Belar FMS-1 User manual

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Broadcast Ec1uipment
FMS-1
STEREC) MONITOR

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WARRANTY AND ASSISTANCE
All Belar
products are warranted against defects in materials and
workmanship. This warranty applies for one year from the date or
delivery, 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. 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.

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Bro~adc~st Equipment
Instructions
FMS-1
Stereo Monitor
BELAR ELECTRONICS LABDRATDRV, INC.

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3
TABLE OF CONTENTS
SECTION 1 PAGE
GENERAL I NFORMAT ION . .. . ...... ... . .. .... ... 5
1- 1
GENERAL DESCRIPTION .... ...... . ... 5
1-2 PHYSICAL DESCRIPTION . . .. .... .. . . . .5
1- 3 EL
ECTRICAL DESCRIPTION .. ..... .... .5
1- 4
ELECTRICAL SPECIFICATIONS . ... .. ... 6
1- 5 MECIHANICAL SPECIFICATIONS
.... .. .. 7
1- 6
INSTRUMENT IDENTIF I CAT ION ... .. . . .7
1- 7 ACCESSORIES ......
.... ... . . .. .... . .. 7
SECTION 2 PAGE
INSTALLATIO N! . ..... . . .. .... . . . .. .. .... .. ... .. 9
2- 1
IN I TIAL INSPECTION . . ... ... ...... . . .. 9
2- 2 CLAII
MS . .. . . . ....... .. ... . .... .. .. . .9
2- 3 REPl~CKING FOR SHIPMENT
.... . . ... . .9
2- 4 PREPARATION FOR
USE ... .. ..... . . ... 9
SECTION 3 PAGE
OPERATION .
.... . ......... . . . ......... . ...... 11
3- 1
3- 2
3- 3
3- 3-1
3-3- 2
3-
3-3
3- 3-4
3- 3- 5
3-3- 6
3-3- 7
3-3 - 8
3-3-9
3-3- 10
3-3- 11
3-3-12
3-3 - 13
3-3 - 14
3-3-15
3- 3- 16
3- 3- 17
3-3- 18
INITIAL OPERAT ION . .. . . ..... . ...... 11
NORMAL OPERATION ... . . .. ... . ..... 11
STEHEO MEASUREMENTS .... . ....... 11
Tota l Modula ti on ... ........ . ......... 11
Left Channel Modulat io n . ... ........ . .. 11
Ri ght Channel Modulation .. ..... . ...... 11
L+R Modulat io n ..... . ...... . ... .. .... 11
L- R Modulation . . ...... .. . . ...... . .. . 11
Pilot Carrier Modulation . .. ... . ......... 11
38 k Hz Subcarrier Suppr ess ion . ... . ... . .. 12
Sterno Separation
........... ... ....... 12
Cros:stalk (Main to Sub) ... .. .... ..... .. 12
Cro s: stalk (Sub to Ma in) .. ........ .. .. . . 12
FM Noise . .. .. . ........ . .... . ... .. .. 12
AM INoise ...... .. . . ... . ... .. .. . .. . .. 12
Incidental
AM ... . .. ......... .. . ...... 12
Frequency
Response ...... .. ..... . .. . . . 13
Distortion Measurements .. .......... . .. 13
left Channel Noise Measurement .... . . .. . 13
Righlt Channe l Noise Measurement ... . ... . 13
Intermodulation ... .. . ... ...... .... ... 13
SECTION 3 (CONTINUED) PAGE
3- 3-
19 Phase Calibrate .. ... .... . . .... .. ......14
3- 3- 20 Pilot Frequency
........... .. .. . ... . . . 14
SECTION 4 PAGE
PRINCIPLES OF OPERATION . .
.. .... .... . .. .. . .. 15
4- 1 CIRCUIT DESCRIPTION . ....... . .. . ... 15
4-1 - 1 Stereo Demodulat or & Phase
Discriminator Card Al ... .... .. ... ... 15
4- 1- 2
Audio & Voltmet er Card A2 .. . .. . . ...... 16
4- 1- 3
Pi l ot Frequency Me ter Card A3 ... . . . . .. . 16
SECTION 5 PAGE
MAINTENANCE ...... . .............. .. ... . .. . .18
5-1
5- 2
5- 2- 1
5- 2- 2
5- 2- 3
5- 3
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
INTRODUCTION .
........... ... .. . ... 18
PERFORMANCE CHECKS . . . . .. ..... .. 18
Frequency Deviation Meter Check .... . . . . 18
Modulation Mod Zero Meter Check ... . ... 18
Function .. .. .. ........... . ... .. . .. .. 18
ADJUSTMENT & CA LI BRAT ION . .. .... . 18
Pr eliminary ............ . .. .. ......... 18
A2R15 Adjustment .. ... .. .. ......... . . 18
A1R47 & A1R50 Adjustment ......... .. .18
A 1R40 Adjustment
............ . .. . .. . .19
A1R25 Adjustment
........ . .. .. ... .... 19
A1R36 Adjustme nt .... . ... .. ... . .... . .19
Norma
li z ati on ..... . . ... ... . .......... 19
19
kH z Filter Adjustments .... . ......... 20
Incidental
AM Ca libration ..... . ......... 20
AM Noise Calibration .... . .... .. . . ... . .20
19 kHz S ca le Calibra tion (R24) . ... . ..... 20
19 kHz Frequency Calibra
tion s . . ......... 20
SECTION 6 PAGE
REPLACEABLE PARTS
.... . ....... ... ... . . .. ... 26
6- 1 INTRODUCTION .
....... . ..... . .. .... 26
6-2 ORDERING I NFORMAT ION .... . .... . .26
SECTION 7 PAGE
SCHEMATIC DI
AGRAMS . . . .. . . ............. . . . 31
LIST OF ILLUSTRATIONS
1- 1
1- 2
1- 3
1- 4
2- 1
3- 1
3- 2
5-1
5- 2
5-3
5- 4
FMS: - 1 STEREO FREQUENCY
& MODULATION MONITOR . . ... .... .5
FRONT PANEL VIEW .. . ...... . . ..... .. 6
REJl1R PANEL VIEW . . .. .... .. . .. ..... .6
MECHANICA L DIMENSIONS . . . .. ....... 7
REJltR PANEL CONNECTIONS . .. . .... . .. 8
OPERATING CONTROLS
.. .... .... .. .. 10
INTIERMODULATION SPECTRUM . . . .. .. 13
OSCILLOSCOPE WAVEFORMS .. . ... .. .17
Al
CARD . .. . . ... ... . .. . . ...... . .. . . 21
A2 CARD .. . .... .. .. . .. ... ........ .. 22
A3 CARD .. .. .. . . . .. . ...... . . ....... 23
5- 5
5- 6
7- 1
7- 2
7- 3
7-4
CHASSIS, TOP VI EW .... . . ... . .. ...... 24
CHASSIS, BOTTOM VI
EW ...... . .. ... . .25
STEREO DEMODULATOR &
PHASE DISCRIMINATOR
CARD Al, SCHEMATIC ... . .. .. ..... 32
AUDIO & VOLTMETER CARD
A2, SCHEMATIC . . . .. . ..... . ... . ... 33
Pl
LOT FREQUENCY METER CARD
A3, SCHEMA TI C ......... ...... .. . .34
STEREO FREQUENCY &
MODULATION MONITOR
CHASSIS, SCHEMATIC .
..... . ... .. . .35

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5
SECTION 1
GENERAL INFORMATION
1-1 GENERJl1L DESCRIPTION.
The Belar F MS - 1 Stereo Frequency and Modul ation
Monitor (FCC l rype Approval Number 3-146). Figure
1-
1, is an all so l id state stereo demodu l ator designed to
operate in conjuinction with the Belar FMM - 1 Frequency
and Modulati
on Mo nit or to provide all of the stereo
monitoring requi1rements outlined in P
art 73 of the Federal
Communications Commission's Rules
and Regulations for
FM radio stations engaged in multiplex stereophonic
programming. In addition,
the FMS- 1 may be used as a
low distortion, low noise
FM stereo demodulator for
driving audio monitors and associated
test equipment. The
FMS - 1, used in conjunction with the FMM-1, provides
complete monitoring and
test functions to meet the daily
requirements for stereo monitoring and provides
addit i ona l
facilities for proof-of-performance measurements and for
making the proper tests for weekly and monthly
maintenance che,cks
to insure maximum performance from
stereo transmitte1rs.
1- 2 PHYSICAL DESCRIPTION
The FMS- 1, Figure 1- 2, is constructed on a standard 5¼ x
19-inch rack
mount. Seldom used contro ls and test points
are located
under the hinged front cover bar. Factory
adjustments are located wi
th in the unit and on the back
panel. The baseband input, power connections, and
monitor outputs are located at the rear of the FMS - 1
chassis
on individual connectors and rear terminal block as
shown
in Figure 1- 3. Th e FM S- 1 is completely solid state
utilizing all silicon transistorsfor long,
troub le-free life. The
individual circuits are constructed on three military grade,
glass-epoxy, plated printed circuit boards. High reliability
industrial and military grade components are used
throughout.
1 -3 ELECTRICAL DESCRIPTION
The FMS- 1 is a solid state stereo demodulator to
accurately demodulate a stereo composite baseband signal.
The pilot phase regeneration system utilizes a phase
discriminator so
that a null reading is obtained with the
correct phase, allowing the phase to be regenerated to
within ¼ degree. Various metering and testing provisions
are contained within
the monitor to measure stereo output
characteristics. These provisions include a 19 kHz pi l ot
center frequency deviation meter; a peak reading
modulation meter; an average reading sensitive voltmeter; a
function switch
to measure total modulation, (l + R)
modulation, (L-R) modulation, pilot modulation, left
channel modulation, right. channel modulation,
38 kHz
Figure
1-1

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6
suppression, FM no i se, AM noi se, an d incidental AM noise.
Outputs obtained 1from the
monitor include individual left
an d right channel distortion meter test o utput s (both aural
outputs an d di stortion meter outputs have front panel
sw it ched de-emphasis), oscilloscope ou tp ut that follows the
sensitivity of the a•ve rage voltmeter, and pilot indicator for
au tomatic logging. FCC Type Approved remote metering of
the FMS- 1 may bte externally provided for the pilot center
frequency deviation meter and modulation meter.
As a test instrument,
the FMS- 1 permi ts the measurement
of:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11 .
12.
13 .
14 .
15.
Incident al AM
AM Noise
Pil
ot Ph ase
Crosstalk into th e (L+R) Channel
Crosstalk
into th e (L- R) Channel
Suppression of
the 38 kHz Carrier
Separation-Right in
to Left Channel
Separation-L e ,ft into Rig ht Channel
Int ermodul ation
Di stortion of tlhe Left Channel
Distortion of tl he Right Channel
Noise
of the LHft Ch annel
Noise
of the Rii ght Channel
Re sponse of the L eft Channel
Re sponse of the Right Channel
Cl
111 1
1- 4 ELECTRICAL SPECIFICATIONS
Pil ot Frequency Meter Range ..................... ±3 Hz
Pilot Frequency Mete r Accuracy ........... ± 0.2 Hz (0.001%)
Modulation Meter Range .................. 133% to - 70 db
Modul ation Meter Accuracy .. . .. Better than 5% over enti re scale
Frequency Response
(Land RI . . ...... ± 0.5 db 50 - 1 5000 Hz
Separ ation ....................... 45 db (50 - 15000 Hz)
(Meter range - 70 db)
Crosstalk ............ ... ........ 60 db (L+R) to (L - R)
Outputs
60 db IL- RI to (L+R)
66 db SCA to (L+ R ), (L - R)
Left & Right Channel Monitor ing ..... 600 Ohms, unbalanced
Left & Right Channel Test .............. 10K , unbalanced
Oscilloscope .
............ · .......... 10K, unbalanced
Distortion (Eit h er Channel) ....................... 0.2%
Signal-to-Noise
Ratio (Either Channel) ....... 70 db with 75 usec
de-emphasis
Monitoring Modes (Modulat i on Meter Switched, 13 3% to -70 db)
Left Channel Audio, Right Channel Audio, (L+R), (L - R). 38
kHz (May be measured with modulating frequencies greater than
5
kHz), 19 kHz Pilot Injection (1 2% full scale), Total Modulation,
FM Noise, AM Noise, Inc. AM.
Remote Meter ing ................. Both pilot frequency and
modulation meters may be remotely metered,
5000 Ohms external loop resistance
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Figure 1- 2
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1 -5 MECHANICAL SPECIFICATIONS
Dimens ion s ...•....•••..•..... 5¼ x 19 x 11 71' 8 in ches overa ll
Deta iled Dime nsions . . . ... .. .................... . Figure 1 -4
Net Weight . . .... . ...................... . . .. . . . 12 pound s
S
hipping Weight .... . .... . .. . . . ................. 16 pounds
1 -6 INSTRUMENT IDENTIFICATION
The instrument is identified by the model numberand asix
digit serial number. The model number and serial number
appear
on a plate located on therear panel, Fiigure 1- 3. All
I
10
n
.,
~~
SIDE VI EW
7
correspondence to your Belar representative or to the Belar
factory in regard to the instrument should reference the
model numberand complete serial number.
1- 7 ACCESSORIES
The Belar FMS- 1 Stereo Frequency and Modulation
Monitor may be used for the remote monitoring of astereo
FM transmitter
with the Be lar MP - 2 Remote Meter Panel.
The MP- 2 Remote Meter
Panel contains a pilot frequency
deviation meter and a modulation meter,
both designed for
5000 ohms loop resistance.
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FRO NT VIEW
Figure 1- 4

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8
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9
SECTION 2
INSTALLATION
2- 1
INITIAL INSPECTION
Check the shipping carton for external damage. If the
carton exhibitsevidence
of abuse in handling (holes, broken
corners, etc.).
ask the carrier'sagent to be preSEmt when the
unit is unpacked. Carefully unpack the unit to avoid
damaging the equipment through use of careless
procedures. Inspect all equipment for phys;ical 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 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 pack•~. industry
approved, shock absorbing material such
as ; extra firm
~lyurethane foam or rubberized hair. NEWSPAPER IS
~ SUFFI CIENT FOR CUSHIONI NG 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 fre iight. Be sure
to insure the unit for full value.
2- 4 PREPARATION FOR USE
The FMS- 1 Stereo Frequency and Modulation Monitor is
designed
to be mounted in a standard 19-inch rack mount .
The
monitor may be mounted below the companion Model
FMM- 1 FM Frequency and Modulation Monitor.
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 around the FMS- 1. In no instance
should the ambient
chassis temperature be allowed to rise
above 50
degrees C (122 degrees F). Mount the FMS- 1 to
the rack mount using four No. 10 screws and four No. 10
countersunk finishing washers .
The Model FMS- 1 derives
its power from the Model
FMM-1. The F
MS - 1 also derives the baseband signal and
AM signals from the FMM-1. Interconnect the FMS- 1 to
the FMM- 1 with the cables supplied as shown in Figure
2- 1 -
that is, connect an 18-inch 75 ohm coaxial cable
(RG-59) between the wideband
output jack (J - 1) of the
FMM- 1 Frequency and Modulation
Monitor and the
composite
input jack (J -1) of the FMS- 1 Stereo Monitor ;
connect
an 18-inch 75ohm coaxial cable (RG-59) between
the INC
AM jack (J -5) of the FMM- 1 and the INC AM
jack (J -3) of the FMS- 1; connect an 18-inch 75 ohm
coaxial cable
(RG-59) between the AM NOISE jack (J - 6)
of the FMM- 1 and the AM NOISE jack (J -2) of the
FMS- 1; connect the r
ed -white lead between TB2 - 4 of
FMM- 1 and TB 1-9 of FMS-1; connect the green -white
lead between TB2 - 11 of FMM- 1 and TB 1- 11 of FMS -1;
and connect the black-white l
ead between TB2-12 of
FMM- 1 and TB1-12of FMS- 1.
CAUTION : DO NOT S HORT TER M INA LS9 a nd 11 TO
GROUND .
If desired, connect external aural left and right channel
monitoring amplifiers
to terminals 1, 2 and 3 on TB1. Note
that these are unbalanced 600 ohm outputs with terminal 2
being the common ground. A remote
pilot center frequency
deviation meter and remote modulation meter may
be
connected to terminals 6, 7 and 4, 5 respectively, if desired.
Observe the proper polarities (5
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 in order to comply with FCC regulations on
remote metering. The remote meters
are contained in the
Remote Meter
Panel MP -2.

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10
S4 · REMOTE METERS
S1 • FUNCTION S2 • TEST ATTEN.
c~•:; ~ "'" - •• l
NOi
l •
,.,
IOI Al
R3 · FREQ. ZERO R2 •MOD. ZERO
Figure 3- 1
1. FUNCT I ON SWITCH-When in TOTAL position, measur es the
total negative modulation of the baseband including the main
channel
and all subcarriers. Note that this is the same reading as the
reading on the modulation meter on the FMM -1.
2.
FUNCTION SWITCH-When in (L +R) position, measures the
main channel modulation.
3. FUNCTION SWITCH-When in (L -R) pos,uon, measures the
stereo subchannel (38 kHz DSB suppressed carrier modu l ation .
4.
FUNCTION SWITCH-When in PlL OT position, measures the 19
kHz pilot amp l itude .
5.
FUNCTION SWITCH-When in LEFT position, measures peak
l
eft channel modulation when the test attenuato r is in the MOD
position. When the test attenuator is in the 0- 50 position, the
meter reads
the average left channel modulation .
6.
FUNCTION SWITCH-When in RIGHT position, measures peak
right channel modu l ation when the test attenuator is in the MOD
position. When the test attenuator is in the 0- 50 position, the
meterreads the average right channel mo d ulation.
7. FUNCTION SWITCH- When in 38 kHz posi tion, measures the
38 kHz subcarrier suppression of the balanced modulator. When the
monitor is used as an intermodulation analyzer, this position
measur es the difference products or distor1ion product s in the
(L -R) channel.
8.
FUNCTION SWITCH-When in FM NOISE position, measures
the de-emphasized FM noise of the transmi tted baseband signal.
9. FUNC TI ON SWITCH-When in AM NOISE position, measures
the de-emphasized AM noise of the transmitted signal.
10.
FUNCTION SWITCH-When in INC . AM position, measures the
AM generated by the FM modulation process in the transmitter.
11 . METER RANGE SWITCH-When in MOD position, measur es
the pe rcentage of modulation with the peak reading vo lt meter.
12. METER RANGE SWITCH -When in O to 50 DECIBELS
positions, measu r es the crosstalk, noise and intermodulation with
the average reading voltmeter.
13. FREQUENCY CALIBRATE SWITCH-When depressed,
permits
the 19 kHz frequency deviation meter to be calibrated.
14.
FREQUENCY OPERATE SWI TCH-When depressed, places
the
unit in operation for measurement of the 19 kHz pilot
frequency deviation.
15. REMOTE
METER SWITCH-When depressed, removes both
metering circuits from the remote meter ing terminals and
substitutes
the equivalent resistance.
16 . PHASE CAL SWITCH-When depressed, pl aces into operation
the phase discriminator to calib rate the phase of the monitor
regenerated subcarrier with the 19 kHz pilot carrier so that exact
zero crossing isobtained.
17. DE-
EMPHASIS SWITCH L- When released, removes the 75
usec de-emphasis from the left monito ring am plifier . This is also
e
ff ect ive on the left audio output test jack.
18 . DE -EMPHASIS SWITCH A- When released, removes the 75
usec de-emphasis from the right monitoring amp li fier. This is also
effective
on the right audio output test jack.
19. PHASE ADJUST - Adjusts the phase of the monitor subcarrier
with respect to the 19 kHz pilot carrier.
20.
FREQUENCY A DJU ST - Ad justs the zero center of the pilot
frequency devia ti on meter.
21. OSCILLOSCOPE TEST JACK -Permits visual observation of
the signal selected by the FUNCTION switch .
22.
LEFT A UDI O TEST JACK -Permits monitoring of th ~ lett
audio channe l.
23. RIGHT AUDIO TEST JACK -Permits monitoring of the right
audio channel.

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11
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.
Place the FMM-1 Frequency and Modulation Moni tor
into normal operation as out lined in the F MM - 1
instruction book.
2. Turn the FMS- 1 Stereo
Monitor FUNCTION switch to
TOTA L an d the RANGE switch to MOD positions.
3. On the F MM - 1, release the MOD P OL switch S4
~- '=ation) and depress the MOD CA L switch.
4.
Adju R1 oo tl'\e rear of the FMS- 1 chassis so that the
FMS- 1
mo dulation meter reads 10 0%.Thisadjustment wi ll
be necessary only during the initial set- up or installation.
The modulat
io n percentage me t er on bo th the FMM- 1 and
the F
MS - 1 will r ead 10 0%. This adjustment standardi zes
the F MS - 1 with the FMM- 1.
5.
Depress the OP switch on the FMM- 1.
6. P lace the transmitter into the stereo mode of operation
with approximately 9% pilot and WITH NO OTHER
MODUL
ATION. D epress the PHASE CAL switch on the
FMS- 1 and adjust the
PH ASE -control for a minimum
reading (nu
ll ) on the modulation meter. This procedure
estab
li shes the exact ph ase relation between the 19 kHz
pi
lot and th e regenerated 38 kHz carrier.
7. On the F
MS - 1 depress the FREQ CAL switch and
adjust the FREQ ZERO potentiometer
to read center zero
on the pi
lot frequency deviation meter.
8.
Depress FREQ OPswitch and the monitors are ready for
normal operation.
3- 2 NORMAL OPERATION
To monitor normal stereo programming, it is recommended
that the FREQ OP switch
be left depressed for continuous
pilot frequency monitoring.The FUNC TI ON switch should
be turned to the (L -R) position and the RANGE switch
turned
to the .MOD position. Thus the FMM- 1 wi ll
monitor tota l modulation and the FMS- 1 will mon itor the
(L -R) or the separa tion of the stereo program material.
Monaural programming should indicate zero and good
stereo programming
will peak up scale. Note that monaural
program material w
ill in dicate approximately the same
modulat io n levels on the left an d r ight ·channel metering
positions
as with a we ll b al anced stereo program. Th is is
why
it is preferable to monito r the (L- R) leve l whic h
indi
cates t he deg ree of separation. This also is an easy way
to precisely balance the left and right channel levels into a
stereo transmitter.
If monaur al programming is applied to
the stereo transmitter, th e balance may be adjusted to
indicate a minimum (L- R). In this manner, the whole
au di o-transnnitter system becomes dynamically balanced.
3- 3 STEBEO MEASUREMENTS
The followiing operating procedures describe methods that
may
be uSl!d to operated each of the functions of the
FMS - 1 Stureo Monitor . Refer to Figure 3-1 for the
location
of the front panel controls, etc. Figure 3- 1 also
gives a brief explanation of the controls.
3- 3- 1 TOT
AL MODULA TI ON
Turn the
FUNCT ION switch to TOTAL and the RANGE
switch
to MOD. The FMS- 1 measures tota l negative
modulation. If the FMM- 1 MOD
PO L switch is depressed
(positive mo dul atio n), both positi ve and negative
modulation polarities may
be observed simultaneously to
check asy·mmetrical program material and / or stereo
modulator unbal
ance.
3- 3- 2 LEFT CHANNEL MODU LATION
Turn th e FUNC TI ON switch to LEFT and the RANGE
switch
to MOD . A fully modulated left channel signal will
indicate 90% on the modulation meter.
3- 3- 3 RI
GHT CH ANNEL MODULA TI ON
Turn the F UN CTION sw itch to RIGHT and the RANGE
switch
to MOD. A fully modulated right channel signal wi ll
indicate 90%on the modulation meter.
3- 3- 4 L
+F I MODUL ATION
Turn t he FUNC TI ON switch to (L+R) and t he RANGE
switch
to MOD. A fully modulated left cha nnel only sig nal
will indicate 45% on the modulation meter. A fully
modulated L=R signal wi ll indicate 90% and a fully
modulated L. = - R signal wi ll indicate 0.
3- 3- 5 L- I =! MOD UL ATION
Turn t
he FUNCTION switch to (L- R) and the RAN GE
switch to MOD. A fully modulated left channel only signal
w
ill indicate 45 % on the modulati on meter. A fully
modulated L= - R sig nal wi ll indicate 90% an d a fully
modulated L. =R signa l will indicate 0.
3-
3-6 PILOT CARRIER MO DULA TI ON
Turn the FIUNCTION switch
to P IL OT and the RANGE
switch
to MOD. The modulation meter indicates pilot
.
..
;

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12
modulation level automatically normalized with the 100%
reading representing 10% pilot carrier injection. A normal
pilot carrier level is 9% (90% on scale) -halfway between
the
FCC specified 8 to 10 %.
3-3-7 38 kHz SUBCARRIER SUPPRESSION
Apply a 5 to 15 kHz modulating signal to either the left or
right channel of the stereo transmitter and adjust the level
to 90 %. Turn the FUNCTION switch to 38 kHz and the
RANGE switch from 0 to a position that a reading is
obtained on the modulation meter. The algebraic sum of
the meterreading and the range switch setting isthe 38 kHz
subcarrier suppression normalized to 100 % total
modulation. For example, a meter reading of - 8 db and a
range switch setting of -40 db yields a 38 kHz suppression
of - 48 db below 100 %modulation.
3- 3- 8 STEREO SEPARATION
Apply a 50 to 15 kHz modulating signal to the left channel
of the stereo transmitter and adjust the level to 90 % as read
on the modulation meter with the FUNCTION switch
turned to LEFT. Now turn the FUNCTION switch to
RIGHT and the RANGE switch from Oto a position that a
reading is obtained on the modulation meter. The algebraic
sum
of the meter reading and the range switch setting is the
separation from left channel into right channel, subtracting
1
db from the reading since the left channel was set to 90 %
(- 1
db). For example, a meter reading of - 6 db and a
range switch setting of -30 db yields - 36 db, and
subtracting the 1
db (90% left channel level) provides a
separation reading
of - 35 db.
To measure separations at other levels, subtract the level
from the algebraic sum of the meter reading and range
switch setting. For example, 50 % left channel level (- 6 db).
- 1 db meter reading and - 40 db range switch setting on
the right channel yields a separation reading of -35 db. To
measure separation from right channel into left channel,
repeat the above measurements applying modulating
to the
right channel, taking the measurements on the left channel,
and substituting right for left and left for right.
3- 3- 9 CROSSTALK
(MAIN TO SUB)
To measure crosstalk from main channel (L+R) into
subchannel (L - R). apply an L=R modulating signal to the
stereo transmitter and adjust the level
for 90 % (L+R)
reading
with the FUNCTION switch turned to (L+R) and
the RANGE switch to MOD positions. Now turn the
FUNCTION switch
to (L - R) and the RANGE switch from
0 to a position that a reading is obtained on the modulation
meter. The algebraic sum
of the meter reading and the
range switch setting is the crosstalk, subtracting 1 db from
the reading since the (L+R) was set at 90 % (-1 db). Note
that since this reading is a function of L being exactly equal
to R, the amplitude of one or the other may be adjusted to
minimize the reading in the (L - R) channel, Also note that
any harmonic distortion in the (L+R) channel may appear
as a reading in the (L - R) channel. For example, the second
and
third harmonics of 15 kHz are 30 and 45 kHz and may
appear
as a crosstalk reading (2 % distortion is only 34 db
down).
3-3 - 10 CROSSTALK (SUB TO MAIN)
To measure crosstalk from subchannel (L -R) into main
channel (L +R), apply an L aa - R modulating signal to the
stereo transmitter and adjust the level
for 90 % (L - R)
reading with the FUNCTION switch turned to (L -R) and
the RANGE switch to MOD positions. Now turn the
FUNCTION switch
to (L+R) and the RANGE switch from
0 to a position that areading is obtained on the modulation
meter. The algebraic sum
of the meter reading and the
range ~witch setting is the crosstalk, subtracting 1 db from
the reading since the (L - R) was set to 90 % (- 1 db). Note
that since thisreading is a function of L being exactlyequal
to R in amplitude but opposite in phase, the amplitude of
one or the other may be adjusted to minimize the reading
in the (L +R) channel. Also note that any distortion in the
transmitter's stereo modulator may appear
as a reading in
the (L+R) channel.
For example, the second harmonic of a
15 kHz modulating signal has sidebands of 38 kHz 30 kHz
so that 8 kHz will be measured in the (L+R) channel.
3- 3-
11 FM NOISE
Turn the FUNCTION switch to FM NOISE and the
RANGE switch from 0 to a position that a reading is
obtained. The algebraic sum
of the meter reading and the
range switch setting is the monaural FM noise. With the
transmitter
pilot carrier turned off , this is equivalent to the
noise
on the (L +R) channel. For example, a meter reading
of - 13 db and a range switch setting of - 50 db yields a
- 63 db FM signal- to -noise ratio.
3- 3- 12 AM NOISE
Turn the FUNCTION switch to AM NOISE and the
RANGE switch
from 0 to a positi on that a reading is
obtained. The algebraic sum of the meter reading and the
range switch setting is the AM noise reading WHEN THE
RF LEVEL IS SET TO 100 % on the FMM-1. For example,
a meter reading
of - 5 db and a range switch setting of - 50
db yields an AM noise measurements of - 55 db .
3-3 - 13 INCIDENTAL AM
Turn the FUNCTION switch to INC. AM and the RANGE
switch
from 0 to a position that a reading is obtained. The
transmitter is modulated for this measurement. The
algebraic sum
of the meter reading and the range switch
setting is the incidental
AM noise. There is no FCC
specification
on this measurement but it may be used as an
aid for proper tuning of an FM transmitter.
If a transmitter is tuned
so that the VSWR is a minimum in
all of the tuned circuits, the incidental AM will also be a
minimum. Conversely,
if the transmitter is tuned so that

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the incidental AM is a mi n imum , the VSW R is also
minimum. A VSWR th at is not constant over a bandwidth
will cause crosstalk and distortion, hen ce it is desirable to
maintain a l ow VSWR or low incidental AM.
Using this procedure, apply a 15 kHz modulati ng signa l to
the left channel and ad just the level for 90 %. Note the I NC .
AM reading. Ch ange the IPA loading slightly and rea dj ust
the IPA
tun i ng for a plate current dip . Note the INC. AM
reading. It may have eit h er inc r eased or decreased . Adjust
the I
PA loadi ng in the direction to obtain a minimum IN C.
AM read in g. Repeat these steps in the remaining coupling
stages, i.e., exciter to I PA and final outpu t stage.
3- 3- 14 FREQUENCY RESPONSE
Frequency
response may be measured by applying the
modulati
ng si gna l to the transmitter and measuring the
input signal level from the audio oscillator wit h an AC
audio voltmeter, such as one contained in a distortion
ana lyzer. For monaural, adjust the le vel at 400 Hz to
indicate t
he des ired modulation as read on the F MM - 1,
usually
10 0 %, 50% or 25% modulation. Change the
frequency
of the audio osci ll ator to all the frequencies to
be measured, adjusting the audio oscillator output to keep
the
total modulation constant. T he AC voltmeter indication
of the oscillator output should follow the standard FCC 75
usec de-emphasis. Standard modulating frequencies used are
50, 10
0,4 00, 10 00, 5000, 7500, 10 , 000 and 15,000 Hz.
To measure frequency response
of the l eft and right
channels, repeat the above steps,
but applythe modulating
signa l to the left and r ight channels respectively. Standard
levels
are 99% (90% signal pl us 9% pilot), 59% (50%signal
pl
us 9% pi l ot) , and 34% (25% signal plus 9% pilot) . Note
that 90% signa l pl us 9% pilot will not add on total
modulation to yield exactly 99 %. This is because the peaks
of the 19 kHz pilot do not occur simultaneously with the
' '
I
. I
10 11 19 27 28
13
pea ks of the 38 kHz do uble si d eba nd (L- R) signa l. T he
reading is .1bout 1½%lower.
3- 3- 15 DISTORTION MEASUREMENTS
Distortion measurements may
be made by connecting an
external distortion analyzer to the L or R output jacks on
t
he front pa nel and applying a modulating signal to the
respective channel
of the transmitter. The measurements
may
be made with de-emph asis by depressing the respective
DE -EM PH switch.
Monaural distortion measurements may
be made using the
AUD IO TEST jack on the F MM - 1 monitor in the same
manner. De-emphasis is controlled by its DE-EMPH switch.
3-3- 16 LEFT CHANNEL NOISE MEASUREMENT
Left channel noise may be measured using the L output
jack on the front panel. The measurement may be made
w
ith de-ernphasis by depressing the L DE-EMPH switch.
Apply a 400 Hz modulating signal to the left channel of the
transmitter and adjust the level
for 100% total modulation.
Normalize the voltmeter in the distortion analyzer, remove
the modulation and take the noise reading in th e
conventiornal manner.
3- 3- 17 FllGHT CHANNEL NOI
SE MEASUREMENT
Ri
ght channel noise may be measured as in step 3- 3- 16
and su
bstituting left for right and right for left .
3- 3-
18 INTERMODUL AT ION
Intermodulation may
be measured with FMS- 1 by using
the internal (L- R) and 38 kHz bandpass filters. The
principle o,f the measurement is
that when two tones are
u sed to modulate the transmitter wh ose stereo modulator is
II I
II 1
11 l
~17 39 48 49
f(kHz)
Figure 3 -2

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14
non-linear, difference frequencies will be produced that are
equal
in frequency to the difference between the two
modu l ating frequencies. These difference frequencies
appear in
the (L+R) channel in addition to appearing as
sidebands around the 38 kHz as shown in Figure 3-2.
The rat io of the desired sidebands (due to modulation) to
the unwanted sidebands (due to the difference frequencies)
is
the intermodulation. The amp litudes of the desired
sidebands are measured with
the (L- R) filter and the
amplitudes of the unwanted sidebands are measured with
the 38 kHz filter. The frequencies of the two modulating
signals must be greater
than 5 kHz so that the 38 kHz filter
will reject
the desired sidebands. The difference between
the two modulating signals must be less than 1 200 Hz so
that the 38 kHz filter will pass the unwanted sidebands.
For example, apply a
10 kHz modulating signal to the left
channel, adjusting its level
for 90 % left channel modulation.
Apply an 11 kHz modulating signal
to the right channel,
adjusting its level for a 90% right channel modulation.
Turn
the FUNCTION switch to (L -R) and the RANGE switch
to O and note the reading on the modulation meter. Turn
the FUNCTION switch to 38 kHz and the RANGE switch
from O
to a position that a reading is obtained on the
modulation meter. The algebraic sum of the meter reading
and
the range switch setting is the measurement of the
unwanted sidebands. The difference between the (L+R) and
38 kHz readings is the ratio between the desired sidebands
and unwanted sidebands and is the intermodulation
between
the left and right channels.
There are no standards
for this measurement, but it is a
useful
test since harmonic distortion of a stereo signal
above 5 kHz
is filter ed out by the 15 kHz filters, rendering
a harmonic distortion
test invalid.
3-3- 19 PHASE CALIBRATE
Place
the transmitter into the stereo mode of operation
wit h pilot modulation on l y. It is important that th ere is no
other modulation present, hence remove audio modulations
and any subcarriers if present. Depress the PHASE CAL
switch
on the FMS-1 and adjust the PHASE control for a
minimum reading (null)
on the modulation meter. This
procedure establishes the exact phase relation between the
19 kHz pilot and the regenerated 38 kHz carrier.
To set the transmitter phase, apply a 400 Hz L= - R
modulating signal
to the stereo transmitter and adjust the
level for 90 % (L-R) reading with the FUNCTION switch
turned to (L-R) and the RANGE switch turned to MOD.
Now
turn the FUNCTION switch to either L EFT or
RIGHT channel and adjust the transmitter pilot ca rrier
phase
for a maximum reading on the modulation meter.
The transmitter phase may also be set by using a left on ly
modu lating signal and adjust ing the transmitter pilot carrier
phase
for a maximum reading on the LEFT channel.
3- 3-
20 PILOT FREQUENCY
Depress
FREQ CAL switch and adjust FREQ ZERO
potentiometer, R
3, to read center zero on the pilot
frequency deviation meter. This calibration may be
done
with program material.
Depress
FREQ OP switch and read pilot frequency
deviation
from 19.0000 kHz.

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15
SECTION 4
PR INCIPLES OF OPERAT-ION
4- 1 CIRCUIT DESCRIPTION
Figure 7- 4 is the chassis sch ematic and may be referred to
for operation along with the individual card schematics,
Figures 7- 1, 2
and 3. The incoming stereo composite input
is applied to the BASEBAND INPUT J1. Buffer amplifier
A2O1 and
02 on CARD A2 applies the signal to both the
stereo demodulator, on CARD Al, and the FUNCTION
switch Sl .
/
The stereo and phase discriminator CARD A1 regenerates
the 38 kHz suppressed carrier, demodulates the stereo
composite signal
with the regenerated subcarrier, and
provides phase calibration.
The outputs of the stereo
demodulator
are app lied to the left and right channel filters
FL 1 and FL2, which are in turn applied to the left and
right channel monitoring amplifiers
on CARD A2. A
filtered 19 kHz output is also taken from the A1 card and
app lied to the FUNCTION switch for pilot amplitude
measuremen
t_;,,,
The FUNCTION switch Sl selects the particular function
to be measured and applies it to the voltmeter circuits on
CARD A2. Note that the (L+R). (L- R). and 38 kHz filters
as well as the TOTAL modulation potentiometer R4 are
disconnected
from the circuit when not switched in . The
FM NOISE position switches in the inductor L2 to
de -emphasize the baseband signal.
CARD
A2 contains the peak and average voltmeter circuits
for the various measurements. It also contains the left and
right channel monitoring amplifiers
that are used for aural
monitoring
as well as audio tests. Switches S6 and S7
de-emphasize the individual amplifiers. /
/
CARD A3 contains the pilot frequency meter circuit. The
19 kHz pilot is multiplied to 190 kHz and is compared with
a reference oscillator. The difference frequency is measured
with a
counter discriminator and displayed on the pilot
frequency deviation
meter -/
Power is supplied to the FMS-1 from the FMM - 1 through
the terminal blocks. Twenty-five vol ts DC supplies the
operating power and 19 volts AC powers the calibrating
circuits. The
FMM - 1 is protected against short circuiting
the 25 volt DC bus connecting the FMS- 1/
4- 1-1 STEREO DEMODULATOR AND PHASE
DISCRIMINATOR CARD A1
The baseband signal containing the stereo composite signal
is applied
to pin 14 of the stereo demodulator and Phase
Discriminator CARD
Al. The 19 kHz pilot is filtered out
by the bandpass filter consisting of inductors A1L1 through
L3 and capacitors A1C1 through CS.
The oltput of the 19
kHz filter is buffered by emitter fo ll ower A 101 and is
app lied to the FUNCTION switch through pin 9 to be
measured in the PlLOT position. The output of A 10 1 is
also amplified by A
102 and applied to th•~ 19 kHz doubler
consisting
of the pha splitter A1 03 and foll wave rectifier
A1
CA 1 and CR2.
The 38 kHz output of the doubler is am1Plified by A 104.
PHASE ADJUST inductor L1, Jw ith capacitor A1C12,
filters
the 38 kHz and p ro vides the necessary phase
adjustment
for pilot phase calibration. Tlhe output of the
38 kHz amplifier is applied to the limiter A1 05 and 06,
which amplifies a n~ squares the 38 kHz waveform.
Potentiom
et e ~t 1A 25 ovides a s mmetr~ justment for
the square-w ve. Transistors A 107 and 08 buffer the
limiter output and provide a very low output impedance to
drive the stereo demodulator through transformer A1T1.
The square-wave drive to the stereo demodlulator allows the
demodulator ro be relatively independent c,f pilot level.
,/
The stereo demodulator is the series diode type for
maximum stereo performance. Its function is to separate
the original left and right channels from the wideband
stereo composite signal. Matched diodes A1CA4 through
CR7 and resistorsA1R47 through R52
form a bridge which
is driven
at a 38 kHz r ate by the output of transformer
A1T1.
The wideband stereo composite si!Jnal is applied in
series through the center - tap of transforme1r A1T7
Since the incoming stereo composite signail was formed by
alternate switching
of the left and right 1channels at a 38
kHz rate (time d i vision multiplex system). the
demodulation process is just the reverse. Th e dibde switches
are alternately turned
on and off at the 38 kHz rate to
allow the left and right channels to pass 1at the prescribed
tim
1/
The left and right outputs of the demodulator are applied
to the amplitude correction amplifiers, transistors A 1011
and O 12. Since the original stereo composiite signal consists
of equal amplitude (L+A) and (L- R) signals and no odd
harmonic components of the 38 kHz subcarrier,
square-wave switching
i11 the demodulato r adds an (L-R)
component which is 4/TT times the original! (L-R), and this
difference in amplitude is corrected ini the amplitude
correction amplifier by cross coupling
the outputs through
A1
R36 and R37. If the transmitted stereo composite signal
contained an (L-
R) signal that was squa1 re-wave switched
without filtering out the odd harmonic 1components the
amplitude correction would not be needed. T he amplitude
correction may
be eliminated by removing the short from
pins 19 and 20. The outputs of the amplitude correction
amplifiers are buffered
by emitter followers A1 09 and 010
and applied to 15 kHz lowpass filters FL 1 and FL2 to
remove all frequencies above 15 k!;lz present on the
demodulated l eft and right channe1y
For accurate stereo demodulation it is important th at the
exact phase relationship be maintained between the 19 kHz
and
the regenerated 38 kHz subcarrier that drives the
demodulator . Proper phasing is indicated when th e 19 kHz

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16
component from either side of the demodulator is exactly
equal
to the other. The conventional method of measuring
this is to filt er out the 19 kHz from one side of the
demodulator and measure its amplitude and then reverse
the phase of the 38 kHz with a relay or switch and compare
the new amplitude, trying
to adjust the phase for equal
amplitudes. As
the correct phase is approached, the
difference in amplitude, be }° mes very small, hence the
method is subject to erro/
The phase discriminator on the A1 card does not have the
above disadvantage in that the amplitude difference is a null
reading rather
than a peak reading. Each side of the
demodulator is buffered by emitter followers A1Q13 and
014. The outputs of the buffer amplifiers which contain
the 19 kHz components are alternately switched at a 60 Hz
rate by diodes A1CR8
and CR9 to form an amplitude
modulated signal whose degree
of modulation is a function
of the inequality of the 19 kH z components from each side
of the demodulator. The 19 kHz component is amplified by
transistor A 1015 filtered by the bandpass filter consisting
of inductors A1L4 through L6 and capacitors AC31
through C35.
The bandpass filter is wide enough to pass the
harmonics of the 60 Hz square-wave modulation. Figure
5-1 - 11 illustrates this waveform with correct phase.
Figure 5- 1-
12 shows that there is a phase d i!!: ~ ce
between the 19 kHz and regenerated 38 kHz subcar~ .T "·
The output of the bandpass filter is buffered by emitter
follower A1 016 and demodulated by the envelope dete c tor
A1CR10 and CR1 1. The phase error output is a
square-wave whose amplitude is proportional
to the phase
difference. This
output is measured by the sensitive
voltmeter as a null reading
for the correct phase. Depressing
the PHASE CAL switch applies 60 Hz to pin 16 to switch
diodes A1CR8 and CR9.
At the same time the input of the
sensitive average voltmeter amplifier is switched to the
phase error output and the PHASE Ag.JUST inductor L1
may
be adjusted for the null readin g/"
4- 1- 2 AUDIO AND VOLTMETER CARD A2
The incoming baseband signal is amplified by transistor
A2Q1. Potentiomet
E!( R1 UNPUT LEVEL) adjusts the gain
slightly
to allow the FMS- 1 to be normalized with the
F MM -1. Transistor A2O2 provides a low impedance to
drive
the stereo demodulator on CARD A1 and also the
FUNCTION switch S1. The FUNCTION switch applies the
particular function selected to the input of the wideband
feedback amplifier
A2Q3, 04 and 05 which drives the peak
voltmeter circuit. Section 4- 2-
3, in the FMM - 1 manual,
may be referred
to for i ts operation since the circuits are
the same/
The output of the feedback amplifier also drives the
RANGE switch S2 which provides attenuation steps for the
sensitive average voltmeter. The output of the RANGE
switch
S2 is applied to the average voltmeter amplifier
A2O9 and
01 0. Diode bridge A2CR3 through CR6rect,~
the output to drive the modulation meter. A sample of the
output is applied to the emitter of A2Q9 to provide
feedback
to stabilize the gain and linearize the meter
reading. The gain is adjusted by,. A2R4 '!,... An output is also
taken from the amplif1 er to pr ov i8e an oscilloscope output
(SCOPE) that follows the sensitivity setting of the RANGE
switch/
When
the RANGE switch is on MOD, the modulation meter
is switched to the peak reading voltmeter circuit on pins 24
and 25 . When the RANGE switch is on 0- 50 db positions,
the modulation meter is switched to the diode bridge
A2CR3 through CR6. Note that if a remote modulation
meter is used, it al ways remains on the peak voltmeter
circuit. Wh
en the RANGE switch is on MOD, the average
voltmeter is connected to the - 20 db position of the
attenuator through a jumper on switch section S2 -C. This
is to normalize the PlL OT reading on the FUNCTION
switch. Since
the average v oltmeter is connected to the - 20
db position of the attenuator , the SCOPE output will
indicate a distorted waveform when
the RANGE switch is
in the MOD positio 1/
The input circuits to left and right channel monito ring
amplifiers
terminate the left and right channel lowpas.s
filters
FL 1 and FL2. The amp li fiers are the same as used in
the FMM - 1 and its manual may be referred to for
operation.
4- 1- 3 PILOT FREQUENCY METER CARD A3
The square-wave output from pin 1 on CARD A1 is applied
to the input of the frequency multiplier A3Q9 and 010 .
The bandpass filter consisting of inductors A2 L1 and L2
and capacitors A2C16 through C18 select the fifth
harmonic
of the 38 kHz. This harmonic is also the tenth
harmonic of 19 kHz. The 190 kHz output of the filter is
mixed
with the 190 . 060 kHz local oscillator frequency in
the balanced mixer A2O7 and 08. The output of the mixer
is
the 60 Hz difference frequency. One Hz deviation at 19
kHz then causes 10 Hz difference frequency deviation/
The 60 Hz difference frequency is applied to the pulse
counter discriminator consisting of the Schmitt trigger and
monostable . multivibrator through the switching diode
A3CR2. The output of the monostable multivibrator is
integrated
by A3R 16 , A3C23 and A3R23, A3C24 and
applied to the pilot frequency deviation meter tbrough pins
7
and 10. FREQ ZERO pot ~iomete~ calibrates the
discriminator. In the absence of pilot, transistor A3O5 is
conducting and transistor A3O3 is
off , which will cause the
meter to read off scale. Transi stor A3Q4 clamps pin 7 to
ground to return the meter to zero Diodes A3CR3 and
CR4 rectify an output from the Schmitt trigger to provide a
negative voltage
to turn off A3O4 when there is 19 kHz
pil~
The pulse counter discriminator is calibrated wit h the 60
Hz line frequency. Depressing the FREQ CAL switch S3
applies 60 Hz line frequency to pin 2. Fifteen volts DC is
also applied
to pin 4 to turn on diode A3CR1 to permit
calibration. Depressing the FREQ OP switch removes the
60 Hz line frequency and returns the 15 volts DC to pin 3
to turn on diode A3CR2. Capacitor A3C9 calibrates the
190 .060 kHz local oscilla/

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1.
Composite Stereo Waveform
4.
Composite Stereo Waveform,
Insufficient (L- R)
7.
(L-R) Subcarrier with Pilot,
Pilot in Phase
10.
Stereo Demodulator Waveform,
Incorrect Balance
2.
(L-R) Subcarrier with Pilot
5.
Composite Stereo Waveform,
Excess
(L - R)
8.
(L- R Subcarrier with Pilot,
Pilot Phase Incorrect
11.
Phase Discriminator Carrier
Figure 5- 1
3.
(L +R) Main Channel with Pilot
6.
Composite Stereo Wav11form, Phase
Error Between
(L +R) and (L- R)
9.
Stereo Demodulator Waveform,
No Modulation
1 2.
Phase Discriminato1r Carrier,
Incorrect Pilot Phase
17

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18
SECTION 5
MAINTENANCE
5- 1 INTRODUCTION
✓ This section contains maintenance and service information
for the FMS- 1 Stereo Frequency and Modulation Monitor.
I ncluded are Performance Checks, Adjustments and
Calibration Procedures.
5- 2 PERFORMANCE CHECKS
/Before performing any checks on the FMS-1, it is
V suggested that the F MM - 1 performance be verified. See the
instruction manual for the FMM -1.
5- 2- 1 FREQUENCY
DEVIATION ME T ER CHECK
Depress FREQ CAL switch. Verify that by rotating the
5- 3- 1 PRELIMI NARY
Connect an RF sample from a properly operating stereo
exciter
to the RF i nput jack of the FMM - 1 FM monitor.
Set FMM- 1 input level potentiometer R7 for an indication
✓ of 100% on the FMM - 1 modulation meter with th e RF
LEVEL switch depressed. Apply pilot tone in stereo
generator. Set pilot level to approximately 9% using
FMM - 1 modulation meter. Ver ify that pil ot phase is
correct by the following procedure:
a. Wit h scope connected to WIDEBAND TEST output jack
✓ of FMM- 1, with external sync fed directly from audio
generator, feed L = -R signals to the stereo generator audio
inputs
(4 00 Hz).
FREQ ZERO control from maximum clockwise to \/" b. Set audio level for 100% modulation of main carrier.
maximum counterclockwise the Hz DEV I AT ION meter
V
v
V
pointer will go up scale in the positive and negative
di rections respectively. Return the pointer to zero. Depress
the FREQ OP switch and read the deviati on. Depress the
FREQ
CA L switch and set the pointer to - 1 Hz. Depress
t he F
REQ OP switch and read the deviation. By
algebraically adding the - 1 Hz, the same deviation should
be obtained
as in the preceding test where the FREQ CAL
is set at zero. Re zero the FREQ CAL control after test and
return to FREQ OP mode.
5- 2- 2
MODULAT ION MOD ZERO METER CHECK
Verify
that without any modulation, by rotating the MOD
ZERO control
from maximum clockwise to maximum
counterclockwise the modulation meter pointer
will move
in a positive
to negative di r ect ion about zero. Return the
pointer to zero aftercheck.
5- 2- 3 FUNCTION
Sections 3- 3- 1 through 3- 3-
20 may be used for the
r
ema inder of the performance checks.
5- 3 ADJUSTMENTS AND CALIBRATIONS
✓ Place the FMM- 1 in normal operation. Before performing
any adjustments
on the F MS -1, verify that the FMM- 1 is
operating normally
as outlined in the manual on the
FMM- 1 under Section 5- 2.
V
Before proceedi ng wi th F MS - 1 alignment, depress the
FMM- 1
AM P BAL switch and make su re that the FMM- 1
modulation meter reads zero: reset to zero if necessary,
usi ng the MOD ZERO con trol on the FM M- 1.
Place the FMS- 1 F
UNCT ION switch to the TOTA L
position. Adjust the FMS- 1 MOD ZERO control
for ze ro
indication on the FMS- 1 modul a tion meter.
c.
Ad just exciter Pl L OT PH ASE adjustment (in the stereo
/g ener ator) for alignment of crossover points on scope
presentation,
Fi gure 5- 1- 7.
✓ Remove audio~ depress PHASE CAL switch and adjust
PHASE
CA L control for minimum indication on the
FM S- 1 modulation meter.
Set FMS- 1 FUNCTION switch
to the 38 kHz position
jw ith no audio input to exciter, exciter set to STEREO
✓ r:node). Set stereo generator CARRIER BALANCE con trol
for optimum 38 kHz suppression (suppression should be
greater than 40 db).
5- 3- 2 A2R1 5ADJUS T MENT
With pilot amplitude set to zero, apply a 4 00 Hz L only
_,,s ignal to the stereo generator. Adjust audio level fo r 90 %
V modulation of the FM carrier, ref1?rring to the FMM- 1
modulation meter. Insert approximately 9%
pilot tone by
setting stereo gene r ator Pl LOT LEVEL control for a
FMM - 1 modulation meter ind i ca tion of 99 %.
Set the
FMS- 1 FUNC TI ON switch to the L position, and
V the DECI BE LS switch to the MOD position. Adjust the
voltmeter gain contrQI
A2R15 on the A2 circuit board for
an indication of 90% o iith e FMS- 1 modulation meter.
5-3 - 3 A1R47 AND A1 R5 0 AD JUSTMENT
/ .
\./ Per form t he fo ll owing adjustment of the stereo
demodulator
circuitry only if absolutely necessary.
Ba lance stereo demodulator as follows: Connect scope at ff ' I
J he ju n ctio n of A 1R 50 and A 1C23 in the FMS- 1 stere o'
\/ ~emodulator (A 1 circu it boar d). With no mod_!:!.W- io.a_.
applied, but wit h pilot still present, adjust cont r I A1 R5 0 'i
fo r optimum waveform, Figure 5- 1- 9. There should 6e no