
the
waveform
on
the
collector
of
tra
nsistor A2O9. A
l
ow
capacity
probe
should
be
used
with
the
oscilloscope
to
preserve
the
waveshape
and
the
waveshape
should
be
as
shown
in Figure 4- 2
-3.
If
the
waveshape
does
not
have a
straig
ht
base
-l
ine as in Figure 4
-2-
10
,
transistor
A2Q9
is
not
driven
into
full
saturation
and
should
be
replaced.
Note
that
this
malfunction
can
also cause excessive frequency
drift
in
the
discriminator.
c.
If t
he
FREQUENCY
meter
M1 is
of
f scale
and
the
modu
l
ation
calibrator
does
not
check
as
in
step
5- 2
-6,
but
the
unit
fu
n
ctions
normally
in
the
OPERATE position,
the
calibrating oscillator is
not
function
ing
or
the
diode
switch
A2C
R2 is
open.
Check
al
so
that
15
VDC is applied
to
the
diode
anode.
d.
If the un
it
does
not
function
in
the
OPERATE
position
in
step
(c) above,
the
counter-discrimin
ator
circuits
are
ma
lfun
ct
i
on
in
g,
and
th
e signal may
be
traced
wit
h
the
aid
of
the
waveforms in
Figure
4
-2.
A l
ow
capacity
pr
obe
shou
ld
be
used
with
the
oscilloscope
to
preserve
the
waveshape.
5
-3-5
MOD METER AMPLIFIER ZERO
a.
If
the
MODULATI
ON
meter
M2 will
not
zero,
and
the
modulation
calibrator
functions
but
does
n
ot
indi
cate
accurate
l
y.
the
bias
on
transistor
A3O3
is
off.
Increasing
the
value
of
A3R
16 will decrease
the
meter
reading
by
shifting
the
ze
ro
to
the
negative
direction,
and
decreasing
A3R
16
will increase
the
meter
reading
by
shifting
the
zero
to
the positive
direction.
A3R
16 should range
between
24K
and
30K
o
hm
s
and
if
it
does
not,
replace
A3O5
or
A3Q3.

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b.
If
the
MODULATION meter
M2
reads
off
scale, check
resistors
A3R24
and
25
for
an
open
circuit.
5-3-6
MODULATION CALIBRATOR
a. If
the
MODULATION meter
M2
reads in error
but
is
within 20%
for
positive pola
rit
y
[MOD
POL switch
S4
depressed)
and
the
PERCENT
MOD
checks as in step
5- 2-
8,
adjust potentiometer A3R
15
for
the
correct
reading
of
100% after zeroing
the
meter as in
step
5-
2-5.
b.
If
both
the
MODULATION meter M2
and
the
PERCENT
MOD
potentiometer R9 read in error, check
the
voltage
output
of
the
15 volt regulator
on
card A2 and
adjust
A2R52
for
15 volts
output
if necessary. Usually
the
FREQ METER DISCRIMINATOR CHECK will
be
off
in
step 5- 2- 4
with
the
15
volt regulator
out
of
adjustment.
5- 3- 7 REMOTE METER SWITCH
a. With remote meters connected
to
the
monitor,
the
readings
of
the
FREQUENCY meter Ml and
the
MODULATION meter
M2
should remain unchanged with
the
REMOTE METER switch
S5
depressed
or
released. If
the
readings
do
change, check
for
faults
on
the
remote
meter lines. When
the
remote meters are
not
connected
to
the
monitor,
the
readingswill change as in step 5- 2-
7.
5-
3-8
PERCENT
MOD
POTENTIOMETER
a.
If
the
PERCENT
MOD
potentiometer R9 reads in error,
the
knob may
be
slipped
to
the
correct reading
by
loosening
the
two
set
screws and retightening
after
adjusting.
b.
The
span
of
the
PERCENT
MOD
potentiometer may
be
checked
by
applying a
400
cycle modulated signal
to
the
monitor
and
checking
the
tracking
at
the
50%
and
100%
modulation points. Adjust
A3R49
so
that
the
percentage
difference
on
the
PERCENT
MOD
potentiometer
is
50%
when
the
modulation level is changed from 100%
to
50%.
Slip the
knob
as
in
step
(a)
above if
it
is necessary
to
correct
the
reading
at
100% after
the
span has been
adjusted.
5-3-9
MODULATION POLARITY
a. With a 400 cycle, 100% modulated signal, adjust
A3R5
to
obtain equal reading
on
MODULATION meter M2 when
17
the
MOD
POL switch
S4
is
cycled from positive
to
negative.
Note
that
the
adjustment can
be
observed
in
the
negative
polarity position.
b.
If
the
negative polarity if
off
seriously and
the
monitor
is noisy, check
the
pre-regulated power supply as
in
step
5- 3-
1~.
5- 3-
10
CARRIER LEVEL
a.
If
no
RF level
is
observed and
the
monitor
is
functioning
normally
in
the
OPERATE position, check diode A1CR3.
5- 3- 11 OPERATE
a. If
the
monitor fails
to
function
in
the
OPERATE
position and all
other
functions are correct, check diode
switch A2CR1. Check also
that
15 VDC
is
applied
to
the
diode anode.
b. If
the
FREQUENCY deviation is
off
scale and
the
MODULATION meter
is
normal
in
the
OPERATE position,
check local oscillator peaking as in step 5- 3- 2.
c. If
the
FREQUENCY deviation
is
off
scale and
the
MODULATION meter
is
normal
in
the
OPERATE position,
check
the
oven cycling as
in
step 5-
3-1
-b. If
the
oven
is
cycling and
the
transmitter frequency
is
correct, crystal
Yl
[in oven)
is
defective.
d.
If
the
monitor fails
to
function
in
the
OPERATE
position and
the
diode switch circuit
is
functioning, check
transistorsA
102
and A
10
3.
5- 3-
12
DE-EMPHASIS SWITCH
a.
If
DE
-EMPHASIS switch
S3
does
not
function normally,
check capacitors A3C20 and
22.
In
the
DE-EMPHASIS
position, capacitor A3C20
is
connected
to
the
circuit
by
S3
switch contacts connecting pins
24
and
26,
and capacitor
A3C22 is connected
to
the
circuit
by
S3
switch contacts
connecting pins
23
and
27
.

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18
A1
ASS'(,
Figure 5- 1
REF G
RI
D REF GRID REF GRID REF GR
ID
REF GR
ID
REF G
RI
D
D
ES
IG LOC DESIG LOC
DE
SIG LOC
DE
S
IG
L
OC
DESIG L
OC
DE
SIG L
OC
R1
85
R10 A2 C4 85 C13
82
RFC5
A1
PIN
S
R2 A5
R11
A2 C5
84
C
14
82 C
R1
82 1 A2
R3 A4
R1
2 81
C6
A4
C1
5
Al
CR2 82 2
Al
R4
84
R1
3 81 C7 83 C16 A2 CR3 81 3 Al
R5
84
R14
84
cs
A3
C17 81 0 1 A4 4 81
R6 A4 C1A A5
C9
A2 RFC1 84 0 2
A3
5 81
R7 83 C
18
A5 C10 A3 RFC2 A4 0 3
A2
6 81
RS 82 C2 A5 C11 Al RFC3
A3
L1 A5 7
84
t
R9
82
C3 85 C12 A2 RFC4 82 L2
A3
s 85
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